Gear won’t fit back on shaft

[John_Dennis]

I have my lathe spindle removed and need to reassemble it. The problem is that the gear which is keyed, is a press fit not a slip fit and it is impossible to perfectly align the keyway. You can see in the photo where the gear was damaged by forcing it over the key. I see two options, I can either heat the gear to expand it and hope I can reassemble the spindle before it shrinks or I can cobble together an ID grinder using the mill and rotary table. The shaft is 1.9695 and the gear is 1.9680 Obviously, heating the gear is easy and low risk other than burning my fingers but I am uncertain if it will expand enough. The gear seems to be hardened and the ID may have been ground, it has a very nice finish. Any ideas or advice?

 

[Jim in Wisconsin]

I think warming it up and working fast is the right approach. Make sure you don't get it on backwards!

 

[woodchucker]

Don't warm it up. You need to get it off when disassembling for service of the spindle.
Take a flap sanding disk and lightly sand it. I have a bunch of different sized shafts, that have a split cut in with a hack saw.
I take AL Oxide cloth backed abrasive and run it in a die grinder, drill or mill or drill press. you just want a snug fit, that can slide on without too much effort. If you heat it, how will you get it apart?

 

[Jim in Wisconsin]

It seems like it was designed to be a press fit - getting it off is easy with a press, aligning the key when putting it on is trickier.
I would think the manufacturer did it right, I know I wouldn't grind anything out of the bore of the gear or off the shaft diameter.

 

[John_Dennis]

It seems like it was designed to be a press fit - getting it off is easy with a press, aligning the key when putting it on is trickier.
I would think the manufacturer did it right, I know I wouldn't grind anything out of the bore of the gear or off the shaft diameter.

The manufacturer's instruction for disassembly do not describe using this much force to remove the spindle. I have never seen a press fit part that needed to be blindly aligned with a key.

I can remove the spindle including this gear using a threaded rod as a puller, this is how I got it apart the first time.

 

[John_Dennis]

I think warming it up and working fast is the right approach. Make sure you don't get it on backwards!

My math is very bad with this sort of thing. Will heating get me more than .0015 and how hot would I need to get it?

 

[piper184]

Purely a guess here, but if it is supposed to be a press fit, it would probably be a very light press fit, otherwise there would be no need for the key. Also, it probably shouldn't be a slip fit as that could cause fretting between the shaft and the gear.
Does this need to be assembled in the headstock or can it be done before the spindle is installed?
Did you have to use a press to get it apart? How much force did it take?

If it were mine, I would first make sure that there are no burrs anywhere on any of the parts, especially the key to gear fitment. Then using nothing more than a red Scotch-brite pad, make sure that all the debris is cleaned off of the parts. Even a thin film of varnish from dried oil will cause friction and binding. Clean and shiny, no burrs or debris..

I wouldn't be afraid of warming up the gear to say 300F and maybe putting the spindle in the freezer for an hour or two. 300 won't hurt the metal structure and can be handled with heavy leather gloves. If it truly supposed to be a light press fit, this should give you clearance to slide it together and when it is normalized, it should be tight, but not so tight as to need a heavy press to get it apart.

Best of luck and let us know how it turns out.

 

[Uglydog]

.... make sure that there are no burrs anywhere on any of the parts, especially the key to gear fitment. Then using nothing more than a red Scotch-brite pad, make sure that all the debris is cleaned off of the parts. Even a thin film of varnish from dried oil will cause friction and binding. Clean and shiny, no burrs or debris..

I wouldn't be afraid of warming up the gear to say 300F and maybe putting the spindle in the freezer for an hour or two. 300 won't hurt the metal structure and can be handled with heavy leather gloves. If it truly supposed to be a light press fit, this should give you clearance to slide it together and when it is normalized, it should be tight, but not so tight as to need a heavy press to get it apart....

Warm it evenly.
Do you have an oven available (don't get in trouble in the kitchen)?
I 2nd vote on the freezer.

Daryl
MN

 

[mmcmdl]

All of the above , and grind a lead on the key to make things easier . Bearing heater and dry ice would be my way to do this .

 

[Forty Niner]

I have my lathe spindle removed and need to reassemble it. The problem is that the gear which is keyed, is a press fit not a slip fit and it is impossible to perfectly align the keyway. You can see in the photo where the gear was damaged by forcing it over the key. I see two options, I can either heat the gear to expand it and hope I can reassemble the spindle before it shrinks or I can cobble together an ID grinder using the mill and rotary table. The shaft is 1.9695 and the gear is 1.9680 Obviously, heating the gear is easy and low risk other than burning my fingers but I am uncertain if it will expand enough. The gear seems to be hardened and the ID may have been ground, it has a very nice finish. Any ideas or advice?

An excellent tool for warming something like that gear or a bearing is the induction bearing heater. Used them many times in a repair shop a long time ago.

Picture for reference, there are many brands. Just clipped this from a search: