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Author Topic: Is it Backlash...still?  (Read 1510 times)

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Offline Keith

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Is it Backlash...still?
« on: September 20, 2014, 04:20:01 PM »
Hey there, not sure if this is a mach question, so may not belong here, but in an effort to knock out some terribly wacky backlash (X-axis) I replaced gibs, lead screws, even one motor. Figured I'd do it on the Y and Z while I was at it, on my Sherline 2000.
It looked like I got out as much backlash as is possible on that machine but if you'll view the attached photo, you'll see where the arrow annotation is, there's this scalloped look to the cut. I tested with Kiran's wizard for cutting a circle.
Anyway, I'm wondering what's causing this. Is it motor tuning? Too tight a gib? Smoothstepper setting?
Any ideas would be appreciated. -Keith
Re: Is it Backlash...still?
« Reply #1 on: September 21, 2014, 03:10:56 AM »
If you have eliminated all the axis slides backlash, two things spring to mind, tool deflection or spindle bearings either worn or in need of adjustment. What happens if you repeat the program using the same component (fresh air cutting till it reaches the step), does the side step disappear or reduce? I had to adjust my spindle bearings to eliminate a similar problem. I discovered it by putting a dial indicator on the plain part of the tool whilst cutting a slot and changing x axis direction. Hope this helps. Jim   

Offline Keith

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Re: Is it Backlash...still?
« Reply #2 on: September 21, 2014, 08:01:35 AM »
Thanks Jim. I hadn't thought about the spindle but there is certainly a possibility of this since earlier on, I had taken it apart and possibly hadn't put enough pre-load on the bearings. I'll put the indicator on it today and report back.-Keith

Offline Keith

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Re: Is it Backlash...still?
« Reply #3 on: September 21, 2014, 09:18:10 AM »
Okay, this is embarassing. Spindle was fine. But I watched the cut carefully this time and when it got to the spot in question, it was a very apparent 'leap' (at least to my eye). Too weird to even be backlash (although it technically was a form in effect). Then it hit me; during the period that the mill was really funky (particularly the X axis) I had to seriously do some work on a part and I was trying everything to compensate for the mill's problems. I wound up using 'backlash compensation' in Mach 3 and forgot to turn it off. The X axis had a relatively high number in there to do the correction.
So I turned off backlash and have a very nice circle without the artifacts. I must say though that Mach's backlash compensation does work very well and did what it was told.
Thanks again for looking at my problem.-Keith