# How did this happen?  Bent gear shaft...



## WobblyHand (Jul 8, 2020)

When I was setting up to thread some delrin on my lathe I noticed the carriage crank had an odd periodicity to it.  Kind of a thump, kathump sort of feeling.  Removed the apron from the lathe and found a bent shaft, or at least it looks that way to me.  The bend is towards the front, like there was a crash into the tailstock.  But I didn't crash into the tailstock.  Recently I stalled the motor while parting, but that's about it.  


That gear shouldn't look like that, right?

I'll try to disassemble it further.  Hopefully it isn't the apron itself.


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## benmychree (Jul 8, 2020)

It certainly got jammed up somehow, since it appears that there is no power feed other than the lead screw, I'd think that something was about to jam up and someone grabbed the carriage handwheel in an attempt to stop it.  Panic!


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## WobblyHand (Jul 8, 2020)

Apparently there was some kind of jam.  Well, stuff happens.  I'm surprised there's that much of a bend.  Need to pull it apart and inspect the damage.  Maybe its something simple that I can fix or fabricate myself.  Diving in...


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## benmychree (Jul 8, 2020)

It looks like it may be an easy fix, perhaps straighten or replace the shaft that the gear rotates on.


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## WobblyHand (Jul 8, 2020)

Anyone know how the hand wheel is held on?  I removed the acorn nut and the set screw but the wheel seems to be stuck on.  Does it thread off or do I use a wheel puller?

The hand wheel needs to be removed to get access to the back of the shaft.  I hope then I could use a punch to push out the pin.  Rather do that then grab the shaft in vise grips and twist it.


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## benmychree (Jul 8, 2020)

I think the bent shaft gear assembly is bearing against the pinion gear attached to the handwheel, you may have to straighten the shaft somewhat in place to be able to get things apart.  The handwheel would not be threaded on, you likely need a puller.


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## RJSakowski (Jul 8, 2020)

The hand wheel drives a second gear.  The shaft should just be sitting in a socket.  Once the retainer is unfastened, the assembly should slide out.


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## WobblyHand (Jul 8, 2020)

The large gear on the shaft pulled right off easily. The shaft is bent near the bottom.

Tried a wheel puller and it didn't want to move.  It was a 2 arm puller.  Not comfortable cranking down on that aluminum wheel.  Have to look around for a 3 jaw puller, know there is one somewhere!


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## WobblyHand (Jul 8, 2020)

RJSakowski said:


> The hand wheel drives a second gear.  The shaft should just be sitting in a socket.  Once the retainer is unfastened, the assembly should slide out.


Is there another retainer besides the set screw and nut?


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## Manual Mac (Jul 8, 2020)

My guess someone on swing shift did it.


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## RJSakowski (Jul 8, 2020)

WobblyHand said:


> Is there another retainer besides the set screw and nut?


I'm not familiar with that lathe .  There has to be some sort of retainer to keep the gear assembly in place. though.   On my lathe, there is a screw and washer threaded into the shaft from the outside.  My hand wheel is pinned but you shouldn't need to remove the hand wheel and its gear to remove the bent assembly.


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## RJSakowski (Jul 8, 2020)

Manual Mac said:


> My guess someone on swing shift did it.



Something may have been caught between the pinion and the rack while using power feed.  An unstoppable force meeting an immovable object would more likely have taken out gear teeth.


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## Tim9 (Jul 8, 2020)

What kind of lathe is it.

fwiw....bent shafts sometimes can be easily fixed by heating until it just begins to turn blue. Mount the shaft in v-blocks. Mount with high spot pointing upward. And locate the high spot pointing upward directly under a press. An arbor press would be ideal but I’ve used a hydraulic press on the last two I did.
So heat it till it’s blue. I used two small portable plumbing propane torches. Once it just discolors to a blue tinge....and we’re only aiming for the bent area to be blue, not the entire shaft. Use the press to then straighten the shaft.
    FWIW....It seldom is going to come out perfect. But, what you will have is a fairly straight shaft. In your case, you’ll have a shaft in which will allow you to take measurements of the shaft.....then put the lathe back together.... and then use the lathe to make a replacement. It may come out good enough to forego making a replacement. I’ve had good luck doing a couple shafts like this. Now I’m not talking about large diameter shafts like the boat driveshafts Kieth Fenner straightens. I’m talking about shafts like you have there. About 1/2” diameter.


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## 4ssss (Jul 8, 2020)

There's probably a taper pin there somewhere holding that


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## WobblyHand (Jul 8, 2020)

Hand wheel didn't want to come off because of this.


Yes that is a gouge.  The real dimple is present as well.  I didn't do that. The gouge, that is.

Now to remove the bent shaft.  Tried using a punch. Nope, going to need an arbor or something like that.


