Author Topic: Variator for small lathe  (Read 13639 times)

Offline BillTodd

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Variator for small lathe
« on: October 21, 2022, 03:09:42 PM »
AKA Distraction 4

Small disc variator for the mini lathe I've just bought .

It's fairly simple in operation : The input wheel from the motor drives the two rubber faced side discs. The out put wheel slides along a keyed shaft and spins fast as it gets closer to the edge. It should have about an 8:1 range
Bill

Offline vtsteam

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Re: Variator for small lathe
« Reply #1 on: October 21, 2022, 05:09:44 PM »
That should definitely be a distraction! Looking forward to seeing it in the flesh.  :coffee: :coffee: :coffee: :beer:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline BillTodd

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Re: Variator for small lathe
« Reply #2 on: October 22, 2022, 05:50:52 AM »
Having most of the materials in stock seems a good Omen.
Bill

Online philf

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Re: Variator for small lathe
« Reply #3 on: October 22, 2022, 10:51:46 AM »
Bill,

Would a Kopp variator do?

I've got a couple of 1/3hp units doing nothing on  a shelf.

Phil.
Phil Fern
Location: Marple, Cheshire

Offline BillTodd

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Re: Variator for small lathe
« Reply #4 on: October 22, 2022, 04:40:30 PM »
A Kopp would do fine...

But I've started cutting the metal 8⁠-⁠)

What range do the kopp unit have?

Bill

Online philf

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Re: Variator for small lathe
« Reply #5 on: October 23, 2022, 03:10:17 AM »
Hi Bill,

1:3 to 3:1

Phil.
Phil Fern
Location: Marple, Cheshire

Offline BillTodd

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Re: Variator for small lathe
« Reply #6 on: October 23, 2022, 05:58:20 AM »
PM sent
Bill

Offline Muzzerboy

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Re: Variator for small lathe
« Reply #7 on: October 23, 2022, 06:27:07 AM »
It's hard to tell from the CAD views but I can't see how the pressure is applied between the 2 large disks in this concept. On a Kopp variator, a higher input torque results in a greater compression of the input / output cones, drive balls and containment ring. Equally, I'm not sure how well a rubber face would survive. Kopps use plain (hardened and ground) steel surfaces. Hopefully Phil has the answer for you!

Offline BillTodd

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Re: Variator for small lathe
« Reply #8 on: October 23, 2022, 07:05:24 AM »
Pressure is set by adjusting the depth of the two side bearing blocks (by either shims or a set of screws pushing the bearings inwards - design is still in flux) . I did consider other designs that would regulate tractor force, notably a cone/ring design , but it wasn't particularly compact.

I'm aware that all commercial variators tend to use hardened surfaces , but that is not really doable in the home shop hence using rubber facing .

I'm calculating /hoping that the traction beats torque, for most operations of a small lathe  at high speeds.

I may well end up with something from Phil :⁠-⁠)  but I have an attraction for making this thing anyway
« Last Edit: October 25, 2022, 05:50:32 AM by BillTodd »
Bill

Offline kayzed1

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Re: Variator for small lathe
« Reply #9 on: October 23, 2022, 05:24:44 PM »
Have you checked on how a variator works on Google, as small scooters have compact units and are available cheaply from places online.
May well be the start of a solution ...lyn.

Offline BillTodd

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Re: Variator for small lathe
« Reply #10 on: October 24, 2022, 05:42:45 AM »
Actually, I used a scooter variator on a milldrill conversion, a while ago ( is it really 15 years ?) .

Most automotive variatirs will only have about a 3 and a bit to 1 range (it is all that's required for most engines) 

But , yes they work well 8⁠-⁠)

Well only 14 years :

https://www.cnczone.com/forums/uncategorised-metalworking-machines/89480-cvt-continuously-variable-drive-rf30-type-drill.html
« Last Edit: October 24, 2022, 12:53:30 PM by BillTodd »
Bill

Offline vtsteam

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Re: Variator for small lathe
« Reply #11 on: October 24, 2022, 08:55:02 AM »
I'd like to see one built, naturally. Far more interesting than installing a manufactured unit. Whether it has problems in development or construction is irrelevant to a good project thread. It's what is tried and learned that is so valuable to read about and follow. I understand if it's just easier to go with an existing unit, and I've done that many times myself. But I do hope for something truly inventive to liven up these MadModder pages.  :coffee:
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Variator for small lathe
« Reply #12 on: October 24, 2022, 09:21:16 AM »
I think the biggest obstacle in the disk design is that the driving area of contact is very small by comparison with a belt drive. You can't widen the rollers to increase the contact area since that will cause increased skidding. The two edges of the rollers will apply against different areas of the driving disks. Rubber might make up for a small differential there, but not a large one. Also the wider the roller the smaller the reduction ratio range.

All of this will be a matter of degree -- whether it is practical for a small lathe vs a vehicle is the question.

Factors that would be helpful with the relatively low torque capacity of the disk drive are, a relatively high rpm motor, and a reduction after the variator.

A disk variator like the above can apply more pressure to the driven surfaces than a pulley and belt drive can because a belt is tensioned along its length and isn't actually trapped between the sheaves as a roller between disks is.
« Last Edit: October 24, 2022, 09:46:04 AM by vtsteam »
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline Sea.dog

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Re: Variator for small lathe
« Reply #13 on: October 24, 2022, 10:26:58 AM »
A conical roller surely would be best? The rolling radius of the inner and outer would automatically be compensated for.

