A railmotor or two - using the skills of others - etching

andrewnummelin
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A railmotor or two - using the skills of others - etching

Postby andrewnummelin » Sun Mar 05, 2017 9:20 pm

I'm not quite sure whether this is the most appropriate place for this topic - bits may be better in "Railmotors, Railcars and Multiple Units" and others in "Tools and Techniques", but as Jeremy Suter has put his fascinating thread https://www.scalefour.org/forum/viewtopic.php?f=89&t=5287 in "On My Workbench" I'll do the same. The project is to construct a couple of steam railmotors and the trailers into which they were subsequently rebuilt.
A goodly number of years ago I worked on producing a drawing
ADRmotor1.PDF
(386.92 KiB) Downloaded 64 times
from the bits and pieces of information I could find at the time and I received a number of useful suggestions as to errors I may have made. I thought the real challenge would be making the valve gear and indeed this proved to be beyond my skills in metal working - the expansion link even defeated a well known modeller of delightful old tiny locos! Things were left in abeyance until a colleague in the HMRS pointed me to things he was helping to catalogue at the NRM, and I followed a session at Great Missenden on the use of CAD.
So, having just booked for their summer school I've decided the railmotor shall be the main project and it's time to stop prevarication - armchair modelling is one of my fortés! I want to arrive with an etch, or etches, and leave with a running chassis.
I found at York a full set of drawings of the chassis and motor unit for the No. 2 railcar - I believe the motor unit was the same on No. 1 and probably (nearly) identical to the LSWR unit, so I've redrawn all the motion and valve gear components. My disappointment was that the original drawings gave no information on the bodywork at all - I was hoping for at least an outline to check my assumptions.
Capture.JPG

So now I come to the first appeals for help.
1. The real valve gear components were of varying thicknesses but I guess this will be impracticable in a model: what would be advised as the most appropriate material to use? How thick and which metal? I guess nickel silver though there's a temptation to try steel.
2. What's the best way to build up the forked ends, particularly the non-symmetrical ones?
3. Would one follow the standard guidelines of companies like PPD for drawing components? Or does anyone have specific advice when dealing with such small items?
Regards,

Andrew Nummelin

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Russ Elliott
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Re: A railmotor or two - using the skills of others - etching

Postby Russ Elliott » Sat Apr 01, 2017 12:14 pm

I doubt you will have the space for proper forked joints, assuming a standard 12 thou nickel etch.

andrewnummelin
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Re: A railmotor or two - using the skills of others - etching

Postby andrewnummelin » Mon Apr 10, 2017 2:29 pm

Russ Elliott wrote:I doubt you will have the space for proper forked joints, assuming a standard 12 thou nickel etch.

Russ,
Sorry for the delay in replying - gardening got in the way!

I went back over the stuff I learnt at the Missenden CAD course last year and started to draw out the design for my first ever etch. I've based it on the use of 0.2mm (8 thou) nickel silver and worked on a 0.03mm allowance for undercutting, and drawing all holes too small (easier to drill out than fill in!). I've drawn overlays, for bosses, as tabbed on and folding by 180° for assembly (the very little bits would be too small to handle otherwise).

I'd be very grateful if some of you could have a look at the drawing below and let me know if I have made any stupid mistakes. I started with the combination lever and the radius link as being items with and without forks: the green items represent the prototype.
The black should not be etched, the red is to be half etched from the front, the blue is to be half etched from the back, the yellow lines on the black correspond to the prototype so you can see the etch allowance.
The cyan items show the thickness of what I should get once the bits are folded - I have assumed a zero thickness for solder!
The eagle eyed may spot that the levers are a little longer than the protoype to allow for the bends.
Capture.JPG

Indeed clearances will have to be adjusted: the first spotted is that the clearance between front and back of the expansion link will need to be increased, but this particular one should not cause problems.

