# Sherline Thread Cutting Attachment Slipping



## sully2161 (Jan 22, 2016)

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


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## mikey (Jan 23, 2016)

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.


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## sully2161 (Jan 23, 2016)

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


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## mikey (Jan 23, 2016)

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!


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## sully2161 (Jan 26, 2016)

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)


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## mikey (Jan 26, 2016)

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.


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## Forty Niner (Jan 27, 2016)

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?


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## sully2161 (Jan 27, 2016)

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.


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## Forty Niner (Jan 28, 2016)

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.


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## tharperidaho (Feb 25, 2016)

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.


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## mikey (Feb 26, 2016)

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.


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## tharperidaho (Feb 26, 2016)

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.


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## tharperidaho (Feb 27, 2016)

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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## mikey (Feb 28, 2016)

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!


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## john.oliver35 (Mar 7, 2016)

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


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## mikey (Mar 8, 2016)

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.


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## tharperidaho (Mar 8, 2016)

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.


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## mikey (Mar 8, 2016)

tharperidaho said:


> 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.



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.


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## tharperidaho (Mar 8, 2016)

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.


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## mikey (Mar 8, 2016)

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.


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## tharperidaho (Mar 8, 2016)

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


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## ProfessorGuy (Apr 12, 2016)

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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## j ferguson (Nov 11, 2017)

I suppose I should assume that the guys who wrote this stuff a year ago have all made their threading attachments work.  Did anyone talk to Sherline about this?  I ask because my new Sherline 17" 4400 showed up yesterday and is now secured to an MDF board attached to one of Harbor Fright's $20 folding workbenches.  So I got out the additional gizmos I bought with it and when I got to the threading attachment - set it up and found that it slipped just like the ones reported above.
.
It looks like the wisdom shared above is that the gears need lubrication and some experience - sort of run-in.  This sounds pretty good. I must remember to spend some time on this before I get boxed in and have to produce some threads in a hurry.

I've been away from this stuff for a bit more than 50 years having gotten stuck in another profession, but now that I'm back to what I really like, I'm burdened to some extent by what I remember from the late '50s, or possibly mis-remembered.

I thought we cut threads on one face using the compound slide set at an angle which agreed with the geometry ot the threads we were cutting.  The threads were cut in the direction of the chuck.  We'd back off with the compund slide run the thing back bring it in some thoudsandths and do the next cut.

This obviously requires a compound slide.  It looks as if this cannot be done with Sherline's compound slide unles you do the cutting on the back side ot the work where it would be hard to see what was going on.

Sherline offers a riser which would make it possible, but it doesn't look like the threading attachment could handle a head-stock sitting on a riser so this it out.

I realize that what I'm asking is probably nuts, but has anyone tried using the compound and cutting threads on the back?


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## mikey (Nov 11, 2017)

You actually do not need or use a compound slide on the Sherline lathe to cut threads. You just mount the threading tool in the tool post, get it at center height and perpendicular to the work and then cut threads with the cross slide by feeding straight in. It works really well. The Sherline threading attachment works much better than you might think, and turning the leadscrew by hand actually gives you very fine control of the operation. I rather like it, myself.

You will be able to cut class 3 threads with this attachment. I don't happen to have any slippage issues with my set up.


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## j ferguson (Nov 11, 2017)

I realize that the Sherline setup coes not require the compound, but at a cost of cutting both sides of a thread instead of one side.  It's probabaly more of an artifact of the way I learned to do this that I was looking to do threads the same way I did 55 years ago.  I haven't tried the Sherline method yet, but I am looking forward to it. I'm sure I'll get the geartrain reliable.

thanks for the thoughts.

john


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## Forty Niner (Nov 11, 2017)

j ferguson said:


> I suppose I should assume that the guys who wrote this stuff a year ago have all made their threading attachments work.  Did anyone talk to Sherline about this?  I ask because my new Sherline 17" 4400 showed up yesterday and is now secured to an MDF board attached to one of Harbor Fright's $20 folding workbenches.  So I got out the additional gizmos I bought with it and when I got to the threading attachment - set it up and found that it slipped just like the ones reported above.
> .
> It looks like the wisdom shared above is that the gears need lubrication and some experience - sort of run-in.  This sounds pretty good. I must remember to spend some time on this before I get boxed in and have to produce some threads in a hurry.
> 
> ...



