For convenience and especially for operation by students, newbies and the
generally clueless, build or modify the gantry so both sides are mechanically
linked so it is Not Possible for it to get out of square.
If you have a screw running lengthwise on both sides, Put a chain or belt and
idler across one end and on the other, use a center shaft with three stacked
sprockets so there's a chain to each screw and the third has its own belt or
chain to the motor.
Another method uses racks along the sides and a shaft across with gears on each
end. A variation on that is with a length of roller chain fixed at the ends
then wrapped around sprockets and idlers in the vertical ends of the gantry,
with a cross shaft to drive like with the racks.
Then there's the 'wraparound' gantry with a beam that crosses under the table
with a single drive down the center. The weakness there is the gantry can still
rack a bit freely if the bearing parts are any bit loose or aren't long enough
to stay self aligning. The design also needs a very stiff and strong table
structure due to the impossibility of having any supports except at the ends.
Why does anyone want a gantry that's has the built in ability to try and rack
and jam up when it's simple to build one where that isn't possible?
It simplifies the software and the electronics, eliminating one motor and
driver and the need to home each side of the gantry and tweak the software to
keep it straight.
From: "dan...@austin.rr.com" <dan...@austin.rr.com>
To: Enhanced Machine Controller (EMC) <emc-users@lists.sourceforge.net>
Cc: Dewey Garrett <dgarr...@panix.com>
Sent: Thursday, March 31, 2016 10:13 AM
Subject: Re: [Emc-users] XHC-HB04 on LinuxCNC
But wouldn't that break the ability to home the gantry's sides independently?
That's a huge problem. The gantry isn't going to align itself.
A relevant point of the context here is this is going into a community shop,
with a constant stream of new users with very limited supervision. So "power
down these axes and mechanically align them" doesn't sound like a viable
option. In the past I've had the stops aligned and ran the gantry into the
stops until both sides' steppers stalled... gently.
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