Loco Suspension, fitting CSBs

[Will L]

So let’s look at what we have got to be getting on with.

The Existing Loco

CSB J10T 8.jpg (178.62 KiB) Viewed 4993 times

This time I remembered to take a photo of the loco before I started taking it apart, something I forgot with the tender. This is a DJH kit which was built mumble mumble years ago in OO to run on a previous exhibition layout. My intention is to replace the OO chassis with a completely new one suitable for P4. The body is very likely to need attention underneath to provide clearance for the wheels. It will also need a cosmetic update above the footplate. You will note that the body comes apart at footplate level which should make fitting the footplate to the chassis a lot simpler when we get there.

CSB J10T 9.jpg (167.17 KiB) Viewed 4993 times

Bits for the new Chassis

I noticed that Gibson did profile milled chassis frames for the J10. I decided to base the new chassis on these. So I wrote off to Gibson's for the chassis frames, 6 of the wheels closest to the prototype and a universal 6 wheel connecting rod etch. I had hornbock components from HighLevel (on the left) and Exactoscale (on the right) in stock. When I took the picture I hadn't decided which ones I was going to use.

CSB J10T 7.jpg (306.51 KiB) Viewed 4993 times

Drive will be through a HighLevel LoadHauler+ gearbox with a DriveStretcher. This should enable the motor to be mounted pointing forward on, or close to, the boiler centre line without the need for the existing visible cut out in the bottom of the boiler. The drive train will be down through the firebox and the drive on the rear wheels under the cab floor.

CSB J10T 6.jpg (192.27 KiB) Viewed 4993 times

The choice of gearbox is important as it has implications for the choice of hornblocks. The DriveStretcher is 9.8mm wide which doesn’t leave a lot of room for chucky bearing blocks. The Gibson frames are 0.75mm thick and a standard HighLevel hornblock mounted inside the frame projects 3mm. With a frames width of 16mm, a little arithmetic will tell you that there is only 8.5mm left for the gearbox.

So I considered doing something with the Exactoscale hornblocks which, with a little effort, could be mounted flush with the outside face of the frames. These have bearing blocks 3.2mm thick, which could be reduced if necessary and would just allow enough space to get the gearbox in. However they don’t fit the frame cut outs in the Gibson frame, and though I have planned out a way to get them in, it was going to be labour intensive and I would have to do six.

So back to the Highlevel blocks. It is possible to mount a standard round top hat bearing in the carrier. This gives you a much thinner result and will fit with the gearbox, so that is the way I am planning to go. More details of how it is done later.

Sorting out the Fulcrum Points

I used my spread sheet to produce the fulcrum plot below. I got a perfectly acceptable result using the auto calculate option with fulcrum points rounded to the nearest 0.5mm. I.e. all I had to tell the spread sheet was the wheelbase.

CSB exel J10.jpg (83.82 KiB) Viewed 4993 times

Building Considerations

Looking at the Gibson frame sides, you will notice that these accurately reflect the prototype profile. This isn’t going to work with the cast metal footplate, so we must assume I am going to have to saw a fair chunk off the top. If I started again it might well be just as easy to make my own frames from scratch, but as I’ve got them I’ll use them.

Then there is the question of the Gibson universal coupling rods. These are all very well, but I tend not to believe in rods jointed on the centre crank pin. So the first thing I’m going to have to do is convert the bits of the universal rods into a properly jointed set. When I started this thread I was expecting just to do a blow by blow on fitting CSB’s, but somehow I keep on being diverted into other associated things. As the rods are key in constructing the frames , I’m afraid making jointed rods is going to be another such diversion, and that’s what I will cover in the next post.

[Mike Garwood]

Will

Carry on being diverted...really good stuff!! Looking forward to the rest of the build.

Mike

[Will L]

As I said, I have come to the understanding that coupling rods that are jointed on a crank pin aren’t a good idea, and the way to go is to articulate them using a pivot adjacent to the centre crank pin boss. That’s the way they did it on the real thing, and the O4 came with articulated rods that proved easy to get running smoothly. Unfortunately as far as I am aware, the only assistance available for producing coupling rods for the J10, and hence avoiding a total scratch building job, is the Gibson universal coupling rods etch. This produces a reasonable looking set of rods, but they are jointed on the centre crank pin and are thus unacceptable. Previous experience also suggests that when assembled as intended, the results were a bit flimsy.

The question is, can one use the Gibson offering as a stepping stone to rods that are articulated as per the prototype and a bit more robust as well. The fact that I’m posting this should suggest that the answer to that question is probably, yes.

This is the Gibson Fret

The thing about these “universal” coupling rods is that you normally start from an existing chassis, with the axle centres established, and build the rods to fit what you have. The rods are made from a two layer etch, and you can have plain or fluted depending on which way round you mount them. No part has more than one crank pin hole. Using the chassis plus some reduced end axles as a jig, you put a fluted and a plain part back to back to fit between the ends of one pair of axles, then solder them together, finally adding the boss ends to make up the thickness. When using this etch to make jointed rods, the process is rather different. I produced rods to measured axle centres and I shall be using the rods to set the axle centres on the chassis.

To articulate a coupling rod, the best way is to build a forked joint. To me this suggests a three layer construction. The Gibson etch provided the two outer layers, so all I needed to was make a central core from Nickel Silver (N/S) strip and, for the pivot, use a small valve gear rivet. The rivets are not obligatory, I had some in stock so I used them, but a couple of brass pins would have done the job. This drawing illustrates where I’m planning to go.

CSB rods 1D.jpg (37.65 KiB) Viewed 4905 times

Firstly I found two strips of N/S wide and long enough to make the core layer of the new rods. They came from the edge of a N/S etch. I sweated these strips together, and carefully marked out a centre line, or more accurately an off centre line because the lubricators on the rods stick out further on the top edge. I then marked out the wheel centres along the rod centre line, drilled them 0.5mm, and opened out the hole to 0.95mm. I also fretted away some of the excess metal.

You will see from the picture of the etch that it contains a good representation of the articulation pivot points. I drilled through all these pivot points 0.5mm and all the crank pin holes 9.5mm. I used a combined crank pin/articulation pivot boss from the etched to establish and drill out the articulation pivot point on the rod core strips. Finally I cut part way through the core strips between the centre crank pin hole and the articulation pivot hole. The following picture shows one of the resulting embryo rod cores, once I had delaminated it from its twin.

CSB rods 6.jpg (52.26 KiB) Viewed 4905 times

As a matter of interest, all the metal pictured in this post is N/S, no matter what it looks like. The background to this picture was blue but this seems to have foxed my camera and I can’t be bothered to correct the colour balance!

Because I have recently got extravagant and splashed out on an Avonside Works Chassis Pro jig, I used these coupling rod cores to set up the axle centres on the jig. But fear not you can also set up the chassis from the finished rods in the traditional fashion.

