Crab Comet conversion

User avatar
Le Corbusier
Posts: 1012
Joined: Wed Feb 11, 2015 3:39 pm

Re: Crab Comet conversion

Postby Le Corbusier » Sun Dec 31, 2017 11:06 pm

20171230_161227.jpg
Tim Lee

Philip Hall
Posts: 1103
Joined: Mon Aug 10, 2009 7:49 pm

Re: Crab Comet conversion

Postby Philip Hall » Sun Dec 31, 2017 11:42 pm

Julian,

Looks as though you are getting somewhere, pereseverance pays. May I say though, that I think your pickup wire looks very stiff from the picture, and might be restricting the free movement of the wheelsets.

I prefer a very thin wire (0.3mm hard brass) bearing on the edge of the flange, at 90° or thereabouts to it, often in the coiled arrangement we have seen on here. I have found that on wheelsets that can move up and down, such movement is restricted or even prevented by collectors that bear at 45° to the flange as you have. An alternative is for the collector to bear directly in the back of the flange, but that means periodic cleaning upside down. The flange edge idea means you can clean wheels and contact area at the same time by running the wheelsets on a solvent soaked tissue or rag placed on the track. I do use the 45° arrangement on fixed axles.

Happy New Year to all!

Philip

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Tue Jan 02, 2018 3:45 pm

Hear hear!

Many thanks again Philip. And Tim for photo magic again!

Yes pickups...however these with some subsequent adjustment are not causing problems, meanwhile I will try to learn the neater and better way of doing it.

As the motion was mostly done in September I have briefly looked at the Comet tender. This isn't a simple slot in replacement as I had thought and severe butchery of either the plastic or brass will be called for. I wonder if anyone has a picture of a converted one? My thoughts had been for a simple compensated tender but now I think a simpler approach may be to stay with the Bachmann chassis, simply stick in some replacement back wheels and somehow arrange to let the other two axles float Sharman style, hanging the front from the loco back. This will give some serious pulling power which I had not been much bothered with getting as the group layouts do not have particularly long trains..

At present the loco CofG is forward of the centre wheel so I can afford some more weight at the back from the tender, without, I surmise, (though others may be able to do better than surmise?), losing weight at the front.
Attachments
20180101_223756.jpg

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Tue Jan 02, 2018 10:16 pm

Just in case anyone was going to dig up a picture, to save them any bother I've started hacking the brass to fit the Bachmann chassis. Haven't got a full plan...probably use the usual buffer springs for the floating wheelsets. They do the job adequately on one other tender I converted.

I made two mistakes earlier. The pony wheelset is 1763-71 area. Bad, I know, but not quite as awful as I measured two days ago.

Lightly loaded floating tender wheels have derailed occasionally on my straight plank running in track. Beefing up of the springs, or other surgery, has followed. The loco is now running in impeccably and hopefully will be tested on a proper layout later this week.
Attachments
20180102_220302.jpg

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Tue Jan 09, 2018 8:53 pm

Jumping ahead a bit here is the first test on the pointwork of the group layout.
https://youtu.be/hhI32G9ckT8
https://youtu.be/5y7ACZ4HvrU
The tender has now had some I would think fairly standard butchery for those familiar with mashing up 00 gauge models. As has the Comet chassis kit, to make it fit. I imagine most people reading this would be more familiar with such tasks than I am. The main issue was to get the ride height correct. I am only having one fixed axle, the rear one. It was necessary to file notches in the plastic chassis, and the guard irons are filed nearly right through, hence a bit of wire to give strength - rather than file away part of the buffer beam.

20180105_132936.jpg
Levels as per the real thing


Even with massive amounts taken out there is only just enough width for the P4 wheels. I had to remove the plastic brakegear. The other two wheelsets will need sideplay so that will be some fun.

20180104_143417.jpg
More needed to come off still...


20180104_222543.jpg
Rear wheels in fixed bearings.


