Thomas Bennett
02-04-2009, 8:27 PM
I'm in the middle of producing some Longworth chucks. One is quite large, about 28" . the rest are 16 inches, one is 12 inches. I glued an inch thick block of maple, six inches in diameter, onto a 3/4 inch thick piece of Russian ply covered with plastic laminate . The outside pieces are 3/8(some 1/4)Russian birch covered with laminate. The idea is to have both laminate surfaces rub against each other upon completion. These constructions seem very flat.
Next I screwed a face plate as close to the center of the maple black as possible. The face plates are home made, but trued up( on a metal lathe) on the “nut side” and recessed to fit nice and snug against the headstock. The outside of the face plates are untouched but seem flat enough, although not perfect. Then I mounted the whole construction on the lathe. I noticed a pretty big “wobble” on the 28 incher. Some of the 16 inch and the 12 inch are also out of true. I continued and turned the outside of the ply construction to a perfect round. Obviously, I can’t turn the face true, as it’s covered with the laminate.
I was hoping this wobble might “go way” or “fix itself a little” after I route the arcs for the mounting hardware. I was also hoping my truck might fix itself after the engine light came on. Would a wobble matter if one is only turning a mounted bowl closer to the center of the chuck, to clean up the bottom of a bowl or platter?
I know of one way to remedy the situation. I could cut off the maple blocks, then mount a new maple block on the faceplate and true it up on the lathe, then glue the ply/laminate construction on the block. I have the ply/laminate constructions screwed together . I drilled a ¼ inch hole through the middle of each construction while it was on the lathe, with a drill in a chuck mounted in the tailstock. I can use this ¼ hole to reference the future glue-up to get it really close to round. I realize I probably should have worked from the face plate out. If the faceplate is out just a hair, the wobble become extreme out at 16 or more inches. If I go to all this trouble, cutting off the maple block, re-glueing it etc. will the chucks be any truer than they are right now? Is there a limit to the size most turners make them? Do they have to be absolutely flat and true? Do any of you that have made these chucks have any insight into this situation?
Next I screwed a face plate as close to the center of the maple black as possible. The face plates are home made, but trued up( on a metal lathe) on the “nut side” and recessed to fit nice and snug against the headstock. The outside of the face plates are untouched but seem flat enough, although not perfect. Then I mounted the whole construction on the lathe. I noticed a pretty big “wobble” on the 28 incher. Some of the 16 inch and the 12 inch are also out of true. I continued and turned the outside of the ply construction to a perfect round. Obviously, I can’t turn the face true, as it’s covered with the laminate.
I was hoping this wobble might “go way” or “fix itself a little” after I route the arcs for the mounting hardware. I was also hoping my truck might fix itself after the engine light came on. Would a wobble matter if one is only turning a mounted bowl closer to the center of the chuck, to clean up the bottom of a bowl or platter?
I know of one way to remedy the situation. I could cut off the maple blocks, then mount a new maple block on the faceplate and true it up on the lathe, then glue the ply/laminate construction on the block. I have the ply/laminate constructions screwed together . I drilled a ¼ inch hole through the middle of each construction while it was on the lathe, with a drill in a chuck mounted in the tailstock. I can use this ¼ hole to reference the future glue-up to get it really close to round. I realize I probably should have worked from the face plate out. If the faceplate is out just a hair, the wobble become extreme out at 16 or more inches. If I go to all this trouble, cutting off the maple block, re-glueing it etc. will the chucks be any truer than they are right now? Is there a limit to the size most turners make them? Do they have to be absolutely flat and true? Do any of you that have made these chucks have any insight into this situation?