Tell me the critical features of an idler wheel
 

Now here's a (hopefully) interesting topic. What are the critical features of a record changer's idler wheel? (think 60s BSR, Garrard , Phillips etc)

I ask because I'd like to make one, just to see if it can be done. I'm a dab hand at building hard-to-find record player bits using a 3d printer and it will be mainly done via this method.

Some thought provoking questions I already have are:

1) why so much rubber? why not a centimetre (or less) of rubber round the edge? is there so much rubber to absorb shocks? (seems unlikely), to flex and conform? (again seem unlikely, it's just running round in a totally circular platter)
2) is the square profile of the rubber edge critical? I mean it were round like an 'o' ring would that be less effective?
3) how good does the centre bearing have to be? plain bronze bush should be fine?
4) how critical is the diameter? I've heard people say any size (within reason) is ok as it simply transfers the speed from spindle to rim
5) if in the 60s they had access to cheaper/different rubber alternatives or some of our newer rubber type things (silicone etc) would they have used something other than rubber? if so why/what?
6) is the weight of the idler wheel important? maybe more weight has better torque to get the arm and cam mechanism working

My initial thoughts were a plastic printed pulley with a fat 'o' ring stretched (or glued) around the edge in a groove, and plain bronze bush glued into the centre. Can you see problems with this?

Look forward to your replies and ideas

regards
Joe

Re: Tell me the critical features of an idler wheel
 

You mean a bit like these

https://www.usaudiomart.com/details/...mages/1291470/

Re: Tell me the critical features of an idler wheel
 

Or for the deep of pocket https://www.artisanfidelity.com/accessories

Craig

Re: Tell me the critical features of an idler wheel
 

Or even

http://www.audiosilente.com/spare-pa...21-td-184.html

Re: Tell me the critical features of an idler wheel
 

yes exactly like that, except mine would cost 12 cents to print!

So '0' ring looks like a goer
plain bronze bush looks like a goer

only remaining question is heft, will a plastic idler need weight to create torque and drive the cam mech?

I think this is worth a prototype effort already.

Re: Tell me the critical features of an idler wheel
 

I think this would be a worthwhile project if you can find a suitable chunky O-ring.

The most important feature would be concentricity.

Re: Tell me the critical features of an idler wheel
 

40mm chunky '0' rings easy to get on eBay, and 3D printers, despite their prints looking a bit rough (grooved) are amazingly accurate dimensionally especially producing large (over 5mm) circles. Now gluing a bush dead centre would be the tricky bit!

Re: Tell me the critical features of an idler wheel
 

I think glue the bush first then spin in a lathe to true up while also machining the grove for the O-ring.

Re: Tell me the critical features of an idler wheel
 

Surely an O ring, with what is in effect a point contact on the circumference of the cross section, would not have as much traction as a flat edge where the contact is about 2-3mm
There is not that much pressure on the idler to drum to flatten an O ring.
Mike

Re: Tell me the critical features of an idler wheel
 

There is not much pressure on the idler, true but given a reasonably constant coeficient of friction the traction will be the same, since the point pressure is greater.

Re: Tell me the critical features of an idler wheel
 

Square section O-rings are available, we use quite a few here but ours are huge things!
Something like these in the link may be better or more suited to your purpose?
https://simplybearings.co.uk/shop/p8...duct_info.html

Re: Tell me the critical features of an idler wheel
 

Plus, those commercial versions that Craig Sawyers posted were using round section '0' rings, so if they think they work well enough to charge 150 quid each then I guess they do work. But I agree square section does kinda feel more 'right'

Re: Tell me the critical features of an idler wheel
 

That's the traditional way of doing things, but a 3d printer just when printing just doesn't print plastic where the groove would be. You design it on a computer, then print it and wait 2 hours and it comes out fully finished, no lathe or groove cutting required! its quite amazing

That said your idea is a good alternative, for example making an idler wheel using a round perspex disk, trued up, then a groove machined on the edge. Would work just as well I think

Re: Tell me the critical features of an idler wheel
 

'Oilite' oil-impregnated sintered bronze would be a better choice for the bearing bush, and likely what the originals were. Finish the shaft hole to size with a reamer to get a better bearing surface than a drill leaves behind. Because the oilite retains oil, it's not suitable to glue to, so something mechanical rather than chemical is needed to retain it.

With an elastomer O-ring, the places of contact from the motor shaft and platter drive ring will press in a little, depending on pressure. The contact areas will be different for the motor shaft and the platter, so there will be a tiny speed error. This will be slightly different for round section and flat section O-rings.

This ought to be trivial, but once the audio world has thought of something, you know how it ends. Shouldn't matter at all on 401s and 301s with variable speed controls. Just don't tell those audiophiles that there is any theoretical reason, even the slightest, why a flat profile might be better for those very expensive idlers....

David

Re: Tell me the critical features of an idler wheel
 

That’s interesting Radio Wrangler, about the contact surface affecting the speed, I’m still trying to understand it, as I say interesting.
John

Re: Tell me the critical features of an idler wheel
 

This is where a cheap 3d printer comes unstuck. basically it 'prints' in plastic, but it's not terribly strong, certainly not strong enough to push fit a bearing. Superglue works fantastically but would not work on oil impregnated bearing. The alternative mechanical means could be a key way but would the printed plastic be strong enough?

I've just checked and superglue will work with plain bronze, but I'm sure you're right that the original bearing was oil-impregnated sintered bronze. Would a plain bronze bearing work? and if so for how long? there's the questions

Re: Tell me the critical features of an idler wheel
 

hmmm maybe a simple bronze bearing is the wrong way to go? Look at the attached, 10 proper carbon steel 5mm bearings for not much more than a pound! Steel would be easily superglued into my plastic idler

Re: Tell me the critical features of an idler wheel
 

Could push the oil-impregnated sintered bronze into a steel sleeve then glue that.

Re: Tell me the critical features of an idler wheel
 

I like it! Best of both worlds.

David

Re: Tell me the critical features of an idler wheel
 

Ball races rumble a bit, though it is not a problem for an idler wheel (unless it is really bad) because it is floating, the bearing just keeping it in place. The running torque on a turntable is so low I would think the very slight distortion of an "O" ring vs. flat will have very little impact.