wierd skip in cutting file

[SKeller]

has anyone ever experienced a 'semi-random' skip in a cutting file? I have a project where I am cutting 110 identical parts. The paths include a large pocket, three small pockets and one profile cut. On most occasions, the CNC cuts just fine, but every 4th or 5th time, there is a screwup...As the CNC travels on the Y axis after cutting the large pocket (8 minute file) it sometimes pause/skips and tries to cut the next pocket in the wrong place... somewhere between 1/4 and 3/4" short of where it is supposed to. This throws off the orig. y position and makes all of the subsequent cuts in the wrong place. I am able to watch and see if the path will screw up/hesitates and stop the cutting. I move the router to home (which is always off only in the y axis) and find home again at which point I run a second file I have created which does the four paths excluding the large pocket. UUgh. I just wish I didn't have to manage this and it would do it without failing every so often. Any thoughts? I am thinking it may be in the gears of the y motor??? I don;'t think it is grounding as it is not as 'random' as other times I have experienced grounding problems...
Thanks in advance!
Seth

[garyc]

Seth...
There are 3 issues that create the scenario that you describe.

1) Static.
May show up as almost repeatable when the DC hose touches a portion of the YZ car or the Zzero plate or ground. Usually the axis in motion is affected. Check by running the file, paying particular attention to DC hose and/or its ground connections. Also test to see if problem persists when DC hose is removed from and not touching the gantry or YZ car.

2) A physical bind in the axis mechanics. To check, disengage the motor(s) and move the axes thru their full motion by hand. Also use a light and check for debris in the rack. Check all axes as the Z may be the most clogged and the least visible. Clean and lube as needed.

3) Cutting speeds too high for the material or machine type. Test by cutting speeds in half (or more) and re run the file.

[SKeller]

I imagine it is the second scenario. I actually don't have DC hooked up because of static issues. accumulated dust may get up into the gears in approximately the same way after cutting that big pocket 3-4 times I suppose. I'll watch more closely and see. THanks.
Seth

[garyc]

Seth...
Sometimes (when the bind is a clogged rack) it is neccessary to move the axes with the rack engaged to properly diagnose. Slow speeds and/or motor cables disconnected will ensure that the steppers dont generate pulses that destroy the driver(s)