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Old 2nd December 2008, 09:11 PM   #21
SCD is offline SCD  Canada
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Has anybody ever tried to melt and re-cast records to use as a blank to start from. I have this box of "not to my taste" records that have been taking up space in my garage. I was thinking it might be possible to melt them down in a double boiler bath with an oil as the boiling liquid then cast into a simple round mould and turn on a lathe.
Maybe this is too far out there.
Dumb idea?
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Old 2nd December 2008, 09:16 PM   #22
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Quote:
Originally posted by Poindexter
Polycarbonate (Lexan, Tuffak) is both denser and 'deader' (lower Qm) than acrylic, and commonly available at the same plastic places.  A little more difficult to machine cleanly, higher cutting effort, a little more flexible.

P
Can you post the specs. pertaining to the "lower Qm" for both acrylic and polycarbonate? I can't find any such info anywhere.
Actually, from what I can find Acrylic is slightly denser than Polycarbonate. I don't think you need a material deader than acrylic. It's already a very inert material.

http://www.machinist-materials.com/c...r_plastics.htm

Polycarbonate density
0.043 Density (lb/in³)

Acrylic density
0.044 Density (lb/in³)
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Old 3rd December 2008, 02:56 AM   #23
Nanook is offline Nanook  Canada
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Default SCD...

some time ago I suggested a glued and stacked platter made of old records (only the worst possible records to be used of course)...

As far as density goes, with a little more research...

PVC record compound: 1.34g/cc
acrylic, cast (as most pieces are cast and then machined): 1.18-1.19g/cc
polycarbonate: .950-1.54, g/cc, 1.20g/cc average
Lexan (DuPont, polycarbonate): 1.19g/cc

later,

stew
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Old 3rd December 2008, 03:24 AM   #24
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Yah, all that stuff is somewhat variable, as all the manufacturers have their own secret sauce.

I based my read just on feel, as I worked with both materials in another life, back in Honolulu in the seventies and eighties.  The polycarb (actually Tuffak) felt a little denser to me, and the difference in resonant qualities was quite noticeable.  If I held a piece (say, a couple sqare feet) of Plex by a corner and tunked it with a fingernail, it would ring some.   The polycarb was more flexible, and sort of leathery, tough; it just went thud.  Gimme a break, I'm an instrument maker; tunking stuff is, like, a compulsion.

I can see, however, how that tough nonresonant character might make the polycarb a lot more of a headache to machine accurately.

P
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Old 3rd December 2008, 03:45 AM   #25
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Quote:
Originally posted by SCD
Dumb idea?
I think it's clever, though I was reading further up the thread, thought it up, then found your post beating me to it, so consider the source.

But, I think you could take an existing platter, make a plaster cast, then pour in the hot vinyl. You might even just take a tub of plaster and push a record into it to make the cast. You'd probably need to do some sanding ans shaping after, but you'd have to do that anyway.
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Old 3rd December 2008, 04:41 AM   #26
Nanook is offline Nanook  Canada
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Default dsavitsk...

the moulding method may not be that great, but SCD has some excellent machining capabilities (ask to see some pix of his stuff...it's absolutely gorgeous)...

Poindexter, it does make absolute sense. Think of Lexan vs regular old acrylic or polycarbonate sheet. hit it with a hammer or a sharp object...the poly/acrylic usually shatters, the Lexan doesn't. That in itself suggests that the Lexan is better at energy dissipation than the regular old poly/acrylic.

One thing that continues to blow me away is the idea that somehow massive/denser, blah, blah blah, is the way to go in audio. From my own personal experience I can say that often (although counter intuitive) the opposite holds true. Lighter stuff doesn't store as much energy, it can dissipate the energy introduced to it at a much faster rate. This of course does not help the idea of using a platter as a flywheel ...but there are very easy ways to overcome the lower mass (because , after all, the mass only serves one purpose and that is to conserve the angular momentum and hence the Inertia).

peace out ..

stew
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Old 3rd December 2008, 04:25 PM   #27
SCD is offline SCD  Canada
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Well I am still thinking the recycled record concept has some possibilities. The wikopedia referenence indicates it has an 80'c melting point. Tha seems a little low to me but if it is accurate then it will be even easier to experiment.

dsavitsk has helped me along with my idea. A simple plaster cast or anything similar, that is just a bit bigger than the diameter of the desired circle will work for the casting. You could even make the mould from a stack of 3/4" plywood ssections with a +-13" hole in them. Use a bit of cling wrap as a liner and you have a simple mould made.
A person will need a lathe to do the turning. Given the diameter of the disc, it will need to be a lathe of a decent size. I would think the lathe would have to be capable of swinging a 14" disc at least.

Maintaining a constant temperature in the melting pot so as not to over heat the plastic will be important.
The turning and shaping part will likely be by design then trial and error.
I think it has potential

Becoming less of a dumb idea?
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Old 3rd December 2008, 06:58 PM   #28
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Quote:
Originally posted by SCD
Maintaining a constant temperature in the melting pot so as not to over heat the plastic will be important.
How about some sort of epoxy, like what they use to pot transformers, or fill in the ends of caps in metal tubes?

Click the image to open in full size.

For making a mold, you might also start with a block of something -- a couple pieces of plywood glued together -- and machine it out with a router.
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Old 3rd December 2008, 07:10 PM   #29
okapi is offline okapi  United States
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at the student machine shop (read - old equipment)i have cut acrylic on a lathe on several occasions.

i use kerosene as a lubricant and have found that a sharp hard cutting tool is essential. a carbide tool is the best that i've used - there may be something better.

there have been some other good material suggestions but one i don't think has been mentioned is delran. delran is much easier to machine and cheaper than acrylic (doesn't come on cool colors though). not sure how susceptible it is to warping though.
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Old 3rd December 2008, 07:39 PM   #30
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Quote:
Originally posted by okapi
at the student machine shop (read - old equipment)i have cut acrylic on a lathe on several occasions.

i use kerosene as a lubricant and have found that a sharp hard cutting tool is essential. a carbide tool is the best that i've used - there may be something better.

there have been some other good material suggestions but one i don't think has been mentioned is delran. delran is much easier to machine and cheaper than acrylic (doesn't come on cool colors though). not sure how susceptible it is to warping though.
A water soluble coolant works best in machining acrylic, at least in my experience. Delrin (trademarked by Dupont) costs me more than acrylic. Are you sure you're not talking about a generic acetal rather than Delrin?
Any plastic or performance plastic will warp or move during machining, especially if excessive tool force or heat is generated during the cutting process. The key to success is cutting all surfaces to remove stress as equally as possible. I've been machining various performance plastics for the past 25 years without issue but I have the proper tools and equipment to do the job.
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