How to repair gear keyway

boeingone · Thu Jun 11, 2015 10:46 am

I have a gear from a lathe that needs to be repaired.
There is a crack along the keyway.
The manufacturer wants $975 dollars for this gear. Ouch!
Any tips on how to grind and what to use to weld it.

Thanks

ldbtx · Thu Jun 11, 2015 1:19 pm

Any chance of picking up a used gear on one of the lathe or machining forums?

LDB

Thu Jun 11, 2015 6:42 pm

I'd do a little NDE to see the full extent. A good long soak in lacquer thinner or MEK, blow dry and hot dry, then dye penetrant. If the crack extends less than about a third of the length of the gear teeth, I'd consider a stop-drill, then bevel with a dremel, then weld with a Ni-55 type rod with TIG (full penetration, and leave the stop-drill hole, then square up the keyway).

If the crack extends more than half the depth of the gear, I'd consider an acid-soak for pre-fluxing, then flux and silver-braze it (and, yes, stop-drill it), clean it up, and hope for the best.

I agree with taking a long search on machinist forums for a used part from someone scrapping a similar lathe as the long-term solution.

Another alternative is to find an eager machine shop in your neighborhood, perhaps a technical college, and have them duplicate the part. I recently had bushings made at a regular machine shop for an old Buffalo flywheel punch. The guy with the parts wanted us to spend upwards of two grand to ship him the flywheel, do a bunch of work we didn't request, and install the bushings. I sent a drawing down the road, and about $250 later, I had new bushings.

Steve S

pigpen60 · Fri Jun 12, 2015 2:13 am

the gear isn't timed is it?

TRACKRANGER · Fri Jun 12, 2015 5:21 am

pigpen60 wrote:the gear isn't timed is it?

If it's a lathe gear, I certainly doubt it. It's probably run from the spindle shaft and connected in mesh with other gears to the screw cutting gearbox and lead screw / feed screw. From the looks of it, it's had some pretty rough mesh engagement actions, being used like a dog clutch.

Braehill · Fri Jun 12, 2015 7:41 am

I'm not saying that this gear is made this way but a lot of gears now are being made from sintered pressed metal and other pressed metals. I'm not sure if the can be welded with any positive results or not. I know that the gears that I ordered for my little Sears (Enco/Emco?) lathe were indeed pressed metal. Just something to consider.

Len

Rick_H · Fri Jun 12, 2015 5:53 pm

Just my $.02

If it can be welded I'd weld it up including the old key area, bore/hone it back to proper size and broach the new key 90 degrees out, this way that stress isnt right on the repaired area.

ESENTI · Sat Jun 13, 2015 3:03 am

Dear Rick , the idea is great but this thing is very very hard how could you cut the key again . It is heat treated to very hard
so machining is almost impossible .

Mike · Sat Jun 13, 2015 8:15 am

Len welcome to the forum.

Braehill · Sat Jun 13, 2015 2:33 pm

@Mike,
Are you kidding.

Len

GreinTime · Sat Jun 13, 2015 7:42 pm

@braehill
Welcome to the forum

motox · Sat Jun 13, 2015 7:58 pm

breahill
are you a twin or are you doing it
with mirrors? lol
craig

LtBadd · Sun Jun 14, 2015 12:09 pm

GreinTime wrote:@braehill
Welcome to the forum

Hello Len, and welcome to the forums, did you pay money to start with such a large post count?

Mon Jun 15, 2015 10:04 pm

I apparently missed this joke.

I am, so far, grateful

Steve S

Braehill · Tue Jun 16, 2015 10:53 am

Steve,
Post 9 and 10 should clear things up for you.

Len

Tue Jun 16, 2015 7:29 pm

Mike wrote:Len welcome to the forum.

Okay, Len, I get the joke now.

Andover Mike was a subject of discussion some time ago, for posting nothing more valuable than "Hi!"

I think this sums up his approach to the forum.

Steve S

TRACKRANGER · Tue Jun 16, 2015 10:05 pm

Getting back on track, I wonder how the poor O/P is getting on with the repair....