Well, See your problem.

Keith Newton
You said, "Been upgrading the lighting". You just need to turn your lighting back down until you can't see it. ha

I've got a Oakley stroke sander that really does a great job. The sanding platen on it is covered with a graphite canvas which rolls up on the front and back end. The belts run about 60 mph, and the platen connects to a traveler car above with a lever arm that I apply the pressure with a 3.5 lever advantage, so if I press down, the pad presses 35. One thing I had to quickly learn when I got it, was that it cuts so fast that if I just just traversed up and down the belt while doing wide panels, there would be small steps along the edges of the path from each pass.

The cure was to sand diagonally by moving the table in and out while the platen strokes are left and right, up from one end of the project then swap the diagonal to the opposite on the way back down. ///////\\\\\\\\ This took care of the problem. But once a chip got behind the canvas, which put deeper shallow marks like that.

I have gotten a chip under my hand held Rockwell 503 which will cut a rounded mark, as will a worn out platen, which buckles on the end. That sander is worm drive, and kinda tall and heavy. If a new user accustom to a lighter sander uses it the same way they normally do, the startup torque will tip it over to one side while it spins out getting traction and dig a hole, so it always needs to be started above the work, then engaged while moving the way you intend to traverse. From what I learned on my stroke sander, I adapted that for when I'm using my hand held sander also, as well as lifting some of the weight at the ends when changing direction.

As for the random orbit swirls, I start at 180 grit. If you start with 120, you really need to spend more time with all the following grits to get those deep swirls out.

So, to sum up using the belt sander, inspect the platen and under the backer pad to make sure they are clear and flat. Set the sander on the work, but lift it before hitting the switch, then come in for a landing like an airplane. If the surface is wide like a table top, make diagonal overlapping paths, and lift some pressure off as you quickly reverse directions. 100 and 120 are what I use most.

By the way, I'm not sure most people know that a belt sander will cut faster across the grain, so if you have some tear out like around knots that requires a lot more sanding, you can get that done faster by going across grain first before doing the in-line sanding. Just don't make that a steep sided dish or it will show up after finish.

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