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## WobblyHand (Jul 8, 2020)

Tim9 said:


> What kind of lathe is it.
> 
> fwiw....bent shafts sometimes can be easily fixed by heating until it just begins to turn blue. Mount the shaft in v-blocks. Mount with high spot pointing upward. And locate the high spot pointing upward directly under a press. An arbor press would be ideal but I’ve used a hydraulic press on the last two I did.
> So heat it till it’s blue. I used two small portable plumbing propane torches. Once it just discolors to a blue tinge....and we’re only aiming for the bent area to be blue, not the entire shaft. Use the press to then straighten the shaft.
> FWIW....It seldom is going to come out perfect. But, what you will have is a fairly straight shaft. In your case, you’ll have a shaft in which will allow you to take measurements of the shaft.....then put the lathe back together.... and then use the lathe to make a replacement. It may come out good enough to forego making a replacement. I’ve had good luck doing a couple shafts like this. Now I’m not talking about large diameter shafts like the boat driveshafts Kieth Fenner straightens. I’m talking about shafts like you have there. About 1/2” diameter.


Just a 7x16 mini-lathe that I bought from LMS.


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## Tim9 (Jul 8, 2020)

Check out page 13. This is a parts breakdown of the 7 x 16 lathe.


			https://www.micromark.com/Instructions/84631lathe.pdf
		

It’s a Micromark....but most Asian lathes are pretty damned similar. It looks like you have 3 set screws going in from the side of the housing.


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## Tim9 (Jul 8, 2020)

Here’s a photo of it. Hard for me to tell....but I’m guessing it’s either set screws or an interlocking mechanism. I see there’s a ball there too. And it’s going in from the far side of where your shaft is. But from the looks of it, your may have something similar as what’s in the pic. Set screws into side of housing holding shafts.


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## Tim9 (Jul 8, 2020)

My bad....just looked at it again and those three screws are for your gib. Then there’s another with the spring and ball which is for a detent.


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## WobblyHand (Jul 9, 2020)

Have parts on order.  LMS is throwing in a new gear assembly gratis.   Still need to find a way to press the shaft out. Wheel pullers don't work very well if the arms are asymmetric.  Would a cheap 1 Ton arbor press work?


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## Tim9 (Jul 10, 2020)

I wouldn’t buy an arbor press for that. Go to the hardware and buy a  piece of  or 1” pipe. Not copper,  a  piece of 6” long black iron pipe .
Slide the shaft In the pipe and rest it on concrete. As long as the pipe is resting flush against the cast iron housing....and other end flush against the ground....you should now have a pretty stable support to drive the shaft out .


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## WobblyHand (Jul 16, 2020)

Probably should have known better...  Cheap vise vs pin, vise loses.    Used an impact socket as a spacer, and a short piece of 1/4" O1 rod to push the pin out.  Result: broken cast iron vise nut in two places.  Drat.  For the record, it was a 5" Central Forge vise that was in my father's garage.  Not crying too much, since the fit and finish on that vise really was awful.  But, it's not good to be down one vise. Still have my 4" Sheffield vise.  Fortunately, the Sheffield was slightly too small, (to fit the socket, apron, pin stack) or it may have suffered the same fate.  Never realized the nuts were cast.


On the positive side, I received all the parts from LMS, including a replacement gear assembly.  Next I'll try a punch and the impact socket with a big hammer.  If that doesn't work, I'm going to farm it out.  Don't have a hydraulic press, nor space to put one.  What's been revealing to me is that I've been thinking that, "gee that would be easy to do, if I had a working lathe...", while trying to repair the lathe.


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## brino (Jul 16, 2020)

Doh!
I was about to suggest using a vise as a press rather than buying an arbor press.
Now I'm glad that I did not suggest it!
-brino


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## WobblyHand (Jul 16, 2020)

In a fit of madness, I suggested it to myself!  @brino (in this case,) it wasn't your fault   Just joking...

This repair has been fighting all my attempts so far.  Going to go nuclear and get the the big fat hammer!  (BFH)


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## WobblyHand (Jul 16, 2020)

2.5 lb head BFH did not produce measurable results.  Can't hold everything still enough to get more than a single hit.  (And not hit myself!) Pin really hasn't moved.  I put a 3/8" thick piece of 1144 on the ground (asphalt driveway), then the heavy wall impact socket, then the cast iron housing with the pin sticking towards the ground.  With the punch centered on the pin, hit it with the BFH.  Multiple times, nay, lots and lots of times, still nothing.  Obviously need to try something different, but am not sure what.


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## brino (Jul 16, 2020)

if these were fixed together with a lock-tite, perhaps heat can break that bond.

heat one and cool the other?
or cool the whole thing(freezer), and then carefully heat the housing

-brino


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## Tim9 (Jul 16, 2020)

If there’s no locking pin anywhere then I’d lean toward Bruno’s suggestion and heat it. Whenever you work on older machines always assume that there’s a chance of Loctite. Heat to about 250 degrees and let cool. That’s usually enough. 
fwiw....double check you don’t have a locking pin anywhere. That diagram isn’t necessary same as yours. One never knows. Use a flashlight and look for any round spots of different colors which may be a roll pin.


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## WobblyHand (Jul 16, 2020)

My parts diagram does not show any pins.  When asked in an email, Little Machine Shop just said to press the shaft out. 

