Trouble with rounded edges with dual action sander

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Forum topic by Woodworker123 posted 03-02-2011 03:20 AM 1448 views 0 times favorited 7 replies Add to Favorites Watch
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89 posts in 2853 days

03-02-2011 03:20 AM

I am trying to use a dual action air sander here at work to sand some panels, but I’m having trouble where the thickness is being tapered off near the edges. Besides simply trying to keep the sander parallel to the workpiece, and not letting it extend too far out, does anyone have any tips to avoid this, and how I might be able to fix it now, without putting through a planer again? The taper starts about 1/2” from the edge, it seems.

If it matters, I think this happens with 240 grit spray adhered to a stickback backing plate, which the edges of are ragged from having sandpaper spray adhered, as opposed to purpose made stick back sanding discs. We have a 3M hookit backer plate, but the coarsest grit we have is 400, and I won’t be able to try and find coarser until tomorrow. I didn’t think this would cause this though, if anything I would have expected it to cause the edges to be thicker…

7 replies so far

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89 posts in 2853 days

#1 posted 03-02-2011 03:33 AM

Now that I’m looking, I don’t know if I’m going to find the grits I need (120,180,220, etc.) for these 3M hook and loop backing plate. In that case, where might I find a 5” or 6” stickback backing plate that would fit a typical pneumatic sander? Am I just way off base, is a sander like this overkill for wood and going to be too difficult to control?

View northwoodsman's profile


242 posts in 3746 days

#2 posted 03-02-2011 03:48 AM

Place pieces of scrap wood, exactly the same thickness, around the edges. Make sure you keep the sander moving all the way out to the edges of the scrap pieces. Pneumatic sanders are far from ideal to be used in wood working for fine finishing. Often they are heavy, bulky and with a hose hanging from them, hard to control. Just my $.02. I’m sure there are many people that would disagree. The scrap trick works with any type of sander, electric, hand or pneumatic.

-- NorthWoodsMan

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530 posts in 2654 days

#3 posted 03-02-2011 04:08 AM

How old is the backing plate? I had a sander that the backing plate was getting old and it would flex really easy and cause these types of problems. Replaced with new plate, all is well.

-- Don, Diamond Lake Custom Woodworks - - "If you make something idiot proof, all they do is make a better idiot"

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89 posts in 2853 days

#4 posted 03-02-2011 04:37 AM

DLCW: Good point, the backing plate is at least a few years old, and has even been used on metal. Where might I find a replacement backing plate, and what is a good brand/model for woodworking? I haven’t figured out if they’re universal, these look like they have a 1/4-20 threaded rod that screws into the sander.

Northwoodsman: That’s a great idea. The nominal size was 1-1/8, but I had to take it a little thinner due to some unfortunate snipe in the timesavers sander. I have plenty of 1-1/8 MDF around, maybe that will work anyway, otherwise I can sand the MDF down a little maybe.

Do you guys use hook and loop discs, or sticky discs? What is a good brand/source of paper? I’m biased towards 3M, but most of their offerings seem to be for auto body/paint work, and maybe they aren’t the best option.

This sort of thing is just discouraging, just when I thought I had figured out a good method of avoiding hours and hours of hand sanding. I’m glad to get some ideas on how to solve it. I know a lot of people use a porter cable DA sander for auto work, and it’s a lot cheaper than the DA Festool sanders, maybe I’ll look around LJ and see how well it’s suited for wood, or what other good inexpensive options are out there.

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89 posts in 2853 days

#5 posted 03-02-2011 08:28 AM

I went ahead and ordered the Porter Cable 390K random orbit sander along with an assortment pack of Mirka hook and loop paper. From the reviews, it sounds like a pretty good sander, and I think sanding discs will be more accessible.

I look forward to trying the support board setup in a few days. Thanks again for the advice.

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250 posts in 2774 days

#6 posted 03-02-2011 08:44 AM

Northwoodsman got the rite idea

-- life an woodworking is one big experiment

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89 posts in 2853 days

#7 posted 03-02-2011 06:24 PM

As far as the issue of my material being slightly thinner than my MDF, I think I’ll try to find a shim material, so I can raise my material up to the level of the MDF.

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