Getting the soldering iron out

Next we have to overlay the Gibson etch components on to the core. I used Carr’s 221 tin/silver solder, which I find runs well on N/S and gives a very clean finish. I had expected to change down to 188 or even 145 solders as I added details, but in practice I found it easy to do the whole job with the 221 stuff. Flux was Carr’s Red Label

The J10 rods are plain, so the fluted components will be fitted to the back of the rods. I began by fitting the plain overlays on the front of one end of the core, starting with the overlay with the articulation pivot point in it, and adding to it one of the separate end bosses. The overlay needs to be trimmed to the correct length. The bit I cut off is in the following photo.

CSB rods 2.jpg (152.32 KiB) Viewed 4905 times

You can see that, to get everything strait, I pinned all the bits together on my trusty wooden block. Once I was happy, I tack soldered the overlay in the centre, hence the unsightly splodge of solder there. The metal pin through the separate crank pin boss was removed and replaced by a wooden cocktail stick. That end of the rod, and about half way down the overlay, was soldered up neatly. Then I removed the other pins and finished the soldering job, making very sure I didn’t get any solder beyond the cut in the core between the centre crank pin hole and the pivot point. Then I re-drilled the crank pin holes from the core side through the new overlays. This makes sure that even if the overlay wasn’t aligned perfectly, the crank pin hole remains centred on the one in the core.

Then I turned the core over and put the overlays on the back. If you have a good look at the Gibson etch you will realize that the matching centre crank pin boss/articulation pivot point is attached to a fluted rod overlay at the articulation pivot end. This overlay will end up on the back of the other half of the connecting rod, so I had to separate the boss/articulation pivot point from the rest of the overlay. This boss is to be soldered to the end of the core I was working on, along with another fluted rod overlay with end boss attached. This also needed to be cut to length. Again pins through the crank pin holes and the pivot points ensured everything was lined up properly, before the overlay was tack soldered to the core in the middle. I replaced the pin through the centre crank pin hole with the cocktail stick and carefully soldered on the boss/pivot point, again not getting solder past the cut in the rod core. Finally I pulled out all the pins and soldered it all up neatly.

Once the soldering was done, I completed the cut through the rod core and pulled out the other end leaving a nice forked joint. I re-drilled the crank pin holes, from the front this time, again to ensure the crank pin hole will be in the right place. Finally I filed the core back to the outline of the overlays. After all that, I ended up with half a finished connecting rod as in the next picture, which also shows that the process of fitting the laminates to the second half has begun.

CSB rods 5.jpg (51.82 KiB) Viewed 4905 times

Cutting the overlay on the second half to the correct length needed care, but pinning it all down to the trusty block helped. I also learned that filing a concave end on the overlay by the articulation pivot point improved things, but only after taking this picture. I ensured the overlay was central on the core by aligning it with the articulation pivot hole. Before doing the others side, I filed the core back to the profile of the overlay for a short distance at the articulation pivot end. By doing this, I could line up the second overlay with the first without difficulty. The next picture shows this has been done, and there is the trusty cocktail stick in use. It should be vertical, but the hand that normally holds it upright is otherwise engaged in holding the camera, and, in turn the viewing angle of the camera is exaggerating the degree to which the stick is leaning.

CSB rods 4.jpg (170.92 KiB) Viewed 4905 times

Diversion re the virtues of cocktails, or at least their sticks.

I’m a great believer in the use of wooden cocktail sticks when trying to align holes I want to keep open, in things I’m trying to solder together. E.g. when soldering on a retaining nut. Being pointed the cocktail stick fits through the hole to start with, then the heat of soldering burns away the bit of the stick which is wider than the hole. This gives a parallel wooden plug through the hole which both stops solder going where you don’t want it to, and ensures the hole is properly aligned. When fitting a retaining nut in this way, the hole in the plate needs to be the tapping size for the bolt that fits the nut. The last stage is to run a tap through the nut and the plate it is solder too, giving a continuous threaded hole through both.

Back to coupling rods

Having re-drilled the crank pin holes from the back, the final side of the second half of the rod was made up of a separate crank pin boss from the Gibson etch, and the fluted overlay I cut off the crank pin boss/articulation pivot earlier on. I aligned the boss to the crank pin hole in the core rod with the cocktail stick, one end of the overlay to the boss, and the other with the filed away section of the core rod. This was about the only operation in the whole job where three hands would have been an advantage.

You should be able to work out how I finished the rest of it by now.

The articulation pivot holes needed to be opened out to fit the crank pin rivet (0.75mm). It was hard to drill a clean hole full size, so I drilled 0.7mm and finished off with a taper reamer until the rivet fitted. I still needed to clean some swarf out of the fork joint, so I used a spare bit of N/S as a file/chisel. Rivet the two halves together and bob’s your auntie. The picture shows a completed rod mounted back on the Avonside chassis jig to show that the axle centre dimensions are still correct.

CSB rods 3.jpg (135.58 KiB) Viewed 4905 times

Theological diversion

You need to have spares of the rivets. They are devotees of the Great Carpet God and tend to fly off the workbench and seek sanctuary with him. I remain a believer in the GCG, even though it is some years now since I regularly modelled in a room with carpet on the floor, and became aware of the tendency of small metal parts to sacrifice themselves to this particular deity. In my house today, the GCG’s latest incarnation inhabits the cork tiles of the room in which I model, but he is still surprisingly adept at hiding those things which fly to him. My wife is the GCGs chief acolyte, and never, ever throws away any small metal fragments revealed when washing the kitchen floor.

Final Thoughts Various

Once I’d done one set of rods as described above, the only thing left to do was the second set, remembering that connecting rods are normally handed and the second set will be a mirror image of the first.

Being a believer in the P4 “getting it all right” mantra, I filed off the fluting on the back of the rods, but even I began to think I was wasting my time.

The point about this whole forum thread was an attempt to convince other modellers that CSB’s were the simplest and best way to go when building loco chassis. I regret that postings like this do rather point to the personal pleasure I take performing rather than avoiding some quite fiddly construction tasks. This may be seen as undermining my original message. So I would like to point you all to a new section Russ has posted on the CLAG website called “CSB Gallery” . This is devoted to pictures and notes illustrating many peoples’ implementations of CSBs. I think this gallery of photos is just the thing for showing people what can be, and is being, done with CSBs.

Having got the connecting rods finished, the next step must be to sort out the chassis frames. These will need quite a lot of thought, and possibly physical attention, before we are ready to start actually fitting CSB fulcrums etc. I haven’t started this yet so the next post could be some time coming. Until then, here is one final picture for you to be going on with.

CSB rods 1.jpg (167.56 KiB) Viewed 4905 times

[Will L]

I shall be helping man the Society Stand at Manchester on Saturday. The bits of the J10 will be there. If anybody wants to stop by for a chat about, I'll only be only to please to see you.

Of course I will have to give preference to the long queue of people wanting to join the society, but I'm sure I will have some time to talk suspension!

Will

[Tim V]

The other way would have been to build the chassis first, then match the rods to the wheelbase, reducing the possibilty of error.

[craig_whilding]

The other way would have been to build the chassis first, then match the rods to the wheelbase, reducing the possibilty of error.

I can't imagine it would be less error prone trying to build the rods onto an existing wheelbase than building the hornblocks on the jig to match the pair of rods.
Personally i'd probably stick them on an etch I was doing now though and make some that way but i'm never very good making anything from a solid sheet without a PC..

