Arbortech Contour Sander causing swirl marks

[Bill Winter]

I sanded the interior area of this tray with an Arbortech Contour Sander to 220 grit. This is the first time I used this tool. I then stained the work piece. As you can see in the picture there are a lot of swirl marks and "pig tails". Does anyone what caused this? I wiped the work piece with Mineral Spirits prior to staining and none of these marks showed up at that time.464644

[Jamie Buxton]

Pigtails and swirls are usually scratches from left from coarse grit which you didn't sand out with your progression through finer grits.

[Kevin Jenness]

Can also be from loose grit left from intermediate sanding steps. Vacuuming between grits can help. I am surprised those didn't show up. Try better raking light for inspection.

[Bill Winter]

What is a raking light?

[Kevin Jenness]

Light coming across the workpiece at a flat angle. If you come in the shop early in the morning and look at a poorly sanded piece sitting on a bench by an east window you will get the idea.

[Bill Winter]

Thanks, Kevin! I purchased a raking light and it revealed imperfections I would have NEVER seen without it.

[Jim Becker]

Bill, you will find that using the same lamp and technique during finishing will also pay major dividends.