Guineafowl21
Nordic Pine
One of those jobs that should have been quick.
My K3 hollow-chisel morticer used an awkward mounting system: each size of auger bit needed its own collet for the sleeve on the motor shaft. You’d have to line up the hole in the collet with the retaining screw, then steer the bit into the collet, trying to line up the flat you filed on the bit with the screw, all while trying not to jab yourself on all the sharp points.
So, I decided to replace all this with a Jacob’s chuck, mounted to the motor shaft.
So, out with the rotor and on to the lathe (sorry for focus):
Here, I’ve taken the shaft down to 0.494” from 5/8”, and am starting to single-point threadcut the 1/2” UNF thread for the Jacob’s chuck. Something not visible is the keyway in the motor shaft, which retained the original sleeve. We’ll encounter this later.
Chuck threaded on:
And a comparison to the old system. You can see the dreaded keyway:
However, the chuck wobbled and made the bit clatter in the chisel far too much. About 15 thou of runout. All apart again, and I checked the machined chuck mount, threads, the motor shaft, the chuck register and jaws, all within a thou or so of runout. There was nothing wrong with the individual bits; it was when they were screwed together the problem appeared.
After some fiddling around and general angst, I realised it had to be the keyway. The high point of the runout was always opposite the keyway, regardless of chuck position and even when trying a different chuck. So, in the lathe again I machined everything I’d done down by 40 thou or so, then MIG (technically MAG) welded the shaft all the way around. Sorry, no pics as too much desperation. Taking off the 40 thou meant I would be machining pure weld, not the weld-shaft junction. Welding all the way around, rather than just filling up the keyway, was to minimise shaft distortion.
After letting the shaft cool naturally, I just did the same again: face, centre, 1/2” UNF, undercut, radial register, face register. Chuck on, and barely 2 thou of runout with a milling cutter in the jaws. Lovely.
So, it looks like the lack of material at the keyway shifted the chuck over on the shaft, despite the accurate registers. Something I hadn’t expected at all.
My K3 hollow-chisel morticer used an awkward mounting system: each size of auger bit needed its own collet for the sleeve on the motor shaft. You’d have to line up the hole in the collet with the retaining screw, then steer the bit into the collet, trying to line up the flat you filed on the bit with the screw, all while trying not to jab yourself on all the sharp points.
So, I decided to replace all this with a Jacob’s chuck, mounted to the motor shaft.
So, out with the rotor and on to the lathe (sorry for focus):
Here, I’ve taken the shaft down to 0.494” from 5/8”, and am starting to single-point threadcut the 1/2” UNF thread for the Jacob’s chuck. Something not visible is the keyway in the motor shaft, which retained the original sleeve. We’ll encounter this later.
Chuck threaded on:
And a comparison to the old system. You can see the dreaded keyway:
However, the chuck wobbled and made the bit clatter in the chisel far too much. About 15 thou of runout. All apart again, and I checked the machined chuck mount, threads, the motor shaft, the chuck register and jaws, all within a thou or so of runout. There was nothing wrong with the individual bits; it was when they were screwed together the problem appeared.
After some fiddling around and general angst, I realised it had to be the keyway. The high point of the runout was always opposite the keyway, regardless of chuck position and even when trying a different chuck. So, in the lathe again I machined everything I’d done down by 40 thou or so, then MIG (technically MAG) welded the shaft all the way around. Sorry, no pics as too much desperation. Taking off the 40 thou meant I would be machining pure weld, not the weld-shaft junction. Welding all the way around, rather than just filling up the keyway, was to minimise shaft distortion.
After letting the shaft cool naturally, I just did the same again: face, centre, 1/2” UNF, undercut, radial register, face register. Chuck on, and barely 2 thou of runout with a milling cutter in the jaws. Lovely.
So, it looks like the lack of material at the keyway shifted the chuck over on the shaft, despite the accurate registers. Something I hadn’t expected at all.