# A mini-lathe boring tale



## WobblyHand (Aug 14, 2021)

I had just finished my boring bar holder this past week and wanted to try it out.  Grabbed a chunk of 1045 steel and drilled a 1/2 hole in it to get clearance for my 3/8" boring bar.  Bored out about an addition 0.1", not all at once, but in 0.010" bites.  Bar was cutting well and making 1/2" tight curls.  





Then I heard a loud noise and some following squeaking and the bar stopped feeding inward.  Thought I damaged the bar, the insert or the half nut.  The spindle was still turning.  I was not at the bottom of the bore, but about 0.150" from the bottom when this happened.  Stopped the lathe and started trying to figure out what had happened.  Moved the carbide boring bar towards the center of the hole and extracted the bar.  It was fine.  Poked around some more and eventually found the B/C gears had seized on the shaft.  They would not move.  Ordinarily, the bushing freewheels on the shaft.



Pulled out the B/C shaft by loosening the nut and tried moving the gears on the shaft.  Very stuck.  Eventually removed the 20T metal gear and examined the 80T gear.  It had turned in the shaft about 180*.  Pressed the gear off.  Well nuts, I'll need a new one.  It appears the bushing seized on the shaft?  I've got it soaking in a little bit of Kroil right now.  Maybe I can free it up.  Or make another one.  The bushing, shaft and gear altogether is only $22.06.  It's the time - it will be a week and a half before I get the parts.  With the shaft assembly in a vise tapped the bushing keyway to try to rotate it on the shaft.  It's not moving.

Glad I had a plastic gear for this.  It was the mechanical fuse for the system, the weak link.  My best guess is the lubrication between the bushing and the shaft was insufficient.  

Well, that puts a damper on things.  Need to check that this is the only damage.  Maybe there is something else.  Suppose more disassembly of the gear train is required.  Anyone have ideas on what else to check?


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## homebrewed (Aug 15, 2021)

Check the lead screw to see if it turns freely when it's not engaged.  Some mini lathes don't have oil ports on the bushings so there's a possibility that the LS seized up and the gear is just a victim.  Probably not the case but worth checking.

Clearance between the bushing and LS can actually be pretty close.  I greased the bushings on mine and later on when I added a handwheel to the LS I noticed it didn't turn very freely.  Cleaning off the grease and replacing it with oil fixed that little problem.


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## WobblyHand (Aug 16, 2021)

homebrewed said:


> Check the lead screw to see if it turns freely when it's not engaged.  Some mini lathes don't have oil ports on the bushings so there's a possibility that the LS seized up and the gear is just a victim.  Probably not the case but worth checking.
> 
> Clearance between the bushing and LS can actually be pretty close.  I greased the bushings on mine and later on when I added a handwheel to the LS I noticed it didn't turn very freely.  Cleaning off the grease and replacing it with oil fixed that little problem.


Since there's no B/C shaft on the lathe, at the moment, I can turn the leadscrew in the pillow blocks by grabbing the 80T gear and turning.  It's not free spinning, but it turns easy.  Gave the blocks a little oil and the leadscrew turned _slightly_ easier.

After soaking the bushing and B/C shaft in Kroil for a day, I was able to rotate the bushing about 0.05" by tapping on the keyway to try to rotate the shaft.  It would rotate 0.05" in either direction but no further.  With more Kroil eventually was able to rotate the bushing 360*, but it would not come off the shaft.  I was able to tap a single edge razor blade in between the flange and the shaft and I got it to slightly move upward.  Still couldn't get it to come off.  An ordinary chisel was far too blunt, so I reground a cheap chisel to have a finer taper and only one edge.  By carefully tapping the chisel in the gap, I moved the bushing slightly upward on the shaft.  It's still stuck.  Now I'm at the dual lever stage trying to lever it off the shaft.  I'll apply a little more Kroil and give it a go again.  Going to put in successively higher fulcrums to get this bushing off, as it is still fighting me. 

I made the mistake of putting on the recommended white grease on the leadscrew in the beginning.  Bad idea.  Just collects chips and swarf and is hard to clean.  I have about 80% of it removed now, still need to do the rest.  The rest of the screw is oiled and is easy to clean off.


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## Cadillac STS (Aug 16, 2021)

Could do most if not all the bore with the hand feed not power feed and avoid the gears altogether.  Maybe just power feed the last finishing pass.


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## WobblyHand (Aug 16, 2021)

Cadillac STS said:


> Could do most if not all the bore with the hand feed not power feed and avoid the gears altogether.  Maybe just power feed the last finishing pass.


Agreed.  I could bore by hand.  Have to say the finish is usually better with power feed.


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## WobblyHand (Aug 16, 2021)

Got the bushing separated from the shaft.  Fought me all the way.  I'm surprised at how little difference there is between OD of the shaft and ID of the bushing.  I measured 8.00mm on the shaft and 8.03mm on the inside of the bushing on the undamaged areas.  I probably haven't quite measured the ID correctly (first time use of small hole gauge) but that's only 0.001" difference in diameters.  Seems very, very tight. From the photo one can see where the parts seized near the top of the shaft.  


The key way is marred from me hitting it to get the bushing to move.  Probably could clean it all up, if I could find a carbide bar to fit inside the bushing.  I could turn off the external bur in the lathe.  For that matter, could make a new shaft out of 0.75" stock. 

