joe greiner
6th July 2007, 05:13 AM
Well, this seems to be an improvement on Version 2 of my Longworth chuck, shown at http://www.woodworkforums.ubeaut.com.au/showthread.php?t=51456
The construction is substantially the same, except I used 6 buttons for more benign clamping of thin-walled bowls. I also laid out the arc centres directly on the disks instead of transferring from a print of my CAD drawing. I used the largest arc radius that would fit on the disk, to provide enough material between the arcs. This is a departure from Longworth's guidance, and it has a steeper crossing angle of the arcs at the maximum bowl diameter. With talcum powder lubrication, it operates quite smoothly, though, and I probably don't need all those thumb holes in the front disk.
I carved and turned a wooden screw to secure the pvc bushing for storage. Looks more handsome than the hermaphrodite hook&loop strip I used at first. I added the burnt rings because I can.
The more careful layout of the arc slots still produced a slight eccentricity, which I think I can live with by use of the "80-grit gouge." This seems to be the luck of the draw; some would be perfect, some not. That's how ball bearings are made, y'know: The races and balls are made to manufacturing tolerances, then sorted via quality control, and mated by selective assembly for acceptable performance.
I suppose I could make further improvements, but frankly I'm weary of fussing with it. At least for now.
Joe
The construction is substantially the same, except I used 6 buttons for more benign clamping of thin-walled bowls. I also laid out the arc centres directly on the disks instead of transferring from a print of my CAD drawing. I used the largest arc radius that would fit on the disk, to provide enough material between the arcs. This is a departure from Longworth's guidance, and it has a steeper crossing angle of the arcs at the maximum bowl diameter. With talcum powder lubrication, it operates quite smoothly, though, and I probably don't need all those thumb holes in the front disk.
I carved and turned a wooden screw to secure the pvc bushing for storage. Looks more handsome than the hermaphrodite hook&loop strip I used at first. I added the burnt rings because I can.
The more careful layout of the arc slots still produced a slight eccentricity, which I think I can live with by use of the "80-grit gouge." This seems to be the luck of the draw; some would be perfect, some not. That's how ball bearings are made, y'know: The races and balls are made to manufacturing tolerances, then sorted via quality control, and mated by selective assembly for acceptable performance.
I suppose I could make further improvements, but frankly I'm weary of fussing with it. At least for now.
Joe