I have often thought about mounting my Unimat SL on my 9x20 lathe for use as a tool post grinder, but then I really don't need a tool post grinder. The recent post on milling threads got me thinking again. There might be lots of other ways to use this setup but one thing that has kept me from doing it is the need for rigidity in a setup like this. The Unimat vertical post is 25mm OD and when mounted in the Unimat base, it is set in a matching hole and locked by a single set screw. It seem rigid enough it practice but I have always felt that there should be a better way.
Plane geometry tells me that if one circle is tangent to the inside of another circle, there is a single point of contact. Solid geometry shows that a cylinder tangent to the inside of a bore has a single line of contact. A press fit or an interference fit is the only way to provide full 360° contact. I think, I could be wrong. But if the fit is loose enough to drop in, it is loose and the set screw is a half a$$ed fix, providing only 2 point contact.
What it really needs is a three point contact. That's why we use a V-block to hold a round shaft in a vise.
The truth is I tried to bore a tight fit for the bar in a block of aluminum so I could do it the way Emco did it and I failed. Sneaking up on the finished ID with my boring head, I missed it. The bore went from to tight to to loose so I tried warming up the part with a stream of well directed curses but that failed as well so I closed up the shop and went home.
This morning I went back and drilled two 1/4" holes, tangent to the outside of the 25mm bore. I then took the 25mm bore out to about 28mm. Two pieces of 1/4" drill rod were dropped in the holes an another hole was drilled and tapped for a set screw. Now the post is a rock solid mount. It looks like this:
Now that it is mounted, I need to think about how it will be used.
Jerry
