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Old 12th October 2007, 03:41 AM   #1
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Default Delrin or HDPE

Howdy Gents,

I am brand spanking new to turntable building but I am determined and going to give it a try. I have access to a machine shop and some raw materials. My first question is about platter material. Is Delrin or HDPE a good material for a platter? I have a 12" dia., 5" long piece of Delrin and a 12" dia., 6" long piece of HDPE. It would be my luck that they are useless, but I have my fingers crossed. Does anyone have an input? Thank you in advance.
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Old 12th October 2007, 11:52 AM   #2
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Delrin could be ok, it does absorb moisture from the air though, so maybe not.

and HDPE, too soft really.

of the two Delrin is the better choice, it's not so much the materials but what you do with them that count .


a 10mm HDPE platter 'mat' could be awesome, but on it's own it will need some support for rigidity...
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Old 12th October 2007, 01:18 PM   #3
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Could you split either of them in half and insert say a 10mm thick piece of alu or brass plate in between? That would give great rigidity - and I'd say the delrin would be better.

Mass loading with lead shot within the delrin would be good too.


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Old 12th October 2007, 01:27 PM   #4
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HDPE may sag, Delrin is much better. That big chunk was also a good bit of change- Delrin isn't cheap. It won't change much with humidity. I'd be worried about the resonant characteristics, and the idea of scooping it out and maybe potting in some lead shot has a lot of merit. Be sure to balance it when done. Also, like most plastics, it will hold a nice static charge- the reason that if I were diy-ing a table for myself, I wouldn't use a plastic or glass platter unless there was a conductive layer involved.
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Old 12th October 2007, 01:30 PM   #5
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Quote:
Originally posted by sq225917
Delrin could be ok, it does absorb moisture from the air though, so maybe not.

This is just half the story

Delrin which is a trade name for POM does as you say absorb moisture, but that is something that has already happened by the time our Kilowattski friend gets his chubby little hands on it.
It is what is referred to as conditioning.

After conditioning there are no dimentional changes or changes in properties worth considering for a platter.

So Kilowattski, you just go ahead and use your piece of POM for your platter, it will be just fine.

Magura
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Old 12th October 2007, 01:46 PM   #6
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Thank you all.
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Old 12th October 2007, 02:53 PM   #7
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the issue with delrin really comes in when lathing it, that beatiful flat piece of Delrin heats up,it's mositure content changes and when it cools hey presto.. slightly out again.

if you take a slow thin cut this shouldn't be an issue but you need the right cutting tool for the job.

worth bearing in mind.
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Old 12th October 2007, 09:05 PM   #8
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I've machined Delrin and what sq3245634531 (!) says is true. Take light cuts at high speed and don't let it get too warm.

If you are careful and mark out some holes symmetrically for the lead shot, then all you have to do is put the same weight of lead shot in each cavity - a la Teres. Some kind of plug then to close the holes. The lead shot should be snug but not absolutely jammed in there. Shouldn't rattle if you shake it. No. 9 lead shot is what you're after, or close to it.


AFAIK Redpoint uses a skin of teflon on their platters so I wouldn't worry too much about the resonance. Sonics will be different with delrin but if everything else is good it will just be different "flavours".

What you do need to worry about is an excelllent bearing, plinth, platter and very important is the drive motor. You can get away without using fancy exotic plinth materials by adding mass and rigidity. I found the bearing and motor drive to be the biggest challenge in making an above par TT.


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Old 13th October 2007, 12:42 AM   #9
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One of my neighbors owns a machine shop and has a Haas CNC Mill. I am going to try to sweet talk him into letting me write some G-Code for the Haas to turn a 5" thick hunk of aluminum into a Teres style plinth over a weekend. Wish me luck. I may cost a case of Pilsner Urqell, his favorite beer.

I have started to look into bearings. I have my eyes on a 1/2" ID Sintered Bronze, Oil-Impregnated, Self-Lubricating sleve bearing with a 1/2" case hardened steel shaft that is dimpled on one end for a ceramic ball. If I use the delrin I don't need a thrust plate. Does this sound ok?

For the motor and controller I plan to take advantage of the Motor and Controller group buy being administered by Algar_emi. I will also purchase the motor top plate and pulley. The rest of the enclosure will be made from a turned piece of 6" aluminum rod stock. I will bore out the center on a mill with a fly cutter.

Well, at least those are the plans. Everything is always subject to change due to suggestions by those more knowledgable than I.
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Old 13th October 2007, 03:43 AM   #10
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Your plan sounds great! I'd like to have a go at a tt someday.

Quote:
The rest of the enclosure will be made from a turned piece of 6" aluminum rod stock. I will bore out the center on a mill with a fly cutter.


I am thinking this would be best bored on a lathe. I'm no expert and I hope an expert will tune in and set me straight. I am curious as to the best way to accomplish this operation. Magura?
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