# Measuring and testing backlash comp.



## skunkworks (Jul 27, 2019)

Backlash compensation (Yes - you should try to get rid of all backlash but....)


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## Karl_T (Jul 28, 2019)

Neat video.  Would you care to repeat your trial on a pocket instead of a boss?

Ancient history - I tried backlash comp to get better part tolerance on my Excello. My findings - if I adjusted it to get in spec on boss cutting, it made pocket cutting worse.  I was doing one inch squares on both with a 1/4" endmill and making the machine work by removing a healthy cut, then a second pass with a light cut. Goal here was to simulate actual machining.

My conclusion, backlash comes from many sources, not just the ballscrews. its far more complex.

I am about to get my new Vectrax mill running. I'd like to understand this better to see if improvements are possible.


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## skunkworks (Jul 28, 2019)

This is getting into the realm of what this machine is capable of..  (splitting hairs...)

This is a 1x1 pocket cut with a 1/4 end mill.   I plunged the endmill and measured the hole at .252

Backlash compensated square measured
1.0017X1.0019

uncompensated measured
0.9989 X .9997

sam


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## Karl_T (Jul 28, 2019)

You got a pretty good machine there.

I've not seen this written up, but in my opinion one should do both pockets and bosses, then find the best comp for the average of both.


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## skunkworks (Jul 28, 2019)

sure - that seems like a plan


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## magicniner (Aug 28, 2019)

Karl_T said:


> Neat video.  Would you care to repeat your trial on a pocket instead of a boss?
> 
> Ancient history - I tried backlash comp to get better part tolerance on my Excello. My findings - if I adjusted it to get in spec on boss cutting, it made pocket cutting worse.  I was doing one inch squares on both with a 1/4" endmill and making the machine work by removing a healthy cut, then a second pass with a light cut. Goal here was to simulate actual machining.
> 
> ...



You compensate backlash to get accurate positioning, not cutting, if you do it correctly you can then, if necessary, use tool compensation in CAM or Controller, to get your parts on size and it will work for inside and outside cuts.


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