Author Topic: No more cast metal chairs!  (Read 4564 times)

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Offline John Candy

No more cast metal chairs!
« on: March 12, 2015, 09:14:06 PM »
Now that G3S are no longer supplying cast whitemetal chairs (or brass rail) what do we do if we want to build track with timber sleepers?

Although all my current track is of the plastic sleeper variety, it had been my intention to lay timber sleepers with metal chairs in the MPD, to avoid any problems with hot ashes damaging plastic track. I have only 100 whitemetal chairs, so hardly enough for a couple of yards of track.

It seems the only alternative is to use plastic chairs with timber sleepers but how to fix them is a problem.

I know Cliff supplies "top hat" plugs with his plastic chairs but how do you fix them to timber sleepers?
You cannot "pin" them and, even though the "plugs" are inserted into holes, glue seems hardly likely to stand up to the effects of damp and timber shrinkage/movement, .
Furthermore, it seems improbable that glue would be practicable for turnouts and other crossings/pointwork, where the forces of "switching" would impose additional stress upon chair to timber fixings.

What is your answer to problem?
My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline Andy B

Re: No more cast metal chairs!
« Reply #1 on: March 13, 2015, 07:07:35 AM »
Sorry, I don't have an answer to the problem - but I think the first paragraph needs clarification as it could eaily be misconstrued as a criticism of the G3S.

From the explanation given at the AGM, the Society is simply finding it impossible to find a caster who can produce the chairs at an acceptable level of quality (90% reject rate was quoted from one supplier, IIRC).
With regards to rail, it was a commercial decision that led to the 'outsourcing' of brass rail supply to Cliff Barker.
I don't wish this thread to be 'derailed' :D - so suggest if there is any discussion to be done on the supply issues then please open a new thread.

Andy

Offline John Candy

Re: No more cast metal chairs!
« Reply #2 on: March 13, 2015, 08:10:52 AM »
Andy,

I am aware that is is an inability to find a suitable caster and not the "fault" of the Society.
Similarly, a chat with Cliff revealed that he orders his stainless rail "by the Ton", so the G3S may be unable to meet the criteria necessary to obtain rail at an acceptable price.

However, it does leave the users of the metal chair/timber sleeper combo with a problem.

What do G0 and G1 use for chairs?
Are they still able to source metal components?

Might it be worth asking a supplier such as Paul Nilanjan (Paul Industrial Co./Pline of Calcutta) whether he would be able to produce them (it would require a substantial order to make it a practical proposition)?

Perhaps more to the point.....what has happened to produce a situation where a 90% rejection rate has become the "norm" ......another "dumbing down" of British engineering capabilities?

John
My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline MikeWilliams

Re: No more cast metal chairs!
« Reply #3 on: March 13, 2015, 09:11:44 AM »
I don't think we will get a response from the committee here, but I understand that the pattern for the chair is also worn out, although another source told me that it had been repaired.  Either way, after all these years I think a new pattern would be a good idea and 3D CAD and solid printing would seem the best method, printing sufficient to fill a mould.

These chairs have never been popular with casting firms, but surely some would be pleased for the business.  Between us I suspect we know many possible sources, but as ordinary members we can't really make any enquiries until we know who has already been approached.  Any ideas on that?

Mike

Offline IanT

Re: No more cast metal chairs!
« Reply #4 on: March 13, 2015, 09:28:20 AM »
White metal casting is pretty much a 'cottage industry' here in UK, e.g. there are a few individuals who do it in their sheds. It is obviously much easier to produce larger 'single' castings for a reasonable cost (loco parts, figures, line-side parts) than many hundreds/thousands of chairs. This is a matter of the volumes required versus the small size/cost of the item. So they are not attractive for people to do being labour intensive.

The issue of quality (90% reject rate) will be a matter of the resin mold quality - they age with time and use. The answer would be to have a new mold(s) made. Otherwise, it's a matter of patience and care.

I would be very concerned to hear that the 'masters' have been shipped anywhere - most especially to India. They are (almost) irreplaceable. When we thought we had lost them a few years ago, we looked at getting replacements made. Commercial sources were quoting over £2K per item (exc. VAT). So the masters are worth £10K+ if you need a specialist to replace them!

I think the main issue (with lack of w/m parts) is with making turnouts. If necessary I am sure small quantities could be made 'internally' - I know of at least one member with a spin caster that could do it. He didn't want to sell it to me a few years ago but he might be willing to 'lend' it. At the moment, I have sufficient stock for my immediate needs but I think this will be a problem for G3 over time.

Regards,

IanT
Nothing's ever Easy - At least the first time around.

Offline John Candy

Re: No more cast metal chairs!
« Reply #5 on: March 13, 2015, 09:28:48 AM »
I am afraid the "committee"appears to be in the same category as "secret squirrel" and communication with the G3S members is a low priority.

With one notable exception, the members never raise their heads above the parapet in this forum!
What are they afraid of.....that someone may take "pot shot" at them?

Let's hope this will be sufficient bait to coax them out of hiding!

Regards,
John.
My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline IanT

Re: No more cast metal chairs!
« Reply #6 on: March 13, 2015, 09:34:13 AM »
As far as I know Mike, the latest w/m investigations were handled for the G3S by John W.

I gave the masters into his care a year or so ago. Just to be clear on this for other readers - the 'masters' are in perfect condition. They are used to make molds (or patterns) which are the parts that wear with repeated use. They are (relatively) inexpensive to make but of course you need the masters to do so.

