# Design help needed for clutch system



## savarin (Mar 10, 2021)

I'm in the process of modifying a dc treadmill motor to fit my 9x20 lathe. 
The main reason for this to get an easier variable speed system to replace the belts. (it was free)
As it will be a 3:1 reduction from the motor to the spindle using cogged pulleys and belt I feel some sort of clutch would be a good idea in case of a crash. (I have been known to be clumsy in the past)
I'm thinking of a steel hub with detants drilled around its circumference, 6 equidistant drilled and tapped holes radially around the cog and using balls and springs tensioned with grub screws with the balls engaging in the detants in the steel hub.
Similar in operation to the original clutch but in a different orientation.
The aluminium cogged pulley will sit on the steel hub with a bearing fit, ie, it will turn but no play.
My questions are
Will this work?
If not why not?
Is 6 balls enough?
What would be the best number of balls?
Thanks.


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## silence dogood (Mar 10, 2021)

Have you considered a shear pin?


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## savarin (Mar 10, 2021)

yes thanks but didnt feel it would be safe enough.
With this design I can vary the tension of the springs from very loose to solid.


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## eugene13 (Mar 10, 2021)

I think it will work, my lathe has a similar clutch on the power feed driveshaft.


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## Bi11Hudson (Mar 10, 2021)

It should work fine, I have a similar clutch on a G-1550 Grizzly 9". What comes to mind is a one way clutch that was posted here a couple-three weeks back. It basically was an overrunning clutch but would be a good starting point. What I would do is use a (ho-made) cone clutch with a (variable) spring load. There are many options for such a problem. One of the reasons we see so many is a manufacturer trying to dodge patents. For an individual, if you see something that would work, build one. Patents are to reduce production opposition.

.


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## pacifica (Mar 11, 2021)

Would something like this work:https://www.amazon.com/Huco-271-25-...173aa&pd_rd_wg=vTqAN&pd_rd_i=B004HW72GC&psc=1, or this: https://dynatect.com/product/clutches/mechanical-slip-clutches/polyclutch-slipper/. Or this: https://www.ebay.com/itm/NEW-MAYR-O...244837?hash=item41e1726525:g:b1cAAOSwWupa75Uk .


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## Ischgl99 (Mar 11, 2021)

I used to have a Jet 9x20 lathe and it had a clutch like that.  If you can find an online manual for that lathe, you can see how it was done.

Here is a website with the formula to calculate the spring force you will need to dislodge the detent ball.






						Design Guidelines for Ball Plungers | S&W Manufacturing
					






					www.swmanufacturing.com


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## savarin (Mar 11, 2021)

Ischgl99 said:


> I used to have a Jet 9x20 lathe and it had a clutch like that.  If you can find an online manual for that lathe, you can see how it was done.
> 
> Here is a website with the formula to calculate the spring force you will need to dislodge the detent ball.
> 
> ...


Thanks for that.
I've started making the hub but cutting the internal keyway 8mm wide and 3mm deep is taking me a long time.
I am using a narrow tool bit and pushing into the bore. I'm halfway so far.


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## FanMan (Mar 11, 2021)

Why a cog belt?  If you use a V-belt, perhaps with a spring loaded idler, it will simply slip if it overloads.


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## savarin (Mar 11, 2021)

Good point with the V belts, never thought of those.
I guess I went with the toothed belt as that one has never snapped on my lathe.
The clutch idea came after I had purchased the cog pulleys.


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## savarin (Mar 18, 2021)

I started making the keyway with a narrow cutter but that became very tedious so I changed to an 8mm wide.


Sliding the carriage back and forth untill I got it 3mm deep, So little was removed on each stroke it took 2 afternoons.
I checked it on the spindle and it was a perfect fit. BUT two days and rust started forming inside, gah!


Then I bored out the cogged pulley to fit, that was way easier.





Now I have to drill six 3/16" holes for the balls where the blue lines are then drill 5mm and tap M6x1 for the grub screws and springs.


