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Old 31st May 2021, 9:36 am   #41
mark_in_manc
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Default Re: Tell me the critical features of an idler wheel

I'm a bit put off by the CAD bit, but I guess (hope? ) I could get into it! A friend gets fed up with me asking to print this and that (and draw it, sometimes) - I have used most of the bits he has given me for patterns for alloy castings. Like the traditional 'lost wax' method for investment casting, people also report 'lost plastic' in various web videos - I've not tried investments, so this is something to look forward to.
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Old 31st May 2021, 10:23 am   #42
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Default Re: Tell me the critical features of an idler wheel

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Originally Posted by hayerjoe View Post
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)
I've always assumed the large quantity of rubber usually used is a balance between coupling the desired constant speed drive and decoupling any motor vibration. A mechanical low pass filter if you like.

I don't see the o-ring performing that function to any great extent.

Cheers
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Old 31st May 2021, 11:04 am   #43
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Default Re: Tell me the critical features of an idler wheel

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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!
Mark I had to read that 10 times, still all I could understand was the glued on washer bit ! I googled 'scotch key' and still struggled with it until I found a photo. My confusion stemmed from thinking you were talking about stopping the outside o-ring moving, but now I understand what a scotch key is I know you're talking about locking the pulley to the old idler wheel, now it makes sense, kinda like a round woodruf key, takes less torque but easier to make. I'll add it to the ideas pile and thanks for introducing me to 'scotch keys'
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Old 31st May 2021, 11:14 am   #44
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Default Re: Tell me the critical features of an idler wheel

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Originally Posted by mark_in_manc View Post
I'm a bit put off by the CAD bit, but I guess (hope? ) I could get into it! A friend gets fed up with me asking to print this and that (and draw it, sometimes) - I have used most of the bits he has given me for patterns for alloy castings. Like the traditional 'lost wax' method for investment casting, people also report 'lost plastic' in various web videos - I've not tried investments, so this is something to look forward to.
CAD bit was so hard to learn, kept thinking it was useless software, so I tried 3 different programs, finally realised I just had to invest a bit of time in learning one of them properly!
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Old 31st May 2021, 11:16 am   #45
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Default Re: Tell me the critical features of an idler wheel

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Quote:
Originally Posted by hayerjoe View Post
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)
I've always assumed the large quantity of rubber usually used is a balance between coupling the desired constant speed drive and decoupling any motor vibration. A mechanical low pass filter if you like.

I don't see the o-ring performing that function to any great extent.

Cheers

Yes I'm not convinced that the O-ring will work well, but it is a cheap starting place
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Old 7th Jun 2021, 6:15 am   #46
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Default Re: Tell me the critical features of an idler wheel

hello all

Sorry for the delay in updating. Ive been waiting for a specfic size o-ring to come in and also waiting for a friend to find a knackered old idler I could practice on.

No progress on an old idler yet BUT I got the o-ring today. In a what-the-hell moment I fitted it to my plastic printed idler which I put on a temporary analog of a real de-rubbered idler wheel, snapped them together (no glue) added the o-ring and put on the BSR idler wheel spindle with a circlip. So no bearing and very lose/wobbly on the shaft. Put the platter back on, put on my test 45 (a well known track so I could judge the speed) and everything worked amazingly well

See photos attached, sorry the idler and analog is black plastic as it makes it harder to see the details and o-ring but black was what was loaded in the printer.

Now obviously this is not a longterm prospect as it has no bearing whatsoever, but I think it proves many concepts such as the o-ring contact point seems ok (rather than square), the v groove seems to work well even without glue, and the line up to the various speed steps works well

Where to from here? well I need an old metal idler to try this out on, I'd like to try the o-ring driving at 33 a record changer cam (will the o-ring transmit enough torque etc). I'm almost thinking can I print the whole thing in plastic and just lightly press fit a plain brass tube as a bearing!! watch this space

Joe
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Old 7th Jun 2021, 10:39 pm   #47
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Default Re: Tell me the critical features of an idler wheel

Joe, I have really enjoyed reading about your design process and the responses that remind me how great a tool the Internet is for designers.
It's great to see the early results, please keep us up to date when you have time.

