Southwold coach

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HugoFitz
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Re: Southwold coach

Post by HugoFitz » Wed Nov 25, 2020 9:02 pm

I found this thread on RM web. Not sure if it helps but near the end someone has a system using wire as compensation for the axels. Not sure if some of the concepts could be borrowed?

https://www.rmweb.co.uk/community/index ... s-drawing/

Ps I now really want to make a 3wheeled milk tanker for no particular reason...

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ge_rik
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Re: Southwold coach

Post by ge_rik » Thu Nov 26, 2020 7:00 am

Thanks chaps. All this talk of piano wires and guitar strings reminds me of my 00n3 days when I constructed a Southwold Cleminson 6 wheel open wagon and used a similar though very much simplified system to Philip's.

But I think I've cracked it overnight, well theoretically anyway. Furthermore, I think I can use some existing printed parts - ones I rejected because their dimensions were wrong.

Problem 1. Raising the centre axle without sacrificing the sliding mechanism. I can do this simple by replacing the existing axle box/ hanger assembly by one where the bearing holes are higher in the axle boxes. I'll need to cut a slot in the bearing plate under the carriage chassis but, as long as the flanges stay within the boundaries of the solebars, it should work 🤔

Problem 2. Allowing the centre axle to float up and down without fouling the sliding mechanism. I can get round this by replacing the four L shaped retaining brackets with taller ones. Again, I got the dimensions wrong initially and printed four taller ones earlier.

Problem 3. Adding compensation to the outer bogies. I think I can get away with a simplified version of Philipy's suggestion. I already have a large 'washer' which I can use for the laterally 'rigid' bogie and then print out a triangular strip to sit on top of the rocking bogie.

I'll give it a try later and let you know the outcome 🙄

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Tropic Blunder
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Re: Southwold coach

Post by Tropic Blunder » Thu Nov 26, 2020 1:31 pm

Seems you've dialled that printer in quite well Rik! Fantastic work
Jake

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Re: Southwold coach

Post by Trevor Thompson » Thu Nov 26, 2020 4:15 pm

I like Philips solution. It is am elegant engineering solution to the problem. As I understand the Cleminson principle it requires springs to hold the axle trucks central under straight track conditions. This solution provides that.

I also made 6 wheel coaches in my 4mm scale days and here are the underneaths of a couple of coaches I built 45 years ago: This solution limits the way in which the middle axle overhangs the bodywork - by effectively making each axle take half of the overhang.
IMG_1095.jpg
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This is effectively a bogie and a half solution. You can see where the two brass frames pivot, each about a third from the end of the coach. They are linked together by the half bogie pressing against the carrier for the middle axle.. Two axles are on one bogie and one axle on the other. Track undulations are catered for by the rather flexible brass shim which is deliberately bent to act as springs for each axle. The result runs well.

This is a slightly different realisation of the same principle:
IMG_1094.jpg
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In this case the bogie is allowed to rock to let the axles rise and fall but prevented from twisting sideways so that the coach doesn't rock from side to side.
The half bogie is allowed to rock freely so that the axle can rise and fall and twist sideways.

Both of these coaches run well - and I think this solution overcomes the issues inherent in the Cleminson principle which make it difficult to model accurately!

Of course what you can do when you are working in 16mm scale can be much more adventurous!

I have already drawn up "W" irons, axle boxes, and springs in sketchup. If you want to try to get them to compensate as per full size I can send you STL files for you to print. If you want to experiment I can easily send them, or modify them to your dimensions and send them.

Trevor

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ge_rik
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Re: Southwold coach

Post by ge_rik » Thu Nov 26, 2020 6:21 pm

Thanks Trevor. I've already drawn (and printed) the W irons and axle boxes, so am just awaiting the printing of the modified centre 'truck' (5 hour print job) before trying it out. I would have re-used the old truck but the glue holding the old W irons was stronger than I thought!

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Re: Southwold coach

Post by Trevor Thompson » Thu Nov 26, 2020 6:31 pm

Rick

I couldn't resist the challenge of drawing up a complete compensated cleminson chassis.

The idea being that the springs actually allow the axle boxes to move up and down in the W irons.
It incorporates Philips arrangement and my arrangement to limit sideways movement of the centre axle.

It looks like this:
Screen Shot 2020-11-26 at 18.17.43.png
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The end trucks are intended to be pivoted at the holes and the centre truck free to do what it likes. A 3mm diameter stainless rod is intended to go through the holes in the uprights under each truck.

Individual components are W irons, spring/ axle box, and truck:
Screen Shot 2020-11-26 at 18.19.24.png
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Screen Shot 2020-11-26 at 18.18.44.png
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If anyone wants the STL files or the Sketchup file then provate message me.

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Re: Southwold coach

Post by ge_rik » Thu Nov 26, 2020 7:33 pm

I like the idea of the functional leaf springs. Would ABS be more flexible than PLA do you think?

