Lathe Back Gear Question

[Murgie]

Hi Greg, my first post here also. Is it possible to find a gear like that busted gear at Boston Gear? If so, perhaps machine off the busted gear and press, braze or whatever you decide to marry the two pieces back together. I am assuming you will still have the ability to use your lathe with that gear removed.

Hhmm, ok. I have sent a few pictures to a tech person with Boston Gear, he thought it looked like a pressed on gear. I thought it looked like a one piece..... I will NOT try to use a gear puller then .
I am at a little bit of a loss now as far as what to do...
Thank you again 4gsr, you saved me a lot of grief I am thinking.

 

[roadie33]

If you do find a gear with the right tooth and pitch you can always bore the ID to a press fit on the shaft, after machining off the old gear.

 

[pdentrem]

That is what I would do. Cut off the old gear and press on a new gear.
Pierre

 

[Dorn]

That is what I would do. Cut off the old gear and press on a new gear.
Pierre

If you can find a replacement gear, that would be the easiest thing to do. If you can't find a replacement it gets more complicated.
1) Take the back gear shaft to a welder and have them build up the area of the 5-6 broken teeth with brazing rod.
2) Make a template of the tooth form from some of the "good" teeth.
3) Gash out a rectangular channel that is approximately the width of the base between teeth with (depending on what you have) either:
A) milling machine with the shaft mounted at an angle so the slot of the helix is in the X or Y direction
B) shaper or shaper attachment on your lathe (again the back gear shaft is mounted at an angle)
or
C) hack saw with multiple blades.
4) File the teeth to the appropriate shape using the template you made in 2).

The fact that it is a helical gear helps in that you don't really have the get the tooth shape as accurate as you might think. If the brazing is well done it will be stronger than the cast iron and will wear at about the same rate.

 

[4GSR]

Dorn,

You are on the right track of fixing the gear without buying a new back gear from the manufacture or making an new back gear from scratch.

This gear will be a trick to get the teeth cut in line with the mating teeth, but can be done.

You could splice a standard straight cut tooth gear in place of the existing gear. Then replace the mating gear with a standard cut gear, too. It will require some machining to get it to fit onto the lathe spindle.

 

[Greg Hudgins]

Thank you everyone!!
I had been thinking about grinding the gear off and looking for one to press on. But, the welding option also sounds good. I will take the back gear to a friends fab shop tomorrow and see what he thinks, as far as welding it up. If I had to use a file and/or hack saw to re-do the teeth, I think that I would do it . My other issue is that my Bull Wheel (the mating gear) is also missing a few teeth. It looks like some one may had dropped something into the gear box during a threading op, and what ever it was landed onto the gears .
Another question though, the smaller gear that I am looking to replace, if it was removed (ground off) would the back gear still work? With just the larger gear being used? In the picture, removing the yellow, and just using the gear (orange). And a follow up question, the smaller gear, is it just to remove the chuck?
Thank you all for helping me with this.

 

[chevydyl]

Those gears have nothing to do removing the chuck, sometimes I leave my lathe in direct drive and put it in back gear to remove the chuck if it's tight after heavy turning

 

[JimDawson]

Another question though, the smaller gear that I am looking to replace, if it was removed (ground off) would the back gear still work? With just the larger gear being used? In the picture, removing the yellow, and just using the gear (orange). And a follow up question, the smaller gear, is it just to remove the chuck?

No, the back gear would no longer work if you grind off the small gear.

When in back gear, the power flow is from the pulley to the left small gear, to the large gear, to the small gear on the right, then to the large gear on the right which is coupled to the spindle.

 

[4GSR]

You should never use your back gears locked in to remove the chuck. That is probably why the teeth are missing from the smaller gear. You should wedge a piece of hardwood into the gear teeth or build wrench that clamps to the back end of the spindle, to remove the chuck.

 

[T Bredehoft]

Thank you, Ken. When I was working, all the chucks had cam locks to secure them to the spindle. Now I don't have that facility and didn't realize the possibility of gear damage. I'll revise my method of chuck removal.