A coupling was confected from a handrail knob to give a similar coupling to a car and caravan. The idea is to give complete freedom of movement between loco and tender. But I should have thought that every mm back from the loco the weight rests increases the leverage, as the real weight bearing back of the loco is between the rear two sets of drivers at the compensation beams fulcrum, the brake rod.

20180105_132538.jpg
Towball!


The tender has been piled high with lead where coal should go. With a weight of 190g predictably the front of the loco became too light on its feet. Some weight was detachable and it now weighs 145g. The loco now weighs 333g. When I've sorted out the valve gear yet more can be squeezed behind the cylinders, just where it'll be most useful.

I've missed out quite a lot of detail which I'll get round to soonish.
Last edited by Julian Roberts on Wed Jan 10, 2018 8:12 am, edited 2 times in total.

User avatar
Le Corbusier
Posts: 1012
Joined: Wed Feb 11, 2015 3:39 pm

Re: Crab Comet conversion

Postby Le Corbusier » Tue Jan 09, 2018 9:12 pm

Julian .... nice to see it running. Will showed me how to embed a youtube video like this ... you simply click the youtube button above and then paste in the specific code without the rest of the address - in this case ALQupJqrGJ8.

You might want to kill the volume? ;)
Last edited by grovenor-2685 on Sat Jan 13, 2018 10:47 am, edited 1 time in total.
Reason: Removed Link as Julian has deleted the video.
Tim Lee

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Tue Jan 09, 2018 9:26 pm

Great thanks Tim. Yes but how to kill the volume?!

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Tue Jan 09, 2018 9:32 pm





User avatar
Le Corbusier
Posts: 1012
Joined: Wed Feb 11, 2015 3:39 pm

Re: Crab Comet conversion

Postby Le Corbusier » Tue Jan 09, 2018 10:37 pm

Julian Roberts wrote:Great thanks Tim. Yes but how to kill the volume?!


I think in the you tube editor you can set the volume to zero.
Tim Lee

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Wed Jan 10, 2018 7:48 am

Crab Test 1 deleted as I can't edit out irrelevant conversation! Tests 2 and 3 still there.

dal-t
Posts: 559
Joined: Mon Jan 11, 2010 8:06 pm

Re: Crab Comet conversion

Postby dal-t » Wed Jan 10, 2018 11:40 am

I really wish people would post large warning notices on videos like that for those of us with extreme vertigo - tummy butterflies just subsiding after three or four minutes! Useful reminder, though, to stick a suitable attention-grabbing notice on the board for my new test track - FIT BUFFER STOPS BEFORE ANYTHING ELSE!
David L-T

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Wed Jan 10, 2018 1:58 pm

Apologies for inducing vertigo or any other illness or annoyance. Only one board of the layout was conveniently available. The point was, to test it over some pointwork. Having folded the tender guard irons to clear the rails running was perfect in each direction.

As this is my first 2-6-0 my interest is primarily in how the loco runs and behaves, though I will write up the rest of the assembly as it happens. Ideally now is the time to explore the issues thoroughly, before the valve gear is on and paint job complete. I think I've understood and solved to my satisfaction the issues of 4-4-0s and 0-4-4s, and locos without carrying wheels, but the issues around a 2-6-0 are less straightforward than I had expected and I want to be sure it runs as perfectly as my previous efforts.

A trip to a layout under construction on Saturday showed up potential faults. There was a board break followed by a curve. A minute downwards change in gradient coincided, as the boards had not been painstakingly levelled to an identical horizontal, this being an informal get together. As I expected, the loco ran onto the curve fine when running solo, but with the heavy 190g tender the front end derailed. The pony stayed on the rails but the front driving wheelset did not, failing to take the curve. So this is the issue I will be looking out for.

Yesterday I increased the weight by about 20g finding a little room for lead near the front driving wheels in the loco body. I then found for the first time a problem going backwards with the loco running solo, the rear wheels derailing. Again, quite predictable. However with the 140g tender (without its detachable weight) order was completely restored, and the ensemble seemed together to be perfectly balanced as per the videos from yesterday evening.

