Tell me the critical features of an idler wheel

[barrymagrec]

On an idler drive system the speed is dependent only on the ratio of the drive and driven pulleys, the diameter of the idler itself has no effect on speed since the peripheral speed remains the same. (neglecting any problems due to slip and indentation of the idler by the smaller pulley, of course)

[Nickthedentist]

What Graham says is true.

But too small a wheel will not "engage" properly with the motor pulley and turntable rim, and so will deliver less torque unless you modify things (e.g. fit a stronger spring, maybe).

Sorry, crossed with Barry.

[Nickthedentist]

Originally Posted by hayerjoe

Other interesting problems I had were with the neoprene O-ring itself From the packet it had a thin layer of oil on it, once cleaned it was still too shiny, I had some difficulty making it dull and more friction-full (new word), but when roughed up it worked well.

I think some O-rings are supplied coated with a film of silicone. When they're used for their intended purpose i.e. as a seal, this enables them to slide into place with ease and without being distorted, ensuring they do their job optimally.

However for this application, it's a potential disaster, as silicone is allegedly impossible to remove with all readily-available solvents.

Keep up the good work, Joe, this is interesting stuff.

Nick

[joebog1]

Oops!!! Sorry gents, hoof in mouth disease again

Joe

[hayerjoe]

Originally Posted by barrymagrec

On an idler drive system the speed is dependent only on the ratio of the drive and driven pulleys, the diameter of the idler itself has no effect on speed since the peripheral speed remains the same. (neglecting any problems due to slip and indentation of the idler by the smaller pulley, of course)

Thanks this is the best explanation I've read on this.

At first glance it seems somehow illogical that the idler wheel size makes no difference, but think of it this way, the drive spindle spins the idler at say 25mm per second, the idler just passes this same speed to the platter, increase the size of the idler to a dinner plate (!) it still moves it at 25mm per second, so at the platter it's still the same speed

thanks for helping me think this through

Now the other question was... being out of round, what impact would THAT have?

[hayerjoe]

Originally Posted by Nickthedentist

However for this application, it's a potential disaster, as silicone is allegedly impossible to remove with all readily-available solvents.

Keep up the good work, Joe, this is interesting stuff.

Nick

Thanks Nick. I'm going to try various solvents to see if anything works effectively and easily

[Radio Wrangler]

Originally Posted by hayerjoe

Now the other question was... being out of round, what impact would THAT have?

With an out of round, or eccentrically mounted idler wheel, because the platter rim and the motor shaft contact the idler in different places, the effective radii they each see will no longer be equal, and the ratio will keep changing as the idler rotates, so the platter speed will be modulated... Wow/flutter at the idler rotation speed.

David

[hayerjoe]

Originally Posted by joebog1

I have a spare 401 idler that I have been thinking of sending down to see what you can make of it. These idlers also have in inner bearing sleeve that causes problems though.

Great progress !!! Keep up these posts..
Joe

I reckon you could send it to Tasmania in a $1 envelope. Would be interesting to break open a Garrard idler to see if I could find a more generic solution... at present I'm thinking it will have to be a unique design for each different idler type (as they'll all be built slightly differently), which is a bit more onerous than just changing 4 dimensions and hitting 'print'

[joebog1]

The Garrard 401 is not such a simple animal!!. It's still just an idler wheel, but somewhat larger than the one you have cranked out. It has a piddlely little bearing in the centre that wears as well as the rubber rim drying out and splitting/cracking/failing. Remember too!! that these days a 401 is an audiophool turntable and requires just the right amount of rubbish to work correctly !! .

BUT, if you wish to have a go I can arrange to send it to you. The centre bearing is where most of the drama lies however. The turntable is speed controlled via a magnetic brake so exact size isn't so important ( and I have been corrected in my thinking without "thinking" about it, that it's just an idler). Rumble seems to be the biggest problem with a 401, and from what I have gleaned from the net is it's due to bearing wear. Mind you I have kept perhaps two dozen running "perfectly" in various AM radio stations for many years.

Keep posting your work!! I might just be tempted to buy an extrusion printer, to go along with my new desktop PC. As I only run Linux I will have to polish up my G-code, but I have used it before on CNC milling machines and lathes. Check, linuxcnc.org , like all Linux variants its 100% free and served by thousands of software/hardware engineers.

Cheers

Joe

[hayerjoe]

[Well I can't do much about the bearing but would be interesting to see how my O-ring adaptation could be applied, do you have an audiophool you could try it on? I believe their hearing is 10+ times better than we vintage HiFi people!

