Heatproof lampholder?

Any guidance please: I am trying to make a holder for a standard G4 capsule type halogen bulb (12v 20W). This is to replace a 6v 15W bulb in a gunlamp on my son's air rifle. The capsule lamps are cheap whereas the special bulb (6425 GBB )in the lamp costs £17.50.... hence the decision to expend hours of time to save a few quid!. (Anyway, we have several 12v batteries available, & no suitable 6v ) The catch is that this holder needs to fit inside the aluminium reflector assembly which I have salvaged from the 6425 GBB after removing the blown halogen insert. So, I can't use the standard 2 pin G4 type holder, 'cos it can't be machined to fit the back of the reflector. My Mark1 effort, made from some unnamed hardish plastic I had lying around, I was a bit dubious about since I know the halogens give off a lot of heat. It worked perfectly for 2-3 mins, when the light gradually reduced accompanied by melting plastic smells. The heat from the bulb had melted the holder & fumes filled the reflector. The holder is trivial to make: just a 13mm rod slightly tapered down to 12.5mm OD, with a 3mm slot

9mm wide & 10mm deep machined in the front face, then a couple of 2mm holes drilled from the back face to meet the slot. What do you all think of ally for this? Any easily available machinable ceramics? Could I use plaster of paris or similar & just cast the bulb in a female form? Would tufnol stand the heat any better ?

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Reply to
jrlloyd
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Mold something from "Milliput"?

Maybe PTFE rod?

--

73 Brian
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Reply to
Brian Reay

RS sell machinable ceramic -not cheap, but then again I don't supose you need all that much. Regards Kevin

Reply to
Kevin Steele

Thanks for the suggestions, but I don't think either would stand the heat. Milliput is only OK up to 130 deg & PTFE is quite reputedly nasty when overheated. I'm pondering over fireclay at the moment. I have some here, & I'll give it a go tomorrow

Reply to
jrlloyd

I just checked RS - thanks for the heads-up, but a 4" rod of 15mm is £132!!! I could mount a pair of Cibie Super Oscars on the gun for that price. ----------------------------------------------------------- snipped-for-privacy@boltblue.com

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Reply to
jrlloyd

What about that Halford exhaust repair crap ?

-- Regards,

John Stevenson Nottingham, England.

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Reply to
John Stevenson

I'm not familiar with the bulb, but ceramic holders for industrial 2-pin bulbs can be bought, there are a few dealers in London who service the film & TV game, and there are also those little dichroic lamps they use in shop windows, they have a bi-pin base.

Just a couple of thought....

Peter

-- Peter A Forbes Prepair Ltd, Luton, UK snipped-for-privacy@easynet.co.uk

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Reply to
Prepair Ltd

Micalex would be suitable. Its glass bonded powdered mica and easily machinable. Don't know of UK supplier but I've a spare 3" length of 3/4" rod if you send me you snail mail adress.

Jim

Reply to
pentagrid

I remembered it was expensive, didn't know it was that expensive!!.

Don't know if you can fit it in, but I've made holders for bulbs like this using ceramic electrical connectors before. I think you're right about the temperature problems with some of the suggested materials

-these get bloody hot in use.

Regards Kevin

Reply to
Kevin Steele

Thanks for all the suggestiones: John S - the Halfords Gungum sounded great, but the new tin I bought last year, & only used a little bit to fill a telescopic exhaust joint, had gone off. Why does NOTHING last these days, you used to be able to keep sealed tins of stuff like this for years, bloody hell the last gungum I had was my uncles & he's been dead for 12 years! Jim many thanks for the kind offer, but a bit of lateral thinking has ( I hope!!) got me sorted. I turned down some 1" ally bar to the required dimensions & used heatproof sleeving to protect the wires to the pins. The 1" dimension I machined grooves into (like an air cooled cylinder head) with a parting tool. The plan is that this will dissipate some of the heat. Apart from cutting my finger on the sharp edges whilst pushing this assy into the reflector, this seems to work OK. I left the lamp on for about 30 minutes tonight, & all seems to be well...

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Reply to
jrlloyd

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