As long as it works and all that though whatever method is used.

A large contingent of the Scalefour Society seem to be demoing various things this weekend so I think there will be plenty of opportunities for punters to fall victim to the sway of P4! I'll try to stop by and have a look at this chassis developing though.

[Will L]

The other way would have been to build the chassis first, then match the rods to the wheelbase, reducing the possibility of error.

I agree Tim, that its perfectly possible to use the Gibson universal rods, as designed, to produce rods that fit an existing chassis. Although articulation on a crank pin is a flawed concept, the result can run perfectly well, even if the axles in the chassis aren't perfectly square and parallel! I know this because in my past there is a loco which ran very nicely, even though you didn't need a vernier gauge to establish that the driving axles were not parallel. However I'm not convinced that trying to convert the Gibson universal rods from crank pin pivoted to properly jointed, while retaining the universal assembly method, was any way to reduce the possibility of error. Though there could be an opening in the market here for a properly jointed universal rod etch that could be assembled against an existing chassis. Could well sort out a lot of poorly performing loco's too.

Given that I had Gibson frames with 6 by 7 cut-outs not axle holes, and I was going to use the Chassis Pro jig because I'd just acquired one, then I was going to have to establish the exact wheelbase measurements somehow so I could set the axle pins in the jig. I thought the easiest way to do that was to measure and drill the coupling rod core and set the jig from that, as described in the posting above. This also fitted in with the easiest way I could see to produce the jointed rods. After that everything else is set from the jig, which is what jigs are for. The theory seems good to me. There is a big post in production that will tell you how I got on.

Brutal honesty also forces me to admit that inexperience with the jig meant I didn't ensure the axle pins were screwed in firmly enough. A little side play was present in one pin, and I didn't realise till I started assembling the chassis sides. Fortunately the method I chose to build the rods meant they did stayed identical despite the play in the jig. I discovered the problem when I did the first chassis side and then tried fitting the rod back on to the jig over the top of the chassis. It didn't fit! So I had to find the problem pin in the jig, reset the jig so all the axle pins were tight, check that both sets of rods still fitted and finally redo the chassis side so it fitted the new set up. One hornblock needed moving slightly.

Having managed to introduce an error on the jig, I can say the method of doing the rods proved good at avoiding errors. Also the jig system did let me know an error had occurred before it had got irrevocably built into the model. I'd call that a success, but, if it proves that loose axle pins in the jig are a regular problem, then I'll begin to wonder if I've waisted my money.

[Will L]

if it proves that loose axle pins in the jig are a regular problem....

Had a chat with the nice man from Avonside/Eileen's at the Manchester show. He pointed out to me that the axle pins have a screwdriver slot in the end which screws into the jig. This can be used to tighten them down without having to grip the business end of the pins and endangering their smooth finish. The screw slot is accessible from underneath the jig. Facts I might have spotted for myself if I'd read the instructions thoroughly it seems. That looks as if it should work, though he did warn against over tightening. It seems likely that I would have found the screwdriver slot in my own time, because what you really need it for is getting the pins out again!

Will

[Will L]

My next steps have to be to prepare the hornblocks and frame sides and put them all together. Traditionally for me this would have meant assembling the frames and frame spacers flat and square on the workbench before adding the hornblocks. All this using a set of the available individual axle jigs that will hold everything true while you solder it all together

Now however, having got the Avonside Chassis Pro to play with, things are a bit different. Using this jig, the favoured approach is to assemble the hornblocks onto the frame sides and only then adding the frame spacers and soldering the lot together. Thought I ought to tell you that so you know where we are going.

CSB J10 frames 0.jpg (127.96 KiB) Viewed 4613 times

We'll do the hornblocks first.

As there have been a lot of postings recently concerning the Highlevel Hornblocks, and as I had got to that stage, I thought it was high time I cover that side of things here.

Do remember that the etches and axle blocks I have used have been in my stock box for a couple of years or more, and so do not represent exactly what you would purchase from Chris today. On the O4 I had had work to do to ensure enough room for the gearbox between the axle blocks, and calculations I went through a few posts ago suggested this problem would happen again. This may or may not be true of today’s offering. In any event I did two horn block assemblies with special thin axle blocks and the other 4 were built as intended.

The etched bits

Making up the etch is very quick and simple. You can do no better than read Keith's posting on the topic. While we are here a warning, do not do what I did the first time I made them and decide that soldering the folded halves together would improve things. It didn’t. A small fillet of solder developed long the base of the fold out horn cheeks which had to be removed before the axle blocks would slide comfortably. A fiddly and time consuming job you really don’t need.

The 4 Standard Axle Blocks

For the four standard sets, the final job, not covered by Keith’s post, is to fold up the CSB Spring Tags etch, fit it round the lip on the back of the axel block and solder up. Etched tags and the lip on the axle block are illustrated below, in all cases I needed to ease the hole in the etch to fit over the lip on the axle block.

CSB J10 frames 6b.jpg (25.56 KiB) Viewed 4613 times

Once these had been fitted, it was necessary to fettle the axle blocks. Firstly by running a knife edge file round the groove in the axle block to ensure there was enough clearance to allow the axle to rock. Secondly by gently filing down opposite sides of the axle block so they were a close sliding fit in the horn cheeks. Using a 4 cut file meant that more than a few strokes are required, but also that only the really cack handed could manage to file away too much in one go.

Producing these 4, plus the folded etch for the other two, took me about 2 hours, so 30 minutes not 30 seconds each! Note the old style CSB Spring Tag with only two holes and a single fold, and the soft wire keeper to ensure the pairs stay together.

CSB J10 frames 5.jpg (114.18 KiB) Viewed 4613 times

Diversion into the identification of parts

So I know which is which, I mark all bits of the chassis with a centre pop code. I prefer a pop mark to paint because it doesn’t easily rub off! Basically everything on the left of the chassis (facing forward), has one pop, and everything on the right has two. The axle blocks are popped on the bottom where you can see them when the chassis is fully assembled. Where there are multiple similar items, like the axle blocks, I pop them again somewhere else and make sure I know the difference between the item coded 1-2 and items coded 2-1. The axle blocks have the second code on the CSB tab, these are visible in this shot. The etched horn blocks are pop marked too but the marks are hard to make out in the photo.

The two special axle blocks

The last two special axle blocks use the fact that the CSB Spring Tag etch fits around a standard round 1/8 top hat bearing and between the etched horn cheeks, but not at tightly as I would like as the next picture shows.

CSB J10 frames 8.jpg (48.86 KiB) Viewed 4613 times

So I added an axle hole, designed to fit a 1/8 top had bearing, cut from the frames of the O4, giving this set of parts.

CSB J10 frames 6 v2.jpg (42.59 KiB) Viewed 4613 times

I both the CSB Tag and the spare axle hole need fettling to fit the top hat bearing. The spare hole was filed down so it was vertically no higher than the square section of the CSB tag, and just a little bit wider. They were then soldered together and to the top hat bearing, using an aluminium sheet spacer to maintain the grove between the top hat bearing flange and the other two bits. Finally the sides were fettled to be a good sliding fit in the horn cheeks. The result gives me rather more than 1mm additional clearance for getting the gearbox in.

