Author Topic: mini-lathe leadscrew clutch?  (Read 18236 times)

Offline MetalMuncher

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mini-lathe leadscrew clutch?
« on: April 25, 2014, 10:27:31 PM »
I have mounted a handwheel on the RH end of my mini-lathe leadscrew, but the only practical way to make use of it means removing a gear. I'd like a more convenient solution. So I am wishing I had some kind of dis-engagement clutch in the leadscrew shaft near the driven end of it. Has anyone done this, or seen it done? Something fairly simple would be best.

Offline Brass_Machine

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Re: mini-lathe leadscrew clutch?
« Reply #1 on: April 25, 2014, 10:30:04 PM »
I have seen it done. I will look for the link.

Eric
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Offline rick barnes

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Re: mini-lathe leadscrew clutch?
« Reply #2 on: April 25, 2014, 11:33:08 PM »
I've always wanted to try a planetary system with a band brake like an old model-T transmission. 
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Offline MetalMuncher

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Re: mini-lathe leadscrew clutch?
« Reply #3 on: April 25, 2014, 11:49:53 PM »
Thank you, Brass_Machine.

Rick that would surely be an interesting project, but it sounds rather complex. :)


Offline rick barnes

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Re: mini-lathe leadscrew clutch?
« Reply #4 on: April 26, 2014, 01:21:02 AM »
Probably.  I have a problem with doing that.
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Offline garym

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Re: mini-lathe leadscrew clutch?
« Reply #5 on: April 26, 2014, 07:17:32 AM »
Hi MetalMuncher,

There is an idea for a leadscrew clutch on an old thread on the Model Engineer forum. Unfortunately, there is not much detail so I can't figure out how it works but others probably can.

http://www.model-engineer.co.uk/forums/postings.asp?th=57688

Gary
Workshop activity resumes now ankle improving :-)

Offline MetalMuncher

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Re: mini-lathe leadscrew clutch?
« Reply #6 on: April 26, 2014, 10:23:07 AM »
This looks like the kind of compact design I was hoping for. But I have no idea how it works either.

One issue crossing my mind while thinking about such a modification is that the clutch will also need to prevent any lateral movement of the shaft, which essentially gets divided into 2 pieces when disengaged. I could not think of a way short of incorporating 2 more pillow blocks with a clutch release mechanism between them. So this solution is much more elegant. I will try to reach the member who originally posted that information.

Thanks Garym!

Rick, some of my brainstorms (complete with lightning! :)    ) are also of the Rube Goldberg variety. But they get the job done! Here, there is little room for anything very complex. I did see one assembly turn up in my own interent searching last night which also incorporates an automatic kick out mechanism to stop the leadscrew drive gear mesh when a set point is reached (something I've always wished for since I got this lathe) but it is very complex and another design whose functioning eludes my understanding. Plus the author mentioned it may not work on the standard lathe gearing assembly, and that he had previously modified his lathe gearing with someone else's design for a "threading banjo" (not sure which part he refers to by that term, but I am guessing from context he refers to the forward/reverse gearing device for the spindle?).

Offline drmico60

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Re: mini-lathe leadscrew clutch?
« Reply #7 on: April 26, 2014, 10:39:34 AM »
Hi Metal Muncher,
I have redesigned the change gear bracket and replaced this with a more conventional banjo, see http://mikesworkshop.weebly.com/new-threading-banjo.html
This new banjo can be easily swung away from the drive gear and this enable the leadscrew handwheel to be turned easily even with the change gears mounted.
I have taken this concept a step further and fitted a separate variable speed leadscrew motor to the lathe, see
http://mikesworkshop.weebly.com/leadscrew-motor.html
The banjo can be swung between the lathe spindle gear (for gear cutting and fine feed) to the variable speed leadscrew motor (for variable speed leadscrew feed). In between these two position the banjo does not engage with either and the handwheel can be used.
I also have an autostop coupled to the variable speed motor for cutting to shoulders, see:
http://mikesworkshop.weebly.com/autostop.html
The autostop can also control the main lathe motor for high speed gear cutting, see:
http://mikesworkshop.weebly.com/lathe-motor-control.html
It would be easy to modify the banjo so that it could be swung by a lever that passed through a opening in the change gear cover.
Mike

Offline garym

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Re: mini-lathe leadscrew clutch?
« Reply #8 on: April 26, 2014, 12:50:55 PM »
..... I will try to reach the member who originally posted that information.........

