smart51
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| posted on 29/12/06 at 11:40 AM |
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moulding rubber
I want to make some rubber trumpets for my carbs. The moulds will be too complicated to pull GRP from them but rubber should be OK. What kind of
rubber should I use and where can I get it from?
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macnab
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| posted on 29/12/06 at 11:46 AM |
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complicated to pull GRP?
is there such a thing???
you can buy trumpets in metal off the net. quite a common thing...
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indykid
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| posted on 29/12/06 at 11:49 AM |
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sikaflex in a well greased mould?
would be a bugger if it stuck, but might be worth a shot if nothing else turns up. would probably take a while to set too.
think Frost do a rubber moulding kit, but like everything else from them, i doubt it'll be cheap!
tom
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Syd Bridge
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| posted on 29/12/06 at 12:03 PM |
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Frosts do the mix up rubber stuff.
http://www.frost.co.uk/result_search.asp
look for product no. R 099
Also available from ITW Devcon direct for larger quantities.
Cheers,
Syd. 
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DaveFJ
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| posted on 29/12/06 at 12:13 PM |
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I have used Devcon flexane many times and it is very good .. but goes off very quickly so you need to work super fast...
(made a fantastic cheat for 'Best Boots' whilst in the Army!!  )
Dave
"In Support of Help the Heroes" - Always
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smart51
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| posted on 29/12/06 at 12:18 PM |
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The trumpets need to clear the top of my airbox and so have an 80° bend in them. Also they are sort-of-eliptical at the mouth but round at the
throat.
Frost do 3 hardnesses but at £48 for 500g its a bit expensive. Any other suggestions?
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macnab
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| posted on 29/12/06 at 12:28 PM |
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still shouldn't be a problem. I would make a mould of the inside out of balsa block, an hour at most. sand it down and varnish it. Then plenty
of candle wax (I use this cos it melts when you pour hot water on the glass fiber then it'll just fall out. repeat till youre done. So long as
the bottom of the trumpet it narrower than the top it'll away's come out regardless of the bend. Would be a bit of a funny looking one if
it did'nt...
oh yeah apply the wax molten (melt it in a small pot) then brush it on. Hair dryer will then smooth it down to a gloss finish.
[Edited on 29/12/06 by macnab]
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mistergrumpy
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| posted on 29/12/06 at 01:33 PM |
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Chuck some industrial condoms in the freezer for a week or so, that should do it.
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macnab
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| posted on 29/12/06 at 02:00 PM |
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quote:
Originally posted by mistergrumpy
Chuck some industrial condoms in the freezer for a week or so, that should do it.
have you posted that on the wrong thread or what??
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James
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| posted on 29/12/06 at 02:24 PM |
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quote:
Originally posted by mistergrumpy
Chuck some industrial condoms in the freezer for a week or so, that should do it.
Is that a 'shrink to fit' method that we weren't previously aware of?
[Edited on 29/12/06 by James]
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"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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ChrisJLW
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| posted on 29/12/06 at 02:33 PM |
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RS components do castable polyurethane for less than Frost.
http://rswww.com/
Stock No. 199-1395
Only do one hardness though.
I've lived a life that's full.
I've traveled each and ev'ry highway.
But more, much more than this,
I did it side-ah-ways.
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mistergrumpy
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| posted on 29/12/06 at 02:56 PM |
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Think its just the way my minds working. I've taken to carrying a tool kit in me car just in case I see some lucky stuff and I always look at
Sierra's suspiciously now, as Zoidberg would say 'reveal your secrets!' There was people giving free condoms away in town last 2
weekends and we stuck one a a bottle of beer then hit it on top to blow it up and fill it with beer. Just reminded me of the plastic trumpets on an
engine though. How sad. 
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smart51
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| posted on 29/12/06 at 05:21 PM |
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The mould in 2 halves idea is good however I want the smooth side to be the inside for better airflow. I've almost finished making a GRP mould
that will be dipped in rubber solution to make the trumpet. I expect to be able to peel the rubber off the mould (so that I can make 4 trumpets.
The problem with a rigid component is that the trumpet has a 42mm diameter throat which morphs to a 36mm x 46mm flattened oval at the mouth which then
has a 6mm radius trumpet mouth on it. No matter which way you pull, a rigid part won't come off an internal mould. The flattened profile tube
is so that the bend doesn't have a zero radius on the inside edge.
I suppose I could make a two piece outer to mould a wax core which can be laminated to and then "lost" with heat. I might try that one
later.
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silex
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| posted on 29/12/06 at 05:36 PM |
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I use RTV Silicon ( RTV = Room Temperature Vulcanizing ) when knocking up small moulds for multiple casts, come in various Shore hardness as well -
very flexible.
Try http://www.tiranti.co.uk/ for some ideas and the materials
Forgot to say - look under "Products" then "Mould Making" section.
[Edited on 29/12/06 by silex]
Murphy's 2 laws
1. If it can go wrong it will
2. In case of emergency - refer to rule 1.
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smart51
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| posted on 5/1/07 at 08:20 AM |
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I tried some RTV silicone (medium) last night and whilst it moulds well, the results are really too flexible. Is there a way of stiffening the
material so that it holds its shape better?
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Peteff
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| posted on 5/1/07 at 11:09 AM |
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Chuck some industrial condoms in the freezer for a week or so, that should do it.
That sounds more like a cure for impotency
Try some
ROMOBOX:NEWLIST" target="_blank">morph
plast or polymer clay to make your mould or try it for the finished item. Polymer clay is baked in the oven after shaping to harden it,
we've used it to make miniatures and replace knobs on small items and it's quite durable.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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Simon
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| posted on 5/1/07 at 08:44 PM |
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quote:
Originally posted by smart51
I tried some RTV silicone (medium) last night and whilst it moulds well, the results are really too flexible. Is there a way of stiffening the
material so that it holds its shape better?
If you're using the rubber for the outside of the mould, and want to keep its shape "off" the original, add keys while brushing on
(assuming you're using "thixo" . We just make up long (3 feet "sausages" that are cut to about 2" or 3" and
stuck on the uncured rubber), then when cured, lay up f/glass over the keys.
Mould is then stiffened with a case of f/g.
I would find somewhere cheaper than taranti's if I were you. Try CFS in Cornwall.
ATB
Simon
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