repairing a gear

savarin

savarin

Active User
H-M Supporter Gold Member
My next door neighbor has an old winch in excellent condition except 1 tooth has broken off one of the 6" dia steel gears.
Spares are unavailable.
Would it be feasible to build up the missing tooth with weld then use a ground profile cutter to shape the tooth back in?
Thanks
 
That would work if you know what the gear is made of. I would try and drill and tap it where the gears is broken put some good screws in it and file it to shape. You could always braze over the pins for a better fit.

Paul
 
Franz© said:
FIRST, you need to determine if it's a cast iron gear or a stamped steel gear, both are pretty common in small winches.

If it's steel you can generally make a graphite form and weld a new tooth right onto the gear that will only require a little filing to finish.

Cast Iron generally works best by inserting a couple steel pins and filling the tooth in with a bronze buildup following the necessary pre heating to preserve the gear from cooling fracture. You can even do a carbon form on one side of the build if you use some caution.
Click to expand...

Hi Franz,
what is a graphite form?
This gear is only about 6mm thick.
 
what about making a new gear ?

In what ever material the winch justifies..

just thinkin out loud ,,,,
 
I have sent gears out to a pro who welded it up and I had it re-cut. So it can be done. I would think you may want to ask this question in the welding forum and ask a welder.. I just Googled "can I weld gear tooth" and found several posts about how to do it. I would think the key is to grind out the old tooth deep enough so when the weld mixes with the original metal it doesn't get hard.
 
FWIW ..cast iron gears are are more "fool proof" repaired by brazing & covering w/ lime , ashes ,or sand for cool down ...the heating up process prior to brazing temperature provides a pre heat ....i have done maybe a 1/2 dozen by filing a shallow dovetail at the root , filling w/ braze & recutting the tooth ,both w/ commerciall gear cutter & fly cutter ground to exiisting tooth form ..dividing head or rigged apparatus using exisiting teeth for indexing ...bronze tensile strength is more than equal to cast iron ...so far , no failures .....the problem w/ welding cast iron is either "cooking " the adjacent metal or causing brittleness.
case in point ....received a logan c/shaft that had been broken in transit ....FIVE breaks , not the previous welds but on either side of PREVIOUS welds ..."cooked" ... into the scrap pile ......the high carbon content simply caused embritlement W/OUT proper pre /post head....olde tyme auto block welders used a pre heat furnace, torch , & cast iron ,& a post weld heat slo down , allowing annealing .....
that said i have gotten away w/ stitch welding cast iron a couple times .....( lay a quick bead from one end , wait till cooled & lay a bead from opposite end , again wait till cool etc......using an expensive nickel rod & peening as weld cools helps to allow for contraction w/ out incipient cracking ...
just my experience ....INFREQUENTLY welding over 40 years .....& relearning each time .....instead of 40 yrs experience i have less than one years experience 40 times !!!
best wishes
doc
 
savarin said:
My next door neighbor has an old winch in excellent condition except 1 tooth has broken off one of the 6" dia steel gears.
Spares are unavailable.
Would it be feasible to build up the missing tooth with weld then use a ground profile cutter to shape the tooth back in?
Thanks
Click to expand...

My dad repaired a broken gear in a David Brown tractor by filling the missing teeth with braze. He then filed to shape. It held for 30 years until a bushfire came through Central QLD and destroyed the tractor.

Paul.
 
For only one tooth missing, the following method may be of use to you:
  1. File the root of the missing tooth flat - only enough to provide a good reference surface. If this means filing into the gear to a point below the root, that's okay, but then you can skip step 2.
  2. File a slight bevel on each side of the root
  3. Cut a piece of keystock to the correct width to match the root of the tooth. The length should match the width of the gear. File the new piece as necessary to properly fit it to the gear.
  4. Braze the piece of keystock to the gear.
  5. Hand file the keystock to the proper shape of the gear tooth.


Another method commonly practiced is to do this:
  1. File the tooth root flat.
  2. Drill a hole into the gear, maybe an 1/8" in diameter. Might be best to drill undersize, then use an undersize reamer to enlarge the hole to 0.124"
  3. Press a 1/8" pin into the hole - if it goes too hard, you might have to sand the pin down a bit to get it to fit - you want a good snug fit, but not so tight as to cause the cast iron to crack (if the gear is made of cast iron). A light drive fit would be good.
  4. Cut a piece of keystock to the correct length to match the width of the gear.
  5. Drill a hole in the keystock, same size as you made in the gear - a light drive fit is desired here.
  6. Drive the keystock onto the pin, then line it up straight with the other gear teeth
  7. Braze the keystock to the gear.
  8. Using a file, shape the keystock into a gear tooth to match the other teeth.

All of this file work might sound like a lot of work, but you will find that it is much easier than you might think, and will go quite quickly.
 
Lots of ideas, thanks guys.
I dont have an oxy set so braze is out the windo.
My new welder arrives this week with manual, mig and tig so I might give the tig a go.
The teeth are quite small, about the size of change gear teeth so and it is steel so I think I will attempt to tig the gap and then file to shape.
No idea when as I have too many of my own projects to finish first but it never hurts to have another up the sleeve.
 
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