MadModder
Gallery, Projects and General => How do I?? => Topic started by: MetalMuncher on April 25, 2014, 10:27:31 PM
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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.
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I have seen it done. I will look for the link.
Eric
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I've always wanted to try a planetary system with a band brake like an old model-T transmission.
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Thank you, Brass_Machine.
Rick that would surely be an interesting project, but it sounds rather complex. :)
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Probably. I have a problem with doing that.
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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 (http://www.model-engineer.co.uk/forums/postings.asp?th=57688)
Gary
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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?).
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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
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..... 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
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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
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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 .
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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
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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.
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..... 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.
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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.
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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.
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Can you have a sliding gear on a idler shaft to engage or disengage the gear?
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Just dog clutch it. Have to stop motor to engage... Well supposed to anyway.
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.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
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I can't find the link I was looking for... I hope I didn't imagine it. :Doh:
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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. :)
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.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.
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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?
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.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
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This Gentleman has made a nice, detailed Desciption of a Dog-Clutch for a Mini-Lathe:
http://www.gadgetbuilder.com/Dog_Clutch.html
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.weebly.com/new-threading-banjo.html
Thanks 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.
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
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This Gentleman has made a nice, detailed Desciption of a Dog-Clutch for a Mini-Lathe:
http://www.gadgetbuilder.com/Dog_Clutch.html
Thanks guminase! And welcome to the forum! :)
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Hi MetalMuncher, and everyone else. I'm a newbie to this forum but have been a reader for a while and learned a lot from folk who are very obviously more skilled than I can ever hope to be.
But I just had to join to post a reply to your plea for a leadscrew clutch for a minilathe. This is my third attempt to post, others seem to have become lost somewhere in the aether, probably because I had some large photos attached.
I faced exactly this problem a while ago and built an electro-mechanical dog-clutch for my minilathe that seems to work very well and also acts as a very accurate and flexible saddle-stop when turning under power.
I am not posting any photos this time in the hope that this post makes it through, if someone can tell me what I'm doing wrong with the photos (attaching jpg's from my desktop) I'll get some photos on. I should also have some hand-drawn dimensioned sketches somewhere if those might be of interest.
Best regards
Dennis
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Hi Dennis, and welcome to the forum!
I am sorry you are having trouble with the pictures. I have problems posting pictures here too, so I usually just post a link to the picture stored somewhere, like in a Dropbox account. I believe in the introductory sections there is mention of another type of online photo storage you can also use.
Electromechanical sounds intriguing, and fancier than the design I am currently making. So I'd love to learn more about it. If this type I am making works out I'll post it on here with some photo reference. Basically it is rather simple. I intend to cut the unthreaded part of the leadscrew (hidden behind the control box) and remove enough to leave a 1/8" gap in the shaft after facing the cut ends. I'll then make a custom washer to fit this gap and set its thickness to assure there is no leadscrew endplay.
In between the cut ends, and through that washer, will be inserted a piece of 5/16 drill rod, to keep the two halves aligned. Two 1/8" dia. by 1" long spring steel roll pins will be inserted crossways through the leadscrew shaft, so their ends stick out. One will pass through the short piece of the leadscrew AND through the 5/16 "pilot shaft" between the leadscrew cut ends. The other will pass through the leadscrew shaft just off the opposite end of the 5/16 shaft, so the long piece of leadscrew will be free spinning on the pilot shaft as long as the clutch is not engaged.
As a clutch, I am making a sleeve that will slide over the leadscrew. The LH end of it will be slotted through both sides, with the slots running parallel to the shaft, and long enough to allow the sleeve to slide past the exposed ends of both roll pins in the engaged position, sliding the sleeve toward the gears. To disengage, the sleeve will be slid back toward the chuck, so that the first roll pin is no longer in the slot. The RH end of the sleeve will stick out just enough beyond the RH end of the control box to grasp a raised ring I'll turn on the end of it, as a sort of knob. I'll have to enlarge the control box cutout for the leadscrew.
I don't anticipate the sleeve moving on its own. But if it does, I have some ideas how to prevent that.
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Hi MetalMuncher,
Sounds similar in some ways. But I fitted additional leadscrew mounting blocks to keep the alignment of the two parts of the cut leadscrew (it is possible in the space available) and disposed of the problem of leadscrew endfloat that way. I then used cross-pins in the two parts of the leadscrew with a sliding sleeve to engage. The sleeve is moved manually into engagement against a spring and held in engagement by a latching mechanism. The latch is released by a low-voltage solenoid that is powered via a switch mounted on the lathe ways and operated by contact with the carriage. In fact because there is no mechanical linkage to the solenoid alternative methods of switching are possible and the switch could be mounted anywhere on the ways or even on the carriage itself. The only sensitive issue is finding a spring that is strong enough to disengage the mechanism while cutting under power, but not so strong that manual engagement is difficult.
I'll have another go at posting a photo.
Dennis
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Another go at posting a picture
d
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Interesting setup, Dennis. What is the vertical rod gizmo out on the end with the gear drive?
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That is the operating lever for manually engaging the clutch. Mabe a bit of overkill in size. See attached.
d
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Switch operating the solenoid.
d
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Well, it is a bit large, but it does look nice! You do nice work. :)
I may need to do something like that on my clutch project. I have it workable now, but the sleeve does tend to stick a bit at either extreme. In a way that is nice. I know it won't ever move on its own. But if I find it to end up being more effort than I like to move the sleeve and work the clutch, I can add a lever something like what you did. But I think it would be inverted, pointing down, as it would be just to the right of the control box.
