Tell me the critical features of an idler wheel

[Leon Crampin]

A porous bronze bush would be much the preferred solution. It would have to be made to size on the bore - reaming a porous bush wrecks its porosity.

A ball race would be too noisy for this job.

Leon.

[Radio Wrangler]

Reaming reduces porosity by 'smearing' the sintered particles on the inside. So you want to finish to accurate size with only a light ream, and do it by hand. Drilling also smears the bronze particles. There is almost no way of cutting the stuff which doesn't do this to an extent.

You need the right fit between the bush and the axle so that it can turn freely, but not chatter.

Drilling will be fine if you have exactly the right size drill for the axle size, and this applies also to reaming.

But if drilling, take it slowly with little pressure. 2-flute drills tend to flex if pressed and drill a triangularly distorted hole, even when drilled in a lathe. If you push smaller drills too hard in a tailstock chuck, you can see the tip wiggle, the drill flexing, to follow the rotation of the workpiece.

In the extreme this sort of thing can be used with a shaped bit in a rotating tailstock chuck to drill square and hexagonal holes (etc) Look up 'rotary broaching' if you're curious. Tartan paint and 'fetch the long stand from stores' are still used as pranks on apprentices, but the drill for square holes is real! Someone mentioned it when I was doing my training at Rolls Royce, so an instructor showed us... laughing all the way.

Lots of Oilite bushes are finished with a reamer and can be found in all sorts of equipment. The tuning drives of HP 8640 signal generators were hand-finished this way. You just want a small path to the sliding surfaces to allow oil through at a very slow rate. After all, the bush only contains a limited amount and you want it to last a good lifetime.

David

[jon_the_id]

I am a Lenco L75 owner and hence am aware of the Audiosilente aftermarket idlers for these decks. Apparently many users have had issues getting the o ring to sit evenly with this design.

[hayerjoe]

Originally Posted by FIXITNOW

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

That is a good solution, thanks

[hayerjoe]

Thanks for everyone's input it was all very useful, please keep it coming

So today I've designed a first prototype (see attached) and tomorrow I'll print it

this first prototype will have no bearing at all, just a 4mm hole to go over the 3.85mm idler axle. Just to see how it goes regarding line up of groove to drive spindle etc

Some interesting facts about the original (BSR) idler:

weight=11.5g
bearing inner =4.1mm
idler axle =3.85mm (so fair bit of slack there! we're not in precision instrument land, but we all knew that I think)
wheel diameter =39.5mm
rubber contact edge height=2.5mm

My ABS plastic wheel will mirror most of the above except it will be lighter (predicted to be 5g, but that's without bearing and o ring), and the contact edge will be round not square. The software tells me it will take 43 minutes to make/print and will cost me 6 Aussie cents of plastic filament!

Sounds like bearing choice and fitment is going to be the biggest issue for prototype 2 onwards

Plus no-one has yet commented on the lightness of my idler wheel, will it need heft to transfer torque to the cycle cam mechanism?

[saxmaniac]

Couple of stray thoughts,
There's a material (rs listed) called graphite nylon which is simply graphite impregnated nylon intended for a bearing material. No lubricant needed and I've seen it used in much more arduous applications without any wear problems. Also, might not rumble be a factor if using relatively narrow o rings, and perhaps the reason there's such a lot of rubber on the original wheels. And why make the whole wheel when it's just the rubber that needs replacing?

[TonyDuell]

I have to wonder why you don't turn a new idler wheel (to take an O-ring 'tyre') from metal rather than 3D-printing one in plastic. I've made drive rollers for computer catridge tape drives many times by doing just that. OK, a turntable idler is rather larger, but certainly within the capabilities of a small lathe.

My experience with 3D printing has not been good. I've had parts printed both by friends and professionally, and they are much weaker and less rigid (those are not the same) than the injection-moulded plastic parts they were to replace. And nowhere near as strong as metal. In fact no 3D printed part I've had made was suitable for the job, really.

[DMcMahon]

Originally Posted by hayerjoe

Plus no-one has yet commented on the lightness of my idler wheel, will it need heft to transfer torque to the cycle cam mechanism?

I assume you mean weight when you say heft. Heft is not commonly used in the UK in my experience.

David

Two things about the 3d printed item, one, I would make the hole a much closer fit, you can always fettle it with a bit of wet and dry rolled up, two, how about a triangular groove, that would make the O ring sit down nicely, no chance of rolling around. And a comment about force on the bearing surface, it will only be that of the spring any extra force required by, say, the auto mechanism will be take care of by the "grab" factor.

[hayerjoe]

Originally Posted by saxmaniac

Couple of stray thoughts,
There's a material (rs listed) called graphite nylon which is simply graphite impregnated nylon intended for a bearing material. No lubricant needed and I've seen it used in much more arduous applications without any wear problems. Also, might not rumble be a factor if using relatively narrow o rings, and perhaps the reason there's such a lot of rubber on the original wheels. And why make the whole wheel when it's just the rubber that needs replacing?

Well saxmaniac you must have been sending mental messages to Tasmania because I had the same thought overnight. Why try and recreate the bushing/bearing when that's already in place in an assumed damaged idler wheel? I could just remove the rubber and print a plashic cup to sit on the existing alloy wheel that holds an o ring at the correct distance from the centre. It has its own issues, like adding a keyway, but overall it will be a better solution I think. I'll mock something up today when the sun comes out (I print using solar!)

Does anyone have a BSR idler wheel with the rubber removed? Please attach a photo

[hayerjoe]

Originally Posted by DMcMahon

I assume you mean weight when you say heft. Heft is not commonly used in the UK in my experience.