CSB J10 frames 9.jpg (48.3 KiB) Viewed 4613 times

Next Time

In the next post we’ll fit the hornblocks into the frames

[essdee]

Will,

That is a very simple yet elegant solution to the issue of getting the High Level gearbox between the driven axles' bearings - thank you indeed.

Many thanks also for your explanation at Manchester Show of the application of the fulcrum physics to locating the handrail knobs. Having gone as far as a continuous spring wire version of the suspension, I am now minded to go the full distance and use the original spring beam concept. I actually have a pair of Maygib MR 3F chassis on the bench at the moment, will do the second as CSB - using Chris Gibbon's nifty setting jig -to compare the running of the two types of suspension.

Look forward to following the thread - thanks.

Regards

Steve

[Will L]

Having got the hornblocks sorted out, my attention turns to the frames

Earlier in this thread Mike Garwood was asking how you established the axle centre line on a set of pre cut Gibson Frames. See his post.
Well I have been there and done that now, and this is what I have found out.

CSB J10 frames 1.jpg (52.04 KiB) Viewed 4521 times

This picture is of the Gibson pre cut frames for the J10. The axle cut outs are 6mm wide and 7 mm deep. My research suggests that these are “standard” dimensions, the Highlevel hornblocks certainly fit neatly against them. My understanding is that the axle centre line on this "standard" is supposed to be 4mm down from the top of the cut out. Working backward, a bit of careful measuring showed that a J10 built on these frames with the axle centres on the 4mm line will sit at the right height. So that’s what I’m going with.

Gibson Frames are cut so as to come up to the top of the footplate between the wheels, and form a backing to the splashers behind the wheels. Given I’m going to sit a DJH cast body on top, it is necessary to reduce the top height of key bits of the frames by 2mm, the effective depth of the cast footplate.

Marking up the frames

Once I was happy that “4mm down from the axle cut out top” gave a satisfactory axle centre line, marking out the rest was relatively simple. The old Highlevel CSB Spring Tags have fulcrum holes at 3mm and 4mm from the axle centre line. I use the 4mm hole as anything less means the CSB wire can foul the folded back horn cheeks. Given the normal 0.5mm static deflection allowance, the fulcrum centre line comes out 3.5mm above the axle centre line, that's 0.5mm down from the cut out tops.

CSB J10 frames 1a.jpg (53.64 KiB) Viewed 4521 times

The picture shows the frames with the cut out top line, the axle horizontal and vertical centre lines, the fulcrum centre line and finally the new reduced height top line, all scribed on. Some of these, particularly the vertical axle centre lines are hard to see, but I promise you, they are there. The fulcrum points, as defined in the spreadsheet print out, have been marked along the fulcrum centre line and centre punched. As the J10 spread sheet output appeared in this thread several posts back, I’ll repeat it here. You will see that all they key horizontal dimensions are given starting from the wheelbase (p and q). It shows that, despite the asymmetric wheelbase, the chassis top will have a gradient of only 1 in 2697 to the rail head. That’s not quite level but close enough to make little difference. Finally it also shows the centre axle is sprung 8% softer than the outer two. This is perhaps a percent or two more than the optimum but again well within the acceptable range.

CSB exel J10.jpg (83.82 KiB) Viewed 4521 times

Preparation of the frame sides

The next job was to sweat the two frames together, drill out the fulcrum points (0.5mm) then cut back the frame tops to suit the body. This picture was taken when all that had been done.

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At this point I decided that the frame arc over the rear axle was going to be invisible under the cab floor and probably in the way of my planned pick up installation, so it got sawn away.

It was then time to separate the two frame sides, and once that was done, the lower holes, intended for Gibson plunger pick ups which I am definitely not going to use, got filled with brass wire and soldered solid.

CSB J10 frames 3.jpg (64.45 KiB) Viewed 4521 times

Putting in the hornblocks

The horn blocks are soldered into the frames using the Chassis pro. An end stop which can be used to hold the frames in the same place relative to the axle pins is provided, but actually it is as easy to set up a fourth axle pin to do the same job. You use one of the movable longitudinal guides to ensure the frames are kept parallel to the axle centre line, and the square end of a metal ruler is held firmly against this guide to ensure the hornblock sides are vertical.

CSB J10 frames 10.jpg (137.63 KiB) Viewed 4521 times

This picture is of course a fake, taken after the event and after the next stage (fitting the fulcrum points) had been completed, but it does show you what I mean, I hope. Also note my own first appearance, if only ever so partial, in any of the photo’s in this thread.

Then its time to set the fulcrums

I used Romford short handrail knobs which are designed to hold the handrail 1mm away from the surface the knobs are fitted into. First drill out the fulcrum points holes to fit the handrail knobs (0.75mm or as I prefer 0.7mm and ream to fit). It turns out that 1 mm isn’t quite long enough, so rather than pushing them fully home, I put a nice rigid wire through the CSB Spring Tags with the handrail knobs threaded on. This held the knobs at just the right height while I soldered them in place. Pictured is the completed chassis side.

CSB J10 frames 4.jpg (74.68 KiB) Viewed 4521 times

Addendum re the special thinner axle block , i.e. the one on the right above

My original calculations suggested that reversing the CSB Spring Tag on the much thinner third axle block would leave the fulcrum point holes well aligned through all the axle blocks. Practicalities proved otherwise. To ensure the CSB spring was kept parallel to the frame, it was necessary to elongate the hole in the thinner third axle block CSB spring tag quite a lot. Easy enough if you have a “seconds” file which fits through a 0.5mm hole. The alternative would have been to re drill close up to the bend in the tag.

Diversion about Seconds files

I don’t know what I would do without my seconds files. They are called this because clock makers used them to file out the filigree in second hands. At the tip they are rather less than 0.5mm and enable you to file out holes and slots that are very hard to do any other way. Trouble is they are expensive. The round ones are about £11 a pop on Shesto’s web site and the square ones are three times that price. They are by Vallorbe but to find them you need to search for “seconds” as they don’t seem to show up in the files list otherwise. Eileen also has them under the name of escapement files, which they are not, and at an even higher price. Escarpment files are rather bigger than seconds files, come in more different and complex shapes and look like needle files that have shrunk a bit.

The fact that these things sell at these prices is some indication of just how useful they can be. I don’t think I paid that sort of price for my stock so you may want to buy them and lay them down as an investment. I’m beginning to wonder if I need a post an armed guard on my tool box. If you do decide to invest you have to remember that, while remarkably flexible when you use them, they do brake quite easily. It is of course the thin bit which brakes, but I keep the stubs so I can use them when the really fine end isn’t required.

I’d be interested to know if anybody has one of the Diamond Reamer & File Sets Shesto are selling and if they are equally thin. Could be a cheaper alternative.

Enough of these ramblings

Next will come sorting out the frame spacers and putting the chassis together.

[Russ Elliott]

Will - when setting the hornguides on the frame, you didn't mention this (not particularly critical) dimension, but I guess you must have considered it:

hornguide-height.gif (1.91 KiB) Viewed 4474 times

[Will L]

Rus

Flattered by your trust but, having used the Highlevel blocks before, I didn't give it a moments though. The O4 set up was identical and that worked OK. But now you have made me think about it...