This is more of an annoyance than anything.  Fortunately there are spare parts, and they are very inexpensive.  ($4.84 for the shaft/bushing/key assembly)  I've ordered everything that I need.  I may try to clean up the damaged parts above since I have nothing to lose.  I think I could remove the 4 jaw chuck with my workpiece installed and install my ER32 chuck to fix up these parts.

Could I make a bushing out of oil filled bronze?  Is that easy to machine?  Would it be ok to make a relatively deep keyway like in the steel bushing?  Oil filled 841 bronze  I could get some 1/2", turn it down to 12mm, then bore it to clearance for 8mm.


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## homebrewed (Aug 17, 2021)

I wonder if a bit of swarf got in the bushing.  In my experience, boring through-holes seems to push a lot of the swarf into the spindle bore.  From there it's a short trip to the drive gear chain (that's why some folks stuff a cork into the back of the spindle hole).

I once bored a number of holes to get a friction fit to some bearings and so much swarf got into my 4-jaw that the jaws froze up.  I had to take the whole thing apart to clean it up.

BTW, while I added the LS hand wheel specifically for using with a ball turner (long story), I've found it handy for fine feeding.  In combination with a carriage stop, it works nicely for boring blind holes -- in contrast with power feed.


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## WobblyHand (Aug 17, 2021)

homebrewed said:


> I wonder if a bit of swarf got in the bushing.  In my experience, boring through-holes seems to push a lot of the swarf into the spindle bore.  From there it's a short trip to the drive gear chain (that's why some folks stuff a cork into the back of the spindle hole).
> 
> I once bored a number of holes to get a friction fit to some bearings and so much swarf got into my 4-jaw that the jaws froze up.  I had to take the whole thing apart to clean it up.
> 
> BTW, while I added the LS hand wheel specifically for using with a ball turner (long story), I've found it handy for fine feeding.  In combination with a carriage stop, it works nicely for boring blind holes -- in contrast with power feed.


Could be.  In this case, though was boring a blind hole, so it wouldn't have been an easy path.  The 1.25" stock was butted up against the chuck, blocking the spindle bore.  But, I'm guessing this was a cumulative sort of thing, aggravated by my slack lubrication schedule.  Good idea on the cork!  I'll look around to find one.

I too have a handwheel that I made for my spindle.  Haven't tried it boring.  But I have threaded with it.  When a thread is only 0.1" long, I just don't quite have the reflexes to stop that quick.  Using the handwheel made that easy.

Parts to repair the mini-lathe should be in by Thursday, although maybe the notification is just to make me _feel better_.  When it is here, it will be here.

Put the B/C shaft in the lathe to clean it up.  It now enters the bushing until it hits the bur.  To clean out the bushing I need to make a boring bar sleeve for a Micro 100 small boring bar.  Honestly don't feel like making that now.  Not motivated.  Even if I clean up the bore of the bushing, the keyway is still damaged.  Of course, I'd make the repair, if the part was unavailable.  If I had a reamer, I'd try that. Probably need to get an inexpensive set of metric reamers anyways.  Could use a 6, 8 & 12 for some projects coming up.  Tooling acquisition never seems to end!


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## WobblyHand (Aug 17, 2021)

More less fixed the B/C shaft and bushing.  Took a round file to the bushing interior and did some light bur shaving.  Finally was able to pass an 8mm dowel pin through the hole.  Used the hardened dowel to sort of scrape the interior and get rid of more burs. After stoning the shaft, the bushing now fits and rotates smoothly.  Mostly repaired the keyway with a file and a stone.  Key is still a tight fit.  The B/C shaft assembly is good enough to keep around as a spare now.  The 80T gear won't hold up, because part of it's keyway sheared, so it will be replaced.  I might try using it tomorrow, but don't think it will last long.


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## WobblyHand (Aug 18, 2021)

The postman brought me a gift a day early!  The B/C shaft, bushing and key, the 80T gear, and a 20T, 25T and 45T gear.  The 20,25, and 45 tooth gears are metal and I bought them because they just weren't much more than the plastic ones.


Won't take long to install these.


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## jpackard56 (Aug 18, 2021)

Could use a 6, 8 & 12 for some projects coming up.  Tooling acquisition never seems to end! 
I'm not out in my shop but seems like I remember getting some 8mm reamers from sdelivery (real nice quality ones) for cheap in our site stuff for sale section a couple months back. Might be worth a look to verify sizes with him.
Jim


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## WobblyHand (Aug 18, 2021)

jpackard56 said:


> Could use a 6, 8 & 12 for some projects coming up.  Tooling acquisition never seems to end!
> I'm not out in my shop but seems like I remember getting some 8mm reamers from sdelivery (real nice quality ones) for cheap in our site stuff for sale section a couple months back. Might be worth a look to verify sizes with him.
> Jim


Thanks for the tip.  I will check that out.


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## WobblyHand (Aug 18, 2021)

Installed all the parts save for the 45T gear.  It is held on by a circlip.  Don't know where I stashed the special pliers in the garage.  And I don't have a spare clip, so I need to put a rag over it when I pull it.  I'll do that later.  Made sure that B/C bushing was oiled!

Back to boring.  Finally.  Starting to get a nicer finish with a 0.005" DOC and a slightly larger bore.  Now it looks like turned steel, rather than frosty stuff.


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## mickri (Aug 18, 2021)

The proper oil is your friend.  Grease not so much.  I don't use my lathe that much.  So I oil everything every time I use it.  For clean up I have found mineral spirits works really good.  I keep some in a spray bottle.  Seems to help get swarf and chips out of places you don't want it.  Then oil everything after I am done with the mineral spirits.


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