Re: [CAD_CAM_EDM_DRO] Linear rail & ball screw size suggestions

In a message dated 09-Apr-02 20:42:31 Central Daylight Time, js3mc@...
writes:

> I'm looking for some help on sizing the linear rails for a small gantry
> router.

Jay: One or more others "in here" will probably have different opinions, but
I have built several "X-Y devices" (see one in "Home-Brew CNC Lathe" in the
PHOTOS section of the CAD_CAM... site).

For the 12" x 18" size you describe, surely ½" dia. "supported" Thomson
60R-case-hard round-way and their OPN-8 linear ball-bearings would do for the
LONGER axis, and you might want to use ¾" dia. "end-supported" for the
carriage-ways. Depends on the actual construction you use. There are
"non-round" ways to do this, too, such as the fine stuff made by HIWIN, THK,
etc., but I think you are talking serious $change, there.

Ball-screws? I think good ACME screws with preloaded Turcite nuts would be
fine for such a small machine, and for that size, I would use 20 mm dia. x 4
mm. pitch ACME from Ball Screws and Actuators. Or, if it must be INCH
measure, 5/8" dia. x 0.2" pitch would do, I think, same source. If the
screws MUST be ball-screws (you must use a whole-nuther discipline, because
the DUST from a router MUST be kept OUT of the ball-screw nuts!!!!!!!!!!!),
SAME source; 13 mm. (½") dia. would do, I imagine. I did a PCB-drill (will
"route" and engrave a bit, too) with only 7/16" dia. screws, and that is
entirely adequate. These do NOT turn faster than, oh, 200 RPM, I guess.

Lotsa luck! Work very, very carefully, and keep debris OUT of those
ball-nuts!!!!! Jan Rowland


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