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Hey Ted, the Vicious1 (so far, you really don’t strike me as being vicious at all… 😉
Here is my solution, at least for now.
I do use Zero Limit Switches, and I’ll explain how shortly.
But, what i did is printed 2 ‘Bumpers’ – mounted them to the corner posts opposite where i have the zero limit switches. When I send the X or Y to home, i have the bumpers just where if the pipe is straight it will just bump the bumper as it hits the Zero sw. After the axis hits the Limit Sw I check the other end and as long as the center roller is just touching my bumper all is good. Now I am getting very good repeatable results.
To test it I Homes it with the Bumpers, then moved the gantry so the bit just barely touches the edge of my work piece. and aligned the piece to the bit just brushes it along it’s edge, from 0 to 1219mm
then i turned off the steppers and manually moved the gantry around, cocking the pipes a little, and hit Home – making sure the bumpers touched – and ran the cutter back to the edge, and it tracked it perfectly from 0 to 1219mm…
I repeated the process several times, and each time it was perfect – enough for what i need. Not sure if it is .2mm, but, actually, it was less that a sheet of paper from touching the work originally, less than a hair. By line of site I could just see a thin space between the bit and the work, and it repeats now, every time. Just what i needed. – Using a Zero Sw on one end and a ‘bumper’ on the other to make the pipe align up the same each time i home it.
Obviously, the stepper that hits the bumper skips a few times when it hits the bumper, but, only the one time to align it. Once it is aligned and i don’t manually move it, when i home it again after that it just touches it without skipping. All i have to do is make sure it does touch it (if it is cocked too far away, it will hit the zero limit before it hits the bumper and there will be a space between the roller and bumper. If that happens then i have to manually uncock the pipe (or slightly cock it the other way) and home it again, and it resets itself.
Now it is working the way i want it to
Here’s how I am using the Zero Switches.
;Created by Estlcam version 9 build 9.007
;Machining time about 12:07:57 AM hours
G90 ; use absolute coordinates
M03 S24000 ; start spindle motor 24000 means to use speed set for Tool
g28 Z ; home to limit sw < Z first, to move Bit up out of the way
g28 Y ; home to limit sw
g28 X ; home to limit sw
; Move spindle to desired Origin – Start Pos (Zero for this File, NOT the Zero Limit Sw Home)
; EDIT NEXT 2 LINES
G00 X20 Y137.9 F8000
g00 z83.4 f1800 ; NOTE I am using the 8mm Lead Screw with x16 stepping, and can get a much faster Z speed
G92 X0.0000 Y0.0000 Z0.0000 ; reset ZERO all axis
;;; now resume the GCode for mill work