Turntable platter from plaster

[magentawhale]

I'm thinking of experimenting with plaster (gypsum) as material for a turntable platter. The platter itself would be casted in a pre-shaped mould, with mesh wire for reinforcement. Since the surface of the casted platter remains vulnerable, I would like to use something to impregnate it with (Pretex, a textile stiffener could be used for this purpose, if I'm informed correctly). Does anyone have any experiences on this matter?

[john blackburn]

magentawhale

There's a product called Jesmonite which may be of use to you...

http://en.wikipedia.org/wiki/Jesmonite

It "rings" like porcelain when thin but if you are casting a large item that should not be a problem.

It also transfers perfect detail in castings so any imperfections in the mould/mold will be perfectly reproduced in the platter.

John

[magentawhale]

Thanks, this might be just what I'm looking for!
I could probably cast the whole platter from this material, and wouldn't have to bother with impregnating it at a later stage.

Hans

[Conrad Hoffman]

Pure plaster, even with wire, sounds too fragile and chip prone. I had never heard of that Jesmonite stuff, and it sounds really interesting. I've considered similar things using fiberglass filled concrete, Structural Skin by Conproco, but the surface would definitely need an overcoat of something nicer, both for cosmetics and if one wanted to machine it true. The Jesmonite sounds like it could possibly be trued up on a lathe with a carbide tool. Now you've got me thinking about casting a plinth.

[magentawhale]

Something I didn't mention in my initial post is that the platter would actually (partially) rest on a subplatter, Rega-style. The platter doesn't become directly attached to the bearing, which I think would be the most vulnerable part. The chipping was something I was more worried about, hence the idea of impregnating it with something more rigid.

[john blackburn]

The mirror frames and clocks are cast with Jesmonite using a retarder to give you more time to get the bubbles out.....

http://www.artsquirrel.com/Sculpture...sculpture.html

Once fully cured it's very hard, you should be able to true it on a lathe with some experimenting. You would have to plan the mould carefully, strong enough to support the considerable weight and accurate enough that minimal trueing up would be needed.

I would think you would be into a fibreglass mould if you want to pour it in one hit. You could also pour in stages but this may cause weak areas in the "strata". That said, you could have some nice layered colours as it takes pigment or metal powders nicely.

Be warned though it's addictive. There's something delightful about turning a mould out and seeing a new thing, until you spot the bubbles that is!

John

[kevinkr]

What about getting this thing balanced? I can't imagine as cast that it would have uniform enough mass distribution not to need balancing..
I could be wrong..

[Nanook]

Basically vibrate the whole mold until th bubbles stop?

[magentawhale]

Just found out that Celestion made a speaker from the same material....

[AuroraB]

There are 4 types of Jesmonite.......?