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Sherline Thread Cutting Attachment Slipping

Discussion in 'SHERLINE, TAIG, TITAN & SIEG MINI-MACHINES' started by sully2161, Jan 22, 2016.

  1. sully2161

    sully2161 United States Iron Registered Member

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    So I've finally gotten around to needing to cut some threads on the lathe. The installation guide was fairly straight-forward and configuration of the gears was no problem. The issue I'm having is that when backing off the tool and reversing the handwheel direction, the arm holding the gears together is loosening and the gears slip. Sometimes it happens almost immediately and sometimes only after several cutting passes.

    I'm wondering if anyone else has had this issue and what they've done to resolve it. I'm debating a couple of modifications but I don't want to do anything drastic because the arms have to support multiple gear configurations (which means a mod that doesn't block a gear today might tomorrow).

    So far I've been thrilled with the lathe (4400) and all the other accessories. The thread cutter falls a bit short, with loose brackets, a cramped fit, and having to remove the motor.

    Any suggestions appreciated. Thanks!

    - Steven
     
  2. mikey

    mikey Active User H-M Supporter-Premium

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    Sully, I've been using the Sherline thread cutting attachment for a long time now and never had any of it slip or loosen, not even a little bit. Are you meshing the gears really tight together? They should have about 0.003" of gap between the teeth (paper thickness or so). It might help to post a pic of how you're setting up the gear train and we can maybe help more.
     
  3. sully2161

    sully2161 United States Iron Registered Member

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    Mike, thanks for the reply. Glad to hear you haven't had any problems -- maybe there's hope for me. I am meshing the gears tightly. I make sure everything is aligned and meshed before tightening the last 2 screws (the arm screw and the sliding gear screw). The problem seems to be the direction reversal puts pressure on the sliding gear at a different angle and forces the arm away, allowing slippage. I've even added lock washers to the arm screw and it still slips.

    I will definitely post a photo. It'll probably be Monday before I can, though. I'm setup in a friend's huge shop and he's out of town until Monday (still owes me a door key!)

    - Sully
     
  4. mikey

    mikey Active User H-M Supporter-Premium

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    We'll iron this one out, Sully. Off the top of my head, I would guess that you're trying to mesh the gears too tightly and that may be causing the RH screws that hold the gear train in place to loosen as you reverse. If you mesh the gears too tightly it becomes hard to turn the leadscrew handle as well. The leadscrew should turn freely and without a lot of effort when you aren't cutting and just a little more effort when you are cutting. It's been a long time since I read the instructions but I seem to recall Sherline doesn't tell you anything about how tightly to mesh the gears so its not your fault.

    Oh, when you get the gear train set up just the way you want, put a single drop of oil on one of the gears and another on the 100 gear. That is enough to lube the entire gear train.

    Another thing to remember is that cutting forces increase as you feed in deeper. I prefer to take 0.002" deep cuts for the first 5 passes for general thread cutting, then I use 0.001" deep cuts for every pass thereafter. This is slower, granted, but it assures accuracy and optimal thread form on a hand-driven lathe with an aluminum gear train.

    Stay with it, Sully. It takes awhile to get used to removing the motor and setting up your gearing but it will become simple and easy as you progress. I don't even think about it anymore - I just do the swap, cut the threads, replace the motor and I'm done very quickly. The Sherline thread cutting attachment looks sort of cheesy but it will cut more threads, both Imperial and Metric, than most full sized lathes with a full set of change gears and like just about everything else with a Sherline, it will cut those threads with precision.

    One last thing. Your lathe tool should have a very accurate 60 degree included angle and I suggest a 15 degree side relief angle on both side. Stone a tiny flat, just visible, at the very tip to prevent tip breakage and keep your tool razor sharp. Keep your tool overhang minimized and be sure your tool is on center and perpendicular to the work. If you haven't made a tool height gauge for your lathe then I suggest you make one calibrated to the centerline of your specific lathe. Use a fishtail to align the tool to the work. If any of this sounds like Greek to you, let us know and someone will clarify it.

    Welcome to the Sherline lathe and to the HM Forum!
     
  5. sully2161

    sully2161 United States Iron Registered Member

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    Thanks for the welcome! Well, you were definitely right about meshing the gears too tightly. I was a bit concerned about the aluminum gears and so I'd meshed them pretty tight. Loosening them up a bit made for much less effort in turning the handwheel.

