Author Topic: No more cast metal chairs!  (Read 4262 times)

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Offline John Candy

Re: No more cast metal chairs!
« Reply #15 on: March 13, 2015, 08:10:05 PM »
Regarding moulds for metal casting, I have moulds I made from RTV101 (a red, hard rubber) some now up to 12 years old. I have successfully "gravity" cast many dozens of buffers, axleboxes, solebars and other wagon parts, etc. from them and they are still in good, serviceable, condition.

Unlike resin, which attacks the chemical structure of the softer RTV types of silicone rubber, the metal has no chemicals to attack the rubber and ultimate failure of the RTV 101 moulds is caused by splitting, when the constant high temperature (300C+) hardens them a bit too far.

The RTV rubber is not that expensive (average price around 20GBP per kilo) but it is the time involved which will put off any commercial producer (or the consequent price will deter the customer).

The only way to get this done will be by a "cottage industry" caster but, as has been said already, the time involved in production is out of all proportion to what the customer might be willing to pay for the product.

What is the solution?
I don't have an answer.

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 #16 on: March 14, 2015, 01:22:03 PM »
"the time involved in production is out of all proportion to what the customer might be willing to pay for the product"

John - do we have any figures to back that up?

Mike

Offline John Candy

Re: No more cast metal chairs!
« Reply #17 on: March 14, 2015, 02:14:31 PM »
Mike,

The chairs were being sold at 10p each (whether that is more than cost price I don't know), so to make £10 per hour you would have to make 100 per hour, out of which the cost of the raw materials and other incidental costs (heat/light/equipment/consumables/equipment maintenance and repairs) would have to be met.
100 chairs weigh 320gm (I've just weighed to 100 you obtained for me) and current cost of a kilo of whitemetal is approx. 20 to 30 GBP (according to the grade).

So the 100 chairs will have cost around 7GBP minimum in metal, leaving 3GBP to cover the moulds, other incidental costs and labour.
If you wanted to make a "minimum wage" income, you would likely have to make around 400 saleable items per hour (excluding rejects that could mean 600+) which would require around 60 moulds, allowing 6 minutes per cycle for set up time, pouring, cooling and removal from moulds. Add on time for making moulds /inspection of castings/removal of rejects/cutting away sprues and flash and it becomes very labour-intensive for (in my view) very little return.

The alternative is to charge a sum which would provide a reasonable "return", then who would be willing to pay, perhaps, 30p per chair?

Maybe, the Society was unable to find a caster because they wanted the item made to a price which the casters were unwilling to meet.....I don't know!

John.
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 #18 on: March 14, 2015, 03:19:24 PM »
John,

Surely a commercial caster is going to be buying their raw materials at a considerably lower cost that you or I could (for small 'home' production), and to be producing these chairs in their thousands (I would have thought 10,000 to be a minimum size batch) so be using a larger mould (at least 20 per mould).
I would assume that (at the prices mentioned by Ian T earlier) the masters are several chairs joined to a sprue, not individual chairs.
The mould would also be cycled - either with another mould for the same job or for a different job, so there is no need to wait for cooling time.
Finally, if the patterns have been made well, then the castings should just break off the sprue. There should be no flash with a knowledgeable caster using a commercial machine and moulds in good condition.

I don't know when the last lot were done, but I understand it was a few years ago. So maybe the price reasonably goes up to 15p each?

Andy

Offline MikeWilliams

Re: No more cast metal chairs!
« Reply #19 on: March 14, 2015, 03:56:25 PM »
John,

You say you would have to make 100 per hour.  I don't know how many you'd get in one mould - maybe 40, and a professional machine would do about 20 spins per hour, which I make 800 chairs per hour.

But we are guessing and somebody in the Society has actual figures and prices - they must have to have discounted the possibility.  So what were they and from whom?

Mike

Offline John Candy

Re: No more cast metal chairs!
« Reply #20 on: March 14, 2015, 06:28:32 PM »
Mike,

I mentioned 600+ per hour needed to be produced , with 400 in "saleable" condition to make a reasonable income .... the 100 was merely used as the basis for working the calculation of unit cost.
So that actually ties in with your figure of 800.
800 per hour equates to 4.5 seconds per item and it would take at least 2 seconds just to inspect each item.

A "commercial" operation would be looking to make decent return on investment after paying staff and all the associated "overheads".
As you said, we don't know who was approached....whether a "one-man" type of supplier or an industrial concern.

Andy,

Yes, a large user on an industrial scale would be able to buy at lower prices but I suspect the "cottage industry" or "one-man" operation may not get much of a reduction.
I would anticipate that to make 400 saleable items per hour (if the reject rate is as high as seems to have been suggested) then at least 60 (or as many as 80) items would be needed from each "spin".

The more moulds the greater the "set-up" cost and with one centrifuge there is a limit to number of spins one person can achieve in an hour.

However, all this is speculation and I currently have more important matters to deal with.... woke up this morning to find my oil boiler had given up!
Spent from 6 a.m until 3 p.m. stripping it down, cleaning and attempting to find the fault.
Having tested the pumps, oil pressure and vacuum have come to conclusion that fault is somewhere in the ignition system since there is no "spark" from the electrodes.

Have ordered new parts which won't arrive until Tuesday....had been due to leave for Sussex in the morning but now postponed!.

John.

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

Offline John Candy

Re: No more cast metal chairs!
« Reply #21 on: March 14, 2015, 08:48:47 PM »
As an afterthought, I wonder what Robin Saxton will do for supplies?

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 #22 on: March 25, 2015, 11:48:31 AM »
This thread has gone quiet, but I still think it worth pursuing the cast chair option.  If anyone knows who has been approached for a quote can they please let me know?  Otherwise I'll have to start from scratch and ask around again.

Thanks,

Mike

Offline Andy B

Re: No more cast metal chairs!
« Reply #23 on: March 25, 2015, 01:14:31 PM »
Mike,

I got the impression at the AGM that Ted Sadler / John Witts were the people who had been involoved and would therefore know who had been approached.

Andy

Offline IanT

Re: No more cast metal chairs!
« Reply #24 on: March 25, 2015, 05:12:58 PM »
As far as I'm aware Mike - any recent sourcing was undertaken by John Witts.

I'd give him a call for the details of whom was contacted. I know some of the previous supply history if you want to give me a call.

Regards,

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