Rim Drive Belt Question

Rim Drive Belt Question

Postby Tirebiter » Thu Jul 11, 2019 9:21 am

After purchasing a Rim Drive and Walker Precision Motor Controller for my TNT with a Mk 5 11.5" platter. I performed the usual lubrication on both the flywheel bearing and the motor bearing. The motor bearing in particular was pretty well gummed up but after a couple of drops of light oil and some lithium grease the notchy feel abated. I was able to set platter speed to 33.3 rpm without a problem but noted that the two drive belts appeared to be slipping so I ordered a new set which included the belt on the flywheel drive itself, the "tire" that rides on the platter providing grip.

The package I received was marked "HR-X and SSM Rim Drive Belt Set". The motor to pulley belts seem fine but the tire belt is thicker, I estimate perhaps 1.5X the old belt. I didn't think it was a big deal until I went to fine tune speed with the Walker and now find that I am running out adjustment. Basically the thicker tire sped the platter up and now I cannot slow the unit down to 33.3 rpm with the Walker controller.

So after all that rambling my question is, did the rim drive use differ sized tire belts for different applications and do I need to order up the proper tire for my setup? I spoke with Lloyd Walker and he can change resistors in the controller to compensate but I would rather not make that change if I can help it.

Thanks,
Brock
TNT Jr, Graham Phantom III, ZYX Universe II LOMC, Tempo Electric Silver Phono Cable, Amazon B-lab Phonoamplifyer, Tom Evans - The Vibe, Lamm ML 2.1 Monoblocks, Avantgarde Duo Grosso....and a Thorens TD 160 Mk I in standby....
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Re: Rim Drive Belt Question

Postby Brf » Thu Jul 11, 2019 11:25 am

I don't believe that VPI has changed the rim drive belt size (other than the smaller diameter used on the Avenger). The belt needs to seat in the rim drive edge relief, otherwise, it will not be concentrically aligned. What color is your belt, orange/brown or black?
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Re: Rim Drive Belt Question

Postby Tirebiter » Thu Jul 11, 2019 4:05 pm

Brent, the belts are both black. The old one is 2.5mm in diameter and the new is 3.5mm. They both seat satisfactorily in the machined groove although the old one seems to have stretched a bit and is hair sloppy while in place.

There also seems to be a bit of an art to setting the pressure that the rim drive exerts on the platter. Too little and I experienced slippage between the rim and the platter. Too much causes the belt to compress against the platter, increasing drag which then causes the two smaller drive belts to slip on the motor pulley. And of course the result is that the platter rpm falls off. This is especially sensitive with the new, thicker belt. Tricky stuff!

Until I get the belt issue sorted I will using the old belt.

Brock
TNT Jr, Graham Phantom III, ZYX Universe II LOMC, Tempo Electric Silver Phono Cable, Amazon B-lab Phonoamplifyer, Tom Evans - The Vibe, Lamm ML 2.1 Monoblocks, Avantgarde Duo Grosso....and a Thorens TD 160 Mk I in standby....
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Re: Rim Drive Belt Question

Postby Brf » Fri Jul 12, 2019 10:20 am

Brock, make sure that the rim drive belt is clean and void of any finger print oil. The rim belt should just kiss the platter and have constant but light pressure. Use a flashlight and back light the rim drive contact area to make sure that the belt is maintaining constant contact. In addition, make sure you run the rim drive on the MK5 SS portion and in contact with the flat surface i.e. don't run it in the belt groove.
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Re: Rim Drive Belt Question

Postby Tirebiter » Fri Jul 12, 2019 6:18 pm

Thanks Brent, Yep, I had cleaned the belt well and played around with a few methods to find least pressure w/o slippage. Analog Magic is what I used to set speed and found it was also useful in setting pressure as it shows the results of too much or little. Rim pressure also has a large effect on wow & flutter readings and helped to find a spot when where I consistently get readings in the range of 0.08. With all of the futzing around I have managed to get a speed graph that has the sharpest peak to date.

As you suggested, contact on SS section, check; contact on flat surface, check. And yes, using a flashlight to look at contact patch is useful.

I guess my next move is measure the diameter of the drive wheel and go on the hunt for a supplier of EPDM belts to see if I can find a source for one at 0.25mm thickness...that is unless there is a compelling reason to go with 0.35mm??
TNT Jr, Graham Phantom III, ZYX Universe II LOMC, Tempo Electric Silver Phono Cable, Amazon B-lab Phonoamplifyer, Tom Evans - The Vibe, Lamm ML 2.1 Monoblocks, Avantgarde Duo Grosso....and a Thorens TD 160 Mk I in standby....
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