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Old 12-23-2005, 08:54 AM
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broke lathe gear tooth ..help

i broke a tooth on the gear closest to the chuck. its a logan 12x 20 " big old metal hobby lathe.

what can i do ? i dont want to try to weld back the tooth. i need a new gear.

help?

merry christmas

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Old 12-23-2005, 10:21 AM
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A replacement gear is probably not economical/available. When I was doing machine repair. I would drill and pin the broken tooth area. Drill into the tooth root with a drill a few thousants smaller than your pins. Drive pins into holes. Trim pins for length and trim sides for profile. Works very well.

I have also built up the area with a MIG weld then cut a tooth profile with a thin cutoff wheel in a die grinder.
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Old 12-23-2005, 11:08 AM
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spinn,

I agree with the ideas BOBCRMAN explained. These can be done without taking the lathe apart.
If you have a milling machine you can use, here is another idea.
Remove the gear from the lathe. This is kind of time consuming but in order to repair the broken tooth it has to come out of the machine.
Place the gear in the milling machine with the broken tooth at the top.
Using an end mill cut away maybe three or four teeth total.
Then cut and fit a piece of metal to fit the area you have removed. Make sure the new metal is taller than the old teeth so you can cut them to be the correct height.
Now to keep this new patch in place drill and tap three or four holes through the patch and into the gear. Then using a center drill make enough counter-sink so a flat headed screw can be installed.
Now using the red loc-tite on the patch and the screws attach the patch to the gear. Let this set over night so it will be good and set before you start machining anyhing.
Put the gear in indexing head with an old tooth facing the bottom of the end mill. Take small cuts by rotating the indexing head os the gear turns under the cutter. Keep doing this until the height of the patch is the same as the old teeth.
With the gear still in the indexing head, set the hand crank onto the proper set of holes so you can cut the same number of teeth that are on the gear now. You may have to make your own tooth cutter so as to match the old teeth but if you take your time this can be done.
This is the best way I have found to repair the bullgear without worring about warpage from welding heat.
With as many students using my old lathes, I have had to do this repair more than once believe me.

Scholman
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Old 12-23-2005, 11:16 AM
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Spinn, I have had a lot of success with building up the area with a brazing rod and then milling a new tooth but on something like this you could even cut the tooth with a cut-off wheel and grinder as has already been mentioned if you cannot cut the tooth on a mill. I assume the gear is cast iron? If so then if you decide to weld it you will need to use a machinable nickle rod for cast iron, MAKE SURE it is machinable, or braze it with a bronze brazing rod and torch then you could take it to a machine shop if you don't have the means to do it your self. If you weld a cast iron gear with a steel rod or MIG then it will be so hard at the weld/base junction that it will not be machinable. There is nothing wrong with doing this type of repair, it is done all the time.
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Old 12-23-2005, 01:20 PM
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lathe gear

hi there,go to Ebay.com,at the top of the home site,there is a place to put in what youre looking for, put in lathe parts... then hit search,....theres a bunch of parts on the e bay site.
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Old 12-23-2005, 02:03 PM
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thanks for the ideas guys. i was hoping to get a new one. the bull gear was already repaired once with the mig . i like the idea of using pins to creat a profile.

i will probably weld it again. and gring it to shape. i dont really have access to a mill.
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Old 12-23-2005, 03:21 PM
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Spinn, I would almost bet those gears are cast iron and if that is the case a MIG is a real no-no because of the incompatibility of the steel wire with with the cast iron. It would be much better to use a Nickel rod or braze it with a bronze rod. If you heat the gear to about 400 deg. before welding warpage should not be a problem. I do this on mining and farm equipment quite often and just about a month ago I welded two teeth side by side on a 6" diameter cast gear using a machinable nickle rod and after machining about the only noticeable difference was the different color of the new teeth.

Last edited by oldred; 12-23-2005 at 07:10 PM.
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