beatcomber
AK Member
Who did the rebuild on your vintage wheel?
Rebuilt idler wheels: can incorrect DUROMETER affect platter speed?
- Thread starter monkboughtlunch
- Start date
monkboughtlunch
Super Member
@beatcomber - would you be happy to post a profile view of your non-rebuilt idler making contact with the 33 RPM pulley on your ROK? I'd like to compare where yours is making contact with my ROK idler wheel.
beatcomber
AK Member
monkboughtlunch
Super Member
Thanks - could you post a photo from this angle showing where your original non-rebuilt ROK wheel touches the pulley?
beatcomber
AK Member
Will do!
monkboughtlunch
Super Member
FYI. The photo I posted above is with the unit "on" in "33" RPM mode. I pushed the arm so the idler would contact the pulley as it spins.
BilboBaggins
Addicted Member
I may be totally off base here, as my experience with Rim drives to this point is as a user, but wouldn’t it make sense that a slightly smaller diameter would rotate slightly faster? Or would it be the opposite?
beatcomber
AK Member
The ratio between the motor and the idler doesn't actually matter any. Its the ratio between the motor and the platter that set the speed. Changing the ratio between the motor and idler inversely affects the ratio between the idler and the platter, so basically any changes to the idler diameter are just cancelled out. If this were a two-step idler wheel, thats a different story.
Is the motor spindle tapered on these, or maybe there is a worn area where the O-ring idler runs? Thinking the contact spot may actually have more to do with it than the durometer of the wheel. If you can adjust the height of the idler so they match it may alter the speed. I know I've run into that on Garrard machines, but I've seen those with visible wear on the motor spindle from heavy use.
BilboBaggins
Addicted Member
Thanks! I’ve got a JVC idler I’m going to try to restore, and all of this helps towards a better understanding.
monkboughtlunch
Super Member
Thanks @beatcomber . Was this photo taken with the motor running or in the off position?
Why is your 33 pulley step a different color than the 45 and 78 steps? The ROK pulleys were phenolic material, but your 33 pulley step looks metallic. Is something wrapped around it, or was something grafted on to the rest of the pulley?
It looks like your ROK idler wheel is making contact exactly in the middle of the pulley step. My fast running ROK (when using the rebuilt wheel) is making contact a little bit higher than that. Not sure if there is any significance.
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monkboughtlunch
Super Member
Here's a direct comparison. beatcomber's unrestored ROK idler wheel on the left. My rebuilt ROK wheel (running 1.4% fast) on the right.
@beatcomber - have you tried timing this unrebuilt wheel? If so, what kind of accuracy are you seeing?
@beatcomber - have you tried timing this unrebuilt wheel? If so, what kind of accuracy are you seeing?
ConradH
Lunatic Member
An o-ring will have a narrow contact area and deflect more against a small diameter shaft. It probably won't transfer exactly 1:1 to a large diameter platter, but a bit less. The theory could be tested by using a soft and hard o-ring, say a silicone one and a regular Buna-N one.
beatcomber
AK Member
My photo shows the speed selector set at 33.
I've just addressed the differences in the pulleys in my other thread...
Just unexpectedly won a Rek-O-Kut B-12-H (!!)
beatcomber
AK Member
I noticed that. It's possible that the relative heights of the different pulley types might not be identical. I'll compare the ones I have here and let you know.