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September 19, 2019, 14:43:43 pm


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Author Topic: Double Check Yourself - From 0.0095 backlash down to 0.002  (Read 200 times)
Bob La Londe
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« on: September 06, 2019, 01:04:27 am »

I put my Hurco KMB1 back in service a while back, but I was getting .0095" backlash on the Y axis.  It was driving me bonkers, but I needed the machine so I couldn't tear it down.  I just had to cut everything in conventional and program to compensate.  I finally started tearing down the Y and found the nut on the stacked ACBs on the drive end of the ballscrew was barely finger tight.  I'm not sure.  I made a special crown socket for it a while back.  After releasing the tab washer the nut moved when I just barely touched it with the socket.  While I was positioning the tabs in the notches.  Don't know how I left it that loose.  I was sure I tightened it with a torque wrench to about 50 lbs.  

I was going to order a new set of ACBs, but they aren't cheap and they would take a couple days to get here.  Just on a lark I decide to reinstall everything.  Just .002 backlash now.  The machine should be less than .001, but .002 could just be wear over time in the ball nut.  The machine is almost 40 years old afterall.  (Made in the early 1980s) The Y axis carries more load than either other axis as well.  

I might take it back apart and have somebody repack the ball nut with oversize bearings, but not today.  
« Last Edit: September 06, 2019, 03:43:40 am by Bob La Londe » Logged

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lloydsp
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« Reply #1 on: September 06, 2019, 01:12:36 am »

Well, it's neat you found that issue, Bob.  Between 0.095 and 0.002 is a HUGE difference!

Lloyd
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Bob La Londe
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« Reply #2 on: September 06, 2019, 03:42:54 am »

Oops. Meant .0095.
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lloydsp
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« Reply #3 on: September 06, 2019, 11:32:05 am »

 Wink  That's still a pretty-significant change.

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Bob La Londe
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« Reply #4 on: September 06, 2019, 17:18:13 pm »

It makes it practical to prepare blanks on the machine for hinged molds.  I make the hinge feature with several thousandths tolerance as molds are aligned with pins.   Before I had to program a HUGE tolerance. 

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Getting started on CNC?  In or passing through my area?
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