I'd set the axle centre line 4mm down from the Chassis cut out top. The hornguide etch is positioned by the turn under tab, which clips the two halves together, resting against the top of the chassis cut out. Hence the horn guide etch cut out top and the chassis cut out top align, but the headroom available for the axle block is reduced by about 0.5mm by the turn under tag. I.e. the effective top of the cut out is now 3.5mm from the axle centre line. That is in line with the fulcrum centre line, which I assume to be the strait answer to your question.

CSB J10 frames 11.jpg (32.21 KiB) Viewed 4394 times

Thinking further. The axle block is 4.8mm (from your post under Hornblock Choices), so will top out 2.4 above the axles centre line. The CSB Spring Tab hole I used is 4mm from the axle centre line leaving 1.6mm from top of the block to the fulcrum hole. So take off the 0.5mm for the static deflection, and another 0.5mm for the dynamic defection and 0.15mm twice because, as you pointed out, the CSB wire won't sit in the centre of the fulcrum holes, and you still have 0.3mm clearance between the top of the axle block and the under side of the turn under tag on the guide.

Which seems to justify my faith that it would work, and suggests Chris knew what he was doing when he designed the hornguide etch.

Will

[Will L]

One of the reasons why there hasn’t been a posting on this thread for a while is because I have been busy doing other things. One of which was doing some upgrades to the O4 which started me off on the CSB thing in the first place.

Ever since it has gained its place as a regular performer on Knutsford East, the O4 has been short of two things. On was the brake gear and the other was the crew. These omissions have now been rectified and strangely both have had an impact on the performance of the CSB chassis, and stranger still it was the crew the proved more significant.

The Break Gear

The break gear was a sad story. There are a lot of relatively small wheels under the O4, all very close together. As a result there isn’t a lot of room for the break gear and the miscellanies sand pipes which live down there. When the loco was first finished and tried out on Knutsford, I left the break gear off. This was to ensure that any shorts, or other difficulties that stemmed from cramming all those bits of metal between the wheels, didn’t mask the underlying chassis performance. Once she had demonstrated that she was a reliable performer, I went to refit the break gear, only to find it had mysteriously vanished from my work bench. Somehow I could never summon up the energy to manufacture a new set, so the poor thing ran breaklessly for a couple of years. About a couple of months ago I was moving a heavy box and there, underneath it, was the rather flattened remains of the O4's beak gears.

You will be pleased to hear that it was recoverable, and this week end, at Huddersfield, she set out for the first time fully clad with brake blocks, hangers pull rods and sand pipes. I think we can now say that reliability has been retained, but half way through Saturday afternoon there was one incident which at first sight looked like a significant CSB problem. The horn blocks on the fourth axle had jammed at the bottom limit of their travel. Not unnaturally the loco no longer stood level on the track and derailed. She also now had a permanent short. Ignominiously she was declared a failure, and removed from her train.

Worried I tried to work out what sort of chassis malfunction could have caused this problem. Was it CSB related? There are non believers on the team and you have to be so careful not to give them ammunition. An examination revealed that for some reason the brake blocks on the fourth axle had moved slightly to one side and got caught on the connecting rod. This pushed the brake block against the wheel tread, which forced the wheel down to the limit of travel in the horn block, and caused a short. Untangling the connecting rod and break gear was not trivial, but once I had them apart, and the break gear readjusted to ensure clearances were maintained, she was fully back to her old self. A test up and down the fiddle yard was successful so she was returned to traffic, and soldiered on reliably for the rest of the show.

The Crew

So while it is reasonably easy to see how the break gear and the suspension could come into conflict, how was fitting a crew so significant from a CSB point of view?

Simple really, the crew are both brawny men cast in white metal, and the cab is well aft of the rear axle. Once the crew was aboard the loco showed a significant tendency to go strait on at corners! My test track has a 3’6” reverse curve in the middle. Nothing leaves the workshop until it will reliably negotiate it. Before crew it did, post crew it would not. Once the initial shock had worn off, it didn’t take long to demonstrate that the advent of the heavy weight crew had moved the locos Centre of Gravity backwards significantly. The result was that surprisingly little weight was now bearing on the front driven axle, certainly less than when the CofG was in its designed place, even though the all up weight was greater. Even then it was not immediately visually obvious that the loco was sitting down at the rear, and high at the front.

Fortunately the smoke box and smoke box end of the boiler was mostly empty. Getting the CofG central over the coupled wheelbase when she was built had required most of the weight to be placed well back in the fire box. The fix to this self, or crew, induced problem was a lead Swiss Roll that was a good tight fit inside the boiler/smoke box. This restored the CofG to its proper place. The loco is now noticeably heavier, but still passes the “is able to spin her wheels if she meets an immovable object” test. Normal performance was fully restored and my test track was once again negotiated reliably. Pulling power has probably improved but will never be adequately tested on Knutsford whose fiddle yards limit train lengths.

The morals of this story

1. Be careful where you put your boxes.
2. When ballasting your loco, don’t forget to include the crew in your calculations. This was an object lesson in the need for the correct relationship between the locations of the fulcrum points and the CofG, and that getting it wrong can have a significant impact. On the positive side it did show that so long as the chassis was properly designed, getting the balance of the chassis right can be done just by adjusting the CofG location and doesn’t require a reconsideration of where the fulcrum points should be.

So here she is, clearly clanking, if only metaphorically, her way through Knutsford on her normal heavy freight duties. Both crew and break gear are in evidence in this photo.

HS-O4.jpg (142.7 KiB) Viewed 4297 times

[martin goodall]

Exactly how much does a pair of cast whitemetal figures weigh? It can't be very much, surely.

Is a few extra grams added to the back of the loco so critical (as it seems to be from this description)?

This seems to suggest that CSB springing requires some very careful balancing of the loco, which I must confess has rather dented any enthusiam I might have felt for experimenting with this system.

[Will L]

Exactly how much does a pair of cast whitemetal figures weigh? It can't be very much, surely.

Is a few extra grams added to the back of the loco so critical (as it seems to be from this description)?

This seems to suggest that CSB springing requires some very careful balancing of the loco, which I must confess has rather dented any enthusiam I might have felt for experimenting with this system.

Don't know, didn't weigh them, perhaps I should have. These were Dart Castings which are quite chunky, unlike the Alan Gibson crew who are lightweights by comparison.

Any way I think your assumption that the crew represents just "a few extra grams added to the back of the loco" is, how can I say this nicely, misguided. Though clearly I made the same assumption myself until I was faced with unexpected behaviour from the loco.

In actuality, it is not just the weight that is important, but also the distance from where you want the CofG to be . In this case, on what is a long loco, there is quite a distance from the back of the cab, where the distinctly chubby fireman is taking his ease on the cab side seat, to the desired balance point between the centre two wheels. The lead weight needed to bring the CofG back to the centre point was substantial, partly because it was not as far forward of the desired CofG point as the crew was behind. Imagine a plug of lead 20 mm long by 12mm in diameter.

