Can anyone give me some idea how far below the infeed and sanding drums the pressure rollers should be? I am trying to eliminate some issues I am having with a SAC 37". I am getting uneven sanding, what feels like valleys in spots. I have re adjusted the platen which I think was too low, but now I am wondering about the feed rollers. Thanks.
From contributor Ge
I call them pinch rollers. I set mine just tight enough that he work piece doesn't get pushed back toward the operator.
From contributor PW
We just went through the EXACT same scenario. We were getting snipe and hesitation marks on both ends.
Our platen was low and after all my research (here mostly) I realized we've been using our platen wrong the entire time. I rebuilt and calibrated that which helped a lot.
The snipe was more the pressure rollers. Ours are manually set with a jam nut system. So with the platen up, I sent 2 boards through on each side of the belt that had already been sent through at the same setting (so that it only smudges a pencil mark) and stopped the machine mid-way through. Then I set the bottom nut so there was approx 1mm between it and its resting point.
That seemed to do it for us.
From contributor Ke
Thanks for the feedback. I think I have everything in order. Biggest issue was the platen being way too low (the scale used to adjust the platen was off), but also the pressure rollers were set too low as well. Boards were actually having a hard time getting under the first roller.
From contributor Ad
Hold down pressure can be tricky. Some machines have strong springs and soft conveyors. I usually start with .030" on stiff springs and .050" on softer springs.
The platen should be only a tiny amount lower than the drum in a single head machine.
Raise up the platen and sand a part with just the drum. Stop the machine and run the part back under the head. You can drop the tension and slide the belt back and forth as you drop the platen until you feel good drag.
Then you can run a part and look for longer scratch. This usually nails it right away. The platen only needs to take a couple thousandths, and only on the finishing pass. I pull them out for roughing so you don't have to find the right setting each time.