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Re: Southwold coach

Post by philipy » Thu Nov 26, 2020 9:03 pm

ge_rik wrote: Thu Nov 26, 2020 7:33 pm I like the idea of the functional leaf springs. Would ABS be more flexible than PLA do you think?

Rik
Definitely. Actually I'm not sure even ABS would be flexible enough though.
Philip

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Re: Southwold coach

Post by Trevor Thompson » Thu Nov 26, 2020 9:15 pm

I think it would be sufficiently flexible.

The springs on the wagonette actually work as springs - that is what makes me think it would.

If a particular spring is too stiff it can be altered. Different parabola. Different width different thickness.

Of course it is an experiment. Nothing ventured nothing gained.

Worth trying?

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Re: Southwold coach

Post by Trevor Thompson » Thu Nov 26, 2020 9:18 pm

If you want to play around with it give me some dimensions for the southward model and I can print off appropriate parts, try it out and send you a set which seems to work best

Trevor

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Re: Southwold coach

Post by ge_rik » Thu Nov 26, 2020 9:56 pm

Trevor Thompson wrote: Thu Nov 26, 2020 9:18 pm If you want to play around with it give me some dimensions for the southward model and I can print off appropriate parts, try it out and send you a set which seems to work best

Trevor
I'll press ahead with what I've printed out for now, but if it doesn't workout, I'll be in touch!

Rik
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Re: Southwold coach

Post by HugoFitz » Thu Nov 26, 2020 10:02 pm

I’ve 3D printed springs in PLA for a 00 gauge tension lock servo operated uncoupling device with great success. ABS is springier so probably even more suitable!

If you want some light bedtime reading try this paper I found.

https://iopscience.iop.org/article/10.1 ... 042008/pdf

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Re: Southwold coach

Post by Jimmyb » Fri Nov 27, 2020 11:13 am

I have to admit I am amazed by the resourcefulness of you 3D printing fraternity, and of course impressed.

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Re: Southwold coach

Post by GTB » Fri Nov 27, 2020 1:40 pm

ge_rik wrote: Thu Nov 26, 2020 7:33 pm I like the idea of the functional leaf springs. Would ABS be more flexible than PLA do you think?
I'd be very wary of trying to make plastic springs work reliably. Especially the polymers available for home printers.

Flexibility and springiness are very two different physical properties, the relevant measurement is Young's Modulus and polymers have very low results.

The other problem with polymers is that they creep under load. It takes time, but over months the shape of the spring will change. We found acetal was the best injection moulding polymer for making springs, but I've seen that creep over time.

If you want working springs, design the print to use phos bronze strip/wire, or music wire, as the spring element which can be threaded through the axle box print and hidden behind the dummy springs.

I have a vague memory that something like this was available in P4 in the distant past when I still read MRJ. Probably based on a fold-up etching and suitable wire, which was the high tech of the time.


The model looks good so far and given your interest in the Southwold, I hope you can get it to run in Cleminson form.

Regards,
Graeme

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philipy
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Re: Southwold coach

Post by philipy » Fri Nov 27, 2020 2:48 pm

GTB wrote: Fri Nov 27, 2020 1:40 pm the relevant measurement is Young's Modulus
Contrary to popular belief, Youngs Modulus has nothing to do with metal, springs etc. It is in fact the definition of a corset: " Extension is proportional to load within the elastic limit"

Sorry, I'll get me coat! :lol:
Philip

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Re: Southwold coach

Post by ge_rik » Fri Nov 27, 2020 3:48 pm

This reminds me of the discussions which occur on my weekly walks with a group of friends from the village (before we were limited to walking with just one other person). One was a Mining Engineer, one was a chemical engineer, one was a mechanical engineer and the other was a secondary school science teacher ( with a First from Imperial).

As a former primary school teacher, I sometimes just let them get on with it ...... 😳🤔😏

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Re: Southwold coach

Post by ge_rik » Thu Dec 03, 2020 4:59 pm

More or less finished the coach.

Not the best photos. The weather has been awful all day here and so not been able to take it out into the garden for a test run and get pictures in decent lighting.
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IMG_1287.JPG
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I've not yet managed to give it a proper run over the whole line, but it now seems OK over the most undulating section .....

Weather permitting, I can test out its running characteristics at some point over the weekend

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Peter Butler
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Re: Southwold coach

Post by Peter Butler » Thu Dec 03, 2020 5:12 pm

That's looking very nice Rik, I do hope it lives up to expectations.
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Re: Southwold coach

Post by philipy » Thu Dec 03, 2020 5:18 pm

Amazingly spacious and open looking. I know nothing about the prototype but that is a very nice model.
Philip

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Re: Southwold coach

Post by Soar Valley Light » Thu Dec 03, 2020 7:11 pm

Hi Rik,

That's lovely! I bet it's going to look the bee's knees with your existing passenger stock. The livery really suits it.

The steps and the handrails have worked out very well. I love the profile of the hand rails and the chain across between them really sets it off.

Are your platforms long enough to accommodate the full rake or is a a project in hand for platform extensions? ;)

All the best,

Andrew
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