Southwold coach
Re: Southwold coach
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...
https://www.rmweb.co.uk/community/index ... s-drawing/
Ps I now really want to make a 3wheeled milk tanker for no particular reason...
Re: Southwold coach
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
Rik
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
Rik
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Re: Southwold coach
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.
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:
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
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.
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:
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
Re: Southwold coach
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!
Rik
Rik
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Re: Southwold coach
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:
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:
If anyone wants the STL files or the Sketchup file then provate message me.
Trevor
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:
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:
If anyone wants the STL files or the Sketchup file then provate message me.
Trevor
Re: Southwold coach
I like the idea of the functional leaf springs. Would ABS be more flexible than PLA do you think?
Rik
Rik
Re: Southwold coach
Definitely. Actually I'm not sure even ABS would be flexible enough though.
Philip
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Re: Southwold coach
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?
Trevor
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?
Trevor
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Re: Southwold coach
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
Trevor
Re: Southwold coach
I'll press ahead with what I've printed out for now, but if it doesn't workout, I'll be in touch!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
Rik
Re: Southwold coach
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
If you want some light bedtime reading try this paper I found.
https://iopscience.iop.org/article/10.1 ... 042008/pdf
Re: Southwold coach
I have to admit I am amazed by the resourcefulness of you 3D printing fraternity, and of course impressed.
Re: Southwold coach
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
Re: Southwold coach
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!
Philip
Re: Southwold coach
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 ......
Rik
As a former primary school teacher, I sometimes just let them get on with it ......
Rik
Re: Southwold coach
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. 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
Rik
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. 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
Rik
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Re: Southwold coach
That's looking very nice Rik, I do hope it lives up to expectations.
The best things in life are free.... so why am I doing this?
Re: Southwold coach
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
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
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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