FINE RUNNING

[Alan Knox]

Thanks to this thread (which I've found to be most interesting) I now understand how Chris's 'Tufnol radial leg jig' shown in MRJ 221 works - the penny didn't drop in 2013!
However I'm still a little puzzled: the photo shows it being used with an already erected chassis, but clearly it would (or should!) have been used originally to set hornguides/axleboxes on each frame and solder in position before erection. I can't find any reference to how the frame members are put together with the spacers - is there another mode of the jig which is used for that which isn't shown? I'm sure jig axles won't be involved.....!

[Will L]

Gordon Bennett, Will, you seem determined to trash my perfectly sound engineering.

Oh I don’t think you should look at it like that Dave. We both know that when playing with chassis we have to have a keen eye for small but potentially significant sources of error. I think on that basis it was a fair question, but I was not at all surprised to find you had already given it thought.

I have already explained how locating the hornguides directly eliminates any error from their uncertain positioning when the axles are fixed by a jig because the hornguides can still be moved a little. …I'm sure that using one of the modern assembly jigs enables more consistent results to be achieved than with jig axles but they don't tackle the basic issue that play in the components leads to uncertain positioning.

But, given that whichever method of setting the thing out one uses, the sames clearance between axles, bearing blocks and horn guide will be present. I remain unclear as to why building around precise placement of the front horn guide face set in the etch source drawing is in practice any better or worse than building around precisely placed axle centres jiged on the rods set by the etch source drawing?

At this point I think I should say that I am not familiar with your kits. Not because I have anything against them, it’s just that our areas of railway interest don’t really overlap. That and the fact that I have long owned as many loco kits as I’m ever likely to build. So I certainly don’t want to suggest there was anything wrong with your kits. In deed I applaud idea that you should designing in ways to help ensure build accuracy. I rather wish the designers of my kit pile had had the same impulse.

As soon as you pick up an etched kit, Will, you're not building a one-off - it's one of a batch.

You’re thinking like a kit designer again Dave. For you, kits may well come in batches. When it hits my work bench my build is a one off.

[davebradwell]

At last, Will. you've come up with the right question - the one I've been trying to answer but not realised what it was. The chassis builders' equivalent of life, the universe and everything.

If you use your jig to hold the axles at the desired spacing and the clearances in the components (as described earlier) allow the hornblocks to be slightly out of position, when you take chassis off the jig the axles will reflect the new positions and will not be the exact match to the rods we require. By actually locating the hornguides correctly (and I've changed the word here because I use separate fronts and rears) then the clearance in the components will allow the axle to move about a bit but the centre of this movement will be the correct position. I further reduce this clearance by separating front and rear hornguides, the second being added using axlebox as a spacer so minimal gap.

To summarise, with axles set in a jig, a hornguide can be out of position by the amount of clearance, the clearance then allows the axle to move about this new position on removal from jig. By setting the hornguides, any clearance will be around the correct position.

When using a jig you might get some of this advantage by always pushing the parts in the same direction but that assumes all clearances are equal.

Looking at the situation differently, if you make a chassis with a very close match between rods and axle spacing then it can wear considerably and still work well. Most rtr are probably in this category as they have significant clearance. If spacings are mis-matched, and chassis relies on oversized holes in rods to function without binding, then I suggest it will start to lurch more as it wears.

Some of us remember clapped out locos at the end of steam, particularly WDs and you could see how much clearance there was in the rods as they set-off. They were heavy things, however, and despite this the overall motion was smooth due to the considerable inertia. Our modes lack this inertia so I try and reduce clearances in order to maintain that essential smoothness of something weighing many tons.

If this doesn't make sense then I'll have another go. I feel we're almost there.

Will, of course I am speaking as a kit designer because etching enables me to do things easily that are more difficult with, say, a scratchbuild or when making an existing kit. I've never doubted that you are a great believer in making the best possible chassis with the facilities you have at your disposal.

