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Tone Arm board material

My VPI Ares3 turntable which is made with a laminated acrylic/aluminum/acrylic plinth, about 2.5 inches thick in total, has a 5/8 inch circular cut through the top layer of acrylic which exposes the center laminate of aluminum.  Set into this circular cut out is the 'puck' arm board mounting disc which is about 7/8 inches thick acrylic.  This bolts to the aluminum via three machine bolts.  My SME Series IV magnesium tone arm is bolted to the acrylic tone arm puck.

Magnesium is known for its superior vibration and sound deadening qualities, so I was wondering if anyone has any thoughts on making the tone arm board 'puck' out of solid magnesium vs. the factory supplied acrylic??  I can see why they probably don't use magnesium as it's super expensive.  I just got a quote on a small piece of magnesium to machine a new tone arm board and its $125.  But if it were to make an improvement in performance, its cheap money.

Does anyone out there have any thoughts on this?

128x128slimpikins5
bdp24's avatar
bdp24
9,408 posts
 

One other material to consider is a close cousin to acrylic---Delrin. That's a brand name I believe, not the material's generic name. Delrin is the material VPI used for the platters of the HW-19 MK.2-4, Aries 1 (top layer), and TNT (pre-Mk.6) tables. It is a little denser and harder than acrylic, and has a matte sheen in contrast to the high gloss of acrylic. I had an acrylic arm board for my Aries 1 made at a good plastics supply house, and the price for a Delrin version was only slightly higher than for the acrylic.

Another option to consider is to have two 1/2" thick boards made, with a thin piece of constrained layer damping placed between them, for damping of any ringing in the material.

slimpikins5's avatar
slimpikins5 OP
191 posts
 
The service dept. at SME sent me a note this morning, they say magnesium would not be beneficial for the arm board, they like to use either aluminum or brass. Delrin is good too as yes its part of the super platter, which by the way I have on my Ares3.

But since the stock acrylic material appears to be a desirable material and its already made, I’ll stick with it. My plan was to make a one piece new arm board with a bump out on one side to accept the Tru-lift arm lift for end of record pick up and another bump out to accept my new micrometer head VTA adjuster. However last night I machined a stainless steel part which will bolt to the acrylic arm board and it will support the Tru-lift and offer adjustment so that the lift can be perfectly dialed in for where I want it to activate. I’ll make up other parts to mount on the other side for the VTA on the fly using the micrometer head.   This is actually easier for me as all I have to do is drill and tap the arm board to accept the new parts.
jollytinker
213 posts
 
another vote for Delrin, if and when you choose to make another armboard. I fabricated an armboard for my Aries 1 using Delrin at the suggestion Harry W. himself.  It wasn't hard to do and it has worked well, although I haven't compared it to other materials. the next one I do will probably be in ebony.  
atmasphere's avatar
atmasphere
11,569 posts
 
The plinth of the turntable should be as dead and rigid as possible.

The thing that most people don't think about is that the arm board is part of the plinth. The base of the arm should couple as rigidly to the bearing mount of the platter as it can. If the arm board is made of a different material than what supports the platter bearing, its possible for vibration to move the platter on one plane while the base of the arm is moving in another or maybe isn't moving at all.

You want the base of the arm and the base of the platter bearing to move in the same plane at the same time or else the difference is interpreted by the pickup as a coloration.

IME for this reason the arm board should be the same material as the structure that supports the base of the platter bearing and hopefully that is the same structure that supports the arm board too.
pryso
1,901 posts
 
sleepwalker, when I began researching plinth building I found a few suggestions for Corian.  However I then read that Corian can in fact be subject to vibration transmission.  Otherwise it might be more commonly used I guess.  One comment stated that transmission will vary depending on the amount and size of the aluminum particles in a given Corian sample.

It may look nice and be easy to work with, but I ask myself if it is so good why is it not more commonly used?

Regardless, I think Ralph offered very good basic advice.
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