Acrylic or Delrin for arm board?

Acrylic or Delrin for arm board?

Postby bdp24 » Thu Jan 11, 2018 5:49 am

I have located a source local to me of all varieties of plastics. They do custom machining too, at reasonable rates. They offer both black Acrylic and Delrin (Acetal), and I am going to have them make me some arm mounting boards for an Aries 1 and HW-19. Thoughts on the relative strengths and weaknesses of Acrylic and Delrin/Acetal in that application welcomed.
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Re: Acrylic or Delrin for arm board?

Postby Peer Gynt » Sat Apr 14, 2018 12:18 pm

Did you complete this project? What did you decide?

Yesterday I made a black acrylic arm board for the “new to me” piano black HW19 Mk III that I recently acquired.

I love the fact that it matches the rest of the top. I think that the fact that the HW19 Mk III top is built on a steel bottom layer makes the choice of Delrin vs Acrylic less of a sonic factor, but I’d love to know what your listening evaluation showed.
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Re: Acrylic or Delrin for arm board?

Postby bdp24 » Thu Apr 19, 2018 1:42 am

Yup, I just picked up the arm boards from the plastics place. I had them make them in black acrylic, figuring I'd stick with the material used by VPI (my HW-19---also in sexy Piano Black---has acrylic plates, and the Aries' arm board is acrylic). I had a 4" (actually 3-15/16", to exactly match the stock board) round 1/2" thick disc made for the Aries 1, so as to have the top of the arm board within the range necessary for the TransFi Terminator arm I will be mounting on the table. That disc will be bolted right on top of the original 7/8" thick board, with a layer of EAR Isodamp constrained layer damping between them.

Then I had a 1/2" thick half-length board made for the HW-19. By half-length I mean instead of being the full 14" length of the stock 1/2" thick arm board, I had one made 7-5/8" long, and the stock 5-1/2" wide. Why 7-5/8"? The 1/2" thick acrylic arm board that came on my HW-19 was cut for an SME mount, and it is not an SME that I will be mounting on the table (though I love SME arms). In addition, I replaced the stock HW-19 7/8" Delrin platter with a TNT-3/4 1-1/4" Delrin/aluminum platter. So the board I had made needed to fulfill two objectives: provide a new uncut platform for the arm that will be going on the HW-19; and raise the height of the board 1/2" to account for the thicker platter. I could have had the new 1/2" thick board made the full 14" length of the original, bolting it in place on top of that original (again, with EAR Isodamp between the two), or even a new board made like the one VPI put on the HW-19 Mk.4, 1" thick with beveled sides (beveling required on the side closest the platter for clearance between the two). But I've never liked the look of that bulky raised (in relation to the height of the plinth the bearing and platter are mounted on) arm board running the full depth of the table.

Looking at the original arm board from above, I saw that I could have a board made that would be bolted to the table via just the rear and middle bolt locations, extending the same distance in front of the middle bolt hole locations as does the rear side of the board behind the back bolt holes. Making the board 7-5/8" long (deep) puts the boards rear and now-front (formerly-middle) bolt holes the same distance from the their respective board ends. Then I had the fabricator bevel all four edges 45 degrees, to give it a finished look. The 1/2" raised arm platform looks right at home, like the table came that way. The new black acrylic matches the original perfectly, and the table looks not only like it came with the added arm board, but fantastic! Of course, I had to get four new mounting bolts 1/2" longer than the stock, as those are only just long enough for the thickness of the stock board. I'll be taking pics of the arm boards and posting them here, as soon as my sis and her digital camera get back from her European vacation in about a month.
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Re: Acrylic or Delrin for arm board?

Postby Peer Gynt » Thu Apr 19, 2018 10:33 am

I love the Piano Black HW19. I’ve just restored a Mk III. It’s very pretty. I made a 1/2” thick black acrylic armboard for a black Ittok LVII I happened to have on the shelf. It turned out surprisingly well. I’ve mounted an Ortofon MC3 Turbo on it while I’m waiting for some other cartridges to come back from retipping.