The balance of pony and front drivers is more delicate than I had surmised for getting them to stay on the rails. I had discovered this on 31st Dec. I think that a compensation arrangement between the two would be ideal as, as has been shown, the force exerted by a spring varies so much with the up and down movement, while what is needed is a consistent weight relationship whatever the up and down situation. However that would be impractical in this situation unless thought out from the start. So on this model it will be a case of adjusting the spring force of the front drivers if that is possible while maintaining sufficient weight on the pony, should any further problems arise.

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Sat Jan 13, 2018 9:16 am

20180112_074953.jpg


From here it's mostly final details...but I've very late in the day seen an obvious problem. The loco body is not firmly made! The footplate (or running board?- not quite sure of
correct term) isn't firmly attached at the front below the smokebox saddle. I don't know if it has come loose during the proceedings or was always like this. Explains why I had problem getting chassis really level even before wheels went on, and why I am not getting a good vertical from the front view. The cab is vertical. It's nearly acceptable - I find getting no twist from front to back at all is very difficult - but the amount here is something I'd like to improve.

What alerted me to this was trying to get the loco and tender footsteps lining up on both sides . (The steps are the only things that are level in this funny hybrid mismatch.)

I will report on remedial action. Prior to this a morning spent reassessing the fit of the motion assemblies into the chassis now that the latter seemed to fit the body well and no distortion was occurring when screwed together. The trio of motion assemblies seemed to disturb that fit so they were separated and reattached to each other rechecking at each stage the fit in the body.

20180112_075042.jpg


The valve gear assemblies look like this. The slide bars are very vulnerable as is the motion bracket until all the separate motion assemblies are soldered together to the cylinder assembly. How robust they will then be remains to be seen. The process of attaching the gear will be like a Catch 22 rubik cube. The crosshead can't be slid into the slide bars if all the gear is riveted on prior to insertion as per instructions. And so on...a very calm mentality is going to be needed!

One thing is clear. The clearance of the motion bracket to front coupling rod is limited and that has more bearing on the sideplay and minimum radius than I thought of right back at the beginning. It's a bit difficult to pick out the bracket in the picture from all the other gubbins.

20180112_080016.jpg


Meanwhile here is a pic showing the front pickup and brakes arrangement. The side on view is not showing them to be super subtle but with all the waggly bits they won't be so obvious. Apologies to Philip that my unsubtle pickups still are in place. Till I learn the better technique these do the job and when blackened won't be very obvious.

20180111_174458.jpg

Philip Hall
Posts: 1103
Joined: Mon Aug 10, 2009 7:49 pm

Re: Crab Comet conversion

Postby Philip Hall » Sat Jan 13, 2018 11:52 am

Julian, No apologies needed about the pickups. They’re not obvious from the side view and from your video they seem to work fine. So job done.

Re the distorted body of the engine: I have found this on many RTR models and usually a gentle twist, or sometimes something more brutal, straightens things. A lot of them these days have the main body assembled from several large components, often glued together with some kind of superglue that is difficult to shift. If they have been put together slightly askew, patience and much heaving is required. As an aside, I wish we could find out what kind of superglue Hornby and Bachmann use as it’s much stronger than the stuff we can buy!

Philip

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Sat Jan 13, 2018 3:00 pm

Yes Philip I'll glue this up with Araldite - the proper 24hr stuff!
Attached are pictures showing how much I can move the smokebox saddle. Also ones I meant to attach to show the front pickups
Attachments
20180102_125153.jpg
20180102_104349.jpg
20180112_075205.jpg
20180112_080340.jpg
20180112_080415.jpg

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Mon Jan 15, 2018 8:07 am

A proper test was done yesterday on the layout Kettlewell, which belongs to one of our WS4G members and was being exhibited at Johnstone near Glasgow.