This brings me on to my next question: how should I design the support for the expansion link (shown below)? Surprisingly I couldn't see anything about this on the prototype drawings! I'd guess at a bracket fixed to the frame supporting a bearing through which the rod passes and is held by the cotter nut and pin - but how should one do this in 4mm?
Capture2.JPG
Capture2.JPG (25.84 KiB) Viewed 2146 times

Finally, for this posting, can anyone interpret the prototype drawing of the union link shown below? Unusually, I think it looks like two separate pieces rather than a single link forked at each end. The photos I have of the prototype are not clear enough to decide between the options, but certainly one of the similar LSWR ones had the expected forked link.
Capture3.JPG
Capture3.JPG (59.34 KiB) Viewed 2146 times
Regards,

Andrew Nummelin

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Penrhos1920
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Re: A railmotor or two - using the skills of others - etching

Postby Penrhos1920 » Mon Apr 10, 2017 3:13 pm

Sorry I can't help you with your etches; they are far more complex than I've managed.

But oh I'm glad that I'm only modelling the railmotors as the trailers they became!!
Getting it Alright

Penrhos Junctions near Caerphilly - Barry Rly, Rhymney Rly and A(N&SW)D&R 1920 and pseudo modern image in S4F
and
Awrhyllgwami for DEMU challenge
and
Dispelling the P4 drop in wheel myth
and
TOERAG Obergruppenführer

David Knight
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Re: A railmotor or two - using the skills of others - etching

Postby David Knight » Mon Apr 10, 2017 4:05 pm

Andrew,

I would say two pieces. I base that on the wording of the description and the fact that the top piece is secured by a flange on the connecting bolt and the bottom piece is secured by a tapered pin. Quite how you plan to do that in 4mm scale will be....interesting ;)

Cheers,

David

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Penrhos1920
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Re: A railmotor or two - using the skills of others - etching

Postby Penrhos1920 » Tue Apr 11, 2017 6:12 pm

IMG_0073.JPG


IMG_0072.JPG


Are these of any use?
Getting it Alright

Penrhos Junctions near Caerphilly - Barry Rly, Rhymney Rly and A(N&SW)D&R 1920 and pseudo modern image in S4F
and
Awrhyllgwami for DEMU challenge
and
Dispelling the P4 drop in wheel myth
and
TOERAG Obergruppenführer

andrewnummelin
Posts: 164
Joined: Mon Jul 21, 2008 9:43 am

Re: A railmotor or two - using the skills of others - etching

Postby andrewnummelin » Wed Apr 12, 2017 7:34 am

Penrhos1920 wrote:
Are these of any use?

Richard,
Thanks - I already have copies of these, and indeed they were useful.

How are your trailers coming on?
Regards,

Andrew Nummelin

JFS
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Re: A railmotor or two - using the skills of others - etching

Postby JFS » Wed Apr 12, 2017 1:41 pm

Hello Andrew,

I wish you luck with your project! Have you built many examples of other peoples etched Walshaerts kits? (Martin Finney or Dave Bradwell's for instance?). This is the best way to learn what works and what does not.

Unfortunately, I fear that you are jumping in rather at the deep end here and I am afraid it shows! I feel you are being far too optimistic about being able to fold layers of etches upon each other and getting a consistent result. Better, is to use a thicker material and to half etch the relief. I don't know why Russ suggested that 12thou is a "standard thickness" - I have had etchings done in 0.2, 0.25, 0.45, 0.5 0.7 and 0.75mm N/S - no standard there! You MUST choose your metal thickness first as it determines the width of fold lines, minimum tag size etc.

Also, in the radius rod, you have put two fold tags between two half-etched parts of the component - that won't work - when you try to fold it, there is no "Line of least resistance" so the bend might go anywhere. You should always put folds / tags to full thickness material - and although it is not always possible, it is in this case.

I also find it very useful to do a "working drawing" showing how the MODEL will go together - trying to replicate how the the prototype bits go together is unlikely to work as clearances, fits and limits are completely out of scale - let alone the need to achieve excessive lateral clearance between crossheads and union links etc. This will enable you to work out what layering will work best - expect to go through a few iterations before you have found the best way. Only at that point can you start to develop the components for etching.

