I have a problem and don't even know the question.

[silverspur1]

Hi, I have a hobby cnc, Although I have had it for over a year, most of that time has been spent scratching my head and wondering "why it did that". I finally have a bit of a handle on the basic things and can make a sign with few surprises. That was until today. My cnc worked fine yesterday, but today it looks like the zero point in the Y direction keeps moving.
For instance, I start a rectangle, it moves on the x, up the y, back on the x, and returns, but it moves past the zero point in the Y direction before going up the x again. On, the next trip around, the y axis does not go as far up the y, but on its return, it goes past the original point on the y and the offset point on the y. Each rectangle moves further down the y axis by about 1/4". The X and Z axis are steady.
I have no idea what to even ask, except, why and how can I fix it? All your suggestions and words of wisdom are appreciated. I have taken a look at the mechanical parts, everything seems tight so I assume it's software?

ps, kicking it does not work.


Please let me know what information you need.



Thank you,
Constance Ijames

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[Jim Dawson]

Kicking it would have been my first choice But it seems that didn't work.

Mark the mechanical parts (couplings, shafts, etc) with a Sharpie. That way you can see if anything is slipping. Then look for any mechanical binding in the system that might cause you to lose steps. Does it only do this when cutting parts? Try an air cut to see if you are getting the same problem, use the Sharpie again to put witness marks on the Y axis to see if the stopping points are the same. Is the position repeatable when jogging?

It really sounds like a mechanical problem, software doesn't change overnight.

[awerby]

As well as all that, if you can't find a mechanical cause for the problem, try powering everything down, taking a short break while the capacitors drain, then unhooking the cables from an axis motor that works and swapping them with the Y axis that's giving problems. If the problems switch over to the new axis, then it's upstream - either the cable, the driver, or something else up there in the controls. If the Y axis continues to fault, look again for a mechanical problem - the stepper motors themselves hardly ever go bad.

[silverspur1]

Thank you Jim and Awerby. Those are both excellent suggestions. I will give it a try tonight after work.