David

Oh dear, I looked it up and it's says 'heft' is a North American term! Sorry about that, I'm British and assumed 'heft' was from my UK past but no. Apologies, yes I do mean something like 'weight' when I say 'heft', actually more like 'mass'

[hayerjoe]

Originally Posted by TonyDuell

I have to wonder why you don't turn a new idler wheel (to take an O-ring 'tyre') from metal rather than 3D-printing one in plastic. I've made drive rollers for computer catridge tape drives many times by doing just that. OK, a turntable idler is rather larger, but certainly within the capabilities of a small lathe.

My experience with 3D printing has not been good. I've had parts printed both by friends and professionally, and they are much weaker and less rigid (those are not the same) than the injection-moulded plastic parts they were to replace. And nowhere near as strong as metal. In fact no 3D printed part I've had made was suitable for the job, really.

I think this shows the industrial difference between UK and Tasmania. I've never lived on a street that has so many blokes with such well equipped workshops (huge floor standing equipment etc) but no-one has any metal turning stuff. Its the difference between a wood based industry and UKs engineering past. So I have no access to such equipment

I'm 100% certain the 3d printed stuff will be fine for this application , you must have been unlucky with your experience. Nothing will be as good as metal, but the 3d ABS plastic part will be almost as good as an injection moulded ABS part, the key is use the right material at the right heat (so it welds) and to design it slightly differently to maximise the strength of a part that is built up of layers (albeit quite well welded layers)

As as example see attached. It's a window opening winder handle I printed, it's right above my printer so is used every 2-3 days (plastic printing needs good ventilation) so it has some good torque applied to it as window is opened and closed and has not failed in over 18 months, and even if it did I'd just print another one for around 15 cents!

[Herald1360]

Originally Posted by hayerjoe

Plus no-one has yet commented on the lightness of my idler wheel, will it need heft to transfer torque to the cycle cam mechanism?

"Hefty" is a common enough adjective in British English to make "heft" perfectly understandable in context. To me at any rate it implies more to do with the right "feel" weight wise of an object rather than its actual weight.

[joebog1]

There will always be purists that say it must be made of Unobtainium.
I reckon "suck it n see", but then I am another aussie.
Make the bit, then post results here, with a few photos if available.
Ifn it dont work proper, its 12 cents I think you said, THAT of course doesnt count the revs of the watt hour meter hangin inside the fuse box. BUT its the future,and like it or not, the purists will have to move aside. Pretty simple I would have thought.

With my best wishes and hopes for its success.

Joe

[hayerjoe]

Originally Posted by joebog1

There will always be purists that say it must be made of Unobtainium.
I reckon "suck it n see", but then I am another aussie.
Make the bit, then post results here, with a few photos if available.
Ifn it dont work proper, its 12 cents I think you said, THAT of course doesnt count the revs of the watt hour meter hangin inside the fuse box. BUT its the future,and like it or not, the purists will have to move aside. Pretty simple I would have thought.

With my best wishes and hopes for its success.

Joe

Definitely is the future, but such a learning curve using the software, nearly gave up a dozen times! but was worth it now, such a versatile 'tool' for the price of a cheap lawnmower!!!

And I mostly print during the day, so not even any electricity cost!

I'm just about to post my pictures of the prototype I built today... went well

[hayerjoe]

OK prototype has been made. see attached photos. I first made an analog of just the metal part of a standard BSR idler. I then made effectively an o-ring holder (looks like a pulley) that would then be glued on top of a real de-rubbered metal idler wheel. I used merlinmaxwell's suggestion of a V shaped groove, but I will probably print a square grooved one also for trials

Unfortunately it's now a waiting game as I have no suitably large o-ring (will have to order some) and I also i don't have access to a de-rubbered idler wheel, but I think I know where to get one, but will be at least mid-week

The delay is rather frustrating but I do think the concept is going to work. I've trialled it on a BSR TU12 deck and each speed setting puts the groove in a good spot for the o-ring to contact the drive spindle (again see photos)

[qualityten]

Thanks for keeping us posted on your experiments. A tool that enables us to make replacement parts, or completely new parts, is worth learning about!

[joebog1]

Most bearing shops hold a large variety of O rings. Also ANY hydraulic hose company will have umteen dozens of different shapes and sizes. They cost cents but you may have to pay 2 or 3 bucks for singles.

Just a thought

Joe

[mark_in_manc]

I don't know if this will be useful, but a quick way to make sure fitted circular parts which have to transmit some torque don't move, is a 'Scotch Key'. In this case, where one part might be harder than the other, I think I'd file a groove in the inner (hard) bit, push on the plastic part, and then run a drill into the groove which would also mark the plastic. Choose a number drill (ideally) just a little smaller than the diameter of the bit of wire, brazing rod or whatever you want to use for your key. Then push the key in, and it should all stay together. If you are worried about it going squint, use 3 equi-spaced keys. I repaired my kitchen taps like this a while back - a similar thing, plastic on brass in that case, which had stripped their splines - and it works fine, even with the whole family abusing it

(this might be well over the top here, where you can play with the ID of your printed part and perhaps just a snug fit will do).

Oh, and if you want to add weight, glue a washer onto it!

[hayerjoe]

Originally Posted by qualityten

Thanks for keeping us posted on your experiments. A tool that enables us to make replacement parts, or completely new parts, is worth learning about!

Glad its of interest to you. I've said to the wife "this is best tool you've ever bought me" and it's true, so many uses. In fact my proud boast is that there's not a single room in the house that doesn't have something in it fixed via the 3d printer!

As for things for record players, tonearm locks/clips, one off brackets, new plastic buttons where a unique one is missing, short spindles, the sliding plastic controls/buttons for Garrard decks and most useful of all is cartridge clips. I design one clip for a cartridge type and then regardless of the target tonearm (mine are all 50s and 60s) I just alter some parameters to make it sit lower or higher in the arm, or even alter the angle that the cartridge sits