The loco and tender unit was run through the entire layout at full speed put both ways round on the track. No single derailment. I was unable to test it through the place that frequently gives most trouble, the join from fiddle yard to layout, that will have to await another time. But I am reasonably confident that the suspension is working as I intend. The group layout Calderside has more challenging problematic areas but can only be erected in its entirety for shows or on special occasions. I have found however that my ridiculously short test track shows up when there is a problem and when there is not.

So here are a couple of videos. Why do I put this here? Because if a picture says a 1000 words, a video does all the more. You can see what I mean when I say the layout has complex trackwork, and what I mean by full speed, in the first video. The second shows a bit of slow running. And just in case anyone needs reminding this is my 8th loco in P4





Revisiting the issue of the sideways tipping gait of the loco front view, I have realised the problem is one that I thought I'd solved earlier, that I need to adjust one of the beams. Putting a piece of folded paper between beam and axle on the RHS made it stand correctly and was possible without disassembly. So it's quite easy to do the same with a piece of brass but to make it fixed adequately the rods will have to come off and wheel come out. Not a big deal with this fairly easily disassembled loco. (It took a lot more time to make it so but now pays dividends.) I probably won't glue the loco body as discussed on Saturday with Philip simply on the grounds of "if it ain't broke don't fix it" - plainly the glue is broke but it doesn't seem to matter!

User avatar
Le Corbusier
Posts: 1012
Joined: Wed Feb 11, 2015 3:39 pm

Re: Crab Comet conversion

Postby Le Corbusier » Mon Jan 15, 2018 8:18 am

Julian,

I like the videos. As well as helping in following the particular thread, It also gives me a good idea of locos and stock running through P4 trackwork. A good way to set benchmarks for both .... and helpful with problem solving. All very helpful. :thumb

I spent considerable time on Sunday watching Sandford and Banwell this weekend which ran very smoothly.
Tim Lee

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Mon Jan 15, 2018 8:46 am

Cheers Tim. I made the comment about videos in regard to comments made on another thread yesterday that I haven't got time to reply to....!

Philip Hall
Posts: 1103
Joined: Mon Aug 10, 2009 7:49 pm

Re: Crab Comet conversion

Postby Philip Hall » Mon Jan 15, 2018 10:19 am

Julian,

These bodies can be very ‘bendy’ and require a lot of heaving to get them square if they are out of true. Heaving to the point of hearing ominous cracks when you do it! Once I’ve got there, usually they stay put but just as insurance, when assembled, I drop some superglue or plastic solvent into some joints, making sure none gets between the body and chassis.

You say this is your eighth locomotive in P4. I rather think this suggests that you know what you are doing, and the video proves the point...

Philip

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Mon Mar 05, 2018 9:38 pm

Several weeks since I had the right sort of free time to be able to do some concentrated modelling.

A few posts above I referred to an unfortunate tilt of the loco. Having established this was a chassis rather than body fault, this was easily cured by filing a little off one of the beams (the one on the high side) where it meets the centre wheels.

Now to the daunting challenge of the valve gear. I've made a loco with this type of gear before, so I'm not a total newbie. Sometime I'll add a pic of that little beast.

The main problem is the delicacy of the parts, especially the motion bracket. I have to be careful not to grip the model too hard, and I rest it in an old model box with packaging material to support. For now the cylinders assembly is not joined to the three other parts that hold the valve gear (valve crosshead bracket, motion bracket, expansion link bracket).

Having followed the Comet instructions the crosshead is soldered to the droplink, which is linked with rivets to the combination lever and radius rod. The latter has reversing lifting links with solder connection. This means that the slide bars can only be soldered to the motion bracket with the crosshead in position, and with all that lot attached. For the moment I am offering up the cylinders assembly to try it all out, the moment of fixing is being deferred till I'm sure it's all OK.

