View Full Version : Odd glitch around 46 ins. in Y

11-22-2006, 07:27 AM
We were cutting several hundred feet of decorative fascia board
when we noticed that the uppermost part of the pattern
-a 3 inch circle- wasn't cutting quite circular!

The tip-top bit of the circle was being cut as a 1 inch flat, dead straight,
rather than a curve.
We were cutting 12 ft. boards along the FAR edge of the table,
not up close along the usual Near edge,
and so this problem is manifesting itself somewhere around 46 inches in Y,
along the entire X-length of the table.

Upon discovery of this problem, we then did a lil detective work,
going thru the boards we'd cut, to discover that this problem has been incrementally creeping up on us,
and we've only now(now it's got bad!) noticed it!

We re-did the geometry, re-did the NC,
even threw out the lil gold-sprocketed .ini file,
- even reinstalled the SB Control software
(replacing 3.4.25 with the original 3.4.19 wot came with the mid-2006 PRT96..non-Alpha)
Nothing worked...except moving the whole cut down about a foot,
and problem 'disappeared' at least as far as our job goes.

Now we're finished cutting, we did a CR 48 x 96 command running the gantries the extent of the table, while closely checking for the glitch,
to discover it's still there, around 46 ins. in Y
both going up to the far edge of the table,
and coming back down from that far edge..at the other X end of the table.

At speeds below 1.5 inches a second, it's more noticeable
at speeds above 1.6 i.p.s. you'd hardly notice it
(this is without load,router noise,etc., eh?)

It doesn't seem to be anything physical/mechanical on the actual steel machine itself, coz we ran a buncha simple tests with motors off, hanging down from the rack,etc.
Seems to be a software glitch?


11-22-2006, 09:53 AM
Just a thought????
I once had a problem with the plastic wireing harness binding on the wires putting too much tension on the "Y" axis when it moved towards the 47" area, Maybe you could loosed your wires on the harness and re check
That problem was on my PRT not my ALPHA

Good luck

Brady Watson
11-22-2006, 11:13 AM
I would check to see if the tool is mechanically binding or not moving smoothly in that area. Move the tool (under power) near the affected location & then turn off the control box. Physically move the tool (slowly) and feel if there is any mechnical resistance. To play it safe, unplug the Y-motor cable from the control box AFTER you have turned the power off. This will prevent a blown driver when moving the Y motor by hand (they act like generators). Work the Y-car back and forth and see if it is smoother in the center of the X-car or if you feel any difference. Check to make sure that the pinion is not worn, loose or hitting a stop. As John pointed out, check that the wire guide is free-moving and not causing the stepper to stall. If you have limit switches, make sure they are not being triggered. Inspect the gear rack and make sure that there isn't any foreign debris in the teeth. Under power, move the Y car as far is it will go and note the position. Listen for stalling.


11-22-2006, 06:46 PM
Thanks for suggestions.

11-22-2006, 09:34 PM
Did some consulting for a local shop, they had a similar issue. The takeup springs were way over tighten and causing some binding, and, they had a number of worn components as a result.

Just a thought. Brady, any parameters that could cause this kind of issue? Ramping?

11-22-2006, 09:58 PM
From the sound of it, it sure looks like missed steps to me. I think that mechanical interference would be my first guess.

11-22-2006, 10:05 PM
I'd follow Brady's approach.

I have a hard time believing it is a software issue. Just to be sure, re-zero out on your table as far as possible and see if the glitch moves staying at the 46" mark from 0.

The gantry moving smoothly with the motors hanging off the rack proves the rails and wheels are smooth. Check your pinions and tracks, there's gotta be something binding.