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Upgrade for users of 1/2" mylar belt

This thread will be of interest to Galibier, Redpoint and Teres belt drive TT owners, or anyone using or thinking of using a drive belt made from 1/2" mylar. The belt material of choice on these tables for several years has been the silver holographic mylar streamers from sources linked on the Teres and Galibier websites. This outperforms everything else we've tried but like anything it's not perfect - and we've now found something better.

One of the silver holographic mylar's assets can also become a liability. That metallic layer, when new, gives the belt exceptional "grip" on the platter and motor capstan. Minimal slippage on transients is one reason the material works so well. Unfortunately, that layer can wear over time, leaving a silvery gray residue and allowing performance to deteriorate. The only solution has been a good cleaning and a new belt. No big deal, but if there was a better or more stable belt Paul and I wanted to find it.

I'll spare you a recounting of our many experiments and jump to the good news: thanks to (yet another) brainstorm by my resident genius/partner, we've developed a belt that both performs better and lasts longer. I've held off posting until we were sure, but after 4 months of steady use Paul’s idea is still working perfectly. The only negative is that making this new belt takes an hour or more of work spread over two days, but to us it's worth the effort.

HOW TO MAKE ONE

1. Cut a length of the silver holographic mylar tape sufficient for your TT, plus 3-4" extra.

2. Remove the silver metallic coating off the backside of the mylar. Paul used an acid etching cream popular with stained glass hobbyists to dissolve the metal - safe, quick and easy (use skin and eye protection).

3. Rinse thoroughly under running water, inspect to make sure you got all the silver off, wipe and hang to dry overnight.

4. Splice as normal to make a TT belt, making sure you tape on the OUTSIDE (which will be smoother than the now bare inside).

5. As always, the best splicing technique is to overlap the ends and cut on a 30-40 degree angle. Apply 1” video splicing tape (*not* tabs) across the belt at the *same* angle and trim away the excess.


WHY IT PERFORMS BETTER

Unlike any plain mylar ribbon you could easily buy, the silver holographic streamer has an ultra fine texture embossed on the back side of the *mylar* during manufacturing (*before* the metallic backing is applied). Once the silver layer is applied you can't see this texture, but that's what diffracts light like a million tiny prisms to produce the shimmery rainbow effect. Stripping the metal backing away exposes this texture, which becomes the contact surface of your new belt.

Paul realized this texture must exist and then hypothesized that using it for the working side of a TT belt might provide more “grip” on the platter rim and motor capstan than either plain mylar (which is extremely smooth) or the metallic backing. He was right. This belt produces more lifelike dynamics, both macro- and micro-, than even a brand new silver holographic belt - which heretofore was the best.

WHY IT LASTS LONGER

Removing the metallic backing exposes bare mylar, which is much sturdier than that fine layer of metal. Under normal use and assuming no accidents, one of these belts should last many, many months, perhaps years, while delivering consistent performance. Ours is going into its fifth month with few visible and no audible signs of wear.

Different motor capstan materials might interact with this belt differently, but I urge anyone with a compatible table to give this a try. Like all our favorite little tweaks, we'd find it hard to go back.

A FEW TIPS

1. Clean any silver/grey residue from your old belt off the motor capstan and platter before mounting the new belt.

2. As many of us have learned, the more inelastic the belt, the more critical motor leveling becomes. That is truer than ever with this new belt. Getting the motor set just right is touchy. Take care that your new belt is riding level in the center of the capstan before you start to play. You don't want it sliding up or down and mangling itself.

3. Motor distancing is also more critical than ever. Since this belt will not slip *or* stretch, tension must be perfect. The right amount is just shy of the tension that would tilt the motor off its feet.

4. Depending on your climate, the belt can build up static potential during use. Not enough to spark, but more than enough to attract airborne dust. I dust the belt's inside with my CF brush after each side before stopping the platter.

5. With this or any belt, always start your platter spinning with a helping push. Just pressing the motor's ON button creates lots of belt-wearing friction as the rapidly spinning motor tries to drag that heavy platter up to speed.

It all sounds like a pain, and it is! But the sonic and longevity results are worth the effort.

Cheers,
Doug
dougdeacon
dougdeacon OP
3,338 posts
 
Dan,

Dust buildup seems to vary with the weather. In the winter when our New England air is so dry, static builds up more and more brushing is needed. Less so in summer.

I did test static reduction in a simple and somewhat extreme way. Paul warned me it wouldn't help, but you know I never listen to him if I can make a fool of myself independently. With the platter spinning I zapped the belt with the Zerostat. INSTANT and TOTAL loss of grip between belt and platter. I could hear the belt whizzing past the slowing platter, it couldn't maintain its grip.

Dr. Chuckles wryly explained that the electrostic potential between belt molecules and platter molecules is what makes the whole system work. I knew that...

Dave,

I'm not saying mylar has no elasticity, just that the loads applied in this particular application are not high enough to reach its elastic threshhold. The "proof" is what I said above. Except for the occasional marauding cat, the motor position can be ignored for months with no change in performance or belt tension. In practical terms, it's pretty elastic-free.

BTW, the length of mylar under actual tension is not the full 50" length of the belt. Only the segment between the motor pulley and the contact area of the platter on the drive side is being tensioned.
stltrains
845 posts
 
Hello Paul and Doug i was able to get my mylar etched and installed today and would like to say thank you for a very good upgrade. When you have such small tweaks like this that make large improvements its a wonderful thing.
dougdeacon OP
3,338 posts
 
Stltrains,

Glad to hear you're all back together after the evacuation for the hurricane, and glad you're enjoying this upgrade like the others who've tried it.
dougdeacon OP
3,338 posts
 
Dgarretson,

Further thoughts on your implementation of a VPI idler wheel as a pulley for a 1/2" wide belt...

Clearly this will necessitate running your motor at vastly reduced RPM's. Assuming your controller has the range to allow this, you still run the risk of exaggerating the audible effects of your motor's cogging behavior. As the ratio between motor RPM and platter RPM approaches 1:1, motor cogging is directly translated to platter cogging.

By all means go ahead and try. But if you aren't happy with the results the fault may lie with the motor and the large pulley, not the belt. A way to test that would be to machine a small diameter pulley and use it with the same 1/2" belt. The faster the motor runs (relative to the platter) the less audible motor cogging will be.
dgarretson
2,598 posts
 
Doug,
Are you suggesting that cogging effects may be greater with 1/2" tape than with the thread drive I'm currently using, owing to improved grip of tape? I had considered this possibility when earlier converting VPI from soft rubber belt to thread. But there was nothing but improvement. So perhaps this experiment with tape will determine if too much grip is a bad thing with AC motor.

Looking at your point from a different perspective, the 300RPM Hurst motor in current favor at VPI is audibly quieter and more speed stable than the old 600RPM Hurst motor. It's difficult to account for this if one takes the view that audible cogging effects are in an inverse relationship to motor speed.

BTW, the discontinued Kelley AC-1 controller allows separate control of each phase of a 2-phase synchronous motor, and probably does as good a job as any at reducing cogging.

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