Lathe gearbox rebuild question

[WhoWhatNow]

I am in the middle of rebuilding the quick change gearbox on my 12” Atlas lathe and am stuck on a very simple step. I have everything disassembled and cleaned and am about to start putting the gears back on the shafts. This is my question: should the gears slide easily onto the shafts or should I have to press them on? Most of the gears use a key to lock them on the shaft. In most of the YouTube videos I have seen the gears appear to slide on easily. I can’t feel any burrs on the shaft and the gear bores all look OK. I did have to use a brass drift for disassembly. Any suggestions on how to proceed?

 

[vekster]

if they have a key locking them to the shaft then they should slide on easily .001" or 2 of clearance is ok

 

[vekster]

polish the shaft with some emery if need be.
lube everything with oil and most all should be hand assembly
make sure all bronze bushing have clean oil grooves

 

[TractorJeff]

Polished Surfaces or a hint of Rust?
I have worked on a few items over the years where the surfaces had a little rust and just polished it. I found you need to go back and polish, not sand till a mirror finish is obtained. Then use a little light oil to allow the mating surfaces to slide.
If they are keyed gears a small amount of resistance to move maybe OK as you commented, they are "keyed Gears". If they can slide on and off easily, they may slide past the keys and out of alignment.

 

[bradleykd]

You can put your gears in the oven as low as it will go (200-250*) then get them out and slide them on while they are still hot.

 

[mooseracing]

Is it tight on the shaft or tight on the keyway? I have usually found it is the latter and work form there.

 

[larry_g]

Proper fit for a gear on a shaft is slip fit, near zero clearance. If you have a loose fit then you have room for the gear to move and once it starts moving it starts to pound out the hole. These are zmack material? or are they steel. Are you talking the cluster gear set or the moving gears? If you beat them off with a drift did you upset the hub or deform the bore? Does each gear have the same tightness going on the shaft? Is one end of the shaft reduced diameter to facilitate starting the gear on the shaft?

lg
no neat sig line

 

[WhoWhatNow]

polish the shaft with some emery if need be.
lube everything with oil and most all should be hand assembly
make sure all bronze bushing have clean oil grooves

Polished Surfaces or a hint of Rust?
I have worked on a few items over the years where the surfaces had a little rust and just polished it. I found you need to go back and polish, not sand till a mirror finish is obtained. Then use a little light oil to allow the mating surfaces to slide.
If they are keyed gears a small amount of resistance to move maybe OK as you commented, they are "keyed Gears". If they can slide on and off easily, they may slide past the keys and out of alignment.

What concerns me about polishing/grinding the shaft is the gears are tight on the ends of the shaft (haven't got them on past the first 1/8"). This is the part that fits into the cast iron housing (no bushings/bearings). If I remove too much material I am worried that I will have a very sloppy fit.

 

[WhoWhatNow]

Is it tight on the shaft or tight on the keyway? I have usually found it is the latter and work form there.

Thank you for reminding me of this trick. Can't believe I didn't think of it. Looks like I will be taking some dry ice home from work today.

 

[WhoWhatNow]

Proper fit for a gear on a shaft is slip fit, near zero clearance. If you have a loose fit then you have room for the gear to move and once it starts moving it starts to pound out the hole. These are zmack material? or are they steel. Are you talking the cluster gear set or the moving gears? If you beat them off with a drift did you upset the hub or deform the bore? Does each gear have the same tightness going on the shaft? Is one end of the shaft reduced diameter to facilitate starting the gear on the shaft?

lg
no neat sig line

I pretty sure they are steel. I was thinking I may have mushroomed the ends when I removed them but the shaft fits into the gearbox housing nicely. All of the gears are very tight. The gears will only fit on one way. The shaft is only partially keyed. The gears at one end are not keyed to the shaft and one gear has an integral key.

 

[rlitman]

You can put your gears in the oven as low as it will go (200-250*) then get them out and slide them on while they are still hot.

For bearings, what I do is sit the bearing on an upturned 60W lightbulb for a few minutes.

 

[Falcon67]

Use a coffee warmer for gears, and put the shafts in the freezer for a bit - dry ice not required. I use a coffee warmer to heat side bearings before pressing on a Ford 9" carrier.

 

[richzz]

If the gears are tight on the ends of the shaft only it sounds like that they might have been hammered out at on time mushrooming the ends.

 

[BillK]

Who,
I have a 12x36 Sears / Atlas and I went through the entire gear box a couple of years ago. I don't remember having to press anything apart or back together.

I agree with you that taking anything off the shaft is a mistake if it fits the housing ok. Might just have to use a needle file and deburr the gears a little.

 

[Advan]

If you own a lathe, I'm sure you have some precision tools... Measure your bores and shafts for fit, and be sure to check for mushrooming as mentioned before. mooseracing is right about the key fit as well. Measure keyway depth and the size of the key, and check for dimpling from setscrews.

 

[matt_i]

Imo if the gear is keyed to the shaft, then a light press fit is better. Have you tried the fit without the key in place? The key could not be square or bugged on one or more faces. Also the key should be tight as well in the keyways without being something that's going to break apart due to gross friction fit. Taking off material (that was fine before) to "loosen things up for assembly" is not a good path to longevity...

As I recall the Atlas QC box uses only 1 idler gear and that's the tumbler that slides around and is pinned to the correct gearset.