I don't think what you are asking for is nuts.  I would prefer to do it the same as you.  I, like you, learned to cut single point threads on an engine lathe in the late 60's.  Always used the compound slide set at the correct angle.  Cut many threads that way.  Never did I cut a single point thread by plunging straight in with the cross slide...............until this year when I needed to cut some threads and the only choice is my Sherline lathe.   So I did it the way other posters recommend.  I  did not feel comfortable doing it that way, but I took it slow and it worked.  But I am retired and now am a "hobby machinist" instead of a real machinist because of my tooling.

I too have the Sherline compound slide and was disappointed that it doesn't work like a normal one.  I would much prefer to have the compound slide work from the front instead of the back (and holding the tool upside down).  I've looked at trying to modify compound slide to work on the front but haven't come up with a satisfactory way to do that. You can mount the compound slide like you would on a regular lathe as long as it is set off at some angle to miss the cross slide handles but, because the slide itself holds the 1/4" tool bit directly (instead of a tool post/holder), the tool bit is 1/4" above center if mounted right side up.

Gotta be a way.    You keep thinking about it.


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## j ferguson (Nov 11, 2017)

Forty Niner said:


> I don't think what you are asking for is nuts.  I would prefer to do it the same as you.  I, like you, learned to cut single point threads on an engine lathe in the late 60's.  Always used the compound slide set at the correct angle.  Cut many threads that way.  Never did I cut a single point thread by plunging straight in with the cross slide...............until this year when I needed to cut some threads and the only choice is my Sherline lathe.   So I did it the way other posters recommend.  I  did not feel comfortable doing it that way, but I took it slow and it worked.  But I am retired and now am a "hobby machinist" instead of a real machinist because of my tooling.
> 
> I too have the Sherline compound slide and was disappointed that it doesn't work like a normal one.  I would much prefer to have the compound slide work from the front instead of the back (and holding the tool upside down).  I've looked at trying to modify compound slide to work on the front but haven't come up with a satisfactory way to do that. You can mount the compound slide like you would on a regular lathe as long as it is set off at some angle to miss the cross slide handles but, because the slide itself holds the 1/4" tool bit directly (instead of a tool post/holder), the tool bit is 1/4" above center if mounted right side up.
> 
> Gotta be a way.    You keep thinking about it.



Hi Forty Niner,
I bought the Joe Martin book which is really interesting. I wish he was still around - so many similar experiences over the years.  He writes about why he got into cutting on the back side of the work.  Apparently he found that screw machines which were a bit over the hill could cut on the back such that the tool was lifting the slide instead of forcing it down - and this with tooling which wouldn't work on the front due to chatter. 

I've got a backlog of things I need for projects before I get to threading, but I think I am going to try cutting threads on the back.  No that the way Sherline and Mikey suggest but because I'm a bit perverse.


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## mikey (Nov 11, 2017)

I understand what you guys are saying but I can assure you that the direct feed method works very well. You simply need to take lighter cuts and you will be able to cut beautiful threads on a Sherline lathe. The pic below is one of the few pics I have of theading but this is a class 3, M8 X 1.25 thread at the end of a 1144 stressproof steel leadscrew. Other than blowing off the debris, this is just as it comes off the Sherline lathe.




I wanted to use the compound, too, but it turned out that cutting straight in poses no issues for me. Not trying to convince you not to do it; just saying that it wasn't worth the hassle for me. I've cut many, many threads on this lathe and actually enjoy the process. It is actually easier for me to hold tighter tolerances with this machine, and this extends to my threading.


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## kvt (Nov 11, 2017)

I have not cut a lot of threads on my Sherline lathes but when I did they were good.   Just do not try to take a large bite any any one time.   do not have any pics of ones I have done, bit they look good.


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## j ferguson (Nov 12, 2017)

Exercising new gears seems the answer to them jumping out of engagement.  Mine works just fine now.  I think I'll try the Sherline methiod first. Clearly it's less trouble than setting up the compound and cutting on the backside.


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## john.oliver35 (Nov 12, 2017)

I had the same problems when my threading attachment was new.  Found that putting some oil onto the gears and 'excercising' them seemed to clear off the burrs and make the teeth slide properly.  Also, make sure the gibs are not to tight - the gears will tend to disengage at spots where the carriage drags on the ways.