Day 1 - Sort out the crankpin on the front wheel, arranging the locknut to go upside down. Having done so, plenty of room behind the crosshead which I am fixing in place with 16BA nut and bolt.
20180303_094512.jpg
Crankpin etc arrangement

The valve spindle is at a different level to the representation of the VALVE SPINDLE crosshead GUIDE, it is higher. For the umpteenth time I am adjusting this bracket, this time filing inside to give more room for the top of the combination lever, and re-attaching the crosshead GUIDE piece higher up. Its function on the model is only cosmetic.
20180303_115356.jpg
Valve spindle crosshead guide bracket too low

Test a full revolution is possible with the other end of the radius rod pinned to the dieblock as in mid-gear.
20180303_134724.jpg
Valve guide bracket height ok now

It is apparent that the radius rod is too short, as the top of the combination lever is to the left of the valve bracket that should mostly conceal it. Consider somehow changing the position of the bracket.

Day 2 - Set about how to fix the return crank. I won't solder it to the crankpin BUSH for fear of damaging the other end where it is screwed and glued into the wheel. I solder on a Gibson crankpin retainer with larger side underneath. The long Gibson crankpin BUSH is not long enough, so I countersunk the connecting rod. Now, how to fix the reversing gear in forward position? Looking at close up, I see the radius rod has an outwards step. I'll add pic later. If I can do that with an extra bit of rod it will bring the combination lever forward to the right place under the valve spindle crosshead guide. Tricky soldering job, adding this 1.5mm long piece with 2 holes, one to the radius rod, and one to the expansion link (which must be free to move). For the first time I used some old fashioned hard medicated "Bronco" type toilet tissue that a pal and devotee of retro items had found for me about 15 years ago - and it worked perfectly for this task too! Unfortunately I'd forgotten to ensure the pinhead behind was suitably protected from soldering up. But amazingly I was successful at de-soldering it without everything else at the same time, by covering the pinhead with gear oil and then applying the iron - as soon as it moved I kept moving it while it cooled - lucky.

20180304_142509.jpg
Extending radius rod


All was assembled, no mean task, and it could all go round. Later I found the expansion link to radius rod connection was broken or had unsoldered.

20180304_145026.jpg
Trial fit


Day 3. Bite the bullet, re-fix the errant pin, this time with plenty of blue marker pen where I'd forgotten yesterday. More detail would be even more boring, here is a picture of the set up. I got there in the end. But I made the gear to be nearer midgear so the movement will be less to make things easier.

20180305_100524.jpg
Horror resoldering!


Consider how the return crank is to be screwed on so that at the correct throw it is firmly down on the bush so not totally relying on the Loctite threadlock to keep done up. I found some ancient unused very thin brass shim, thicknesses .03, .06, .10mm. Easily cut and trimmed with scissors. A piece of .1 and .03 below the bush brings it up just nicely.
20180305_121530.jpg
Shim cut to size

Really I need to widen the countersink on the con rod without deepening it, but I haven't thought how to do that yet. (Later I found a 7.5mm drill gave the right width countersink.)
20180305_133615.jpg
Situation now

Haven't time to write this in proper English but doing it in quasi shorthand in case anyone finds these notes useful as some have kindly said.

This has been edited, with correct names in CAPITALS, about two weeks after first posting, which was hurried.
Last edited by Julian Roberts on Fri Mar 16, 2018 8:52 pm, edited 4 times in total.

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Mon Mar 05, 2018 9:59 pm

Some additional pictures.
Attachments
20160506_180352.jpg
Welshpool loco in 4mm scale 009
DSCF7014.JPG
Detail of where radius rod joins the expansion link
Walschaerts Valve Gear diagram Snip.JPG

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Wed Mar 07, 2018 9:00 pm

Next, work on the valve spindle which so far has been a Peco track pin bent to a right angle at the end or a piece of 0.7mm NS rod with a short right angle L shape at the end.

Not much point in making the valve spindle move if it isn't noticeable...but the real thing has some shapes ( I've no idea what they do) that make the movement more obvious and are not difficult to replicate.

