# G0752Z spun the quill :(



## WobblyHand (Feb 18, 2022)

So just drilling out a piece of 12L14 with a 3/8" drill.  Was going to make a boring bar bushing.  Thought I'd put a 3/8" hole through, then put the tube in the boring bar holder to accurately line it up with the spindle.  Then drill to "size" and ream.  That was the plan anyways.  

Seemed a little harder than usual to advance the quill.  Was clearing chips every so often.  Near the end of the hole, (at 2" extension) all of a sudden, the drill chuck, quill and handle started rotating as one assembly!  Took a moment to process this and decide this wasn't good.  More like a moment of astonishment, then realized I had to do something.  Stopped the lathe.  Loosened the drill chuck and backed off the tailstock.  Handle is stiff to move - doesn't want to move.  Removed the tailstock and put it on the bench.  Using an old drill chuck, extracted the drill from the workpiece.  It wasn't hard to remove.

From the parts breakdown, I think if I take off the handle, I might be able to drive out the leadscrew and quill from the handle side out the quill side.  Not looking forward to viewing the carnage.  Maybe the set screw pin sheared under load.  Anyone have tips for disassembly?  Gee, was having fun in the shop, until that bit of excitement!


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## mmcmdl (Feb 18, 2022)

Quill come off the leadscrew and sheared the pin ?


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## Navy Chief (Feb 18, 2022)

It sounds like it either sheared off the setscrew or the setscrew was too short and it jumped /wedged against it. Either way it is probably tight due to what is left of the setscrew not being in the groove and it wedging against the quill. 

Sent from my Pixel 5 using Tapatalk


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## WobblyHand (Feb 18, 2022)

mmcmdl said:


> Quill come off the leadscrew ?


No.  Or at least I don't think so.  Stuck at 2" extension, rotated about 180 degrees from where it should be.

Edit:  Numbers are on bottom of quill now.


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## WobblyHand (Feb 18, 2022)

The set screw will turn outwards, I will remove it.  I had hoped backing it off some might help, but so far it hasn't.


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## mmcmdl (Feb 18, 2022)

I assume this was on the backplate project .


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## WobblyHand (Feb 18, 2022)

mmcmdl said:


> I assume this was on the backplate project .


Of course.  It was me making a 1/2" bushing so I could hold my 1/2" carbide boring bar, in an AXA-4 holder, (3/4" hole) so I could work on the back plate.  Oh well, I'll fix the tailstock somehow.  Minor bump in the road, in the scheme of things.  Stinks though.  Guess I will have to drive it out.  My drill chuck is still attached to the taper, so I don't want to drive the assembly out onto the floor!


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## mmcmdl (Feb 18, 2022)

If I find one , I'll throw it in the box .   Incoming pic on your other thread . It's always something !


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## RJSakowski (Feb 18, 2022)

The G0602/G0752 uses a rather feeble means of preventing quill rotation.  A single set screw atop the tailstock rides in the keyway so that, in essence, a single thread is making contact and at a single point at that.  

I buggered up my keyway when I was using excessive torque.  The symptom was that the quill was hard to move.  I managed to free the quill and extract it from the tailstock.  It had a raised burr where the quill had tried to rotate.  Stoning the burr eliminated the hard travel symptom.

To fix the root cause of the problem, I made a special dog point set screw.  The dog point of the set screw was an unthreaded portion of an 8mm set screw followed by a short thread and capped with a slot for turning.  The set screw had to be inserted from inside the quill  socket which was a bit tricky but I managed to position the set screw so that I could pick up the slot with a screw driver and thread it up into the tailstock.  The dog point now presents a much larger surface to the keyway, preve4nting the future raising of a burr.

An alternative is to re-thread the tailstock to 10mm and use a conventional dog point set screw.  In any case, a jam nut should be used to prevent the set screw from riding in or out during use.


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## Navy Chief (Feb 18, 2022)

RJSakowski said:


> The G0602/G0752 uses a rather feeble means of preventing quill rotation.  A single set screw atop the tailstock rides in the keyway so that, in essence, a single thread is making contact and at a single point at that.
> 
> I buggered up my keyway when I was using excessive torque.  The symptom was that the quill was hard to move.  I managed to free the quill and extract it from the tailstock.  It had a raised burr where the quill had tried to rotate.  Stoning the burr eliminated the hard travel symptom.
> 
> ...


Sounds your custom set screw is a good solution to the problem.


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## RJSakowski (Feb 18, 2022)

Navy Chief said:


> Sounds your custom set screw is a good solution to the problem.


So far.  I have put some really heavy loads on the tailstock with no rotation.  This is also important to me as I have my DRO scale attached to the quill and rotation would screw it up.  A better way to handle this would be to have a real key to engage the keyway.  That way, you would have full surface contact rather than point or line contact. That would involve broaching a slot in the tailstock but that isn't practical for this machine.