DaveB

[Chris Pendlenton]

You are right Alan. I think the caption refers to "Hal o' The Wynd" having an overhaul and thois is it having its hornguide spacings checked against official wheelbase. The engine originally had its hornguides located in the days before I had this jig, probably using Neep style axle jigs. I detected errors which I guess the Dynadrive flywheels mostly ironed out. I used the new jig to correct them and now all is sweetness.
Setting up the frames over the spacers and soldering up is another process involving squares, a flat bedplate and clamps and this version of the jig is not involved.
My procedure now for an etched kit of unknown accuracy would first be to examine the frames and ensure the outlines are identical, and the top profile in harmony with whatever body you are using, correcting as necessary. Then check the horn cut-outs are in the right place and the centre ones on each frame are 100% aligned and a good fit with the hornguides to be used. Nowadays I would be focussing on a single plate for the leading edge with the trailing guide fitted closely over the axlebox (set in its fixed orientation if having to adjust for off centre bores) but no reason not to use the nice High Level guides and boxes, just focus your jig settings on one face.
Frames and spacers need looking at now. I would look carefully at any etched or tabbed spacer locations, and if none, or askew, would locate spacer position with little pin sized holes drilled through both frames with pins threaded through, to act as lands and guides for soldering in. Your choice of gearbox might require a relocation of some spacers. Smooth off the frame fronts as matching datums. I would now lay the frames flat alongside each other, butted up to a set square on their front end datums to confirm the centre hornguide faces are exactly in line. If so you now have a hornguide datum on both frames, truly opposite and both exactly the same distance from the frame front datums.
Now you can proceed to erecting the frames with many clamps set squares and precautions against getting them skewed, and solder out from mid frame to avoid bananas. I use a flat tufnol bedplate on which squared up tufnol or hardwood strips are set with the frames clamped or bolted to them. A transverse block at an absolute ninety degrees at one end ensures frames butted up to it are dead opposite each other. The spacers are soldered in. If no tabs or grooves are featured then use the setting pin idea; they will support spacers in the right positions and at true right angles to the frame while soldering.
Now set the remaining hornguides with the Leg jig whose aluminium studs have previously been set and clamped to the official wheelbases. It is very much advised to check and record all the hornguide positions on the jig after soldering. The turned studs on the jig mean you have to be careful to solder in the guides vertically and set firmly up against the stud.A refinement of the jig would be to machine the studs as rectangles but this raises parallelism issues.

On some erections, and this can be seen in the K1 article in MRJ 183, you will see a homemade jig along Rod Neep principles used to locate the frames via axleboxes but I found that robustly made as it was there was still insufficient stability of dimensions at the outer ends of the jig axles and it was prey to all the dimensional drift issues Dave B mentions so I don't use it anymore. Swinging Legs and GA dimensions now rule in this Works.
Regards
Chris

[Chris Pendlenton]

As a postscript, I should perhaps have mentioned mills, at the risk of copping it from the Committee of Public Safety.
I fairly recently got a small one and of course together with dial indicators they can revolutionise measuring in the way Dave B describes. Ideal for checking your hornguide positions and the exact opposite-ness of your frames. Also of course for milling out hornguide slots to exact spacings in blank frames, or if you are needing to re-model the ones already etched. Also, like a small lathe, useful for hundreds of other unanticipated things. But best keep it dark.
Chris

[Alan Knox]

Thanks for that very comprehensive response Chris. I think it neatly summarises your overall process as well as how the Leg jig fits in. My engine building efforts are invariably scratch-built and not nearly as technically demanding as yours, but the principles you have set out apply nevertheless and I shall be adopting them in future efforts!
I'm a sucker for using jigs to make things simpler and more consistent - as an aside and slightly off-topic, can I say that in my opinion your Alex Jackson 'clipped U' dropper is the best thing since sliced bread - I've now standardised on it for all my wagon fleet. And I've adopted your 'pulling post' for all my new wagons!

Alan

[davebradwell]

I need to add a postscript, too. Both Chris and I have suggested perhaps pushing hornguides one way when using jigs so all clearance is taken up in the same direction. Whereas this seems safe enough with one of the assembly jigs that can be pre-set, if using good old jig axles then think carefully. Pushing one hornblock to the side will shove the remaining axleboxes to the other side of their horns giving the worst outcome. The priciple is still sound but the application requires some thought and care.

DaveB

[Terry Bendall]

As a postscript, I should perhaps have mentioned mills, at the risk of copping it from the Committee of Public Safety.

In the small sizes needed for 4mm scale work, or even 7mm, not a lot of safety hazards

Also, like a small lathe, useful for hundreds of other unanticipated things.

Lathes and milling machines are of course very useful for model making but they are by no means essential. Will I thnk manages very well without either and there are probably others who do the same. Of course just because you have a machine, its use does not make things necessarily more accurate although digital read out scales can help. Use of a machine still needs care and attention to accurate working.

Terry Bendall

[Chris Pendlenton]

The Committee of Public Safety is straight after me as expected. I think the point has been very adequately made that modelling is possible without machine tools. In certain departments it is just less easy, so if you have the money, the aptitude, the space and the inclination they are extremely useful and you wonder how you ever- oh never mind, end of.