To be honest if you know CNC stuff, the 3D print stuff will be easy. The program I use to design is called Freecad and it's available for Linux distros

[hayerjoe]

OK it's been a while but here's an update

This morning I received the 2 little bearings I'd ordered about 6 weeks back (remember they are oil impregnated bronze but encased in copper so they can be super-glued into my 3d printed idler wheel). they must have been the smallest and lightest package I've ever received... they are tiny

Anyhow I just printed my plastic idler wheel with the internal hole adapted to be a push fit with the new bearing. All worked well and I pressed (no glue) the bearing in and it spins beautifully in my test BSR. It's Friday night here in Tasmania so that's your lot for tonight but tomorrow I will fit the outer o-ring and test it for real in the BSR deck

Watch this space!

Cheers
Joe

[hayerjoe]

OK here perhaps is the last update and it's not really good news.

To my mind the answers to 'can you make an adequate replacement for an idler wheel with a 3D printer' is 'no'

In every regard but one the experiment has been a success. So the successes:

1) cheap - each idler cost me 6 cents to print plus a 5 cent o-ring plus a bearing which in one case was simply an 8mm piece of brass tube from a model shop
2) it drives the platter well and consistently at all speeds with no slippage
3) it had the torque to play and carry 6 LPs each dropped via the changer and the mechanism showed no delay or hesitation doing that

Both approaches to the solution achieved the above (remember one was an entire idler wheel printed in plastic, the other was just the rubber bit of an old older wheel replaced by a 3D printed plastic o-ring carrier)

So the failure? Well I simply could not get any of my idlers totally round and I mean TOTALLY round. And any non-roundness made the idler support leg jiggle, which in turn generated some unwelcome noise. My printer can print to an accuracy of 0.2mm, that's no where near good enough, so I then used the poor pivot motor to spin my idler whilst I held a square matchbox against the edge to grind it even more round. I had some success with this but still NEVER fully eliminated the jiggle... it was very disappointing. I mean you can't really hear the jiggle when playing a record unless you listen carefully between tracks and it's an ever so slight rumble.

Unless anyone can think of a better way (without such specialist equipment as a lathe etc) I'm calling this in true Mythbusters fashion "failed - possible, but unlikely"

Hope you all enjoyed the journey?!

cheers
Joe

[John10b]

Yes Joe I have enjoyed reading all about it, thank you.
John

[analogadikt]

The problem reported in post#72 is known to occur. On Lencoheaven forum it has been observed in some cases where the original idler was replaced with an aftermarket one that has a an O ring.

I would suggest grinding on a lathe. The idler shall be held securely in the chuck and the diamond blade in the tool post, idler can be rotated at a slow speed.

I have tried this method to refinish old idlers with hardened edges, and have obtained very satisfactory results.

Regards,

Anwesh

[hayerjoe]

Originally Posted by analogadikt

The problem reported in post#72 is known to occur. On Lencoheaven forum it has been observed in some cases where the original idler was replaced with an aftermarket one that has a an O ring.

I would suggest grinding on a lathe. The idler shall be held securely in the chuck and the diamond blade in the tool post, idler can be rotated at a slow speed.

I have tried this method to refinish old idlers with hardened edges, and have obtained very satisfactory results.

Regards,

Anwesh

Yes, I'm certain it can be fixed via a lathe, but my hope was to provide people with a simple solution that needed the minimum of specialist tools (other than a 3d printer of course!)

In fact it's given me a greater appreciation of the care that BSR, Garrard etc put into their idlers, I'm now 100% sure each was individually ground down in a similar process to what you outline, so something as simple as an idler has been proven to be quite a finely crafted item and not just something stamped out by the 1000s

cheers
Joe

[peter_sol]

Well done for trying. The thing with idler wheels is that when they are new and supple and engaged, the motor spindle ( stepped pulley) digs into the rubber and the idler in turn continuously flattens against the inner rim of the turntable. That's why there is plenty of torque. The more you try to slow it down the more it grips. It is a pity it's not easy to "cast" rubber. Then as you say it has to be carefully ground to a high tolerance.

[Nickthedentist]

Yes, well done from me too, I was impressed you'd got as far as you got.

I can tell you're disappointed, but it's great that you got good torque delivery, and I suspect your concentricity problems aren't insurmountable.

N.

[hayerjoe]

yep, I am a bit disappointed, but as I'd said I've come out of this with a new found respect for idler wheels!

In fact I wonder if the complexity of finishing idler wheels so accurately contributed to the move to belt drives?

[John10b]

That’s an interesting thought.
John