    Unfortunately, this didn't solve my problem. I tried various degrees of meshing and it always jumped out in reverse. In the photo, it's the arm in the foreground that twists slightly clockwise (against a tightening screw & lock washer no less) so that the 40t gear separates from the 20t on the leadscrew. (Handwheel removed for photo)

    IMG_0088.JPG
     
  6. mikey

    mikey Active User H-M Supporter-Premium

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    Your set up looks correct. Be sure all the SHCS are tight except for the one on the end of the leadscrew - that one is just hand tight. If done as above, the set up should not be able to move. The only other thing that could remotely do it is if the hole at the end of the arm that is currently holding the 20T gear is somehow not drilled straight. That might allow the gears to cock and move out of alignment. There really isn't anything else there, Sully. Give it a try and let us know how it goes.
     
  7. Forty Niner

    Forty Niner United States Steel Registered Member

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    Steven,
    I'm curious.
    It looks like, from the 127 tooth gear on the spindle shaft, that your Sherline lathe is the Metric edition. Is that correct? I was looking at my Sherline Gear Selection Chart for Thread Cutting Attachment and the only application for the 127 tooth gear on the spindle shaft is if you have a metric 4100 or 4410 lathe. Your original posting indicates you have a 4400 series lathe. Which do you actually have? What pitch thread were you setting up to cut?
     
  8. sully2161

    sully2161 United States Iron Registered Member

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    Sharp eye. I actually have a 4400 AND 4410 lathe. The attachment works on both and has the same problem on both, so I was testing & taking photos on the metric lathe to leave the 4400 free for use. I'm selling the 4410 shortly so I didn't include it in my equipment list. The gear train is setup for 20 TPI.
     
  9. Forty Niner

    Forty Niner United States Steel Registered Member

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    Some Thoughts.
    The design makes it difficult to tighten the gear that is mounted in the slot. The screw tightens into a short stub with nothing but a thin flange on the back side, providing no way to back it up when tightening. Is that one tight enough?
    At the end of the pivoting arm holding that same gear there is a 10 32 SHCS that threads into the mating arm. Perhaps a longer bolt with and the addition of a locking nut behind it might provide additional holding power at that joint.
    Also, it would be good to make sure the arms, where they mate, are perfectly clean and dry. Any lubricant there would not be good.
     
  10. tharperidaho

    tharperidaho United States Steel Registered Member

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    I've had threading success in the past, but recently ran into the same problem. Oddly enough, I am also experiencing it trying to cut a 20 tpi thread. I've had some luck using the normal leadscrew dial to reverse rather than the screw attachment dial. I also took the lathe apart to clean and chech for any problems. I did find a problem. The threads were stripped on the leadscrew support hole that the screw used to fix the base to the leadscrew support goes in. Once I get this fixed, I am going to continue to study the problem. I also have installed the anti-backlash mechanism and need to see if that might be creating excessive friction for the system when returning the cutting tool to its starting position to begin another pass. I really hope it does not have anything to do with the geometry of the 20 tpi gear train. That's a pretty useful pitch for a lot of things. Once I get the lathe reassembled and some more testing done, I'll report back.
     
  11. mikey

    mikey Active User H-M Supporter-Premium

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    I'm wondering if there isn't some quality control issue with the threading attachment arms. I have never had mine slip or give any problems whatsoever but mine is an old one. Have you considered contacting the factory to see if they have any input? Have either of you guys checked the arms to see if they are actually flat? Please let us know.
     
  12. tharperidaho

    tharperidaho United States Steel Registered Member

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    I haven't contacted the factory, but will once I rule out the possibilities I mentioned. And I'lll check for flatness. My lathe and screw thread assembly are about 6 years old. It seems to be well made to me. Thanks for the ideas. I'll report back.
     
  13. tharperidaho

    tharperidaho United States Steel Registered Member

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    Okay, I've got my lathe reassembled and also discovered a few problems leading to the slippage. The overall issue is too much friction. Here is what I did to reduce friction enough to get the threading working and also a quick but dirty way to create more friction at the "elbow joint" where the 2 arms that hold the gear train in place join. These are called the "Primary Support Shaft" and "Secondary Support Shaft" in the Sherline documenation. They are held at the desired angle by a 10-32 socket head bolt that threads into the primary support shaft.