[Winander]

I still don't understand why locating the axles using the coupling rods is not adequate if done with care, observing sliding tolerances. Whereas setting the hornguides from a drawing and using coupling rods that must match that drawing is adequate given that it may be an "etched kit of unknown accuracy". Plus third party coupling rods may be required.

[Daddyman]

I still don't understand why locating the axles using the coupling rods is not adequate if done with care, observing sliding tolerances. Whereas setting the hornguides from a drawing and using coupling rods that must match that drawing is adequate given that it may be an "etched kit of unknown accuracy". Plus third party coupling rods may be required.

Because, in theory, there are six places where movement/slop can enter: between rod and jig axle, between jig axle and hornblock, and between hornblock and hornway - all multiplied by two as you have the other side of the chassis too. However, HL blocks are initially very snug on the axles and snug in the hornguides, so I wonder if this changes anything? I've now read through the articles in 219 and 221 (thanks to all those who offered scans) and while extremely well-disposed towards them, feel that they're written for a different time, pre-Colin Seymour's improvements at Gibson, and pre-HL. And honestly, I've tried - tried - to drive a Gibson crankpin in wonky and couldn't manage it...

Yes, re-reading Dave's post of last night, there's that hope-giving "if" at the start of the second paragraph, and a later mention of clearances. What if there is no clearance yet - if the axles and hornblocks are very snug as HL are?

[davebradwell]

First, it doesn't matter what dimension you choose for your axle centres but the correct official wheelbase would seem the obvious choice as the kit designer was probably aiming for it in the first place. As the coupling rods are likely different on a hand drawn kit it's a good time to sort them out at the same time. It's far easier to adjust the coupling rods to the chassis than the reverse if it's gone wrong. The writings of LBSC in Model Engineer in the 60s covers this and John Brighton has written his version of the procedure.

Next, no matter how little play there is in the bits, if you locate the hornguides directly there will be less. You can chase yourself round in circles with numbers but the direct approach is likely to give better results.

There is good mileage in the principle of just biasing the parts one way in order to take up clearance as long as it is thought through properly.

DaveB

[Winander]

Because, in theory, there are six places where movement/slop can enter

Which is why I said "with care". If you know how 'slop' can enter then you can guard against it e.g. being extremely careful when setting a jig with the rods. If the jig axles are 1/8inch then there is no problem there and using quality components doesn't guarantee success, but goes a long way to enabling it.

Still waiting for an explanation how setting the hornguides independently to the coupling rods is better. Hint: I am particularly interested in how coupling rods made to the required accuracy are sourced if using "etched kit of unknown accuracy" without resorting to machine tools.

[davebradwell]

Why is it better - I tried to explain this last night. David Addyman's had a go too.

How do you adjust rods - look up John Brighton's writings on this and he has a go at jig setting too. I would have thought it fundamental to any method of chassis assembly for when things go wrong or final tweaks. I just make a bush with a bit of tube and fit this to elongated hole - it's hardly a challenging job. Had to do this every time until I saw the light.

If you don't want to try and do better, I'm not compelling anybody. Just thought folk might find it interesting.

DaveB

[Daddyman]

I am particularly interested in how coupling rods made to the required accuracy are sourced if using "etched kit of unknown accuracy" without resorting to machine tools.

I think Dave would allow that the rods don't have to be precisely correct to the drawing if that's the way they come in the kit (Chris' article calls this dimension sacred, but earlier in the thread Dave has let me off a thou or two EDIT: Dave has said it again at 4.47 this pm). But they do have to be correct (a) to each other, and (b) to the hornguides - preferably the front edge. But if the rods are not correct to the GA and the brakes are, and the cylinders (if there are any) are, then problems could start.

[Chris Pendlenton]

David A: referring to an earlier post where you say 219 and 221 are perhaps no longer relevant to the Colin Seymour era after he has wrought improvements to the wheels themselves. I should be very happy if that is the case. However, there will be many who laid in wheels some years ago which they might like still to use.I know I have. Some will still have the cockeyed crankpin bores that I photographed. And also I would say those articles covered many aspects still very relevant like wheel to axle fixing, sideplay washering, crankpins, strong return crank fixing, quartering and so on, so I'd say there is still value in them and I wouldn't like others to be put off consulting them after your comment.

Chris

[Daddyman]

I wouldn't like others to be put off consulting them after your comment.