In any event all I had to do was ensure that the point of balance of the body returned to somewhere roughly mid way between the middle wheels, which I don't think is a good fit against any definition of "very careful balancing".

Obviously I too was surprised at the level of impact, but I think all this demonstrates is that getting the CofG over the centre of the coupled wheel base is an important, if not technically very difficult, step to take. That then should be all the modeller, who doesn't want to be concerned about the detail of physics behind all this, needs to worry about.

However, for those like me who would like to understand in more detail what is going on, I would like help in understanding what the impact of moving the CofG about has on the weight distribution on a CSB chassis.

Hallow Russ, I'm probably thinking of you here.

I can do the simple two axle case OK, but I'd like to be sure I knew what I was doing when trying to tackle the 3 and 4 axle cases. What I would really like to be able to do is plug into my spread sheet the all up weight of the loco and the position of the CofG relative to the axles, and have the spreadsheet work out how the weight would be shared out across each wheel.

In the case of the O4's 4 axle chassis, it seems that when the CofG got back to the vicinity of the third axle, the effect was to significantly de-load the first axle, but I would like to be able to model the effect in the spread sheet to see exactly how critical the CofG location actually was.

[grovenor-2685]

Hallow Russ, I'm probably thinking of you here.

Should that not be "Hallowed Russ, I'm probably thinking of you here".
Cheers

[Will L]

Should that not be "Hallowed Russ, I'm probably thinking of you here".

Spell checkers, don't you just lov um.

Will

[Hardwick]

I know it's not really relevant to the mechanics of all this CSB stuff but just to show that nothing is new I found a drawing in Model Railway News, December 1954 p260 with what M G Foster calls 'long leaf springs'. The concept seems very familiar.

[Will L]

Right. After a delay while I have been sorting out other things, it is time to get back to the J10 chassis. It is worth remembering at this point that we are fitting a chassis against an existing body here, and that the body separates into footplate and boiler assemblies as seen in the second photo of this previous post.

The Frame Spacers

When we last left it, I had the two frame sides prepared with the horn guides attached. The next step is to sort out the chassis frame spacers. Like the tender I used L shaped ones, but this time only three of them. I like L spacers because, properly made, they help ensure you get a nice square chassis, even if you don’t have a fancy and expensive chassis making jig to play with. Given the thickness of the frames (0.7mm) just two spacers, one at either end, would probably be structurally sufficient, but the middle spacer has other jobs to do as well. The spacers are positioned as the following diagram, which also shows the final profile of the frames. You will note that this profile has undergone further re-work since they last appeared. Basically this was to remove bits that will be invisible under the firebox/cab and where I could use some extra space.

csb draw 10 fspace.jpg (54.11 KiB) Viewed 4525 times

The CSB implication of this set up is of course the need to ensure the path of the beams on the inside of the frames is clear. This was easy to achieve, only requiring that all three spacers have 2mm clearance holes which are centred on the fixed fulcrum points centre line. Simple to do so long as your have thought about it in advance. In practice these holes weren't quite enough on the middle spacer which is quite close to the centre of deflection on the beam. The holes in that one had to be extended upwards a little bit to clear the beam at full deflection, suggesting that this spacer had actually gone in a fraction low.


The Front and Back Spacers

The front and back spacers are fitted flush with the top edge of the frames and contain the bolt holes for mounting the chassis to the body. The measurements of where these holes should go are hard to get exact, so they were drilled under size and opened up to give an exact fit against the cast footplate once the chassis was together. The photo’s to come will tell you I got one of these very wrong and I’m puzzled as to where the 5mm measuring error came from! I considered using the vertical arms of the end two spaces to provide the fulcrum points, but decided against. Partly because one of the body mounting holes aligns with the fulcrum point at that end, but mostly because I thought I ought to do one chassis “by the book” so to speak with a full set of handrail knob fulcrum points.

The Centre Spacer

The centre spacer has a couple of additional uses, beyond holding the frames the right distance apart. It went in the opposite way up to the other two.

The first additional role relates to the fact that, on the cast body, the firebox front is missing, along with a chunk of the bottom of the boiler. This is so you can get a mechanism in. Built as DJH intended, bits of motor remain unashamedly on view. I plan to have the motor fully hidden within the boiler/firebox but you’ve still got to get the new chassis in. Therefore, as I want to replace the missing bits of boiler and firebox, I have to mount them on the chassis under the motor. The vertical arm of the middle spacer is used to emulate the missing front of the firebox, a role which dictated exactly where the spacer had to go within the chassis. In due course it will also have mounted on it a chunk of the underside of the boiler. As I didn't expect to get everything exactly the right shape by measurement, the vertical arm of the spacer started out both wider and longer than necessary, and was cut back to fit once I had the chassis together and fitted to the footplate.

The second use of this spacer is that the horizontal arm forms a tray low in the chassis to which the pickup assembly, and details like the ash pan, can be bolted later. The overall length of this horizontal arm is limited by the gearbox, exactly why will become clear as we go on. I have a strong preference for having the pickups as bolt on sub assemblies, rather than permanently fixed to the chassis. I can’t see how you can possibly give the chassis a proper scrub down before painting if your having to work round carefully adjusted but eminently bendy pickups. As I prefer screwing bolts into tapped holes rather than fiddling about with loose nuts, an additional layer of metal is sweated centrally on to the horizontal arm of the spacer, before being drilled and tapped 12BA. That said I’m not quite sure how the bolt on bits are going to work out yet, so look out for changes of mind in this area.

Making the spacers

To manufacture the spacers I started by producing a brass strip the right width, from which all three will be cut in the same order as they go in the chassis. This is to ensure they are all of matching width. As I wanted the chassis to be 16mm wide and the frame sides are 0.7mm thick, this strip needed to measure 14.6mm. I used 0.45mm brass stock sheet, with a nice strait edge, from which I cut the strip slightly over size. The best way to cut such a strip is by scoring the sheet deeply with a scrawker, and then bending till it brakes. You then file it back to the correct size, cleaning up the edges and achieving a flat parallel sided strip to a tolerance of about ± 0.05mm without to much difficulty. Squaring off one end I then marked out the three spaces I required as in the following diagram.

csb draw 09 fspace.jpg (89.66 KiB) Viewed 4525 times

It is important that the fold lines are truly square across the strip or the spacers will have an inbuilt twist which will defeat all efforts to put the chassis together square. Also note that the position of the holes was measured from the fold lines to ensure they are accurately placed. Once all the holes have been drilled, the fold lines were carefully deepened with a 4 cut triangular needle file until a witness line appears on the other side. The accuracy of the cuts wasn’t critical and I made them with a saw. I tidied up the cut ends with a file and bend up the spacers to a right angle. The filed fold lines ensured they bent the full 90%, with a good sharp corner rather than a radius. Made like this the spacers will be the right width, square, and the holes will be accurately placed where you intended, even if what you intended was wrong!

Putting it all together

The following photo shows the spaces placed on one of the frames but not yet attached.

