Pete.
Member
- Messages
- 14,136
- Location
- Kent, UK
I have a denford lathe that has a problem with the screwcutting gearbox. The problem is caused by their stupid arrangement for engaging the gear clusters, there's a lever on the side for engaging the gears. The lever sits on a spline and the other end has a gear that works a rack. The gear and spine have odd teeth so there are a LOT of combinations to try to get the engagement right. This is made worse by the fact that the front plate can't be removed without removing the lever, but you can't see the engagement without removing the front plate, and the holes that the plunger on the lever locates in are ON the front plate.
Anyway what this boils down to is that the last time I had the plate off I got the gear clusters only half-engaged, so when I was working the lathe hard it broke a tooth and chewed up several gears including one long spline gear.
I got a new gearbox, but for a slightly older model. Everything fits except the spline gear which is too short on one end, it has a different outboard cluster arrangement. Here's how I fixed it.
First I decided where the join was going to be and parted off the wrecked shaft.
I parted off the replacement shaft, then drilled it and reamed it to 1/2" bore.
After that I machined the stub end to 0.5015" to give a thou and a half interference. Coated that in high strength threadlock and cut a small sliding-fit on the end to make sure it started properly. I drilled a 2.5mm hole in the bottom of one of the splines into the bore, to let out any air or trapped threadlock. Set it up in the press.
Pressed the stub home up to the shoulder. It took 3.5tons which I was pleased with. If it had been much less I would have considered pinning through the cross hole.
And that's it. Set up in the lathe and I got 1 thou of runout. Not worried about that because the shaft is already a 0.002" undersized from normal use, it's 30 yrs old and the shaft runs straight on a cast iron bearing. I cleaned it up with a bit of emery and assembled the shaft into the gearbox.
Anyway what this boils down to is that the last time I had the plate off I got the gear clusters only half-engaged, so when I was working the lathe hard it broke a tooth and chewed up several gears including one long spline gear.
I got a new gearbox, but for a slightly older model. Everything fits except the spline gear which is too short on one end, it has a different outboard cluster arrangement. Here's how I fixed it.
First I decided where the join was going to be and parted off the wrecked shaft.
I parted off the replacement shaft, then drilled it and reamed it to 1/2" bore.
After that I machined the stub end to 0.5015" to give a thou and a half interference. Coated that in high strength threadlock and cut a small sliding-fit on the end to make sure it started properly. I drilled a 2.5mm hole in the bottom of one of the splines into the bore, to let out any air or trapped threadlock. Set it up in the press.
Pressed the stub home up to the shoulder. It took 3.5tons which I was pleased with. If it had been much less I would have considered pinning through the cross hole.
And that's it. Set up in the lathe and I got 1 thou of runout. Not worried about that because the shaft is already a 0.002" undersized from normal use, it's 30 yrs old and the shaft runs straight on a cast iron bearing. I cleaned it up with a bit of emery and assembled the shaft into the gearbox.