Bruce White
1st January 2013, 11:21 AM
Thought, because it is the most recommended way, to try using contraction mode on a spigot when turning a 5KG lump of dry burl (described as rib fruited gum - pretty hard wood) today. I habitually turn the outside of the bowl to finish using a faceplate, make a recess and reverse it using expansion mode. Rarely have one come off.
Gave the spigot method a go after finishing the outside and carefully matching the depth and angle of the chuck jaws and spigot. Tightened it as much as I could, ran it for a bit, tightened it again (didn't move) and still had the damn thing come off when I started to level the face. And I was not going hard at it. The same thing happened when I tried spigots on the green turnings I have stashed away for finishing - reverted to expansion mode there too.
I have a Vicmarc 120 and the old black Nova chuck. Both have straight sides in the contraction mode and dovetail on expansion. Could this be the problem?
I mentioned in an earlier post on this subject my theory on inertia on the chuck. If you turn the lathe on with the chuck empty, it naturally flies open, therefore, to my simple mind, expansion mode has to be safer as inertia is helping the chuck do its job. I finished turning a really rough, hard piece if what I think is York Gum burl using the expansion mode on the same Nova chuck with no problems immediately prior to trying the contraction mode on this one.
What am I doing wrong?
Gave the spigot method a go after finishing the outside and carefully matching the depth and angle of the chuck jaws and spigot. Tightened it as much as I could, ran it for a bit, tightened it again (didn't move) and still had the damn thing come off when I started to level the face. And I was not going hard at it. The same thing happened when I tried spigots on the green turnings I have stashed away for finishing - reverted to expansion mode there too.
I have a Vicmarc 120 and the old black Nova chuck. Both have straight sides in the contraction mode and dovetail on expansion. Could this be the problem?
I mentioned in an earlier post on this subject my theory on inertia on the chuck. If you turn the lathe on with the chuck empty, it naturally flies open, therefore, to my simple mind, expansion mode has to be safer as inertia is helping the chuck do its job. I finished turning a really rough, hard piece if what I think is York Gum burl using the expansion mode on the same Nova chuck with no problems immediately prior to trying the contraction mode on this one.
What am I doing wrong?