Why test a stick?

Wide belt stick testing and why you need to learn to do it.

I’ve been traveling the country calibrating wide belt sanders and teaching sanding in general for over 20 years now. I use extremely accurate Mitutoyo Digimatic indicators on custom built bases to measure these machines to within ¼ the size of a human hair. Even with this level of accuracy, I always do a check using pieces of wood to be sure that what I measured is exactly what is actually happening in the machine. Drums are not always round or even a true cylinder. I call this a stick test.

Why should you learn to do the stick test?

1.) No operator is perfect. They make mistakes and do dumb things. The best operators own up to it and learn. Those are the ones you keep.

2.) Sometimes abrasives get damaged. There could be a thousand reasons.

3.) Machines malfuntion.

If something goes wrong, do you want to guess what happened or do you want to know?

The stick test will show you the real cause of the issue and lead you to the fix in very short order.

How to do the stick test.

Picking the right wood

I like to use two pieces of maple around 2” wide and 3 ft long. It should either be dead flat or a slight smooth crown. You do not want ripples or twisting and you don’t want any hard warp. A slight crown (around 1/2” in 8 ft) actually works out very well. I like to get them both out of the same board if possible.

These boards will not be flat enough to trust the numbers you get from sanding them. Preparation for the stick test is as important as the test itself.

I will look over the pieces and lay them down with the crown up in the middle. Then I mark the full length of the pieces with a light pencil marks just to make it easy to see when you have cleaned up the entire side.

Let’s say that our hypothetical machine is a three head with a drum, drum, combi-head running 80,120,180 WITH NEW BELTS. I’ll level the surface I just marked by lightly sanding with the 80 grit. Some times this takes several attempts, closing the machine each time, if you are being properly careful. ONLY THE FIRST SANDING HEAD IS RUNNING.

Once the boards are cleaned up with no trace of pencil mark, write an R toward the end of one and an L on the other. This will help later.

Then pencil mark the other side of both boards and remove another 0.010” off the other side. If you need to remove more to clean up that is fine.

Now that the boards are flat with no funny ripples or bumps that would mess up your measurements, they are ready to be used.

Turn the boards so the R and L are on the bottom for a top sander, and oriented so the letters are on the lead end. Mark both with light pencil marks and close the machine to remove another 0.010”. Run the R on the right and the L on the left a couple inches off the edge of the conveyor.

If both have cleaned up with no pencil marks on them, you are ready to measure. If not close up another 0.010” and run both boards again. Once there is no more pencil mark you are ready to measure, but only in the middle of the boards since the crown is down and pushing the center of the boards tight to the conveyor. Write the thickness of each board on the back of the board.

If the machine has air exclusion you can pop the first drum up out of the way instead of turning it off. If the machine lacks this feature you will have to turn the machine off and wait for it to stop running. You can use the brakes but only if the machine does not change the conveyor height when you hit the emergency brake. It is critical that the machine height doesn’t change.

Fire up the second head and re-mark the part with light pencil marks. Run the part through just the second head and record the thickness on the back.

If the last head is a combi-head the platen needs to be left up out of the way or pulled out if it does not have a bladder that must be protected. Mark the parts with pencil and run the drum of the combi-head.

When you do the platen in a combi head you want to pop the drum up out of the way if you have air exclusion, or just leave it alone if you do not. Run the stick test on the platen and record the thickness on the back.

The numbers on the back of the boards are a map of how your machine is doing. How accurate is the machine side to side? How is the stock removal between heads? This information combined with a stock removal chart showing the correct stock removal to remove the previous scratch will answer numerous questions.

I recommend doing this test once a week. There should be no reason that the machine will need adjusting each time. It should only be confirming that the machines are correct.

 

Adam West

Techdude@surfprepsanding.com