Well that was interesting.
I created a, modest, screw compensation file and I'm most impressed by
the effect.
I added a limit switch for X home in the middle of the table (to get
some repeatability of the axis screw position) and did:
HOME <reset DRO X-Axis>
G0 X100 <take reading from DRO>
X0 <take reading from DRO>
Here's the results without any backlack or screw compensation in the
.ini file.
99.905 0.155
99.905 0.155
99.910 0.165
99.900 0.150
99.910 0.155
Kind of what I expected as the table's being driven in the positive
direction to get to X0 after tripping the home switch so there's no
initial backlash for the positive move to X100. The return trip in the
negative direction shows my typical backlash.
Adding a screw compensation table (type 0 with entries for every 10mm
over a 150mm run) and repeating the above I got:
99.995 0.010
99.995 0.005
99.995 0.010
99.995 0.010
100.000 0.010
That's a lot better and pushed the error down an order of magnitude into
the limits of my DRO's accuracy :-)
Remembering the negating effect of the homing sequence on the positive
backlash I thought I'd be sneaky and drive the table in the negative
direction before the test to maximise the backlash effect.
HOME
G0 X10
X0 <reset DRO X-Axis to zero>
X100 <take reading from DRO>
X0 <take reading from DRO>
Here's what happened:
100.005 0.000
100.000 0.000
100.010 0.000
100.010 0.000
100.010 0.000
I don't quite understand how Linuxcnc managed that but I'm not going to
examine the gift horse's gnashers too closely! I'll just conclude that
the time to produce a screw compensation table is time well spent.
I'm planning on doing a bit of nut tweakery to minimise the backlash and
then doing a proper high-as-I-can-resolution compensation table run
across the whole of the X & Y axis.
When I'm done I'll update the wiki page with my experience for other
newbies.
--
Regards,
Russell
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| Russell Brown | MAIL: russ...@lls.com PHONE: 01780 471800 |
| Lady Lodge Systems | WWW Work: http://www.lls.com |
| Peterborough, England | WWW Play: http://www.ruffle.me.uk |
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