Difficuties measuring Backlash on rebuilt Ballscrew

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cncot
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Difficuties measuring Backlash on rebuilt Ballscrew

Post by cncot »

IMG_5257.jpg
Gentlemen:
I am trying to commission my Centroid Allinone CNC mill.
I must measure backlash in my new rebuilt ball screw.
I am using the procedure in the install manual chapter 6.10 exactly as instructed.
Its a new $300 brown and Sharpe test indicator. The indicator is on a standard ball dovetail grip tightened as much as possible.
I took a series of readings. All readings are in tenths. Where there is a decimal the tenth is subdivided. My results are as follows: 0,1,1,1.5,2,2.5,3,3,3,3.5,3.5,4. Because it is continuing to increase, I think the indicator may be being pushed forward. If that is the case, should I use 0 or 1 tenth? Otherwise how do I change the procedure? back up only 1 thou? I cant get the indicator tighter and there is some rotational slop in the quill with the brake on tight, so the quill could be rotating slightly. Its a Bridgeport series 1 2hp variable speed, so holding a tenth is unlikely...
Can anyone share any thoughts, experience? Any other explanations? The backlash can't be a random selection of the list, nor an average. If it had a normal random distribution, then I would average.
Thanks, Mike
cnckeith
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Re: Difficuties measuring Backlash on rebuilt Ballscrew

Post by cnckeith »

Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
cnckeith
Posts: 7164
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Re: Difficuties measuring Backlash on rebuilt Ballscrew

Post by cnckeith »

i use thousandths indicator and use the out and back difference measurement method. using a tenths indicator and be tricky.
Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
cnckeith
Posts: 7164
Joined: Wed Mar 03, 2010 4:23 pm
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Contact:

Re: Difficuties measuring Backlash on rebuilt Ballscrew

Post by cnckeith »

Need support? READ THIS POST first. http://centroidcncforum.com/viewtopic.php?f=60&t=1043
All Acorn Documentation is located here: viewtopic.php?f=60&t=3397
Answers to common questions: viewforum.php?f=63
and here viewforum.php?f=61
Gear we use but don't sell. https://www.centroidcnc.com/centroid_di ... _gear.html
cncot
Posts: 57
Joined: Wed Jan 06, 2021 1:05 pm
Acorn CNC Controller: No
Allin1DC CNC Controller: Yes
Oak CNC controller: No
CNC Control System Serial Number: console 104030 SysId 0008DC111213-1202202505
DC3IOB: No
CNC12: Yes
CNC11: No
CPU10 or CPU7: No
Location: Mims Florida

Re: Difficuties measuring Backlash on rebuilt Ballscrew

Post by cncot »

Thanks, CNCKeith,I had already read everything you sent....
But the manual says if I have over 1 thou backlash, stop and fix the machine! Therefore Centroid REQUIRES a tenths indicator! Its a newly rebuilt screw pair so the backlash should be in the low tenths... My measurements are all between 1 and 5 tenths, but if the machine is unable to hold that, what is realistic to expect? Since it is a Bridgeport, should the manual say proceed if its under .002 ? or what number? Friends say a Bridgeport can not hold tenths. What is a realistic backlash that the Centroid can compensate for in this situation? Can it do between 1 and 2 thousants and if done, will it stop the dimples that occur when reversing direction?

If I apply the correct backlash compensation and repeat the tests, I should see the backlash go to 0?

I have an expensive probe with wiring. Is there a procedure using a probe? Expect More/less accuracy ?
Marc Leonard is using a 1 thou indicator and 8 IPM but the manual says 0.5 IPM!!

Still pulling my hair out!
Warm Regards, Mike
cncsnw
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Re: Difficuties measuring Backlash on rebuilt Ballscrew

Post by cncsnw »

Marc Leonard is using a 1 thou indicator and 8 IPM but the manual says 0.5 IPM!!
You may recall that the first thing I said on that page is
"There are as many ways of measuring backlash as there are CNC technicians. Each method will give you a different answer."

You can still compensate tenths using a thousandths indicator. For what it's worth, I use a Mitutoyo with half-thousandth graduations (0.050" per revolution), so it is a little easier to see tenths.

As far as the "stop, fix your machine before proceeding" advice, there is no one right answer for everybody. If your machine has 0.002" backlash, but the parts you are machining have 0.005" tolerance, then just skip backlash compensation and start making parts.
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