Equipment Issues for Final Door Sanding

Cross-grain scratches from the wide-belt, then swirl marks from the random-orbit sanders — what's the solution to minimize the final hand-sanding stage? November 26, 2006

Our shop does a lot of stain grade. We usually outsource our doors. When they come in, the rails always have cross scratches from the wide-belts, which means I have to sand out the cross scratches. Anyhow, we do not have air-driven sanders and our random-orbit (and even quarter-sheet finish sanders) leave swirl marks that stains highlight. This means I spend a lot of time hand-sanding doors. I have read that most higher volume companies have pneumatic orbit sanders that have a tight enough pattern that it doesn't show up in the stain. Is this so? The only compressor we have is a 5hp, 25 gallon that puts out, I believe, around 9 cfm. Can something like that handle a pneumatic sander? Likewise, how do I ensure that I'm buying the right pattern sander - what spec do I need to look/ask for? Lastly, what grit are you using on the pneumatic sander as your last grit?

Forum Responses
(Finishing Forum)
From contributor R:
I use a Dynabrade 5" orbital sander with 3/32" orbit. Works great if you don't force it down. We use 150 grit on final sand and usually hit it by hand in the direction of the grain. I'm not sure your compressor will keep up, though?

From contributor H:
If your compressor is a true 5hp and not a fake, "peak" 5hp compressor, then it just might be able to run one Dynabrade sander. It will be pushing it, though. If the compressor runs on a normal 120v circuit, then no way is it a 5hp, and no way is it going to keep up with an air sander.

You might want to try some different brands and types of sandpaper for finishing. Usually the paper backed sandpapers will give a better final finish with less swirl marks than the heavy discs. A quick finish sand with a Dynabrade with 150 usually works for me. Sometimes I'll go to 180 if I think it needs it.

From contributor T:
We pay Conestoga the extra $1 to cross grain/orbital sand (through one of their

100K sanders, I'm sure). Your door supplier have one? Check their catalog to see if you have to write it in like I do. If they don't, change suppliers. We bought a Fein 6" R.O. with vacuum (elec.). Works great - no swirl marks. The air ones just collect dust now.

From contributor C:
Look into an electric orbital like a Bosch. They are quiet and a reasonable entry level one is $80. You'll wear it out in six months, but the $180 will be your replacement. They work very good. We also have the Dynabrade 5" with both the 3/16 orbit and the 3/32 orbit, 2 each. They can only run one continuously or three intermittently on a Quincy 5hp 3 phase with 80 gal tank.

From contributor C:
A follow up to your sanding technique… Try going one grit coarser than you are on your first sand. Also remember the first piece you finish with a new disc is a serious test of your sanding skill. To not get any swirls or pigtails, never let the sander stop or start when in contact with the wood on the finer grits. Pick it up off the surface and then start the throttle.

From contributor A:
The air-drive ROs with vacuum assisted dust collection are the best, but they're real air hogs; most need about 17 scfm at 90 psi. They're expensive to run. If you want to run 1 - 2 of these and anything else (e.g. - paint spray gun), you'll need a big high quality air compressor. (Look on the compressor's tank for a label showing its specs, including its SCFM capacity. Don't go by its HP statement; these can be misleading.) For the best finish results, you'll need two: one 3/16" diameter orbit and one 3/32". They're usually about $150 - $170 with vacuum dust collection. If this doesn't work for you, look at the Bosch electric ROs. They're about as good as electric ROs get. The model 1250 DVS is a 6" dual-mode right-angle RO. It's much more powerful than the palm grip models most folks are familiar with. In the eccentric orbital mode, this thing removes material almost as quickly as a light belt sander. In the (fine finish) RO mode, it's 3/32" orbit will give you an excellent fine finish. They cost about $250.

From contributor L:
We use Dewalt 5" orbital sanders from Home Depot, 120 grit. No problems with swirl marks as long as you use the maxim of start on, stop off. The Dewalt sanders seem to turn much faster if you start them up before contact with the work and leave a deep swirl when you set on the work.

Years ago we had a thirty horse compressor and used the air sanders, but the compressor motor usually would last maybe a year, sometimes only six months before needing a $1000 rewind. Now that was forty people in the shop, but still expensive. One study I read years ago in a professional wood journal claimed that air was ten times more expensive than the equivalent electrical machine. The air sanders never broke down and were smaller and lighter and ran cooler.

We also use the Porter Cable six inch, grinder style handle. It is a little cumbersome for doors, but it doesn't leave swirls.

Are you using the old style "speed blocs" or quarter sheet sanders? What brand? I wouldn't do it myself, but we put countertops on some Home Depot, $36,000 cabinets last week and all the doors had cross grain scratches from the wide belt, along with the particleboard veneered raised panels. They were so cleverly done that I had to show the customer that the fake joints in the raised panels didn't match up on the front and back. Goes back to that old problem of us pros building to a quality that many customers may not appreciate.

From the original questioner:
Thanks for the input. I didn't figure our compressor wouldn't handle an air sander, but it was worth asking. Our sanders include a Makita, Rigid (5" random orbit) and one Bosch quarter-sheet sander. To not have swirl marks, we have to use 220 with the random orbits (which isn't a good idea with high-solids CV's) and 180 with the 1/4 sheet Bosch. And even then, even with a light touch (i.e., not grinding it) you can still see the small swirl marks, especially on darker stains.

We always have to mildly hand-sand with the grain to eliminate the swirlies, which is a major PITB when you have a lot of doors, and you still occasionally get cross-scratches near the rail/stile joint if you aren't very, very careful with the hand paper (I wrap it around an old sanding sponge). We are just trying to find acceptable ways to get away from as much hand sanding as possible while not using really fine grits, like 220.

From contributor H:
I don't know what you're using for stain, but I found that when I switched over to mixing my own dye stains (Sherwin Williams dye concentrate, acetone, and sometimes a little butyl acetate), swirl marks, scratches and glue don't show up nearly as much as with wiping stains. However, I have to say that I haven't been able to make a dye stain that looks as good on oak as a wiping stain. Maple is another story, though. Wiping stains totally ruin it. Just something to think about.

From contributor M:
Take a look at Festool. They might be expensive, but they are worth it!