Removed the gear with the broken tooth from my GBC 400-1000 lathe yesterday, with some help from my brother. Approached the disassembly a bit nervously. Did not want to break or damage anything else.
First took some photographs, so I can put things back together eventually, in the correct places and order.
Then removed the chuck, then the back gears, then the large heavy plates at each end of the spindle. The cap screws came out without any drama, but the end plates required breaking free of the paint, and out of the tightly fitting mounting rebates.
Then loosened the big nuts against the internal gears, the external gears, and one grub screw.
Gradually removed the spindle by tapping the gears along the spindle with brass drifts. Pretty tight. And retrieved the little bits as they fell into the oil in the headstock.
Was finally able to lift the spindle out through the chuck end of the headstock. It is heavy. Took two of us to lift it out without damaging the outer races of the tapered roller bearings.
Then looked at the broken gear, and retrieved the tooth from the headstock oil.
Next step was to look closely at the meshing gear.
Meanwhile, I remembered a tool which might help with the inspection….
So, I have a large, hardened steel gear with at least 2 cracked/broken teeth. Options?….
- Buy a new gear. I will try, but not confident. The local importer of these particular Chinese lathes went out of business last year.
- Get a new gear made. I will get a quote.
- Make a new gear myself. Or, if all else fails….
- Machine off the teeth of the damaged gear, and the adjacent 20-30mm. Then make a new set of teeth on a ring which will be attached to the old core of the damaged gear.
- Use the lathe without that gear. This option does not appeal.
- Install a VSD and use electronic control of spindle speeds. The main spindle motor is 5HP, so it is possible.
More information required. Watch this space.
I had a similar problem many years ago. I was lucky I broke a tooth of the intermediate sharft gear and was able to get one made by a customer of mine at the time over a weekend to get me going very quickly. we did not harden it and used 4140 and it worked for many years with no problem. I still do work for this business he is a one man operation and is very good with gearcutting. If you want I can put you in touch with David for an opinion on making a replacement, he is very good at what he does.
Hi John, yes please email me the name. I have one from Melbourne, but it would be good to get a couple of quotes… John
Nice to get to use a scope without needing an anaesthetist!
I’d be having a crack at repairing the gear, although I’d bet you’d find a supplier of a new one with a google session
Hi Russell, If it was only one tooth I would be attempting a repair. But with multiple teeth involved, I am going to try to replace the gear. Nice to hear from you again. John
Sounds like you have some decisions to make.
My two cents worth: I am a cheapskate at heart so I would make a new gear and find someone with a controllable oven and case harden it using some product like “Casinite”. It is a high carbon powder that you coat the part in then follow instructions on heating cycles. The stuff works really well.
Of course having one made for you by a reputable machine builder is the most painless way to go.
Either way I am sure you will have some fun.