Turntable platter from plaster

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magentawhale

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#1
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?
 
#4
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.
 
#5
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.
 
#6
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/bas-relief-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
 
#13
Hearing all the above, I'm pretty sure the Jesmonite stuff is going to work. I have searched around the internet for it, but haven't been able to find a distributor/reseller over here in the Netherlands, however. Perhaps Jesmonite is sold over here under another brandname - I believe it is known as Forton as well.
 
#19
Hi

I also use Townshend rock turntables with paster turntables. They are very neutrl sounding.

The turntable on the rock is made of plaster of paris cast inside an aluminium shell with an acrylic sheet glued onto the top to accept thr record. The underside is levelled by turning on a lathe and scraping with a machine held scraper.

The plaster of paris does not need a binder but other types of plaster might.

I think you will find the hardest part is levelling the surfaces. I am not sure how you would do that without a lathe.

PLease keep posting as the plaster turntables sound very neutral. If you need more information on the rock deck let me know.

Don
 
#20
AMV8 said:

I think you will find the hardest part is levelling the surfaces. I am not sure how you would do that without a lathe.
Click to expand...


I was thinking of taking a sheet of MDF of the appropiate thickness, and cut a circle the size of the platter in it, using a center-guided router. This would be layed flat on a really flat surface (a mirror or something like that). The top of the mould would be made from another piece of flat material (mirror or trespa) with a hole through which the plaster can be poured.
The individual parts of the mould would be held in place by way of clamping. The recess in the MDF would have to be painted with something to keep the moisture out of the MDF, and, more important, in the plaster during the hardening proces.

I guess this would make a shape that comes pretty close to the intended platter, which would only need some minor truing up. I think I can have acces to a lathe.

Being new to the whole casting thing, I am always open to other suggestions!
 
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