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Author Topic: trouble cutting circles  (Read 3032 times)

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trouble cutting circles
« on: February 29, 2012, 03:50:05 PM »
Hi Guys,

I recently converted a Multicam I purchased to mach 3 using an ethernet smoothstepper, and a c 32 breakout board.  I purchased the unit refurbished from multicam, they failed to properly test it and all the internal logic boards were toast so a mach 3 conversion was my best bet (they refunded some of my money).  The conversion has gone smoothly and we have cut a lot of parts.  We do a lot of sign work etc. so we have been getting usable output for big stuff in spite of the problem I'm writing about. 

The issue I am having is with small, detailed cuts.  Initially, they were out of round erratically, but we found a ton of slop in the Y axis and that cured it from being inconsistent.  Now it is consistently out of round.  It sort of looks like it could be caused by backlash, but I wanted you experts to look at it so I can get some other opinions.

The machine is rack and pinion and feels pretty tight, I have not gotten around to measuring the backlash yet.



-Ed
Re: trouble cutting circles
« Reply #1 on: February 29, 2012, 03:50:26 PM »
Also, that hole is .490"

Offline Hood

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Re: trouble cutting circles
« Reply #2 on: February 29, 2012, 04:05:13 PM »
Looks like backlash in Y axis, X looks fine.
If you have a Dial Indicator you can measure the backlash and try the compensation but best to try and get rid of the backlash mechanically if you can.
Hood
Re: trouble cutting circles
« Reply #3 on: February 29, 2012, 04:07:44 PM »
it looks like there are longish flat spots top and bottom.
Re: trouble cutting circles
« Reply #4 on: February 29, 2012, 04:11:30 PM »
Moving the spindle manually on the rack you can feel varying amounts of slop.  I can adjust the pinion, but if I get it slop free in one area, it is too tight in other spots.  Is this effect possibly a result of a not squared gantry?  I have a slaved axis for the second drive on my X axis.

Offline Hood

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Re: trouble cutting circles
« Reply #5 on: February 29, 2012, 04:15:07 PM »
To me it is backlash, the Y is starting to reverse direction but it is taking up slack so not moving and all the time the X is still driving so you get the straight line.
Hood
Re: trouble cutting circles
« Reply #6 on: March 03, 2012, 09:49:12 PM »
The pinion should be engaged by air or a spring.  If it's fixed, the distance from the rack to the pinon centerline will have to be exact along the length of the machine or you'll have tight spots and loose spots.  Where ever the pinion is not fully engaged, you'll have backlash.