20171119_104949 (Large).jpg


To start with I was going to make a kind of pinhead but realised a square shape could replicate what is really there yet have the same (model) function, to keep the valve spindle hooked onto the radius rod.

A little piece of 2mm strip was attached to the end of the rod, which was then threaded through the radius rod, to look like this:
20180306_115431.jpg
Rectangular "pinhead"

Then a piece of square tube with round tube inside was soldered together. This was slipped over the valve spindle and soldered on to look like this. A trifle over scale perhaps, but for now I'm considering that artistic licence, a bit of exaggeration for effect.
20180306_121607.jpg

Contrary to my expectations it proves possible to wind the assembly on or off at the return crank by moving the wheel back and forth as necessary.

The assembly revolves and waggles freely without any snagging but before going further the LH side has to be made.

I don't know what I have done differently on this side but the valve bracket seems to come in the right place relative to the radius rod and just needs a small height adjustment of the exterior piece to align with the valve spindle. Only a little more clearance is needed for the top
of the radius rod. So the radius rod won't need any perilous extension piece. (I will edit this to be more clear)
20180307_192740.jpg

The angle of the spindle in the cylinder can be altered as the rear hole is a slot. With the tube for the spindle parallel to the slide bars the tube is in the centre of the slot, and lines up with the centre of the dieblock. Which I altered earlier on to be in this position, slightly lower than as the kit design, but as per photos etc.

Here is a picture in more close up of how there isn't quite enough clearance above the radius rod where it joins the combination lever. It is simple to file material away. Bit of a shame, the etch being so nicely modelled.
20180307_192729-1-1.jpg
Not much clearance for top of radius rod and combination lever


Here shows the outside piece removed for repositioning in line with the valve spindle, which is in line with the midgear position. The slot in the rear of the cylinder can be seen, with the tube now in the mid position.
20180307_220622.jpg

20180307_220622-1-1.jpg
Same thing close up


Now the outside piece representing the valve crosshead is back repositioned correctly
20180307_221918.jpg
Last edited by Julian Roberts on Thu Mar 08, 2018 10:16 am, edited 1 time in total.

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Thu Mar 08, 2018 10:10 am

I've expanded and hopefully clarified the previous post.

Looking back I see I didn't cover here the issue, very tiny indeed in the grand scheme of things, of the height of the expansion link bracket. The kit as it comes gives this to be flush with the footplate underside. But if you look back to the prototype photo in the previous post or any photo, and indeed the Bachmann model, there is a gap between the two. It's not difficult to deepen the slot in the chassis to get the right amount of separation.
2009-05-11_123314_crab2.jpg
2009-05-11_123314_crab2.jpg (69.01 KiB) Viewed 743 times


2017-08-31 12.53.03 (Small).jpg
Assembled as per instructions
2017-08-31 12.53.03 (Small).jpg (49.36 KiB) Viewed 743 times

2017-09-03 12.15.37 (Small).jpg
Bachmann model
2017-09-03 12.15.37 (Small).jpg (69.63 KiB) Viewed 743 times


Whether it's correct I don't know, though the Bachmann model is pretty dead on I think, a 3mm piece of strip fits below the footplate to meet the dieblock pivot point.
2017-09-03 12.21.53 (Small).jpg
2017-09-03 12.21.53 (Small).jpg (71.86 KiB) Viewed 743 times


This ends up to give a straight line between the midgear position and pivot of the dieblock, to the valve spindle. This would be as per a drawing one reader kindly sent, but which can't be reproduced here for copyright reasons.

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Mon Apr 02, 2018 7:33 pm

Making Tectonic progress...on the LH side I could remedy some mistakes. Before joining the two layers of connecting rod I opened the hole of the outer one sufficient to clear the Gibson crankpin retainer (which is soldered to the return crank).

The eccentric rod needs a smidgen clearance from the return crank. I had not noticed the generous array of etched washers, some half thickness and ideal for this spot, that come with the kit.