    1. There was some friction inside the leadscrew support that houses the pieces that engage/disengage the threading action (fixed shaft and sliding shaft) due to some burrs I cleaned off the burrs, cleaned and regreased with silicon grease. Leadscrew was cleaned and relubricated as well. There were also some wear spots on the fixed shaft, so I lightly filed them because they seemed to be rubbing a bit inside the support. Once deburred, cleaned and relubed, the shafts rotated nicely inside the support.

    2. The gib strip for the saddle was cleaned, relubricated, and backed off a bit to decrease the pressure it was applying.

    3. The bushing that holds the 40 tooth gear (Gear E in the Sherline documentation) had a rough surface that the gear rotates on. It looked a bit like galling. I cleaned and lubricated.

    3. Leaving the gear train in the arms, I detached the assembly from the lathe and spun the gears. The 40 tooth gear (gear E) had an area of about 4 or 5 teeth where it would catch with it's neighboring 20 tooth gear (Gear C). The same location on the 20 tooth gear seemed fine on the other side of the 40 tooth gear during rotation, so I am assuming the 40 tooth gear has some tooth shape issues. The teeth may be too thick at some elevation within the tooth. There was also some funny wear in this area. The engagement of this area when everything is put back on the lathe is the area that causes the arm to move, disengaging the gears. As a sanity check, I replaced the 40 tooth gear with a 36 tooth gear and found that it worked fine.

    4. I put the 20 tpi gear train back on the lathe and rotated it both directions for a bit. It seemed to be working fine, but finally failed once again. I tightened the bolt holding the arms together a bit more and added a small 1" C-clamp near the screw to apply more pressure without over tightening the bolt. It is now working without failure. I can still feel a bit of periodic friction in the system, so I need to look at the 40 tooth gear some more for a more thorough fix. It could be that my current setup will simply wear the other gears out in time. I like the idea of using a locking bolt too that was offered. I'll give that a try too.

    I checked the flatness of the arms and found that the secondary shaft (the one on the outside, away from the headstock) does have a bit of a bend in it. It bends about 0.003" over 1.5", so the angle change is very small. It could be a contributor to the the gear meshing issue, but it seems like there is more play in the system than the angular change due to the out of flatness. The surfaces of the arms that are engaged when bolted together appears to be flat.

    I'll give the factory a call about the gear. They may know about some issue and have a fix.

    Oh, this is a bit off subject, but I discovered why the thread stripped on my base t0 leadscrew support attachment. Sherline used a 3/8" long 10-32 socket head bolt to attach the base to the support. Sometimes there is an added spacer, which my lathe uses. Once you add the space, lockwasher and thickness of the base and support metal, there are only a couple of threads on a 3/8" long bolt. The fixed shaft has a groove in it and is held in place by the screw. I found that a length a bit less than .470 would pass through all the pieces and hold the shft in place, so I ground down a .5 long socket head bolt to size and used that. I also replaced the bolt holding the leadscrew thrust on the other end with a longer bolt because it appeared not all threads were engaged at that end as well.

    Thanks for the ideas! It's great to have other brains thinking about a problem and also hearing other experiences when trying to come up with a solution to a problem. Sully, I hope something here helps out your slippage. I'd be interested to know if something helps or not.
     
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  14. mikey

    mikey Active User H-M Supporter-Premium

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    Outstanding! This sort of thing will help someone, for sure. I am concerned about the lack of flatness in the arm and the poor surfaces on the gear bushing and on the 40T gear - that should not be the case. I would contact Sherline, too, and ask them what gives. I just looked at my 40T gear and it is perfect. I have used this threading attachment heavily over the years and it performs flawlessly for me. If it did not I would be on the phone fast!
     
  15. john.oliver35

    john.oliver35 United States H-M Supporter - Premium Content H-M Supporter-Premium

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    I used a gear from my Sherline threading set last night that I had not used before. Trying to thread was jerky and took a lot of force, and caused the idler gear to 'jump' out of position just as the OP described. After disengaging the lead screw and applying a liberal dose of way oil (vactra #2), and turning the spindle many times in both directions, the motion smoothed out very nicely. The Sherline aluminum gears don't appear to mesh nicely when new, but after some 'break in' the attachment worked well!

    John
     
  16. mikey

    mikey Active User H-M Supporter-Premium

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    I just used my threading attachment to turn a Class 3 fit M8-1.25 thread. I've found that if the gears are engaged too tightly they may bind or feel "jerky" as you mentioned. This goes for any of the gears but especially the A & B gears. These gears are like any change gear set - they do not need to mesh tightly. A few thousandths clearance between all meshing gears will provide smooth movement.
     
