RobCox
Member
- Messages
- 488
- Location
- Cambridge, UK
I have a smallish bandsaw I bought from Axminster a few years ago. Up to now it's behaved impeccably. It lives tucked in a corner of the workshop and gets dragged out when the effort of shifting a tool cabinet and pulling the saw out is worthwhile. I didn't realise how much I use it, until a couple of weeks ago when it packed up. This is the machine, shown here undergoing some abuse cutting through a slice of rod about an inch bigger than its "maximum" capability:
It took well over an hour to get through, with the workpiece having to be rotated twice. The next time I used it, it scratched the surface of a piece of 1 inch steel rod then stalled. There then followed some disassembly to find out why. The answer was in the gearbox:
The teeth on the wormwheel had been abraded away to leave thin remnants, one of which had folded over and caused the worm to jam. Judging by the gold slurry in the bottom of the gearbox the wear has been going on for some time. By the time I'd cleaned it up to disassemble I looked like a messy makeup artist on the set of "Goldfinger"
.
At this point, if I could have bought a replacement off the shelf I'd have gone down that route. Spares for these cheapo chinesium bandsaws don't seem to exist though, and an off the shelf wormwheel would firstly set me back about £70, if it fitted, and would need adapting anyway, so I decided I'd adapt a piece of bronze bar instead.
I stripped out the gearbox shafts (a couple of the bearings were full of brass) and measured up the worm. Mod 2, 30mm diameter. Fortunately my M300 will cut Mod 2 threads if you have a 56T changewheel. I didn't, so began a project to fix a project...
The changewheels on the M300 are splined, so to cut these on my shaper I had to make a) a backplate to mount a cheapo 3 jaw chuck onto my 6 inch rotary table, b) a keyslotting bar for the shaper clapperbox, c) grind up a 1/4 inch wide toolbit to suit the spline slots, d) drill and tap a locking screw into the side of the clapperbox to stop it clapping, and e) make an arbor to carry the bear blank while I cut the teeth on the horizontal mill. Here's the shaper in action cutting the splines:
I wanted to make the gear out of steel, but the material didn't arrive soon enough so I made it in aluminium instead. It fit perfectly on the arbor and on the lathe spindle. This is a closeup of the arbor after the splines were cut with one of the original lathe gears mounted:
and the finished gear (plus a 48T so I can cut a 30TPI thread for the project I was originally working on, the Taylor Hobson lathe restoration).
This got me to the point where I could cut the thread on the hob to make the new wormwheel.
It took well over an hour to get through, with the workpiece having to be rotated twice. The next time I used it, it scratched the surface of a piece of 1 inch steel rod then stalled. There then followed some disassembly to find out why. The answer was in the gearbox:
The teeth on the wormwheel had been abraded away to leave thin remnants, one of which had folded over and caused the worm to jam. Judging by the gold slurry in the bottom of the gearbox the wear has been going on for some time. By the time I'd cleaned it up to disassemble I looked like a messy makeup artist on the set of "Goldfinger"
.At this point, if I could have bought a replacement off the shelf I'd have gone down that route. Spares for these cheapo chinesium bandsaws don't seem to exist though, and an off the shelf wormwheel would firstly set me back about £70, if it fitted, and would need adapting anyway, so I decided I'd adapt a piece of bronze bar instead.
I stripped out the gearbox shafts (a couple of the bearings were full of brass) and measured up the worm. Mod 2, 30mm diameter. Fortunately my M300 will cut Mod 2 threads if you have a 56T changewheel. I didn't, so began a project to fix a project...
The changewheels on the M300 are splined, so to cut these on my shaper I had to make a) a backplate to mount a cheapo 3 jaw chuck onto my 6 inch rotary table, b) a keyslotting bar for the shaper clapperbox, c) grind up a 1/4 inch wide toolbit to suit the spline slots, d) drill and tap a locking screw into the side of the clapperbox to stop it clapping, and e) make an arbor to carry the bear blank while I cut the teeth on the horizontal mill. Here's the shaper in action cutting the splines:
I wanted to make the gear out of steel, but the material didn't arrive soon enough so I made it in aluminium instead. It fit perfectly on the arbor and on the lathe spindle. This is a closeup of the arbor after the splines were cut with one of the original lathe gears mounted:
and the finished gear (plus a 48T so I can cut a 30TPI thread for the project I was originally working on, the Taylor Hobson lathe restoration).
This got me to the point where I could cut the thread on the hob to make the new wormwheel.
I love seeing this level of how to do things! I'd no idea how much effort you have to go to produce such an item 
. I firstly measured everything as accurately as I could - the shaft centre to centre spacing, the OD of the wormwheel at the centre of its width, the tooth thickness at the PD and the OD and tooth width of the worm at the PD. I came to the conclusion that the wormwheel was pretty spot on so the width of the worm screw needed thinning down. Back to the lathe, pick up the threads, shave 5 thou off - which makes the pitch dia about 20 thou smaller, fit again (the makeshift puller for disassembly was earning it's keep big time), almost right, so dismount and take off 2 thou. Perfect!
A silk purse in a saws ear! 