The member who posted it "Stub Mandrel" was a pseudonym used by the present editor of MEW, Neil Wyatt before he was the editor and he'll probably reply when he sees the posts.

Gary
Workshop activity resumes now ankle improving :-)

Offline DavidA

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Re: mini-lathe leadscrew clutch?
« Reply #9 on: April 26, 2014, 01:51:55 PM »
L C Mason,  in his book 'Building a small lathe' describes a 'clutch' which is part of the lead screw. It is a simple dog clutch and comprises of a muff coupling that has a slot at one end. This slot engages with a pin that passes through the lead screw. When the muff is moved to one side it disengages from the slot thus knocking the lead screw out of drive. Very handy as it can be set,  rather like a milling machine stop, at any point.
The device is shown on page 69 of the book.  Well worth purchasing even if you don't intend to build the lathe. Mine,  like my loco  is in a part finished state.

Dave

Offline chipenter

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Re: mini-lathe leadscrew clutch?
« Reply #10 on: April 26, 2014, 03:18:39 PM »
My Faircut lathe had a dog clutch just a slieve with a keyway and two keys on the split lead screw , I made a micrometer knock off , have a look at lathes co uk for pictures .
Jeff

Offline tomrux

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Re: mini-lathe leadscrew clutch?
« Reply #11 on: April 26, 2014, 05:41:56 PM »
from the description in the referenced thread from ME all that is going on is dropping the banjo in and out of mesh without the need to be twiddling spanners. Instead replacing a tight bolt with spring friction. Don't know that I would trust it not to drop out at the most inconvenient moment.

Tom R

Offline MetalMuncher

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Re: mini-lathe leadscrew clutch?
« Reply #12 on: April 26, 2014, 06:52:58 PM »
Hi Metal Muncher,
I have redesigned the change gear bracket and replaced this with a more conventional banjo, see http://mikesworkshop.weebly.com/new-threading-banjo.html
This new banjo can be easily swung away from the drive gear and this enable the leadscrew handwheel to be turned easily even with the change gears mounted.
I have taken this concept a step further and fitted a separate variable speed leadscrew motor to the lathe, see
http://mikesworkshop.weebly.com/leadscrew-motor.html
The banjo can be swung between the lathe spindle gear (for gear cutting and fine feed) to the variable speed leadscrew motor (for variable speed leadscrew feed). In between these two position the banjo does not engage with either and the handwheel can be used.
I also have an autostop coupled to the variable speed motor for cutting to shoulders, see:
http://mikesworkshop.weebly.com/autostop.html
The autostop can also control the main lathe motor for high speed gear cutting, see:
http://mikesworkshop.weebly.com/lathe-motor-control.html
It would be easy to modify the banjo so that it could be swung by a lever that passed through a opening in the change gear cover.
Mike


Very nice! Now I understand the "banjo" nickname for this device. Your autostop mod looks interesting too. But why do you have it made so you have to choose between auto stop and using the DRO? Is there no way to use them concurrently?

A later post by Tomrux poses a valid concern about things moving out of mesh at the least desirable moment. But I am thinking there must be a way to fit a control lever to the banjo which would have some sort of positive detent arrangement, like the reverse lever on the back of a mini-lathe, so the banjo position would be safely constrained. Maybe even similar to some of the pro lathe controls which protrude from a curved surface, and have a spring loaded knob that is more flat than the shaft used for reversal on thep lathe.

Offline MetalMuncher

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Re: mini-lathe leadscrew clutch?
« Reply #13 on: April 26, 2014, 06:56:19 PM »
..... I will try to reach the member who originally posted that information.........

The member who posted it "Stub Mandrel" was a pseudonym used by the present editor of MEW, Neil Wyatt before he was the editor and he'll probably reply when he sees the posts.

Gary

Thanks Gary.