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## mikey (Nov 12, 2017)

I suspect things have changed in the quality control dept. at Sherline since Joe died. I never had an issue with having to break in a gear or having them jump out of engagement or lock up or anything other than work right. Too bad.

When you set up your gear train, be sure to slip a piece of paper between the gears before you lock it down, then pull the paper out. This gives you the ~0.003" clearance you require. Use lubrication sparingly to avoid a mess; almost any oil will do for this and I usually use a single drop of oil to lube the whole train.

I thought I would tell you guys how I stage my threading passes - might help. My first pass is a 0.001" deep scratch pass, then check with a thread pitch gauge to be sure the pattern is right. If it is, then I take 0.002" deep cuts until I reach a total depth of 0.010". From this point on, I take only 0.001" deep cuts until I am very close to being done. On every fourth pass or so I make a pass without adjusting the depth of cut; this is a spring pass. This spring pass helps to be sure both flanks of the thread are even because there is a lot of flank contact with the tool and defection can be an issue on thinner work pieces.

I always calculate an estimate of total thread depth so I know when to start checking for fits. I use the formula from Darrell Holland: *.750/TPI = approximate thread depth*. I start checking for fits about 0.005" before I hit the calculated depth. Early on, I used the nut I was trying to fit but it is better to use either the three wire method or a thread micrometer - much more precise. Estimating your total depth of cut for metric threads can be a major pain because they use pitch, not TPI. To get around that, use the attached chart from Newman Tools to convert the pitch to TPI and plug it into the Holland formula above.

Remember that if you need to produce a class 3 fit, your blank must be sized correctly. To do that, I am attaching a chart that will give you all the information you require to cut proper thread fits below. To use the chart, find the thread you're trying to cut, then determine the fit you want - 2a, 3a, whatever. Then for that class of fit, find the major diameter; this will be a range. Turn your work piece so the OD falls inside this range. Then, when you turn the thread, use a thread mic or 3-wire calculation to hit the Pitch Diameter range in the chart. If you get both of these right, your thread will be in the class of fit you chose. If this is not clear, let me know.

With regard to cutting in with the cross slide vs the compound, guys cut with the cross slide every day and many prefer it this way. If your tool geometry is precise and the tool is sharp, this method works every bit as well and cuts perfect threads. Yeah, you're cutting on both flanks of the tool but you're taking very small cuts so it isn't a big deal. Truth be told, when I need to cut a class 3 metric thread I prefer to do it on the Sherline lathe instead of my Emco Super 11 because it is faster and easier, believe it or not.

I have cut many, many threads on the Sherline lathe over the 25+ years I've owned it and most of those threads have been cut to tight tolerances, not because it was necessary but because I can. So can you. I suggest you let go of the idea that cutting with the cross slide is an inferior way to cut threads - in my experience, it is not. If your thread form is a problem, look to your lathe tool or technique instead.


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## j ferguson (Nov 12, 2017)

thank you so much Mikey. This is really informative.  Also thanks much for your article on how to improve a belt sander for use in bit forming.  Brilliant.


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## mikey (Nov 12, 2017)

j ferguson said:


> thank you so much Mikey. This is really informative.  Also thanks much for your article on how to improve a belt sander for use in bit forming.  Brilliant.



You're welcome. I hope it helps you to become comfortable with the threading attachment. In the beginning, I thought it was a hassle to set up the gearing and turn the work by hand but I've learned that it allows me to cut more threads than any other lathe I've seen and the handwheel allows me to cut into a narrow thread relief without worrying about a crash. Thanks also for the kudos on the belt sander - works good for me!


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## j ferguson (Nov 13, 2017)

Part of this morning was spent (well, invested in) running in the various gears for the threading attachment,  Virtually every fresh gear would cause the idler to come out of engagement, generally on the back-up move.  It didn't take much more than cranking the carriage out a foot or so and bringing it back a couple of times for the gears to get comfortable with each other.

Having done this, I must say that the attachment runs very smoothly.


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## Aaron_W (Nov 15, 2017)

I'm just curious, when / why do you use the thread cutting attachment vs a tap / die? 