I think your work has borne out the earlier comment about the myth of unobtainium too, to put the cat among the pigeons!
Cheers from Bill.
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Old 8th Jun 2021, 11:17 am   #48
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Default Re: Tell me the critical features of an idler wheel

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Joe, I have really enjoyed reading about your design process and the responses that remind me how great a tool the Internet is for designers.
It's great to see the early results, please keep us up to date when you have time.

I think your work has borne out the earlier comment about the myth of unobtainium too, to put the cat among the pigeons!
Cheers from Bill.
glad you're enjoying it Bill. I've definitely got some good ideas from the forum members. I will report back on progress as-it-happens

thanks Joe
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Old 8th Jun 2021, 11:38 am   #49
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Default Re: Tell me the critical features of an idler wheel

Although I'm not much of a record player collector (but I do have a few) this is good news.
It's all very well being able to get fancy Idlers for your 301 but it's good that lesser turntables may have the opportunity of fresh rubber at affordable prices.

I am following your progress with great interest.

Cheers

Mike T
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Old 8th Jun 2021, 12:54 pm   #50
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Default Re: Tell me the critical features of an idler wheel

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Although I'm not much of a record player collector (but I do have a few) this is good news.
It's all very well being able to get fancy Idlers for your 301 but it's good that lesser turntables may have the opportunity of fresh rubber at affordable prices.

I am following your progress with great interest.

Cheers

Mike T
Regarding price so far. The idler wheel cost 6 cents of plastic and 10 cents of o-ring - so yeh quite affordable, especially when converted to Sterling! About 6p?

Obviously my 3d printer cost me money (A$350), and I need a computer and CAD software (software is actually free), but once designed you don't even need these, you can send away your CAD files to a company who prints it on a very accurate $3000+ printer for about $20 and they mail it back

So if I can get the bearing bit sorted or can use the old idler body to mount my new O-ring holder, it could indeed be a viable option for anyone
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Old 18th Jun 2021, 11:29 am   #51
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Default Re: Tell me the critical features of an idler wheel

Hello everyone

Here's a progress update.

Still haven't been able to get a damaged idler wheel to practice on, but I have ordered some oil impregnated bronze bearings that are incased in copper so can be glued into the plastic idler. Downside is they are coming from China so will take at least 6 weeks!

In the meantime I decided today to make my own very simple bearing from a piece of brass tube. This has been cut and press fitted into the 3D printed idler, the results are very satisfactory (see photos). the previous idler was just a prototype and had no bearing so it was wobbly on the shaft and didn't sound brilliant but proved a few principles. Now with this new version with the simplest of 'bearings' there's no wobble as the bearing makes it fit well and the sound is as good as with the real idler I swapped back in.

Whilst I'm waiting for the proper bearings my next test will be to see if the plastic idler, with O-ring and simple bearing can transmit enough torque to drive the cycle cam on a bigger BSR record changer deck

Cheers
Joe
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Old 19th Jun 2021, 7:49 am   #52
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Default Re: Tell me the critical features of an idler wheel

I'd be interested to know how much rumble you get in the sound due to an 0 ring having less amount of rubber to absorb lower frequency vibration?
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Old 19th Jun 2021, 8:16 am   #53
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I'd be interested to know how much rumble you get in the sound due to an 0 ring having less amount of rubber to absorb lower frequency vibration?
Can you recommend something that would have such low frequencies? My test album was a Booker T greatest hits, whilst being excellent music it also was a really good audio test as sustained organ notes are easy to spot speed variations. It sounded awful with the old un-bearing'd wheel but very good with the new wheel with bearing
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Old 19th Jun 2021, 8:26 am   #54
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Default Re: Tell me the critical features of an idler wheel

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I'd be interested to know how much rumble you get in the sound due to an 0 ring having less amount of rubber to absorb lower frequency vibration?
I did also think about using 2 o-rings, one inside the other, this would double the amount of rubber horizontally. So I still have this option up my sleeve if rumble is a problem
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Old 19th Jun 2021, 8:49 am   #55
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Default Re: Tell me the critical features of an idler wheel

Rumble ought to be OK if the idler's bearing is a good fit.