I took a few pictures tonight. I'll work on getting them posted here.
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DennisS, what did you find out to make posting attached pictures work? I still can't do it. I set up the settings to upload some jpg pictures but they never get posted. In fact my whole post in which they were supposed to BE never gets posted.
So, they can be viewed here.
https://www.dropbox.com/sc/tq50rm3a85ca6tv/OzIQB1jIpy
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OK, it seems trying to add multiple attachments to an original post won't work. But I was able to attach ONE photo to a post. Then using the Modify option on that post, I was able to add 3 more attachments, one at a time, saving after each one, and re-clicking "Modify". Klunky, but it worked. :)
So here you can see the sleeve and modified leadscrew. A 5/16" pilot pin of drill rod is inserted between the 2 pieces of leadscrew, and then I made a custom washer to remove all endplay when the leadscrew is installed. The washer is visible between the two roll pins. The left roll pin holds the drill rod pilot pin in place. The right roll pin passes through the leadscrew shaft away from the pilot pin, so that end of the leadscrew can rotate freely on the pilot pin when the sleeve is disengaged from locking the 2 pins together.
I'll have to enlarge the shaft hole in the right side of the control box. The ring on the sleeve will extend a little to the right of the box when engaged, and extend a little more when disengaged. The sleeve moves about 0.400" to operate the clutch. The sleeve is 1.1" in diameter (not counting the ring on the end for moving the sleeve) and the inside has 2 different diameters, as the threads on the leadscrew are approx. 5/8", but the un-threaded shaft is 0.593". The sleeve is just over 4" long, made from 12L14 leaded steel.
I had to shorten the top setscrew that helps align the motor housing, so it did not stick out so far, as it was in the way of the sleeve turning. I cut down a setscrew so that the locking washer is nearly flush with the socket head, and put that in place of the stock setscrew.
The plastic baffle that keeps the control wiring off the leadscrew may work with some modification, otherwise I may need to make something to replace it.
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Hi Metal Muncher, an elegant solution and probably certainly more easily accommodated within the limited space available. I presume that you will be using a selector fork of some sort to engage/disengage.
I had to relocate the big electrical "choke" that normally occupies space in the bottom of the control box but did manage to fit that within the box and added a cooling fan to the power transistors as well - I was already running low volts to the relay and happened to have an old 12v computer fan sitting doing nothing, so ...
I snipped a little off the black plastic guard that keeps the electrics off the leadscrew and was able to refit that. See photo attached which is an earlier
As for photos, previously I had been posting very large jpg files that were not being accepted. Once I resized those to 640x480 there was no problem at all.
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There's a lot going on in there, DennisS! :)
I had thought I might use a fork to position the sleeve clutch, but with some careful tweaking and lithium grease I have it to where I can move it with a finger. The tendency to stick a little at either extreme of travel, beyond the amount needed to work, got annoying, so tonight I provided a solution. I constrained the "knob" ring's travel so that the sleeve can't dead end against either direction. So it is no longer sticky. Works very smoothly now. :)
I had to deal with that plastic "shelf" inside the box too, because it would have contacted the sleeve in my design. After kicking around some ideas, I settled on creating a wedged spacer to go under the mounting flange for the shelf. One side is flat against the lathe bed, and the other side is at a 15 degree angle. This causes the shelf to tip upward at 15 degrees, missing my clutch sleeve, but still doing its job of keeping the wires away from the leadscrew.
Here's a shot of my constraint bracket. The knob's raised end travels 5/8" between the ridge on either side of the bracket, but has to stay within it.
There must be some difference in the way models of this mini lathe are wired, because I don't have a choke in the bottom of my control box. I can't say I've ever noticed any problem electronically here while the lathe is in use.
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Hi MetalMuncher,
you are right, there are a number of different circuit boards for these mini-lathes, and what will be inside the control box seems to vary from supplier to supplier.
This probably also affects what can be added within the control box, I guess you only find out what you've got when you open it up, and work from there. You are constraining the throw of the sleeve, have you given any thought to adding a detent that would hold the sleeve at either setting, against the possibility of the sleeve "wandering? Detent could easily be implemented on a selector fork.
Dennis
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Hi DennisS,
I have a couple ideas if the sleeve tends to wander, but now that I have the little channel doing its constraint job, the detent style that first comes to mind would be a little curved piece of spring steel mounted in the "valley" of the channel, oriented in the path of the sleeve's ring, so it has to slightly compress the spring to get past it. Or I could accomplish the same goal by mounting a pair of small bearing balls in the line of travel, (one for each position against the channel edges) drilled in from the back side, with something springy behind them, so that they just rise above the flat valley on the front of the channel. Much like how a typical ratchet wrench retains a socket. Perhaps a layer of rubber, inlaid behind the channel, to compress against each ball? The whole thing is only about 0.140" thick, so I am limited to what I can do in that regard.
Or the option for a fork lever would still work. But I like the clean simplicity of how it works now.
Hmm. I made that channel 5/8" wide. I wonder if a piece of broken tape rule, mounted convex outward, in the channel would do the trick? I could screw each end of it and leave the center section free to compress.
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Hi MetalMuncher,
I really like the idea of a piece of a metal tape acting as a two-way detent, that would really be minimalist engineering solution if you could make it work. With the limited depth you'd probably have difficulty implementing the sprung bearing idea, though that could be done on a selector fork rather than on the sleeve.
Dennis