Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: WMARCHEWKA on January 18, 2010, 06:52:35 PM
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Hi all. I have just built a CNC Gantry from this site. http://bluumaxcnc.homestead.com/BluumaxCNC.html (http://bluumaxcnc.homestead.com/BluumaxCNC.html) I am in the process of learning LazyCam and Mach3. I am using an older version (R2.63), which is recommended on his site, not sure why. In order to get a feel for this whole CNC in general, I first wanted to make a 1" square cutout and 1" square piece, and see how they fit into each other. I am cutting into 0.200" press-board (MDF). I read about tool compensation with the G codes, but to keep things simple, i generated the square boxes with Visio, one that is .090" larger than one inch and one .090" smaller to accommodate my bit diameter. My problem is this. My X axis is consistently .005" larger, while the Y is within .001". Now while i am happy with this error with a machine that costs less than $350, i cant help but wonder what is off. I don't think it is backlash, as i checked in both directions with a dial indicator and i have maybe .001". (i jog in one direction, zeroed both the machine and dial, and jogged the other direction until the needle moved). What is bugging me is it is too large. I could see too small with losing steps or maybe some slight slippage. Like i said, it is consistently too large int the X. Any thoughts?
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Just had a look and it seems to be using acme leadscrews, how accurate they will be I dont know so could just be you need to tweak your steps per unit a bit to make things better. Thing is you need to try at different table positions as possibly it will be the Y out more than the X at a different position.
Hood
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I would say its flex in the machine. Try cutting your square in the opossite direction and see if changes anything.