Design shifted while carving

[doug]

Doing a lithopane carving, about 35% through the carving the design shifted 3/8" over and continued carving. The bottom of the design was off the acrylic. What could have cause this?

[fwharris]

Doing a lithopane carving, about 35% through the carving the design shifted 3/8" over and continued carving. The bottom of the design was off the acrylic. What could have cause this?

Dust/chips from your litho material got into the drive belts and gears causing them to skip/jump. Even with dust collection I find in necessary to pause the carving to clear the chips out and away from the belts.

[bergerud]

Welcome to the forum Doug. It is important to have a new bit when carving plastic and to carve on best or optimal. The carving forces can be much larger with sticky plastic. The pattern probably shifted due to the y belt slipping. If you look at what the bit was doing at the slip, you will probably see that it was plunging deeper into the plastic.

If your bit was old, try a new one and that may solve your problem. If the bit is new, you may want to through the y belt "re-tighten" routine. If your machine has upward of 250 - 300 hours, the problem could also be due to worn out bearings in the y gear box.

[CW-HAL9000]

On lithos I always use a sled with masking tape on the bottom for the tracking roller. I also have a dust devil dust collector and sometimes use compressor to blow out clinging chips from the belts, rollers and tracks during a carve. Dont forget the 7 inch rule. I usually do 5x7 1/4 inch thick lithos and I have two 1/4 inch thick 4 inch wide boards on both ends of my corian to ensure my sled and litho are always under the rollers. I use jog to center and mark the center of my 5x7 piece of litho corian before putting sled into machine. Of course I always use best or even optimal if It is a detailed and or high selling price litho.

[Digitalwoodshop]

Like above, Dull Bit and the Y Gearbox Skipped some teeth... due to worn out Y Gear Box Bearings...

AL

[doug]

I'd like to thank all for the replies. I noticed where it had skipped/jumped was at a deep plunge. But before I start another carving, I will give it a GOOD cleaning, restart with new bit. I had done about 8 small (6x4) lithopane carvings with minimum cleaning. I will see what happens then.

[Digitalwoodshop]

Remember the machine has a feed rate set up for WOOD... So this Plastic cutting is really pushing the machine.... The feed rate is really TOO Fast for Plastic... That is why the machine "Gave an Inch" when tasked to do that deep cut... Something "slipped" and likely it was the Servo Motor Shaft to Big Plastic Y Gear.... Because the 2 little 685ZZ Bearings have FAILED letting the big plastic gear TILT toward the center of the machine when tasked to do that big deep cut in the plastic.... This is a over kill worst case.... In all my years, I had never seen a Y Belt slip... It has always been the Servo Shaft to big gear connection or mesh...

Before you go again and waste more plastic, I would pull the Y Gearbox and inspect the Y Gear... If is likely starting to wear THIN at the base... due to worn bearings.....

This is why we recommend replacing the bearings before they fail at 250 cut hours.

http://www.avidrc.com/product/1/bearings/170/5x11x5-Metal-685ZZ-bearings.html

AL