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Homing, offsets, and slaving
« on: November 03, 2012, 05:39:33 PM »
I finally got out to the Green Monster (my home-built CNC router) again today and started feeding in soft limits, home offsets, and auto zeroes.  Before setting Home offsets, it didn't back off the limit switches.  Now it is. Hurray!

I think (confirm my assumptions, please) that I'm using the upper right quadrant in the Cartesian system for positive X and Y.  X home is left, Y home is toward me, Z home is top.
I'm working in inches with 52" X and Y ranges, & a 5" Z range.

In the Motor Home/Softlimits config box, I have
Soft Max 51.00
Soft Min 0.50
Slow Zone 1.00
Home Off. 0.50
Home Neg. Checked
Auto Zero Checked
Speed 20%

in X, Y, and A boxes (Home Neg Xed on A, which is slaved to X).

Pic, far left is home corner.  http://tinyurl.com/com9z8g
Pic, I changed Y back to mirror X  http://tinyurl.com/d3kdnt8
After saving, I have lost a few thou on the DROs.  Curious.

OK, I click the REF all home button and Z goes up, hits the limit switch (home) and backs off less than 1/10 turn, even though the offset is set to half inch.  Then Y comes home and backs off about
0.1" with the offset also set to half an inch. Then the gantry goes left, hits the X1 (A axis) limit switch, stops, reverses 1/8" or so, and then moves left again. This is where I get a limit switch error.

Questions: Why is it erroring out?  Why the small movement when the offset is listed higher in the soft limits?  I had a 0.1" offset at first and it moved the same distance back off the limit switch that it
has with the half inch offset entered there.  Why?  Is it only moving until it deactivates the switch? (if it's even doing that)  With X and A slaved, why isn't it locking one side and doing the other afterward?  Can I unplug A and just test the X by itself, then swap and try again?  Would this do any good?

I get the same small movement off home on all axes despite settings in the offset of 0.1, 0.5, and 1.0.  The Z moves about 19 degrees by my calcs.

The frame is within 1/32" of square, the rails are even from the end, but I just measured about 1/8" difference in the gantry position from side to side. I guess I have a twist somewhere in the gantry. It will flex about an inch while remaining easy to roll down the rails. (2 linear bearings per side, spaced 4" apart)

Offline ger21

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Re: Homing, offsets, and slaving
« Reply #1 on: November 03, 2012, 09:29:54 PM »
I replied to your post at CNC Zone.

2010 Screenset

JointCAM Dovetail and Box Joint software
Re: Homing, offsets, and slaving
« Reply #2 on: November 04, 2012, 01:20:07 PM »
I replied to your post at CNC Zone.

Ditto.  Thanks, Gerry.
Re: Homing, offsets, and slaving
« Reply #3 on: November 10, 2012, 06:23:29 PM »
Thanks larry your post help me with a very similar problems with moving off the limit switches.

have fun
Tom ;D