As I did not have to create any extra length to it, the radius rod is riveted to the dieblock. This gives more range of movement than I managed on the RHS, and to get the most "waggle", the rod is in full forward gear. One could argue that whatever the position of the gear it will be unrealistic some or most of the time!

On this side I had not commenced by soldering the droplink to the crosshead which is the Comet suggestion.

INSTALLATION SEQUENCE AND VALVE GEAR

Once the slide bars and cylinder are fixed to the motion bracket the crosshead may be slid in but not if it is attached to the valve gear, nor even if it has a bolt fixed to it.

However after experimentation I have established it is possible to thread the valve gear into position while the slide bars, crosshead, and connecting rod are all fixed in place as per the photo.
20180319_201937.jpg

Testing the loco without the valve gear but with connecting rod, crosshead and slide bars affixed enabled me to fully check for gremlins in the running before going on to the final valve gear attachment stage.

So, I have abandoned the instructions and separated the RHS droplink and crosshead. The valve gear is separate and removable. For this it needs to be bolted on. A 16BA screw head in the connecting rod is soldered to the crosshead.
20180316_155103.jpg
Crosshead and con rod soldered together.


The droplink does not seem to very readily fit on the crosshead. It is flimsy and easily bent. I attached some metal so that it 'sits' more positively in the crosshead when held down by the nut.
20180316_101749.jpg
Strengthening the droplink, first stage. Then filing...


It is possible, with the droplink separate to the crosshead, to feed the valve gear assembly into position, provided the valve spindle is not too long, and the combination lever is able to swing up to the angle shown in the photo.
20180317_122141.jpg
Trial fitting valve gear.

The shape of the valve spindle pinhead (just as a reminder I am freelancing here with a separate valve spindle) and the cosmetic square section must be minutely filed to achieve the required movement. Once in position the assembly will be retained in the dieblock and reverser shaft with pins which will be removable.

A lesson I have learned before is: never assume each side will be precisely the same! As already found, the valve crosshead is in the right place relative to the end of the radius rod unlike the RHS. But the valve spindle is closer to the outside and so it has to hook on to the combination lever the other way round.

On this LHS the reversing mechanism is located. I can't see part 35 of the instructions on the loco and have left it out.
20180402_141725.jpg
Diagram of valve gear from instructions

Having taken the trouble to photograph the NRM Crab I found myself impelled to make the very simple modification of the kit to represent how the reverser works, with a shaft linking the two passing through the boiler cladding, which drops down vertically behind the frames. This means cutting a little out of the model loco frames, which if visible can easily be repaired with a representation of the boiler cladding through which the shaft passes. A single pin arrangement will be able to retain both reversing arms.
20171119_102617.jpg
Reversing shaft goes through boiler cladding. Frames are not full height


20180312_225333.jpg
Reversing shaft


One thing I had thought was that the reverser was too low on this model and on photos of other ones for the gear to be able to be in reverse. However in fact the arm is cranked and when in full reverse the radius rod is in front of the reversing shaft.
Capture motion 3.JPG
Radius rod goes in front of reverser in higher (reverse) positions


STEPS

After fixing the steps to the lower slidebars it was clear that there is almost no space between step and union link. So the droplink must not be at all bent. There is just about space given that the step is cleaned up and the rivet filed down. Where things may hit each other I file rounded edges to the collision points.

MOTION BRACKET

This bracket is etched to have a gap at the top. Maybe so that it is easier to assemble the Walschaerts gear. But this is not how the prototype is, and a problem is that this gap weakens the assembly.
20171119_102129.jpg
No gap at top of motion bracket

Coupled with this, at least as I have assembled it, the bottom of the bracket fouls the front coupling rod, and would do even if there were no sideplay.
20180316_092724-1.jpg
Bottom of motion bracket fouls coupling rod - at least by my hand!
20180316_092724-1.jpg (326.27 KiB) Viewed 553 times

Significant filing of the bracket was needed to clear the coupling rod. I have slightly bent the bracket outwards which closes the gap at the top a little. With the slidebars firmly attached the motion bracket is reasonably robust. Beefing up this bracket was Tim Venton's suggestion back on Page 1 and this is always in mind. A final step will be to fill the gap at the top.