CSB J10 frames 12.jpg (128.45 KiB) Viewed 4525 times

I determined the position of the front edge of the middle spacer/firebox by very careful measurement of the cast body. A lot more careful than that bolt hole! Then both chassis sides and the spacers went back in the Chassie Pro, this time using long axle pins, so that the two chassis sides can be mounted at the same time. The vertical fence was used to ensure they were square to each other. I then tack soldered the spacers into place, checked all was square etc, and soldered it all up solid. The completed chassis was then tried against the footplate casting to ensure that it was a snug fit and went in the right place. Only at that point did I set about opening out the body mounting holes to suit the existing fixing points on the footplate. It was then I discovered my measuring error. Fortunately I had no difficulty in drilling a new hole in the right place.

Then came the tricky job of trimming back the vertical arm of the central spacer so it fits neatly into the hole in the front of the fire box, and goes up far enough to carry the infill piece for the boiler. Having the boiler casting separate from the footplate made this easier than it might otherwise have been. The following drawing may help visualize what’s going on.

csb draw 11 fspace.jpg (152.43 KiB) Viewed 4525 times

Making and Fitting the Boiler Infill Piece.

Making the infill piece for the boiler was fairly strait forward. Firstly I cut a flat roughly rectangular piece of brass which I trimmed back until it exactly fitted the hole in the boiler. Then I cut a larger piece of brass, a touch longer than the finished first piece and 5 to 10 mm wider, this was curved, width wise, to match the curvature of the boiler. No need to be perfect here, close will do, and the edges, where it is hardest to get the curvature right, will end up getting cut away. Next I laid the flat piece into the curved piece so they touched all along the edges of the flat piece, then I soldered them together where they met. By cutting away the excess metal from the curved piece using the flat piece as a template, I ended up with a piece that both fitted the hole in the boiler and matched the curve. All it needed then was a boiler band of thin strip brass soldered on so as to line up with the one on the rest of the boiler.

What I had to do next was solder the boiler infill piece to the upright spacer arm such that, when the body and chassis are assembled, the infill piece is at exactly the right height to match the profile of the boiler bottom.

At first sight this looked a bit tricky. However I fitted a peg onto the front edge of the cut out in the boiler that located between the curved and flat sides of the infill piece (see drawing). That made sure they aligned properly at that end. At the firebox end, the upright arm of the centre spacer had to be shaped so that there was a step in the edge to match the missing bits of fire box front (see drawing again). This ensures it locates positively into the boiler at the right height. These two things together meant that, when the body and chassis were assembled, the infill peace was held in the right place quite positively, and could be relied upon to sit still long enough to be tack soldered in place.

Once that was done I took the body and chassis apart and soldered the infill piece on solidly. All that then needed doing was to cut the upright arm of the spacer back to the top of the boiler infill piece to leave the way clear for the motor. The truth is that while all this was going on I had been trial fitting the motor and gearbox to ensure that clearances were OK, but we will come back to that in the next post.

The Completed Chassis

The next two photos show the chassis once the jobs described above had been finished.

CSB J10 frames 13.jpg (135.03 KiB) Viewed 4525 times

CSB J10 frames 13a.jpg (149.77 KiB) Viewed 4525 times

The final picture shows how the chassis goes together with the boiler. The infill piece is set so as to be slightly recessed, as this makes the joint less obvious from the normal viewing angle on the finished loco.

This photo also shows one of the 2mm holes the CSB passes through, and the way this hole has been extended a bit to clear the fully deflected CSB.

CSB J10 frames 14.jpg (203.82 KiB) Viewed 4525 times

And Next Time

I think that is quite enough for one posting. Now we have the chassis together, the next trick will be fitting the gearbox, motor, wheels and coupling rods.

[Will L]

Which Handrail Knobs Make The Best Fulcrum Points

There has been some correspondence else where about Markits handrail knobs which we all "know" are the archetypical CSB fulcrum. The question was which ones, given that several shapes and sizes are now available, given they have different lengths and it seems each will hold the CSB a different distance away from the frame.

Those who have read my previous posting may have noticed that there is a simple, if not immediately obvious answer, so I passed it on there, and I decided I would repeat my response here too, just to keep all the thinking in one place. You lucky people get the added bonus of a picture too.

If you can forget the idea that they have to be pushed fully home, the short ones (or the Romford Originals) will always do as they have relatively long tails. What you do is fit a stiff wire through the fulcrums on the axle bearings in place of the CSB. Hang the handrail knob off this wire with the tails down the drilled holes and solder them in place. If they are a good fit in the drilled hole, they will go in straight enough. Best of all, they end up aligned at the pitch set by the fulcrum point on the axle blocks, rather than at whatever the pitch they were designed to give when used as a handrail knob. You will still need to files some of the tail off on the other side of the frame.

CSB knobs.jpg (19.15 KiB) Viewed 4425 times

When you’ve discovered this is the way to fit your fulcrums, the next thought that comes is that making your own out of plain brass wire wouldn’t be much trouble, All you need is a jig to ensure you drill strait through the middle of the wire. 0.7mm wire would do.

The promised next instalment, about the wheels and gearbox on the J10, isn't far away either.

[Will L]

The Gear Box.

Before I can assemble the chassis the last remaining job is to sort out the gear box. What follows is not entirely straightforward. I would not like anybody to get the impressing that this is necessarily so. It was my choices that made for complication, but you should have noticed by now that I may well like it like that. You can make different and simpler choices if that’s what suits you best.

Choice of Gearbox

Way back in this thread I suggested I was going to use a Highlevel Loadhauler+ gearbox, but I was already getting cold feet about this as it was going have to sit very low in the chassis, and the clearance between the CSB wires is limited. As I had in stock a Loadhauler Compact+ which isn’t so high, I thought this was going to be a better fit. In either case I was going to use a DriveStretcher so that I could drive the rear wheel under the cab floor, run the gearbox up through the firebox and have the motor in the boiler. This is an outline of what you get for a £21 donation to Highlevel.

csb W&M 7.jpg (64.35 KiB) Viewed 4336 times

When thinking about how Highlevel gearboxes might fit your model, having a look at the gearbox profile sheet from their web site is a must. These illustrations come from there.

All the Highlevel gearboxes with the + suffix have a separate section of frame to carry the last gear shaft and the wheel axle. This allows quite a lot of flexibility in how you mount your gearbox in the loco. They also have a DriveStretcher option which substitutes a longer additional fame with another gear shaft. This extends the reach of the gearbox much further. The DriveStretcher does not change the gear ratio, as the additional gear is just an idler, but it does allow you to drive the axle under the cab floor and still hide the motor and gearbox in the firebox and boiler. This diagram of the final J10 configuration shows how.

csb W&M 7a.jpg (57.36 KiB) Viewed 4336 times

That looks Ok but it isn't quite as simple as it looks. As others have pointed out, there can be issues in trying to get some of the Highlevel gearboxes and hornblocks on the same axle.

Getting it to fit

The early high level gearbox designs, like the Loadhauler, are actually quite wide, exactly why will become clear in a paragraph or so. At 11.8mm the Loadhauler will go between the frames, but not between the CSB wires, the CSB fulcrums or the horn guides. At first sight this isn’t a problem because the D2 DriveStretcher that goes with the Loadhauler Compact+ design, is narrow enough (8.7mm) to fit comfortably between the reduced size axle blocks I’d made for the rear axle, see this previous post. However there is a snag. Put together as Mr Highlevel intended, the DriveStretcher actually fits off centre of the main gearbox frame. So you can’t take advantage of the D2’s sylph like waist measurement without having the main gearbox and the motor significantly off centre, where they will fowl all sorts of stuff. Also, if you look at the installation diagram above, you can see that the main body of the gearbox still has to fit between the CSB wires.