I got the lathe package that included the thread cutting attachment, but from reading through the Sherline machining book, it sounds as if it is usually preferable to use a tap & die unless you really need a thread pattern that is not easily available.


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## mikey (Nov 15, 2017)

Can't speak for others but I use a die when there is already a thread present and I'm trying to clean it up or complete a partial thread that was made by some other process. Dies do not produce precision threads so if you need one then you need to screw cut it. The other issue with dies is that holding them square can be difficult if doing it with a hand held die holder. On the lathe, you can use a tailstock die holder and get it pretty well aligned but it still won't cut a precision thread, even when using split button dies. When you spend several hours getting a work piece done and the last thing you need to do is cut a good thread on the end, a die is not the method I would recommend; I would screw cut it.

As for taps, when the hole just needs to hold a screw and I have the right size tap then I tap. When I need a precision fit or the hole is a size for which I don't have a tap then I cut it. I've cut a LOT of internal threads over the years and it is no harder for me to cut an internal thread vs an external one. For me, the issue is how small or large the hole is, and also how deep. I have bars that will thread inside a 3/16" ID hole on out, and shallow to 5" deep (all carbide bars) so if I have the need to cut a thread, I can cut it. Taps are faster and easier to use so I use them when I can but when I need a precision fit, I cut it.

You will often work on projects where the male piece is of a non-nominal size and the female part must fit. There are no taps or dies to make this work so you have to be able to screw cut external and internal threads, and you have to be able to cut to the tolerance class you need. My advice is to learn how to cut threads; this will serve you well over the years. Luckily, thread cutting on the Sherline lathe is pretty simple and once you have a handle on it, it frees you to design stuff that you wouldn't otherwise be able to do.

On a related subject, you are cranking the lathe by hand with a Sherline and you're cutting with both flanks of the threading tool. As you get deeper into the thread the resistance goes up. Your tool needs to be accurately ground and sharp or you'll struggle to turn the crank and your thread form will be all messed up. Learn to grind and hone a good threading tool. And don't think a carbide threading tool is the answer; it is not. One option is a HSS inserted threading tool from AR Warner. I haven't used one but I know they're available. Personally, I prefer a tool with a geometry that I control so I only use a shop-ground HSS tool on my lathe.

EDIT: I should mention that when using dies, coarser threads require a lot of torque to cut. On the Sherline lathe, coarse means 3/8" threads or larger. When you turn the work to cut with a die, the chuck cannot hold the part and it will turn and there goes your thread form, not to mention the marring of the work piece. For this reason, many guys will partially screw cut the threads and finish up with the die, or they transfer the work piece to a vise and use a hand held die holder to finish up. This is a hassle for me and I prefer to just cut a clean thread in the first place. Believe it or not, I can cut threads faster on the lathe than going through all the hoops above.


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## Aaron_W (Nov 16, 2017)

Thank you, I was wondering how useful this attachment would be after reading about making threads. It sounded more like a nice to have tool for very specific needs and I was wondering how much I would use it. Nice to hear it may be more useful than I initially thought.

It seems he really downplayed the need for special tools even though Sherline has a fairly extensive product line. An unusual position to take, but kind of refreshing to see.


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## mikey (Nov 16, 2017)

Aaron, screw cutting ability is a *big* deal. What Joe did was to design a gear train that will cut almost any thread you might ever need, both Imperial and Metric, and made it simple to use. In time, you will find that the threading attachment is one of the most valuable accessories made for this lathe. It is often the difference between can and cannot.


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## Aaron_W (Nov 18, 2017)

Thanks, nice to know it is actually a handy accessory. I'm not seeing a need in the short term, as none of my initial projects include threaded bits, but I'm sure as I expand my horizons I will want that ability.  Thanks to this thread I also know I may want to run in the gears a bit before use.


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## kvt (Nov 18, 2017)

I actually have the 4400 set up to do parts and the 4000 set up constant for threading.   Some times you just cannot get a die in close enough like you can a tool.


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## mikey (Nov 18, 2017)

kvt said:


> Some times you just cannot get a die in close enough like you can a tool.



True 'dat!


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## Catshooter (Oct 6, 2019)

I suppose most of y'all know this, but just to sure Sherline makes many more change gears than they catalog.  You just have to ask.  At least it was that way some years back.  I've 20+ gears.  Handy.


Cat


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