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## jmkasunich (Feb 18, 2022)

RJSakowski said:


> So far.  I have put some really heavy loads on the tailstock with no rotation.  This is also important to me as I have my DRO scale attached to the quill and rotation would screw it up.  A better way to handle this would be to have a real key to engage the keyway.  That way, you would have full surface contact rather than point or line contact. That would involve broaching a slot in the tailstock but that isn't practical for this machine.


Next best thing would be a custom screw installed from the inside (see RJSakowski's post) but with the section that fits the slot in the quill milled flat on both sides to match the width of the slot.  That would achieve surface contact without needing to broach a keyway in the bore.


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## WobblyHand (Feb 18, 2022)

Got it apart.  Threads on the set screw had some deformation.  Drove out the screw with a dead blow against a block of wood.  No marks on the quill.  Quill bore is mostly ok.  There's some sort of scratch starting from the setscrew going towards the ball oiler.  It is about 1cm long. Unfortunately I can't feel it, since it is beyond my finger length.  I attempted to use a rod to slowly slide it along the bore to try to tell if there was a burr and couldn't really feel one.  Might be a casting defect, it didn't look fresh.

I have put it back together again, using a new set screw, for the moment.  I will drill it out and put in a dog point set screw.  Seems the easiest solution.  Of course, I don't have any M10 set screws, but that is easy to fix.  So at the moment I am back in business.  I'll take it apart again when I get the M10 set screws.

Oh, probably the real problem was I ran off the end, or was very close to the end.  I was at 2.5" extension when everything went to the dogs.  Lesson learned.


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## RJSakowski (Feb 18, 2022)

jmkasunich said:


> Next best thing would be a custom screw installed from the inside (see RJSakowski's post) but with the section that fits the slot in the quill milled flat on both sides to match the width of the slot.  That would achieve surface contact without needing to broach a keyway in the bore.


I thought of this but the keyway slot is 7.83 mm wide so a simple flat on the end of the screw would create free play.  Since my DRO scale is attached, any undue rotational play can't be tolerated as it would make the scale the restraint.  However a screw like shown below would work.  The doming on the key surface would allow rotating tight to the quill cylindrical surface.  Ideally, the threads would be timed to permit drawing the key close to the socket but at worst case, it would be out by .313 mm. Of course the flat would need to be aligned with the keyway.  The slot would enable that.  Once the quill was engaged the key couldn't rotate so a lock nut wouldn't be required.

As I recall, I had some difficulty installing my key as the lead screw is inserted from inside the socket and there isn't enough clearance between the lead screw and the key to start it.  The lead screw couldn't be inserted after the key was in place because the diameter of the thrust washer was larger than the new clearance.  I remedied that by cutting a flat on one edge of the thrust washer.  Thinking about it now, I may have been able to slide a rod into the tailstock and thread the washer on the rod.  Then I could slide the lead screw in and transfer the washer to the lead screw. and then seat the lead screw.


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## mmcmdl (Feb 18, 2022)

WobblyHand said:


> Oh, probably the real problem was I ran off the end, or was very close to the end. I was at 2.5" extension when everything went to the dogs.


That's what I figured !   Should've told me you needed M-10 set screws an hour ago , they would be on their way also .


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## WobblyHand (Feb 18, 2022)

mmcmdl said:


> That's what I figured !   Should've told me you needed M-10 set screws an hour ago , they would be on their way also .


Didn't know know it, at the time.  Looked at the screws and the slot in the quill, and knew I needed to make a change.  I'll just pick up a few M10s.  Just add them to my growing hardware collection.  Not a big collection, by any means, but it is still growing.

Beginning to feel like I am becoming my Grandfather.  He owned a hardware store in the 1930's.  Made his own paint, among other things.  Here is a picture of him in front of his store in Boston circa 1930.  Guessing that from the Tercentenary Sale sign.  Boston, Mass was founded in 1630.


$1.95 for a gallon of paint.  Used white lead then.  Still have some of his old chemical formulary books.


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## pdentrem (Feb 18, 2022)

Good to see that there was no real damage. My neighbors are always at my door, asking if I have this or that. They call me the hardware store of the street as I have hard to find bit and bobs!
Pierre


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## WobblyHand (Mar 7, 2022)

Was kind of dreary this afternoon.  Wasn't up for much machining today, but managed to machine an M10 set screw to length in my mini-lathe and add a little dogleg to it.  Will have to set up the tailstock on the mill, drill it and tap the existing M8 to M10.  The dogleg is 2.5mm long and 7.98mm in diameter. Figure it is close enough to do a fit check.  If I'm way off, well, I do have quite a few extra set screws to play with.  Held the set screw in a collet, using an extra set screw to get some extra material in the ER32 collet.  Worked well.  Used some TCMT inserts to reduce the 16mm long set screw to 12mm, and to peel off the threads.  No muss, no fuss.  Tomorrow I will do the tailstock.


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## Road_Clam (Mar 13, 2022)

I too was concerned about a whimpy soft set screw acting as a anti-spin component so I custom flat ground an 8mm bolt and seated the bolt as far down into the movable tail stock quill barrel as I could without creating excessive drag. I then also used a jam nut to keep the adjustment. Should add some strength when using a larger drill.


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