I turned a little spigot to centre the spring on the grub screw.
I made a quick test piece to check the spring pressure and if the ball would rise and slip.
At the highest pressure it was immovable, at the lowest it was difficult but did slip.
appologies for the crap photos as I'm coming to grips with a new image processing program.

edit - I forgot to mention the chuck was locked when broaching the keyway.


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## macardoso (Mar 18, 2021)

savarin said:


> I'm in the process of modifying a dc treadmill motor to fit my 9x20 lathe.
> The main reason for this to get an easier variable speed system to replace the belts. (it was free)
> As it will be a 3:1 reduction from the motor to the spindle using cogged pulleys and belt I feel some sort of clutch would be a good idea in case of a crash. (I have been known to be clumsy in the past)
> I'm thinking of a steel hub with detants drilled around its circumference, 6 equidistant drilled and tapped holes radially around the cog and using balls and springs tensioned with grub screws with the balls engaging in the detants in the steel hub.
> ...







Look at that clutch design


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## savarin (Mar 18, 2021)

I remember that and thought it was very elegant, I've been following Martins marble machine builds from the first one.
I also like the bands music.


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## macardoso (Mar 18, 2021)

savarin said:


> I remember that and thought it was very elegant, I've been following Martins marble machine builds from the first one.
> I also like the bands music.



Same here. Watching him constantly undo his work is maddening but he has an awesome result to show for it.


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## savarin (Mar 22, 2021)

It works, I will need to adjust the spring pressure once everything is back working.


I fit the small pulley onto the motor shaft with two grub screws into two dimples.


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## savarin (Jun 2, 2021)

And the motor in place



I decided to use a computer fan for cooling and needed to make a round into a square bit of ducting.
I found this on line and thought excellent, way to go. 



Then I thought again and used a hammer and an empty can of doggie chow and made this


The cutouts are where the brushes stick out from the motor


Its held to the motor with a worm drive clip and is solid.
As luck would have it I had two triangular bits of ally plate that were the exact size to make the extended control box 
to hold the switches and speed controller.


The lid hinges and is closed with knurled screws for ease of access.
I also added more shrouds to cover the motor leaving a little gap at the bottom for air flow.
The fan is always on when there is power to the lathe.
I am most impressed with the use of variable speed


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## savarin (Sep 28, 2021)

update
the motor stalled when I was parting 1.5mm dia aluminium bar.
I guess I have to slacken the screws to the clutch balls a bit.
Once it stalled there was an almighty bang but no smoke.
The glass fuse on the circuit board had exploded, the mosfet had fried and the bridge rectifier had karked it.
They were removed and replaced with larger value ones, I used the aluminium switch housing as the new heat sinks as theres plenty of mass there.
Added a 400V 1000uf cap across the output.
Added a 15A re-setable circuit breaker in place of the 20A glass fuse.
The motor runs as smooth as silk now except at very slow speed where its a little rougher.
I stalled it again but this time it tripped the 10A re-settable on the extension plug board.
Today I will re-set the friction clutch to a weaker setting.
No photos as too busy/lazy to take them.


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## brino (Sep 28, 2021)

Damn, what a polymath!
Machining, cooking, astronomy and also electronics.

Charles, if I ever grow up I want to be like you!

-brino


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## matthewsx (Sep 28, 2021)

An elegant and sophisticated solution....


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## savarin (Sep 29, 2021)

Thanks Brino but my knowledge of electronics can be written on a mozzies bum with a felt tip pen.
I cant read a circuit, very very limited understanding of what the components do, I just replaced the ones that looked damaged with higher rated ones.
Pretty good cook though


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## fixit (Sep 29, 2021)

Will the cog belt induce vibration and cause chatter? I know you have a cog belt now but not directly to the spindle.


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## savarin (Sep 29, 2021)

It doesnt appear to. I cant believe how much smoother it runs.


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