Syk0 saje at 06:16, 30 April 2011

2011-04-30T06:16:55Z

← Older revision		Revision as of 06:16, 30 April 2011
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	Dave		Dave

			[[Category:Notes]]

WikiSysop: New page: I would be worried about the gantry twisting so it's not at right angles to the bed. The gantry is a long skinny triangle that spans 5 feet between the rails, yet has only a 2-foot base of...

2008-02-26T20:02:29Z

New page: I would be worried about the gantry twisting so it's not at right angles to the bed. The gantry is a long skinny triangle that spans 5 feet between the rails, yet has only a 2-foot base of...

New page

I would be worried about the gantry twisting so it's not at right angles
to the bed. The gantry is a long skinny triangle that spans 5 feet
between the rails, yet has only a 2-foot base of the triangle that
engages the main longitudinal rail. In order to deflect the gantry so
it's 10 mm off square, the two sets of bearings running along the rail
need to depart only 2 mm from being aligned with the rail, which could
be a displacement of only 1 mm each. It's seems like that's a 10:1
mechanical disadvantage. The fact that the cross-rail of the gantry is
elevated suggests that it could also be "wound up" in torsion by
pressure out at the far side of the triangle, lessening stiffness further.

I haven't ever built a gantry-based device, but I've looked fairly
closely at several over the years. One was a giant gantry milling
machine, one a CNC wood router, and one a huge device that drew pictures
by dispensing sand from a hopper. All of them had positive drive on
both sides of the gantry, synchronized to keep the gantry square to the
bed. With two-sided drive, any force that would tend to twist the
gantry off square is immediately transferred to the racks, making it
easy to keep the gantry square within the backlash of the rack drive.

With a driver like the Xylotex, it should be easy to put a stepper on
each side of the gantry, engaging two racks. Use one Xylotex channel
for each motor (you can't parallel the motors), but connect the STEP and
DIR signals from the controller to STEP and DIR inputs for both Xylotex
channels. As long as the motors don't stall, they'll stay in sync with
this arrangement.

Dave

Dave from Xylotex - Revision history

Syk0 saje at 06:16, 30 April 2011

WikiSysop: New page: I would be worried about the gantry twisting so it's not at right angles to the bed. The gantry is a long skinny triangle that spans 5 feet between the rails, yet has only a 2-foot base of...