Julian Roberts
Posts: 584
Joined: Sat Jan 09, 2010 11:33 pm

Re: Crab Comet conversion

Postby Julian Roberts » Mon Apr 02, 2018 8:47 pm

SANDBOXES

These are far from being the straightforward task I had imagined. Only the rear ones could be fixed directly onto the frames, the others needed to be spaced out. Provision for the three gauges ceases but the problems were greater than that.

CENTRE SANDBOX

Fortunately I had taken several pictures of this area at the NRM to guide me through this rather inadequate part of the kit. Here is a photo from the past that shows everything nicely clearly. The light must have been just right to catch what are often obscure details.
6731235145_4a48c32159_z.jpg
A useful photo
6731235145_4a48c32159_z.jpg (119.23 KiB) Viewed 536 times


As far as I can see what there is of the box is cast back to front.

A bigger problem however is that it only represents the top half of the box. In reality it drops down behind the D ring.
Both the following photos need to be rotated 90 degrees clockwise.

20171119_103546.jpg
Closer still.


After much time wasting the easiest thing to do was to make a backing piece for the D ring, as per the prototype. The next prototype pics need rotating anticlockwise 90 deg.
20180329_184459.jpg
Backing piece for D ring

This adds to the strength of the motion bracket, and gives a surface on which to solder the casting.
20171119_103837.jpg
The D ring is full depth. The sandbox sits around it. Needs orientating 90 degree anticlockwise

20180329_202758.jpg
Strengthened deepened D ring with casting fixed on LHS

20171119_103819.jpg
Showing D ring depth and fit of sandbox. Again needs rotating anticlockwise 90 deg


The lower part of the box was fabricated from telescoping square tube enclosing a tube of ID 0.5. This was filed to a representation of the shape and fixed to the D ring.



FRONT SANDBOX.

This is correctly shaped but needs to be spaced out from the frames by about 2mm to appear correctly against the cylinder. (I am making this with EM spaced frames.) It is precariously fixed to the cylinder with 70 degree solder. The orientation is horizontal and not in line with the cylinder.
20171119_103313.jpg
Front sandbox. Needs orientating 90 deg clockwise.

DSCF7014.JPG
Shows orientation of front sandbox



The same 0.5 ID tube was first fixed in front and rear sandboxes.
20180331_110543.jpg
Tube inserted in front and rear boxes for sandpipes.


REAR SANDBOX

The height of this is wrong. It needs about 1mm or more filed off the top. Otherwise the rods may clout it as well as looking wrong.
20180331_164751.jpg
Rear sandboxes height reduction.


SANDPIPES

It was at this point I realised I won't have this finished by Scalefour North! Looking at Dave Holt's model I could see there was plenty of subtlety still to go, and how was I to make the various parts still disassemble?

The rear box sandpipes are fixed. The bracket descending from the frame is boiler band material, very thin. The hope is that the pipes will be able to flex out of the way when removing the centre wheelset.

As an aside it's interesting that two jets sand the centre wheels but the rear ones get none.

The centre box sandpipe is just a slide fit. The pipe is anchored at the business end by soldering to the brake shaft and a bracket which is itself soldered to the brake pull rod. Thus the detachable brakes now have the centre sandbox pipes to thread into place too when removing and refitting.
20180402_093859.jpg
Current state of play.


The front pipes will be fixed to the front brakes (another removable assembly which retains the front wheels). They will not thread into the box as they get hidden on their way up there so will not exist.

Looking at the last photo I see the running board is slightly bent. So that's another thing to be corrected, hopefully a small task.
Last edited by Julian Roberts on Fri Apr 20, 2018 8:17 am, edited 1 time in total.


Return to “Steam Locomotives”

Who is online

Users browsing this forum: No registered users and 1 guest