Offline MetalMuncher

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Re: mini-lathe leadscrew clutch?
« Reply #14 on: April 26, 2014, 07:03:44 PM »
Thanks DavidA and Chipenter, for the dog clutch info. The slotted sleeve and cross pin is how the Micromark power feed is connected on my X axis mill leadscrew. I like that idea, and it probably would be fairly easy to implement as a clutch. I hadn't thought of that.

Offline MetalMuncher

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Re: mini-lathe leadscrew clutch?
« Reply #15 on: April 26, 2014, 09:31:02 PM »
While deciding how to proceed with this idea, one thing I am concerned about is the integrity (rigidity, endplay) of the leadscrew itself. Many of us have taken pains to make sure the leadscrew has no unwanted movement. Adding a dog or yoke style clutch to the shaft would require separating it into 2 pieces. That would mean needing ways to support the new ends of each half, in addition to also designing the clutch itself to not allow unwanted movement, such as endplay or flex of the shaft across the clutch joint.


Offline tom osselton

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Re: mini-lathe leadscrew clutch?
« Reply #16 on: April 27, 2014, 01:21:29 AM »
Can you have a sliding gear on a idler shaft to engage or disengage the gear?

Offline rick barnes

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Re: mini-lathe leadscrew clutch?
« Reply #17 on: April 27, 2014, 04:03:39 AM »
Just dog clutch it.  Have to stop motor to engage... Well supposed to anyway. 
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Offline drmico60

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Re: mini-lathe leadscrew clutch?
« Reply #18 on: April 27, 2014, 05:49:20 AM »
.weebly.com/new-threading-banjo.html


Very nice! Now I understand the "banjo" nickname for this device. Your autostop mod looks interesting too. But why do you have it made so you have to choose between auto stop and using the DRO? Is there no way to use them concurrently?

A later post by Tomrux poses a valid concern about things moving out of mesh at the least desirable moment. But I am thinking there must be a way to fit a control lever to the banjo which would have some sort of positive detent arrangement, like the reverse lever on the back of a mini-lathe, so the banjo position would be safely constrained. Maybe even similar to some of the pro lathe controls which protrude from a curved surface, and have a spring loaded knob that is more flat than the shaft used for reversal on thep lathe.

I cannot see how you can effectively use the dro whilst using the autostop. You use the DRO to set the autostop but once the cut is being made the dro serves no purpose.

With my banjo it is clamped very securely to the lefthand pillow block extension and I have had no problems with the gears disengaging during use.
Mike

Offline Brass_Machine

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Re: mini-lathe leadscrew clutch?
« Reply #19 on: April 27, 2014, 08:49:05 AM »
I can't find the link I was looking for... I hope I didn't imagine it.  :Doh:
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Offline MetalMuncher

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Re: mini-lathe leadscrew clutch?
« Reply #20 on: April 27, 2014, 10:47:37 AM »
I can't find the link I was looking for... I hope I didn't imagine it.  :Doh:

No problem. We've got some good ideas flying here. :)

Offline MetalMuncher

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Re: mini-lathe leadscrew clutch?
« Reply #21 on: April 27, 2014, 10:56:20 AM »
.weebly.com/new-threading-banjo.html


Very nice! Now I understand the "banjo" nickname for this device. Your autostop mod looks interesting too. But why do you have it made so you have to choose between auto stop and using the DRO? Is there no way to use them concurrently?

A later post by Tomrux poses a valid concern about things moving out of mesh at the least desirable moment. But I am thinking there must be a way to fit a control lever to the banjo which would have some sort of positive detent arrangement, like the reverse lever on the back of a mini-lathe, so the banjo position would be safely constrained. Maybe even similar to some of the pro lathe controls which protrude from a curved surface, and have a spring loaded knob that is more flat than the shaft used for reversal on thep lathe.

I cannot see how you can effectively use the dro whilst using the autostop. You use the DRO to set the autostop but once the cut is being made the dro serves no purpose.