  17. tharperidaho

    tharperidaho United States Steel Registered Member

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    No matter what I did with the clearance, I could not get the 20 tpi arrangement to work without the work I did to remove the friction, although other combinations worked fine. I do have a useful update that follows John's and Mike's recent entrys. I cut a 20tpi thread in a piece of O-1 rod as a test. By the end of the test, my gears were running much more smoothly. I was careful to make sure that the meshing was engaged, but not too tight. Perhaps I caused a bit of damage to the one gear by meshing too tightly the first time I tried it. I think that if I find myself using a new combination of gears in the train, I will spend a bit of time running them in with the back and forth motion John describes before making a cut. Thanks for reorting back on your discoveries.

    Hey Mike,
    Are you the same Mikey that wrote up the back-side hoizontally oriented cutoff tool project over on machinistsblog a few years back? I'm in the process of making one, and want to say thanks for the writeup if you're the author.
     
  18. mikey

    mikey Active User H-M Supporter-Premium

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    Yeah, that's me. I hope it works out for you because it is one of the most useful tools you will have for your lathe. The one in that write up was a prototype but I'm still using it because I can't figure out how to improve it. A new one would look better but wouldn't work better.

    By the way, I just used some gears I haven't used before to cut that metric thread I made and had no binding once I got the clearance right. Something has changed in their production or design.
     
  19. tharperidaho

    tharperidaho United States Steel Registered Member

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    I'm wondering if my problem was a combination of a slightly misshapen gear compounded by initially having the mesh too tight and the slightly out of flat arm. The odd wear I mentioned earlier could be attributed to the lack of flatness issue, since the wear is squewed to one side. I am on a trip right now, so I can't check some of the other gears. There are small discrepencies among individual tooth profiles though, perhaps enough to add to the issue. Bottom line is that fiddling around in the direction of the info posted in this thread resulted in getting some decent threads cut. Forums get problems solved!

    I'm looking forward to getting the backside cutoff done. I had some bad crashes early on getting cutoff figured out with the Sherline setup, bad enough the the jaws in my 3 jaw chuck need work and I flinch whenever I have to part off. Some new blades are waiting for me at the post office and I need to finish up the mill work when I get back. I've got a bunch of parting off to do for my main prject, so I'm pretty excited to get a copy of your tool made. I'll let you know how it goes. The good news about messing up the 3 jaw is that I am better at centering stuff in a 4 jaw than I would be if I wasn't forced into using it so much.
     
  20. mikey

    mikey Active User H-M Supporter-Premium

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    Yup, been there, done that. Major dig ins on a Sherline can happen in an instant and it is amazing how much a cobalt parting tool can bend before it snaps. Its what made me go looking for a better option and the rear mounted tool is it. I haven't had a bad moment or problem since I built it.

    If I may, let me offer one bit of advice. Make SURE the bottom of the blade slot is on the dead center of YOUR spindle. As long as you do this the tool will work. The ledge also helps keep the tool aligned under load and lets you mount the tool on the cross slide in seconds.

    Do let us know how your tool turns out.
     
  21. tharperidaho

    tharperidaho United States Steel Registered Member

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    Yup, I'll send a project report in once I finish up the tool. And I'll be very careful measuring the center elevation and cutting the result into the tool. Thanks again for the help.
    -Tom
     
  22. ProfessorGuy

    ProfessorGuy United States Active Member Active Member

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    I have had a 4410 (metric) for just over a year and the thread attachment is awesome. Reading some machinists' magazines shows that the biggest issue everyone has to deal with in threading is to make the automatic stop repeatable. Since I spin the work by hand under a loupe, stopping the thread at the right point is impossible to mess up.

    Some of the gearing does tend to be a little 'touchy'. I find if I use a gear that hasn't been used yet, the setup can be a little tentative (seems about to skip). I've slipped once or twice (reefing down the bolts was enough to fix it), but never after I've started a thread.

    Even though I've used the threading attachment only a few dozen times, I can get the motor off, the gears and handwheel on in less than 2 minutes, it really is pretty easy. And from everything I've read, threading under power seems a complete pain in the neck. Especially since I cut very small screws (0.25mm pitch), never more than 10 or 15 mm long, and I need only a few.

    Where do you plan to sell your 4410?
     

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