Hope that does not sound too negative - but I feel you might need to crawl a bit more before attempting thus particular 100m race - why no try some simple test pieces first?

Best wishes,

Howard

JFS
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Re: A railmotor or two - using the skills of others - etching

Postby JFS » Wed Apr 12, 2017 1:51 pm

Andrew,

Sorry meant to say... 8thou is very thin for etching motion (even though it is such a tiny prototype). I etch my signals out of that - and I laminate them to a double thickness!

www.scalefour.org/forum/viewtopic.php?f ... es+signals

Best wishes,

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Jol Wilkinson
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Re: A railmotor or two - using the skills of others - etching

Postby Jol Wilkinson » Wed Apr 12, 2017 8:17 pm

Andrew,

I would also add that you can't assume zero thickness for solder. While the theory might suggest that, in practise it isn't so. Very thin material tends to distort a bit when heated which may be explain it.

Russ suggests that 12 thou is the "standard" thickness. It is the size that has been most commonly used for brass etchex, althugh as Howard points out there are other thicknesses available (dependent on the etcher).

Like Howard, I think that 8 thou would, especially when half etched, be both fragile and difficult to handle.

Jol

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Russ Elliott
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Re: A railmotor or two - using the skills of others - etching

Postby Russ Elliott » Wed Apr 12, 2017 9:36 pm

Yes, sorry, by 'standard' (thickness) I meant common. And, as Howard himself noted, a thicker material can give decent half etch relief. A working drawing of the cross-section between wheel and cylinder centre will indicate what kind of thickness might be best.

billbedford
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Re: A railmotor or two - using the skills of others - etching

Postby billbedford » Thu Apr 13, 2017 8:44 am

Just to add to what Howard was saying. I would suggest that instead of trying to fold the components, you build them in separate layers each in it's own 'frame'. The frames can have registration holes and can be soldered together with solder paint and, for instance, a hot plate or a a hot air gun. The one thing you would have to be careful of is the each sub-component would need at least two tabs, otherwise they could twist out of line.

Cutting out the components would be more of a challenge, but not impossible.

This is how I have used this technique to form the knuckles on coupling rods:

Coupling rods.png
Coupling rods.png (12.48 KiB) Viewed 1832 times
Bill Bedford
Mousa Models
http://www.mousa.biz

andrewnummelin
Posts: 164
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Re: A railmotor or two - using the skills of others - etching

Postby andrewnummelin » Thu Apr 13, 2017 8:16 pm

Gentlemen,
Very many thanks for all the hints and suggestions - most helpful indeed. One however I shall not follow: I'm going for the 110yard hurdles before learning to crawl! (It was the only thing I was not terrible at when in school, and I was told that my parents got rid of our dog when it made me crawl and would knock me over whenever I tried to walk!)
Now it will be back to the "drawing board" to incorporate what I have learnt and produce something that can go to the etchers as an experiment.
Regards,

Andrew Nummelin

andrewnummelin
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Re: A railmotor or two - using the skills of others - etching

Postby andrewnummelin » Wed Jun 28, 2017 4:57 pm

Life got in the way... so it was clear that I was not going to have time to follow all the good advice given about etch design. So I've gone ahead and had an etch made of my first, far from optimum, drawing. At first examination, I am delighted with what came back from PPD.
valve_gear_etch.jpg

There are several copies on the etch so I can practice, sacrifice bits to the carpet god,.....
Now I've got to go shopping for a few extras, like wheels and gears, so that I can occupy myself at Great Missenden in a few week time. I'm hoping the air will be blue with sunshine rather than with my expletives when everyone hears me making mistakes!

Any advice on the order of assembly that is likely to cause the fewest problems? I'm still wondering about how to attach the drop lever to the crosshead and the combination lever to the valve rod.....
Regards,

Andrew Nummelin


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