Regards,  IanT
Nothing's ever Easy - At least the first time around.

Offline John Candy

Re: No more cast metal chairs!
« Reply #7 on: March 13, 2015, 10:02:30 AM »
I take Ian's point about risk of loss but, if they would cost that much to replace, I have to ask, "Are they insured?".
They might be just as easily stolen or lost here in the UK (apparently they were, at one time, thought to have been lost)!


All this brings me back to the original question, how do you fix plastic chairs to timber sleepers?

John
My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline IanT

Re: No more cast metal chairs!
« Reply #8 on: March 13, 2015, 10:21:44 AM »
And I think the best answer to your original question John is - "not easily" !

 :)

IanT
 
Nothing's ever Easy - At least the first time around.

Offline John Candy

Re: No more cast metal chairs!
« Reply #9 on: March 13, 2015, 11:32:51 AM »
Ian,

Only way I can think of (and it isn't a very practical solution in view of the thousands involved in any reasonable length of track) is to insert the plastic "top hat" plugs from underneath the sleepers.

This would involve drilling right through the sleeper at the lesser diameter and then drilling  (to a precise depth) a recess to accept the larger diameter flange underneath.

The plug is then inserted and the chair glued to the plug .... the problem would be getting the tops of all the plugs (the bit you glue the chair to) at precisely the right height ... i.e. just enough projecting above the sleeper to provide an anchor for the chair.

I don't see anyone going to all that trouble... I certainly won't be!!!

Regards,
John.

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline AllWight

Re: No more cast metal chairs!
« Reply #10 on: March 13, 2015, 11:52:27 AM »
Can we not use resin chairs as these can be reproduced with relative ease. If there is a small rejection rate that would not be an issue.

Designing a new chair or variety of chairs on 3D CAD, then 3D printing to give a master to then cast a rubber mould from may be another way to go. Some resins are heat resistant and if the chairs were damaged at a low cheap cost to replace them most of the G3S members could afford a few pence for the odd damaged chair from the steam locos

Mark   

Offline John Candy

Re: No more cast metal chairs!
« Reply #11 on: March 13, 2015, 12:30:16 PM »
Mark,

Yes, they can be produced in resin but how would you fix them to the timber?
It would be possible to make them with holes for pinning but I am not sure just how much force/pressure could be applied when inserting the pins before the resin would crack.
Similarly, if they did not hold the rail tightly enough they would be of little use, while if too tight, they would split when forcing the rail through.
The casting would have to be to very fine tolerances and it is extremely difficult to achieve.....the silicone RTV rubber has a shrinkage factor which is difficult to control (it shrinks on curing and again with casting).
Similarly, the resin itself is subject to shrinkage and varies with environmental factors.

Another problem with resin (unlike metal which solidifies almost instantly) is that it takes up to an hour before it can be removed from the mould and then continues to cure further for several days.......again subject to shrinkage. So to produce in the very large quantities required would require whole batteries of moulds.

I know in the "small" scales resin has been used for trackwork but I suspect the small size of the components means that a 0.4% shrinkage is negligible but the larger the scale, the larger the actual size of any disparity.

If this were to be tried (and no, I'm not volunteering) I suspect it would be very much an experimental "hit or miss" project.

Mike, what do you think?

Regards,
John.
 

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline hornbeam

Re: No more cast metal chairs!
« Reply #12 on: March 13, 2015, 05:33:16 PM »
tenmille make plug in chairs that go with their/GRS rail that have a spigot on that are designed for use with drilled sleepers, I've used them and they seem to hold ok.

Offline John Candy

Re: No more cast metal chairs!
« Reply #13 on: March 13, 2015, 06:14:29 PM »
Simon,

The Tenmille chairs (a flat bottom rail clip) are made of polypropylene, a very flexible plastic, which cannot be successfully glued to anything (it resists all solvents).
The spigots are of the split type and expand when pushed into the plastic sleepers providing some grip.
When I constructed my code 330 turnouts, using Cliff's (ABS) sleepers and Tenmille chairs, I melted the spigots to prevent them popping out.

By contrast, the ABS chairs supplied by Cliff are not very flexible and have solid mounting plugs which are intended to be "welded" with solvent to the sleepers.
Resin is not very flexible (except when warm) and prone to cracking if stressed.
 In my experience, at low temperatures (particularly below 5C) it becomes very brittle and easily shatters.

It would not be possible to produce curved track by "curving" an assembled straight section (as can be done with Cliff's track) since resin chairs would shatter.

Regards,
John.

My fellow Members, ask not what your Society can do for you, ask what you can do for your Society.

Offline MikeWilliams

Re: No more cast metal chairs!
« Reply #14 on: March 13, 2015, 07:15:39 PM »
Personally, I prefer whitemetal chairs for several reasons.  One is that they grip the rail better than the plastic ones I have which are quite sloppy.

If the patterns are safe and in good condition, then making a mould is, as you say, relatively cheap.  However, you would need several chairs in the mould and as I assume we have one pattern, the easiest thing may be to cast a few dozen in resin.  The moulds can be cold-cure "rubber" which would last for several hundred spins, or vulcanised rubber which would normally last several thousand, though I understand there have been problems recently with supplies of rubber.

I still think it is worth investigating further.

Mike