Offline BillTodd

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Re: Variator for small lathe
« Reply #14 on: October 24, 2022, 12:00:19 PM »
The trouble with conical wheels is that it they can only really be used with one conical disc and then one or both have to be able to move laterally .

Vtstream :

The contact patch limits the available traction. Increasing wheel size increases torque for a given traction (and slightly increases contact) so bigger wheels are better.  The wheels in this design are set by the depth of the extrusion, as are the disc diameter. The disc diameter determines range , from minimum contact diameter to the edge if the disc.

I could couple two sections of extrusion to make a bigger box for larger wheels, but then it starts to get quite big

As to making it, I don't want to upset Phil and his the kind generosity , but I may still make it just for kicks.
« Last Edit: October 25, 2022, 05:52:30 AM by BillTodd »
Bill

Offline BillTodd

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Re: Variator for small lathe
« Reply #15 on: October 24, 2022, 12:09:39 PM »
As to the actual torque:  the 200w motor that I was intending to use produces about 1.3Nm at 1450rpm  so that's not a whole lot for the rubber faced disc to transmit.

I think I can get a 1.5 :1 speed reducer at the spindle pulleys and I may add a larger pulley back-gear anyway .

I don't think it'll produce too much smoke :zap:
Bill

Offline vtsteam

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Re: Variator for small lathe
« Reply #16 on: October 24, 2022, 12:21:57 PM »
Hi Bill, just a clarification: earlier I meant transferable torque, limited by the slipping of the rotors. Yes the size of the disks can increase the theoretical torque (vs RPM) as in all physical reductions. But the actual amount transferable is limited by the point at which the rotors slip.

If however the motor speed is high, and there is a reduction after the variator to compensate, more power can be transferred through the variator than otherwise, before slip happens, since power is a factor of both torque and rpm.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline BillTodd

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Re: Variator for small lathe
« Reply #17 on: October 29, 2022, 10:01:35 AM »
PhilF's generous donation arrived a few days ago, Cheers Phil  :headbang:

I have now to work out how everything will fit together.

With the pulleys shown, I should get a range if 240 to 2100 rpm , which should be about right for a plain bearing spindle. (Edit 9:1 range not 6:1 !)

Tony has just updated the lathes page with more pictures http://lathes.co.uk/unknown164/
« Last Edit: October 29, 2022, 01:32:25 PM by BillTodd »
Bill

Online philf

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Re: Variator for small lathe
« Reply #18 on: October 29, 2022, 11:34:00 AM »
Bill,

Looking good.

A scan of the Kopp manual is winging it's way to you!

Phil.
Phil Fern
Location: Marple, Cheshire

Offline vtsteam

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Re: Variator for small lathe
« Reply #19 on: October 29, 2022, 03:03:50 PM »
Just noticing that the tailstock base is split, and the lock basically pulls the two lower sections together. Also the locking lever is on the backside of the tailstock.

Also, no set-over adjustment for the tailstock.

One possible solution for that last if you want to turn tapers would be to adapt a small boring head design as a tailstock center.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline vtsteam

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Re: Variator for small lathe
« Reply #20 on: October 29, 2022, 03:18:28 PM »
Hmmm, no gib adjustment screws either? Tailstock gibs? Maybe none..

I guess this lathe will need the headstock to be adjusted in position with scraping and/or shims to match the tailstock center location. The reverse of the normal method.
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline BillTodd

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Re: Variator for small lathe
« Reply #21 on: October 29, 2022, 04:30:43 PM »
Hmmm, no gib adjustment screws either? Tailstock gibs? Maybe none..

I guess this lathe will need the headstock to be adjusted in position with scraping and/or shims to match the tailstock center location. The reverse of the normal method.

This does seem to have taken its design cues from Hardinge, my HLV-H also has no real adjustment for the tail stock.

The headstock has a small amount of lateral adjust , so I'll have to square up the headstock to the tail stock .

As for taper cutting, I have plans/dreams for a taper attachment. The cross slide nut has a lot of backlash and one option is to replace it with a tubular design that will slide in the existing hole. That will allow it to be controlled by a taper slide on the back of the lathe.




Bill

Offline vtsteam

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Re: Variator for small lathe
« Reply #22 on: October 29, 2022, 05:40:34 PM »
I've always wanted to do a taper attachment. Never did. That's a lot more fun than setting the tailstock over!
I love it when a Plan B comes together!
Steve
https://www.youtube.com/watch?v=4sDubB0-REg

Offline BillTodd

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Re: Variator for small lathe
« Reply #23 on: October 29, 2022, 06:08:14 PM »
I have a taper attachment on the HLVH,  you just set it up using the DRO (like a sine bar) abd it's bang on every time.

I cut a Jacob taper for a chuck the other day, when I slapped the chuck on to test it , I couldn't get it off!  So thought that's probably good enough.
Bill

Offline awemawson

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Re: Variator for small lathe
« Reply #24 on: October 30, 2022, 03:42:06 AM »
If you fit a boring head in your tail stock and a centre where the boring bit goes you can avoid mucking up the setting of your tail stock and cut accurate tapers.

There is a commercial version available. Obviously the tail stock taper has to be rigidly fitted as if it slips you are in trouble.
Andrew Mawson
East Sussex