With my banjo it is clamped very securely to the lefthand pillow block extension and I have had no problems with the gears disengaging during use.
Mike

I think the concern with your setup, at least for me anyway, is that if it is easy to swing the banjo to adjust it when you want to, could it possibly move on its own when you don't want it to? What holds it in the position you set? If it is the clamping action on the pillow block that holds it from moving, well, that seems just as much work to adjust as manually removing a gear from the stock setup. And still requires removing the gear cover. I had thought the clamp was a means of mounting it to something that is allowed to turn, so it could be effortlessly engaged/disengaged. That's why I envisioned a means of moving a control lever/knob attached to it, with a detent system.

What I am after is something that can be adjusted as easily as moving a knob or lever, with no tools required.

Offline MetalMuncher

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Re: mini-lathe leadscrew clutch?
« Reply #22 on: April 27, 2014, 11:23:16 AM »
My current thinking is to cut the leadscrew shaft (this would reside behind the lower portion of the control box) and bore a 1/4" hole in the cut end of each segment. Ream the holes to end up with a nice slip fit for a piece of 1/4" drill rod. In the short piece of leadscrew shaft, toward the gears, hold the rod in place with a roll pin, extending out from the surface on each side of the leadscrew shaft enough to provide a dog for engagement. On the longer section of leadscrew, toward the carriage, another roll pin through it, but past the depth of the inserted drill rod, which now acts as a pilot shaft to hold the rods aligned as they rotate freely from one another.

Because the length of the leadscrew needs to remain a constant, the material sawn out of the cut will need to be replaced, so a bushing washer will need to be made to fill that gap, turning freely on the pilot shaft.

Next, make a sleeve that is reamed to a slip fit over the surfaces of the adjoining shaft segments. In that sleeve, mill a slot from one end on opposing sides that will fit to span the two roll pins as it slides toward the gears, providing the dog clutch engagement. It will need to be long enough to have abundant material toward the right end of it, unslotted, so it will be strong enough to keep the sleeve slots from trying to widen under the load of engagement. Round the inside corners of the open end of the slot to assist engagement as the sleeve is moved.

I need to do some measuring, but I am hoping to have enough clearance on the unthreaded section of the leadscrew to park the sleeve when disengaged, and have some way to slide it (lever, knob, etc.) protruding out the right end of the control box, yet not get into where I have my carriage stop clamped to keep things from hitting the chuck jaws. I use an aftermarket 4" chuck, which is rather large, so there is a lot of leadscrew below it that never sees use. If necessary, I may have to allow the back end of this sleeve to cover some of the unused leadscrew threads when it is disengaged.

Depending on how these dimensions work out, I may have room to put a yoke lever on the RH end of the sleeve to move it. (Like a clutch yoke on a manual transmisson car.) Otherwise I am thinking a sort of top hat shaped knob on the end of the sleeve, to pull it right or push it left. I wonder if such an arrangement would stay where it is set while using the lathe, or if a detent system would be needed to hold it in each engaged/disengaged position?

Offline drmico60

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Re: mini-lathe leadscrew clutch?
« Reply #23 on: April 27, 2014, 12:05:22 PM »
.weebly.com/new-threading-banjo.html




I think the concern with your setup, at least for me anyway, is that if it is easy to swing the banjo to adjust it when you want to, could it possibly move on its own when you don't want it to? What holds it in the position you set? If it is the clamping action on the pillow block that holds it from moving, well, that seems just as much work to adjust as manually removing a gear from the stock setup. And still requires removing the gear cover. I had thought the clamp was a means of mounting it to something that is allowed to turn, so it could be effortlessly engaged/disengaged. That's why I envisioned a means of moving a control lever/knob attached to it, with a detent system.

What I am after is something that can be adjusted as easily as moving a knob or lever, with no tools required.
Hi Metal Muncher,
The banjo clamps to the pillow block extension with a screw. A quarter of a turn will lock the banjo securely to the pillow block. If you replaced the screw by a rod threaded at one end and cut a small piece of the gear cover away then all the operations to swing and lock the banjo can take place from outside the gear box cover. No tools would be required.
Mike

Offline guminase

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Re: mini-lathe leadscrew clutch?
« Reply #24 on: April 27, 2014, 12:45:24 PM »
This Gentleman has made a nice, detailed Desciption of a Dog-Clutch for a Mini-Lathe:
http://www.gadgetbuilder.com/Dog_Clutch.html