Carve 'shifted' location on board after starting

[want2b]

Just had a really wild experience. Started a carve for a lithopane using the sled I made just for them. Watched it start and went into the next room
to work on something else, came back in a few minutes and the carving was going on but it had shifted the entire carve toward the keyboard
side of the machine. Attached pic shows the shift of 1 7/8 inches. You can see the first passes going across. I had just upgraded from 1.186 to 1.187
and thought at first there was a bug. Cut a scrap piece of 3/4 plywood and reran the same MPC and it went fine( I shut it down after 10%).
Am going to replace the sled and try again, just glad it didn't shift far enough to hit a screw. I think I will use glue only to laminate on the new sled.
Anybody else ever seen anything like this happen??
Sled idsa piece of 1/2 MDF with a piece of 1/4 with the center removed laminated on top.
Material was 1/4 bronze acrylic, trying the method Jeff Birt used without backlite.
Bit was 1/32 used in the same project.
MPC is attached with pic of carve.

Rick H.

[fwharris]

Your probably lost tracking on the Y to do some chips getting into the drive belt/gears...

[Digitalwoodshop]

This is a Classic.... Your Y Gear box is SHOT.... The 2 bearings inside the Y Gearbox and likely the bearings are shot and the machine has been shaving down the shaft on a taper. This lets the big plastic gear lean toward the center of the machine under load and AWAY from the Spline Shaft of the Servo Motor... The TIP here is that the Servo Motor ENCODER is HAPPY... SO the slip was AFTER the Servo Motor SPLINES.

Order the bearings from LHR or on line OR buy locally. LHR sells the Y Gear and Shaft too...

A DULL bit can Contribute to this but for the Y to slip that much the Bearings are shot... AND if the machine HAD fully completed the carving BUT off in the Y toward the keyboard... when the machine HOMED AFTER finishing Carving it would SLAM into the Keyboard side before it expected and you would see a Y STALL on the LCD or even a Clean Rails.... "Adding" confusion to the real issue.... Bad Bearings.... The Machine will usually CLICK 3 times when the Y is at the Bit Plate TOO....

Looking at the Photo again....It could be a DULL BIT.... To do Plastic you should stock up on NEW Bits.... Once the cutting edge is WORN.... You can have this happen and even SNAP the Truck.... LOTS of STRESS.... And you uses the very best settings to slow the machine down correct? The machine is DESIGNED with a Feed RATE for WOOD.... Plastic is VERY STRESSFUL on the machine.... It cuts TOO FAST for Plastic....

I wonder if 2.0 gave us any feed rate control??????

AL

http://www.avidrc.com/product/1/bearings/170/5x11x5-Metal-685ZZ-bearings.html TWO EACH in the Gearbox.