It’s projecting a very nice sound stage and demonstrating nicely defined bass. This cartridge is not “one of the best,” but it’s rocking for now.

Preamp is a period correct black Conrad Johnson PV11. Amp is a period correct black Conrad Johnson MF2200.

Speakers are not period correct. They’re recent black Revel M106s. The sound reminds me of the period correct Thiel CS 2.
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Re: Acrylic or Delrin for arm board?

Postby bdp24 » Sat Apr 21, 2018 11:32 pm

The HW-19 really is a classic, and the first one I got (a used Mk.1, bought in the late 80's) was the first turntable I really loved (previous one's being the AR XA, Thorens 150, Thorens 125, and AR ES-1). My current one (Mk.2 acrylic but with a TNT-3/4 platter & bearing, and SIMS Navcom Silencers as the suspension) is gettin' buried with me!

For anyone wanting a cheap, easy upgrade for their HW-19, go to the website of well-known audiophile parts and accessories vendor Michael Percy and look at the various EAR Isodamp products he sells. One is named Isoloss Sandwich Mount, which is a small solid tube of Isodamp rubber with a short male stud on one end and female internal threads on the other. The Mount is offered in three sizes, the smallest of which has #4-40 threads, the exact same size as the threads on the stock rubber isolation stand-off studs separating the plate the HW-19's motor is mounted on from the plate attached to the outer base of the table. A direct swap! The EAR Isodamp rubber provides superior isolation to the regular rubber used in the stock mount. Michael sells the #4-40 Isoloss Sandwich Mount for $3.95 apiece (the HW-19 requires four), but has a minimum order requirement of $25, plus shipping (mine came to $8). The largest mount ($5.95) offered has 1/4-20 threads, the same as the rubber feet on the HW-19. The feet are even almost exactly the same size as the stock---another direct swap! The Isodamp rubber is also available molded into 1" D x 1/2" H and 1.5" D x 3/4" H feet for components, as well as in thin (1/64"-1/4") sheets for constrained layer damping. I got some 1/16" to install between the two layers of my acrylic arm boards. Great stuff!
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Re: Acrylic or Delrin for arm board?

Postby Peer Gynt » Sun Apr 22, 2018 8:59 am

Thanks for the info!

My recently acquired HW19 Mk3 had large, conical spike type feet, and they were seriously stressing the plinth.

I made some flat bottomed feet from license plat reflectors, covered the load bearing surface with furniture foot felt, painted them black to match the plinth, and they’re working well, but I’d love me to try the ones you’ve described.

I like having leveling feet. It’s a lot easier than fiddling with the LP12 Trampline 2 which cannot be leveled using the feet.
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Re: Acrylic or Delrin for arm board?

Postby bdp24 » Sun Apr 22, 2018 4:03 pm

Oops, I just realized I misspoke above. The threading on the HW stock rubber feet is not 1/4-20, but rather 10/32. To be able to use the EAR Isoloss Mounts as feet, one could easily replace the stock 10/32 T-nuts that are on the four bottom corners of the base with 1/4-20 T-nuts, not at all hard to do. Where the HW-19 DOES have 1/4-20 threading is on the T-nuts that the stock isolation springs screw into. So the Isoloss Mounts could be used as replacements for those springs, maintaining the ability to level the plinth via their threads. Cool! The EAR rubber formulation provides isolation superior to that provided by Sorbothane, which many HW-19 owners use in place of the stock springs. My SIMS Navcom Silencers are great too, but don't afford leveling (I level the plinth via the screw-in feet on the base), so I may eventually compare the EAR to them.
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Re: Acrylic or Delrin for arm board?

Postby Peer Gynt » Sun Apr 22, 2018 10:01 pm

Yeah, I knew the threads were wrong, but I still like your info.
Thanks!
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Re: Acrylic or Delrin for arm board?

Postby bdp24 » Mon Apr 23, 2018 4:51 am

The VPI cone feet on my Aries 1 have 1/4-20 threads, so that's my excuse for the mistake ;-).
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