alternate offset determination method?

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alternate offset determination method?

Post by timdeagan on Sat Mar 11, 2017 7:04 pm

I'm getting nowhere on determining my offset. I'm using a GRBL based X-Carve, so I can't use the ShopBot CC method described elsewhere. The GRBL has serious problems (or at least I and a lot of other people on various forums have serious problems,) getting GRBL to play nice with the G-Code G02 and G03 commands to create arc movement.

When I try, both in SheetCam and VCarve Pro to create circles of the appropriate diameter, the working post processors generate point by point movement to create the circles. I'm not managing, with any of my attempts, to generate a toolpath that creates the movement around the tip of the blade.

I tried just spinning the blade with it lightly scratching the surface, to create a circle. I then used calipers to measure this with the assumption that the radius was equivalent to the offset. But it's difficult to be precise with any degree of precision.

Are there other methods I could try?

Thanks.

timdeagan

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Re: alternate offset determination method?

Post by timdeagan on Sun Mar 12, 2017 11:40 am

Got it working with GRBL.  This will execute a clockwise circle at X0 Y0 (easier to do repeatedly.)  

G21
G00 Z4
G00 X0 Y0
G00 Z1.5
G02 X0 Y0 I4.5212 J0 F300
G00 Z4
G00 X0 Y0

To test the Donek Dragknife with that G-code, aim the blade as if it were about to cut in the X- direction.  Any other position will not make a circle.  Change the I value to represent the offset you'd like to test.  I've set this up in mm, change the G21 to G20 and use inches if desired.

Some variants of G-Code (apparently not GRBL,) accept a P command on the G02/G03 line that defines repetitions.  That would be nice, but doesn't seem to work.

--Tim
(cross posted on the X-Carve forum)


Last edited by timdeagan on Sun Mar 12, 2017 11:41 am; edited 1 time in total (Reason for editing : formatting from other board didn't work here.)

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