The round section of the O ring compared to the flat face of the original idler rubber will mean there is more pressure from the motor shaft (real pressure force/area of contact) and so the motor shaft will press further into the rubber, assuming the rubber to have the same hardness. So the idler diameter will act as baing slightly different to the motor than to the turntable rim.

This will create a different speed error to the flat-surfaced idler, worse for the slower speeds there the motor saft diameter is smallest.

I'm hoping this comes out insignificant on the speeds that people use 78, 45, 33 and I don't suppose anyone is much bothered with 16.

I'd thought a bit about the flat cross-section of the contact face of original idler wheels and wondered why they'd gone to trouble to make them flat. Was it easier to make? or did it confer some advantage?

I'm unsure of the speed effect. In simple geometry, the input radius seems smaller so there might be a speed-up effect, but then the rubber is elastic, and it's the rate of passage of its elastic surface in metres/sec that counts, and that surface is deformed around the drive shaft due to the applied force from the spring so length isn't a constant.

Whatever it does, I think it will do a bit more of it with the round section tyre, but I hope it all comes out as insignificant.

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Old 19th Jun 2021, 9:38 am   #56
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Rumble ought to be OK if the idler's bearing is a good fit.

The round section of the O ring compared to the flat face of the original idler rubber will mean there is more pressure from the motor shaft (real pressure force/area of contact) and so the motor shaft will press further into the rubber, assuming the rubber to have the same hardness. So the idler diameter will act as baing slightly different to the motor than to the turntable rim.

This will create a different speed error to the flat-surfaced idler, worse for the slower speeds there the motor saft diameter is smallest.

I'm hoping this comes out insignificant on the speeds that people use 78, 45, 33 and I don't suppose anyone is much bothered with 16.

I'd thought a bit about the flat cross-section of the contact face of original idler wheels and wondered why they'd gone to trouble to make them flat. Was it easier to make? or did it confer some advantage?

I'm unsure of the speed effect. In simple geometry, the input radius seems smaller so there might be a speed-up effect, but then the rubber is elastic, and it's the rate of passage of its elastic surface in metres/sec that counts, and that surface is deformed around the drive shaft due to the applied force from the spring so length isn't a constant.

Whatever it does, I think it will do a bit more of it with the round section tyre, but I hope it all comes out as insignificant.

David
Well it's interesting that today I printed a new idler wheel, but this time for a more readily available 3.5mm cross section O-ring. I altered the CAD program to make the groove an extra 1mm high but forgot to alter the overall diameter of the printed wheel. End result was I had an idler that was 2-3mm bigger than the correct idler. It all worked but I altered my program to reduce the diameter for the next print, but then thought well the sound worked OK, and perhaps the larger wheel puts more pressure on the spring (and lets be honest most of these 60 year old springs will be weaker than new and could use all the help they can get) which would help with torque and spinning the platter? But as you are also experiencing it's hard to work out how it will all go as there's so many variables! Here the beauty of each idker wheel costing just 6 cents comes in, you print a bigger one, you print a smaller one, then see which works best!
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Old 21st Jun 2021, 6:51 am   #57
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Default Re: Tell me the critical features of an idler wheel

Hello everyone

Here's another update.

At the weekend I got a damaged BSR idler wheel to practice on, and it's quite an interesting thing which means some of our assumptions were wrong and some elements of my designs need to change.

See photos.

First thing to note is the rubber part is not 100% rubber at all, it sits on a metallic extension of the central idler wheel. So the debate about whether an O-ring will provide enough shock absorbing characteristics compared to the real idler is now academic, the solid bit of rubber at the edge of the wheel actually provides LESS solid rubber than a 3.5mm o-ring

Note how the rubber has buttons molded into it that fit in the holes in the wheel. The next puzzle was why so many holes? at first I was impressed that BSR cared about locking the rubber to the wheel thinking it was to do with torque transference (well not slipping) but I thought surely 3 holes would do that not 12. But I think I now know what's going on, the 12 holes are really to stop the rubber part moving vertically rather than slipping axially (ie stays horizontal and square)

Anyhow I'm very impressed with the care and thought that's gone into the idler wheel from BSR, the buttons are somehow moulded right through the holes and attached both sides to the rubber. Rubber part moulded in situ, i don't really know? Who say the British don't ever over-engineer things?!

