Making resin seat castings for 7mm carriages

Dog Star

Dog Star

Western Thunderer
Looks like I am going to have to make some resin seats for our carriages and I recall that other WTers have trodden this path so I am asking for guidance and recommendations on some aspects of this work.

When making the master... do I allow for shrinkage of either the mould or the casting?

When making the mould... do I make the mould for one seat casting or can I get one mould to produce two seats at one time?

What is the best orientation for the master in the mould?

What is a recommended product for the master and for the casting resin?


If I limit myself to making just the master... is there a recommended casting service?


thank you, Graham
 
Oz7mm

Oz7mm

Western Thunderer
Graham

I made a seat mould a few years back though I have produced very few seats from it.

I would make a mould that will cast more than one seat otherwise you will be mixing up small amounts of resin each time. I found it gets harder to get the resin / hardener mix right in smaller amounts.

Assuming it will be an open top mould then the orientation should be so that the exposed side is one you can easily finish later, so either the bottom or the back at the top of the mould

I got all my moulding rubber and resin and hardener from Tiranti. Don't forget release agent. I actually visited them and they were very helpful. I am sure a phone call would tell you all you need. Dig out your Lego bricks - Tiranti do a very useful booklet on the subject though doubtless Google will serve you just as well.

John
 
unklian

unklian

Western Thunderer
Sound advice from John there. Shrinkage using modern silicon rubber moulds and resin should be fairly low, 1 or 2 percent. At your scale less than a coat of paint I would hope. If you go to Tiranti I would use their T28 rubber and G26 Sika polyurethane resin. Don't use polyester resin it stinks and is quite brittle ! If you are not sure about doing it yourself, I will hopefully be casting some similar seats for Heather Kay of this parish. When they are done you could check them out and I could do yours too if you like.
Ian
 
simond

simond

Western Thunderer
I made some resin wheels for a Corgi Thorneycroft van, I didn't notice any significant shrinkage. Just measured the master and the finished part, and they are 20.9 and 20.8 mm diameter respectively.

I used a kit from Sylmasta, very happy with it, but I regularly fail to get the mix right for the RTV silicone - I must buy a very small set of digital scales. Mixing the resin is easy, even in small quantities, I use a pair of the polythene droppers, one for each component.

I agree that arranging your parts so that there is a flat "sacrificial" surface is beneficial, and certainly easier than making a "closing mould".

There are pictures at Porth Dinllaen in 0 - Page 9 - 7mm+ modelling

HTH
Simon
 
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