It can all be made to fit, but it takes a little work. The following diagrams show how I did it.

csb W&M 8.jpg (101.36 KiB) Viewed 4336 times

The Highlevel gearboxes are all built around plastic spur gears that are free to turn on metal gear shafts fixed into the gearbox frame. The various gear ratios offered by each design come from different pitch worm gears on the first step down. The subsequent two steps down are common to all ratios and the small and large spur gear pairs that do this are moulded as a single unit. The “as intended” diagram shows how two of these together dictate the width of the box.

As the small spur gear is made quite wide (about 4.5mm), the first step is to reduce the width of the second small gear by 1mm. This is easily done with a fine file. The DriveStretcher can now sit central in the gearbox, and it would be possible to make the main gearbox frame 2mm narrower! I didn’t bother to go quite that far, but I did reduce the width of the bottom section of the gear box frame which is where I need the clearance.

I needed to replicate the bottom section of the gearbox frame sides and mount them just a bit closer together. The original second part of the gearbox frame that I discarded in favour of the DriveStretcher provided me with replacement frame sides. These were already pretty much the right shape down one edge and had the right size hole in the right place. I cut and shaped these to exactly match the shape of the piece of the sides I needed to move inward. To get the right amount of narrowing, I added spacing strips between the original side and the new one. The strip, which was an arbitrary 1.5mm wide was taken from the edge of the gearbox fret.

The new sides were assembled on a length of gear shaft which was threaded through the bottom holes in the original frame sides, and the new side pieces soldered to the frame as in the “as modified” diagram, thus making sure the gear shaft holes remained in the right place. The original sides of the frame were then cut away below the spacing strip. As the gearbox frame was etched from 0.45mm nickel silver, the net result was a reduction in width of 1.8mm. The following picture jumps ahead a bit to show the completed gearbox mounted on the driving axle with the wheels in place.

csb W&M 2.jpg (122.78 KiB) Viewed 4336 times

A couple of final details.

The DriveStretcher, in common with all the extension pieces on these gearboxes, is free to rotate about the gear shaft it has in common with the main gearbox frame. This may be ok if you are mounting the gearbox on a rigid axle and with the motor attached firmly to the chassis, but it is no use where the motor and gearbox are axle hung. The problem with making them a single unit is that you can then find it quite tricky to thread the complete gearbox through the various fixed points in the frames. So I decided not to resort to solder this time. Instead I installed a catch that would hold the two halves in the configuration I wanted but that I could undo at need. To achieve this I drilled a 0.5mm hole through both parts where they overlapped. I then fixed a spring wire to the outside of the gearbox frame which then sticks through the holes. The spring wire that makes the catch can be seen in this picture and also on the installation diagram above.

The bracket on the front face of the gearbox frame is for the torque reaction link, again see the installation diagram above. This allows the gearbox to rise and fall with the axle but not to revolve around it. In theory, to ensure the torque reaction doesn’t interfere with the performance of the suspension, the link must be at right angles to the horn guides (i.e parallel to the track/axle centre line). Judging by some of the posts on the forum, some of you seem to be getting away with breaking this rule, which presumably means the effect isn’t very great, but better safe than sorry.

csb W&M 3.jpg (135.3 KiB) Viewed 4336 times

Finally, another jump ahead picture which shows the gearbox mounted in the chassis just to show how crowded it gets in there.

The next post, about fettling the wheels and assembling the rolling chassis, follows shortly

[iak]

Fascinating Will
To see an auld beastie getting such a tasty new undercarriage is very enlightening.
Its after doing all this of course that a new all singing and dancing J10 kit will appear?
Am I correct in assuming the new High Level CSB bits and bobs will make such re-jigs as this a lot easier?

[Will L]

...
Am I correct in assuming the new High Level CSB bits and bobs will make such re-jigs as this a lot easier?

One would hope!

The new jig certainly looks like it could make setting things out simpler, though I can't comment authoritatively as I haven't got one.

I think Chris has found himself at the cutting edge on CSBs by accident rather than design, and is having to play catch up.
Of his gearboxes it is still only the MicroMisers which offer big reduction ratios in a narrow gearbox frame. As these also go in off centre on the motor, which is in turn very close to the driven axle, they still may not solve the "space on driving axle" problem. As a result, those who want better than 54:1 may be chopping up LoadHaulers, and invalidating their guarantee, for a while yet.

Will

[Will L]

Prepping the wheels

The wheels are from Alan Gibson, and I was a little surprised to discover that they didn't have crankpin hole moulded in. This implies somebody was going to have to drill them. Unfortunately my household is a machine tool free zone, and I was concerned as to how exactly I was going to get all of them drilled with the same, correct, crank pin throw, not to mention at right angles to the face of the wheel. At this point, membership of the Crewe Area Group proved its worth, and Bill Newton volunteered to produce the very thing for me. Bill's home is very much not a machine tool free zone.

csb W&M 1.jpg (97.07 KiB) Viewed 4201 times

The brass block he made for me has a stub axle which is a close sliding fit in the wheel axle hole, and it is drilled 0.5mm at a scale 11” from the axles centre, correct for the J10. The 0.5mm hole and the stub axle are on the centre line of the brass block. In use the block was fitted as shown in the second picture, and aligned by eye so as to be centred on the crack pin hub. A 0.5mm drill was a close fit in the pre-drilled hole which tended to keep it square to the wheel. With a bit of care it was possible to drill the wheels by hand with the drill in a pin chuck. There is a dimple to mark the spot cast in to the crank pin hub on each wheel and I didn’t miss it once.

The drill came out the other side of the wheel just beside the raised hub on the wheel back, this was cut away a little so there was sufficient room for the head of the Gibson crank pin (a 14ba countersunk bolt) to screw in and be set below the top of the hub. No further countersinking was required. You can see this, just, in the third picture. The drilled hole was enlarged to slightly more than 0.7mm using a fine taper reamer and the crank pins run in so as to cut there own thread in the plastic.

You can test if the crank pins are in square quite simply, by spinning the wheel on it crank pin. This can be done in the fingers but is better done in a crank pin bush held in a pin chuck. Either way, the wobble produced by an out of true crank pin is quite obvious. I know I had one. Fortunately, fearing that this whole process might prove a little less than absolutely accurate, I had done a spare pair of wheels. So now I had seven usable ones.

Update. I now gather that the absence of crankpin holes is because these wheels come from early tooling, and while, for the moment, there remain a few wheels in the AG range like this, all later wheels do have the crankpin hole moulded in. I have to say the moulding on these wheels was nice and crisp, and if the tooling is getting older, then these wheels show no sign of it.

So as not to mislead later readers, I've changed the first paragraph above so as not to suggest the absence was in some way a recent change, but as it was quoted by the posts that follow you can still see what I originally said.