I can heat the apron.  First I have to remove the lead screw half nut assembly.  Along with the little gib.  No need to cook that, or the grease that's there.  Got to check if we have a junk toaster oven to try out this half baked idea.


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## Tim9 (Jul 16, 2020)

Loctite says 250 degrees. Stick it in a preheated oven at 275 to 300 degrees for 45 minutes. That should do the trick. And just turn oven off....let it cool overnight in the oven. Don’t want to risk cooling cast iron too quickly.


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## WobblyHand (Jul 17, 2020)

No spare toaster oven.  Not been feeling to well this past week, so not going out "there" to find one.

Since I've disassembled everything on the lathe apron, could I partially mill or drill out the pin?  The new pin mikes out at 0.316" on one end and 0.31375" on the other.  The 0.316" section is about 0.4" long, and it appears to be the part that presses in the apron. The 0.316" end will not fit through the gear assembly, but the longer 0.31375" diameter part does.


Not sure how to center a drill, through...  Not much to center on.  Maybe I could eye a 0.25" end mill down the middle. Hopefully I could then drive the pin out.  Or is this a bad idea?


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## WobblyHand (Jul 17, 2020)

Not a bad idea, it turns out, although I did lose an end mill doing it.  Breaking the mill, was my fault.  Tried to plunge mill with a 0.250 end mill.  For some reason it didn't want to cut at some point, pushed it a little further and pop goes the carbide end mill.  I was withdrawing the mill after going 40-50 thousandths, cleaning off the fine chips and plunging back in.  After cleaning up the carbide carnage, I used a cheap carbide 1/8" end mill to drill deeper.  This time, I maxed out the mill RPM.  Should have done that with the 0.250" end mill, but forgot.  Yet another expensive lesson.  The 1/8" cutter cut to depth easily.  Then I followed it up with a cheap 0.25" HSS drill to depth.  Followed that drill with a 17/64" HSS drill.  Moved the mill table over to the side and tapped out the pin with little effort.  Success!

After some cleanup, I look in the hole and find some white paint - the same color as the outside.  Maybe that's why it was really tight. Other than that, the bore is clean, my drilling didn't touch the bore.  Somehow I have to strip that paint without messing up the bore. Anyone have recommendations for what strips off Chinese paint on mini-lathes?

Following that, need to repaint and "assembly is just the reverse of disassembly".


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## Tim9 (Jul 17, 2020)

WobblyHand said:


> No spare toaster oven.  Not been feeling to well this past week, so not going out "there" to find one.
> 
> Since I've disassembled everything on the lathe apron, could I partially mill or drill out the pin?  The new pin mikes out at 0.316" on one end and 0.31375" on the other.  The 0.316" section is about 0.4" long, and it appears to be the part that presses in the apron. The 0.316" end will not fit through the gear assembly, but the longer 0.31375" diameter part does.
> View attachment 330642
> ...



well....not sure why I didn’t see your reply but I replied and then saw success. Good for you. And...I didn’t know you had a mill. Anyway....just ignore the rest.

A propane torch would work fine to heat up the shaft.
You just need a drill bushing. Steel is best but who knows...a wooden dowel would work in a pinch. Center drill ....Using a 1/8” drill bit a small piece of 3/8” dowel about 3/4 long .  Put that in a drill and make a small taper on one end by holding a file against it. Now you have a drill bushing. Put that in the recess of the bent shaft. Looking at the picture, it looks like you have a small recess.
Now you have a drill bushing to guide your 1/8” drill bit. Get a couple of good cobalt drill bits because I’m guessing that shaft is hardened. Use oil also when drilling.
once you center drill about 1/2” in.....then go with a 1/4” drill bit. And then 5/16”.  And then 11/32”
At that point it should come out.


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## WobblyHand (Jul 17, 2020)

Maybe some forum time shifting / tomfoolery?  I have some walnut shell media - going to blast the apron tomorrow to get it ready for paint.  It's definitely looking sad after all this work (beating!) on it.  From what I understand from engine work, walnut shells don't significantly affect dimensions of iron, but do remove paint.  If anyone knows otherwise, please let me know soon!


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## WobblyHand (Jul 21, 2020)

Walnut blasting cleaned up the apron nicely.  Found a local machine shop to press in the new shaft into the apron.  Supplied him a bushing to use as a backer.  It was a 2" diameter disk of 1018 that I fly cut flat with my new Sherline flycutter.  Came out well considering I ran it too slow on one side.  Upping the RPM improved the finish a lot.


The disk was smaller than the smallest U on the shop's arbor press.  That arbor press was big!  The machinist reached way over his head and pulled the lever down and the pin was pushed in with no drama or effort.  Best part, it was gratis!  I tried to pay him, (twice) but he wouldn't take anything. He just said, see you next time...

Test assembled everything onto the lathe.  Everything fit   

Next week, when the paint arrives, I'll paint the apron, and do the final adjustments.  Have little cork stoppers and dummy screws to plug all the holes for paint.


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