12-24-2010, 03:38 PM

Hello, I'm a new member here. I am restoring an old car, and recently acquired an old lathe to help with my restoration. The bull gear has damaged teeth with a repair that was made. The photo above shows the kind of damage to which I refer. What is a person doing wrong to cause this kind of damage? I am planning to replace the bull gear, and as a newbie to machine work, would like to avoid damaging the replacement bull gear. Thanks in advance for your expert opinions.

12-24-2010, 03:40 PM
Someone put it in back gear to remove the chuck.

12-24-2010, 03:42 PM
Someone put it in back gear to remove the chuck.

Yeah, seen that happen! (and please don't ask where).

12-24-2010, 03:58 PM
Could that damage happen by leaving the bull gear pin in, with the bull gear engaged, and attempting to turn on the lathe?
Just wondering.

j king
12-24-2010, 04:39 PM
machine wouldnt have enough ass to do that. A dumb ass would..

12-24-2010, 05:05 PM
Note that a repair is already evident (3 pins ground to tooth form) near the two teeth that are missing.

Pounding on the chuck with the lathe in back gear is one cause; however I've also heard of folks leaving the lathe with both back gear and high speed engaged and stripping teeth. This lathe (with 2 v-belts) might have just enough locked rotor power to do that).

Could also be that the repair to one tooth was poorly done with either cracks or progressive damage to the other two (now departed) teeth.

12-24-2010, 05:27 PM
It could also result from a very hard crash such as a chuck jaw catching on the tool post or top slide while in back gear. It usually takes some sort of shock to do that. Either trying to remove the chuck by hammering with a lever or a crash or something stupid like a stray piece of metal making it's way into the gears. You aren't likely to break cast iron gears when removing the chuck in back gear if you smoothly apply steady pressure to a wooden pry bar between the jaws. The gears have enough snoose to tighten the chuck up so they will also withstand the same amount of force in the other direction as long as there are no shocks.

12-24-2010, 05:32 PM
Unrelated but, I really like the early 'Link belt' :)

12-24-2010, 05:35 PM
Ditto Evan, Peter

12-24-2010, 08:05 PM
I have had threaded stuck chucks and jammed them up and reverse bull gear and they always come loose,. never had gear damage like that one. I have to suspect non conforming material used to make the gears or they wwere damaged when you bought the machine. If you make new ones 8640 material case hardened .060 to a hardness of R c 59 to 62 rockwell. This is what a engineer told me to make my last set of gears to for a replacemnt hypoid austrian thing I fixed.

12-25-2010, 06:15 PM
Someone put it in back gear to remove the chuck.
that is exactly what the bull gear on my 9"sb looked like after i did,nt succeed in removing the chuck lol

12-26-2010, 01:04 AM
Thanks guys! I suspect it was a stuck chuck at one time. I'll be cautious to not get into that predicament in the future. Amazing how it does not seem to affect how the lathe runs. I will replace the bad gearing though.