Similariites Betwixt Super Shop and Unimat 3

On Wed, 3 Sep 2008 03:01:46 -0700 (PDT) in rec.crafts.metalworking, snipped-for-privacy@replikon.net wrote,

You mean the cylindrical shaft bed of the older Unimat and Unimat SL? No, the Unimat 3 has a cast iron bed with an inverted V in front and a flat in back.

That's right, it was the Unimat and the Unimat SL, as as well as the NC version, that had twin column bed ways. I remember now...

Doug

The dual column design, convertible from table saw to drill press, seems to be the basis for almost all my thoughts on universal machine tool design lately. I wonder if a lead screw could be run through the column closeest to the operator in lathe mode. If that were done, thread cutting would be available and that is one thing the Super Shop does NOT have.

In such a dual-column machine, of Super Shop scale, might the tubular bed ways be slotted full length allowing access to a nicely shielded lead screw, without them springing open with an increase in diameter? It's a question of residual stress in the steel. Perhaps MSC Direct can check with the maker of the 2 inch hollow linear motion ways they sell for me. I have two such bed ways spare from Smithy; when I complained they were finished to about 16 microinches and were abrading a fine aluminum dust from the castings of headstock and carriage, they sent two to me. One each with rack teeth milled in place, and one without. I'd explained to them I have accessorized my Super Shop to hold the tubes for hand polishing, hanging from the headstock in the vertical position. Such bed ways from MSC are $500 each. Smithy provided these two GRATIS! Way to go, Smithy! I'll have to ask Smithy about residual stresses, too.

Doug

The residual stresses you could probably compensate for. It's the reduced stiffness under load that I'd be worried about. Under bending, I'd expect the slot to open and close as loads are applied. If there are twisting loads, then either side of the slot may move in opposite directions axially, giving much less resistance to that sort of load. Take something like a paper towel core, and expriment with bending and twisting with and without a slot up the side, I think you will find the differences are significant, even if it retains it's shape (which is what I think your biggest worry is with the residual stress).

I would not be supprised if to get an equivalent stiffness with a slot, that you'll have to double or more the wall thickness of an unslotted column. And of course, any deflections in the columns may also cause sliding assemblies to jam at the most inopportune times... --Glenn Lyford