Step Loss (again)

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Kevin - 21 Apr 2009 08:48 GMT

I've been trying a few things before replacing the drivers and/or
stepper motors. I ran a 2D program, that cut a name plate. The
program was 5200 lines long, and cut 1mm deep in two pecks. I'm
looking at the difference in position between the upper and lower
level. The lower level is out of position to the top one. I ran the
program twice, once with the feed rate set at 1000mmpm and
acceleration at 50 and once with feed rate set at 400 and acceleration
at 10 (on motor tuning). If this was a problem with losing steps due
to over accelerating or going too fast I'd have expected a noticable
difference in the test pieces, but there isn't. The movement between
the two levels is +0.35 in Y and +0.2 in X. Actual size of the sign
(80mm x 40mm) is within 0.1mm -which is reasonable measured with a
digital vernier and allowing for possible cuttter wear. Any
suggestions where to go next gratefully received, as I'm not too sure
right now.

Regards
Kevin

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BooBoo - 22 Apr 2009 23:49 GMT

Help is out there Kevin but you're a little too pedantic for me.

What machine?

What software?

What work?

Set your work near the centre of your machines envelope. Try cutting a
simple circle, say 50mm in diameter. Do 2 passes, 1 at 0.2mm & 1 at 0.5mm.
Returning to zero after the first pass. Do this at a slow speed like 60mmpm.
WRITE THE CODE YOURSELF, that way you can rule in/out at least 1 thing.

The only times I've lost steps is (1) My computer running Mach3 couldn't
cope & (2) I asked the machine to go to the very limits of its envelope.

In trying to decipher your problem I'm guessing that you're cutting
something in 2 passes but the 2 aren't matching exactly?

Have you browsed whatever code you're feeding the machine? The X & Y
co-ordinates should be exactly the same, only the Z is differant.

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Lester Caine - 23 Apr 2009 07:39 GMT

> Help is out there Kevin but you're a little too pedantic for me.
>
[quoted text clipped - 3 lines]
>
> What work?

Seconded ;)
We need to eliminate something from the list of possible problems so we
can help.

Signature

Lester Caine - G8HFL
-----------------------------
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Kevin - 25 Apr 2009 04:31 GMT

> > Help is out there Kevin but you're a little too pedantic for me.
>
[quoted text clipped - 16 lines]
> Model Engineers Digital Workshop -http://medw.co.uk//
> Firebird -http://www.firebirdsql.org/index.php

Sorry, just to recap from my earlier post. Machine is a Denford
Triac, which has had the original stepper drivers replaced with the 3A
ones from Arc Euro and a new PSU but retains the original stepper
motors. Control is now via a PC running mach3, through a CNC4PC C11
board. I'm happy the program is correct, and yes the problem is that
the two levels of machining are out of position to each other. I'll
try the circle trial suggested, but on small programs I haven't been
able to find dicrepencies before. I only started to notice the error
when I started sending larger programs to the machine.

Regards
Kevin

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Kevin - 27 Apr 2009 04:39 GMT

> Help is out there Kevin but you're a little too pedantic for me.
>
[quoted text clipped - 17 lines]
> Have you browsed whatever code you're feeding the machine? The X & Y
> co-ordinates should be exactly the same, only the Z is differant.

I've just run some more test programs, using the wizards in mach3 to
generate the code (but I'm positive it's not a code issue as it has
done it with code from different sources). I cut two square pockets
with a round upstand in the middle. Measuring round the circles they
are, as close as I can measure, round and the correct size. Measuring
the step between the circles (which is why I left them standing up -
easier to measure) in Y the gap is 4.95 on both sides, but in X the
gap is 5.00 one side and 4.90 the other. So it seems that I've lost
position again. This is the same as all the other tests, a very small
step loss. This program had rapid moves in it, between the passes
clearing the material away. My next move is to edit the program and
make all moves at feed rate.

Regards
Kevin

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Model Forum / General / Models / April 2009

Step Loss (again)