Me neither, Chris! I realise I had in fact read them some years ago, and they taught me loads. However, your solutions to

wheel to axle fixing, sideplay washering, crankpins, strong return crank fixing, quartering and so on

all require machine tools. (You even use a machine tool to create a tool to use in a machine tool!) I don't have such tools (or don't yet know how to use the ones I have), and I can't even see from the photo how the swinging arms work - but in any case, there is some lathe work involved further upstream in creating the parts to use with those arms. So all that I could take from your approach was your philosophy, and it's that that led me to my gauges - they're an attempt to build to your standards without your tools.

there will be many who laid in wheels some years ago which they might like still to use.

Sorry, but I can't help thinking this is perverse! On the one hand, I can see how it makes sense - you having the tools that you do, etc. But your articles give us work-arounds for sub-standard products (old Gibson wheels, Exactoscale blocks): spend hundreds or thousands on a lathe rather than shelling out six quid an axle for some Seymour wheels. What someone like me, coming to P4 today, needs to know is whether the components available today are as good as I think they are, and thus obviate the need for some of your techniques (while still acknowledging the usefulness and ingenuity of those techniques if things go wrong, and for those who have the tools). In other words....

Can a fine-running P4 chassis be built without machine tools?

I have a spare pug chassis, some spare Seymour wheels and plenty of HL blocks and hornguides if you'd like to try?

[johndarch]

[quote="Daddyman"]

Can a fine-running P4 chassis be built without machine tools?

YES!

[Daddyman]

Sorry, I'll rephrase that: a fine-running chassis to Chris and Dave's standards, that isn't built pre-knackered with 0.1 clearance on the crankpins to compensate for inaccuracies elsewhere (which is not to imply in the slightest that's what you do, John).

[Will L]

Sorry, I'll rephrase that: a fine-running chassis to Chris and Dave's standards, that isn't built pre-knackered with 0.1 clearance on the crankpins to compensate for inaccuracies elsewhere (which is not to imply in the slightest that's what you do, John).

Ok still YES but I do question your definition. They and I would both try and build chassis with the minimum basic clearances throughout and it is possible we might manage it although this is probably easier if your fully tooled up. However given the multiple place errors can creep in, the judicious use of a little additional clearance on coupling rods can give fine performance and would not produce the driving wheel starting noticeably before the rest effect and the observer would be entirely unaware.

By the by. If you are looking to see what’s possible, an 0-4-0 chassis is not really any sort of challenge. If you can’t get that spinning properly you have real problems. The more axles the bigger the problem. You should try one of these

[davebradwell]

I think this thread has lost its way. Of course you can make a fine running chassis anyway you like but it will take skill and perseverance. Using some ingenuity when planning the approach will certainly pay off. My initial contribution concerned making the job easier and this may, or may not, involve some better tools including machinery to de-skill the task. The location of hornblocks directly deserves some thought and should be possible with simple tools.

It's worth digging out Chris's articles to see what the critical points are. Of course there are other ways of tackling them and I have my own approach - that doesn't invalidate what he's written.

No-one has commented on my reference to John Brighton's writings on this subject. He uses a different route to a sound finish.

DaveB

[Chris Pendlenton]

Replying again to David Addyman.
It seems impossible to say anything in this Society about techniques that may involve a small lathe without attracting defensive reactions. Best perhaps that those of us who invested in a Unimat as I did in 1976 from proceeds of some loco building commissions, should go and play somewhere else so readers thus put off can avoid wasting their time.
As for the Leg jig I thought I had exhaustively described the thing in my reply to Alan Knox. But yes of course it does feature turned studs (Hand drill/ vernier?) If you really want further description then I am happy to oblige.
And Seymour wheels and what you need to know as a newcomer to P4, well you'll have to try them and see. I look forward to reading how it goes. I shall be ordering some myself very soon and we could swap notes.
Chris

[Daddyman]

defensive

Not defensive, no - just trying to understand. I've bought MRJ 175 today with your article on the 4MT, hoping to learn more, and got the lathe out of its cupboard...

It's worth digging out Chris's articles to see what the critical points are.

Agreed.

No-one has commented on my reference to John Brighton's writings on this subject.

I use his rod-sighting method all the time - first port of call for checking rod-to-hornblock agreement once the hornguides are fitted to the frames.

[Chris Pendlenton]

So you actually have a lathe- in a cupboard! I begin to get some idea of your sense of fun!
Chris

[Tim V]

John Brighton and his sub-contractors built professionally.

The professional attitude is worth repeating.

Do it once, do it right, and don't expect it back under guarantee.

A professional does not have time for 'fettling', they expect to build it quickly and right. Once I started adopting this mantra, I found I could build more quickly, with less rejects and they didn't need to be looked at again.