What's the cause of board slipping on sand paper belt?

[TurtleCove]

I've been carving some cedar boards that are 41" long, and 3.5" wide.
All of a sudden, when it measures the board in the beginning, part way thru the measurement, I see the sand paper belt moving, but the board not. I've tried a couple of boards, and it's happening with both. Boards are nice and flat.

What's the typical cause of such behavior ?

[bergerud]

Does it happen when the ends of the board are trying to push up the rollers? Head pressure or non level head? Tape on the bottom of the board for traction?

[fwharris]

Adding to Bergerud's comments,

Dust between the belts and the tray.

Belts are stretched on one end (keyboard side) from doing lots of narrow board carvings.

[TurtleCove]

Does it happen when the ends of the board are trying to push up the rollers? Head pressure or non level head? Tape on the bottom of the board for traction?

No, it's happening about 1/2 way thru the board.
ok, I'll add masking tape to the board bottom, for traction.

[TurtleCove]

Adding to Bergerud's comments,

Dust between the belts and the tray.

Belts are stretched on one end (keyboard side) from doing lots of narrow board carvings.

Are you suggesting I remove the best, and clean underneath it?
Or are you suggesting I replace my belt?
This belt has less then 15 carvings on it.

[bergerud]

No, it's happening about 1/2 way thru the board.
ok, I'll add masking tape to the board bottom, for traction.

There must be something causing drag. Something jammed above the rollers? Check the rollers. (It is not that the out feed tables are too high is it?)

[fwharris]

Are you suggesting I remove the best, and clean underneath it?
Or are you suggesting I replace my belt?
This belt has less then 15 carvings on it.

I was just tossing out possible causes. If the belts are basically new I would not think they are stretched. You might be able to blow air under them with out taking the belt tray out.

Can you manually push on the belts and move the them with out them slipping on the belt tray?

Also make sure they are not rolled over on the ends.

[TurtleCove]

The rollers turn freely, when I try to turn them by hand. So, nothing is jammed.
The outfeed tables are not too high....maybe a bit low, but they are not the cause.
Maybe the cedar is just too smooth on the bottom...and masking tape will help.

You suggest "too much drag". Like too much head pressure? I would think not enuf head pressure would cause slippage.....

[bergerud]

I did not mean head pressure when I said drag. I meant something else like a piece of wood jammed in above a roller. Try pushing the board by hand. Can you make it slip? If so, head pressure or head not level could be it.

[bergerud]

Could the gear on one belt be slipping (so that belt is not driven). Watch to see if both belts are slipping together on the board. If one belt slips and the other is stationary, it would be a drive problem. Did you adjust those end gears when you changed the belts? Just another thought.