On Sunday 13 April 2008, Ian W. Wright wrote:
>Hi,
>
>Can one of you boffins enlighten me a little please on the subject of
>backlash. It hasn't bothered me before but one of my axes has now
>developed a little backlash (0.06mm) and I'm not sure how EMC2 handles
>it. To be specific.... I run without limit or home switches at the
>moment and so when I put a new job on I first jog the axes to my known
>start point, touch off and then run the program.
>What happens at first -
>do the axes take into account the backlash as they start to move
Yes, but only if the next move is a reversal of the last move.
>and if
>so how - or, more particularly, how can they know whether backlash
>compensation is needed on the first move or not.
If the first move is not in the same direction as the move to the touch off
point was, then I believe backlash comp will be done before the real move
starts.
>Does EMC2 remember the
>direction it last jogged in?
Yes
>Whether or not backlash is compensated for
>in the initial move obviously determines the direction I need to jog the
>axes in to get to the start position. Even though the backlash is quite
>small on my machine, it really matters as I am making parts for watches
>and the odd thou can ruin a piece....
Generally, when backlash due to wear or slippage should be minimized
mechanically if possible, then the remainder determined by removing it from
the software and indicating the machines behavior without lash comp, then
plugging that amount into the software's characterization of that axis.
I just recently installed some ball bearing thrust washers in my X & Y table
drives on that micromill of mine with the expanded tables. This has allowed
me to get mechanical lash down to the 1.5 thousandth range so the software
can now do a circle that with comp, is well within a thou of a perfect
circle. Till next week when the nuts will have worn some more anyway. :)
--
Cheers, Gene
"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
Love is in the offing.
-- The Homicidal Maniac
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