After some discussion on another thread on this board, I've finally finished my "clamp on" Toolpost. My C2 Sieg lathe came with a standard dovetail cheap toolpost, which has been adequate for the 3 or 4 years that I've had the lathe. There were always problems with chatter, especially when parting off, which I put down to overhang of the compound slide, and general flexibility in the whole "system". I spent a lot of time doodling the alternatives, which mainly fell into the dovetail or clamp on styles. The dovetail type was discounted because I felt that they were unnecessarily complicated, also I was concerned about some of the wear points with unhardened metal. I do worry a lot. So it was to be a pillar with clamp on toolholders, following especially the ideas of Ralph Patterson, George Carlson and Bruce Simpson....thanks guys!!.
The toolholders were 25mm slices off of a 50mm x 50mm square S1214 (free machining)bar. After that the details pretty much sorted themselves out. A 35mm diameter central post was used to provide the maximum clamping area and the maximum stiffness. The hardest bit was generating the nominally 35mm diameter hole, but it ended up ok, using the 4 jaw in the lathe. I did investigate the possibility of watercutting the bore, the person I spoke to wanted $432 for twelve holes. Laser cutting was a possibility at $10 per hole, but there was the problem of the heat affected bit possibly being hard to get through. A holesaw was bought, but neither my C2 lathe, or the X2 mill provided enough oomph, so the 35mm holes were drilled and bored. The diameter of the bore was kept as close as possible to the post size, I have no way of measuring the bore other than a vernier, which wasn't a great deal of help, the last couple of cuts on the bore were very light!! That effort has been vindicated by the clamping provided by the two screws being huge. I'm pretty sure that non arthritic fingers could provide sufficient torque to enable light cuts to be taken.
Originally there was to be a single M8 clamp screw, but this was changed to two M6 clamp screws when the M8 one wouldn't fit!! Rather than make all the set screws and stuff, good quality (Unbrako) socket head fasteners were sourced.
So far the "upside down" parting off process has been a revelation. Running the lathe backwards at 1200rpm, chatter free, no dramas is fantastic. Worth the effort for that alone. Today I turned a piece of Grade 5 titanium, and ended up with a superb surface finish!! All in all its turned out very well, and it would be fair to say I'm pretty chuffed. I ended up with twelve standard toolholders, and two parting toolholders.
cheers
Bill Pudney
