websterz wrote:Great design!! I have been looking to build a tailstock for my own rotab, mind if I copy yours?
Feel free . . . especially as I can't really claim that there is a design, as such. Usually when I machine something I draw it up on a CAD program, but this one I mostly just did by the TLAR method (that looks about right).
A large part of the "design" was dictated by the fact that I acquired a stock of 1" x 3" x 12" steel blocks for free -- they came out of a discarded weight machine. I don't know the exact composition of the steel, but I strongly suspect that it was leaded steel, because it machines very, very nicely. So the tailstock is 3" wide, and each of the blocks started out 1" thick before machining the "square ways." The main upright is a little under 4" tall; the movable block is around 2.5". The base on which it all sits, and which will be used to clamp to the table, is 3" x 3" x 1/2" thick. Had I not already cut this (several years ago when I first started the proejct), I would have made it a little larger.
One bit of advice that may not be obvious -- the split sleeve that pinches the center to lock it in place is 1/2" diameter. This hole is set so that it overlaps or protrudes slightly into the .625" bore that the center slides in. I meant to have it protrude about .050" into the bore, but due to a brain malfunction when I was laying out, it only protrudes about .012". I was concerned that it would either not provide adequate clamping power, or that it would be hard to unclamp because of wedging itself into place. As it turns out, it does work okay ... but I'd still advise going with .050" or even more.
Here's the machining trick for this split sleeve. First drill the hole for the split sleeve. Machine the sleeve as a single piece, about .020" shorter than the width of the block. Drill and tap all the way through, 1/4-20. Use a short 1/4" SHCS or bolt with a washer and tighten it all the way up on one side. Slide the sleeve into the hole with the bolt & washer on the outside face. Use another short SHCS or bolt and washer on the other side; tighten very securely so that the sleeve is held immobile in its hole. Then drill the .625" hole -- which will simultaneously machine the concave in the sleeve. Finally, remove the bolts and the sleeve, and cut it in half on the band saw, right in the middle of the concave. File off any burrs. Drill out the outside half of the sleeve to 1/4".
When you assemble everything, use a 1/4" SHCS just a bit shorter than the total sleeve length; slide on the outside half and thread on the other half; make sure the concave parts are in the middle! Slide the sleeve into its hole, and adjust so that the concaves situated to fit the .625" bore. Slide in the hardened center rod; you may have to wiggle a bit to get the sleeve pieces just right. Once the center rod is in place, the sleeve can't fall out. When you tighten the SHCS, it pinches the two halves the sleeve together on the center rod, and does an incredible job of clamping it in place.