So the fact there's a hidden extension to the metal idler wheel has upset my design and made it all a little more complex. There's now not enough gap beyond that metal lip to make a one piece plastic o-ring holder, so now I've had to make the O-ring holder in 2 identical parts (again see photos). I moulded 6 buttons on each, 60 degrees apart so they both mount in the 12 holes in the wheel in a balanced way, and then superglued them to the wheel and to each other through the holes. I'm hoping this will be strong enough to not be prised apart when I squeeze a tight O-ring into the groove. I won't be trying this for 24h as superglue needs to fully cure

I will report back

So I currently I have 2 designs in the mix:

1) add a replacement for the rubber to an existing idler wheel. pros - uses existing bearing, ends up looking like a real idler wheel. cons - has to be a special design for each manufacturers idler wheel which is a pain

2) make the entire idler wheel from plastic and an O-ring. pros - easy to modify the design to print a larger/smaller, taller/shorter wheel on a different sized axle. cons - hard to fit a bearing to a plastic wheel, may not have enough mass to drive a changer's cycle cam

I'm still not yet sure which is the best approach

cheers
Joe
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Old 23rd Jun 2021, 7:29 am   #58
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Default Re: Tell me the critical features of an idler wheel

Hello everyone

Here's another update Some failures, some successes, but definitely interesting findings

I tested my 2 design options on a BSR UA25 record changer. I loaded it with 5 LPs and set it off. Not that I ever use a stacker but it's a good test for the driving power of my designs because if it can drive a platter loaded with 4 LPs and still drive the cycle cam for the 5th LP then that's good enough.

So the results...

test#1 - The idler wheel using an old idler metal centre and bearing with my add-on O-ring did not work! Spun the platter ok, but couldn't drive even the first cycle to move to the next record

test#2 - My totally plastic idler wheel (with brass tube as a temp bearing) did complete the test right to the 5th LP.

So what was the difference?

The idler in test#1 was the exact diameter of a real BSR idler. the plastic idler in test#2 was 1.9mm bigger. not a big difference but I think it proves that the round o-ring with its smaller contact surface to both spindle and platter does indeed NOT drive as strongly

So I printed another idler for test #1 1.9mm bigger and it worked just as well as the full plastic idler. So size does matter!

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. Also there's a tendency to roll the O-ring into the groove, this is a mistake and can leave a subtle twist in the o-ring, best stretch it then slowly release it evenly into the groove (easier said than done). I wonder if this twisting motion is why people complain about the £150 commercial idlers that also use an o-ring?

Second thing is both designs exhibited more wobble than a BSR idler (and by wobble I mean the arm that presses the idler against the spindle moves/jiggles constantly). I think the bsr idlers are actually ground exactly round at the factory to finish them (another reason for the square edge I think). With a lathe or even a matchbox squarely placed against the idler whilst rotating I reckon I can stop this wobble, but it's an extra hassle that I wanted to avoid, but realistically it makes sense that it has to be ground perfectly round. Does this wobble impact playback? well I couldn't hear any difference

So a few questions for you all out there:

1) Will a diameter difference of +2mm make any difference to anything?
2) what problem could a slight wobble cause?

look forward to your comments

cheers
Joe
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Old 23rd Jun 2021, 11:52 pm   #59
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Default Re: Tell me the critical features of an idler wheel

As you are changing a drive chain using wheels, changing the diameter MUST change the end speed result. For old fashioned "record munchers" ( my name for record stackers ) it probably won't matter at all.

If you have some slow piano or violin music, the wobble will most likely be audible. In fact with a bit of modification you could make a mechanical true vibrato for guitar heads, using a speed variable motor setup. ( read lots of money made for the gullible )

Still watching this thread. 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
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Old 24th Jun 2021, 8:57 am   #60
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Default Re: Tell me the critical features of an idler wheel

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As you are changing a drive chain using wheels, changing the diameter MUST change the end speed result.
Joe
No. This is an idler wheel and by definition its diameter will have no effect on speed. The same applies if using gears. The number of teeth on an idler gear has no effect on speed.

With idler driven turntables it's the diameter of the motor pulley and internal diameter of the turntable that control the speed.
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