Pneumatic Random Orbit Sander Marks

[Dry Pond Boat Works]

I recently bought one of those Dynabrade 5" random orbit (3/32" orbit) sanders thinking that it would be great, but I can't seem to get it to sand without leaving little "pigtail" marks that show up when you varnish the piece. I have had this sanding bare wood and cured epoxy as well as between coats of varnish. I have used conventional sanding pads and Mirka Abranet. It's gotten to the point that I don't trust it. I don't know if it's just the soft nature of varnish and epoxy as opposed to automotive paints.

Any similar experiences??

[Banjo]

Some random orbs are not true "random" and will leave pig tails no matter what paper you use. I normally finish of an orbital session with some hand sanding parralel with the grain it it's bright finished, going up in paper grades until the pigtails are gone or not noticable to the naked eye.

[JimConlin]

Before I condemned the sander, i'd try a different brand of paper. If the grits are of uneven size, the big 'uns will leave their mark.

[Ron Williamson]

Move the sander slower so that the curlies bunch up.
It also doesn't hurt to make sure that there are no leftovers from the last grit.
R

[Todd D]

I am with Banjo. If you plan to finish a surface bright, you really have to hand sand it with the grain. I now only use my RO sander for rough sanding at the beginning of prep before the first coat of varnish goes on. Even then, I only use it on big jobs. I then switch to hand sanding with the same grit used on the RO and work down to 320 before I lay first drop of varnish on.

[Canoez]

There is also a great deal of variation between sanders. While not pneumatic sanders, Fine Woodworking reviewed the new crop of electric RO sanders. They used a test where they sanded a piece of plastic so that they could see the scratch pattern. There was a wide variation between the sanders - on some you couldn't see the pattern at all, on others it was apparent.

I second the paper comment - good quality paper makes a huge difference. If the grit isn't bonded well, you can have problems from loose bits of grit gouging the surface. Also, if the dust isn't being cleared from the sanding area, that can be another problem.

[TerryLL]

I have two palm sanders, both Porter-Cable. One is very aggressive, the other not aggressive at all. Same speeds, same paper, but different orbit sizes. The aggressive one leaves pigtails in any grit, the non-aggressive one doesn't. I use the aggressive one for the first two grits, and the not aggressive one for the final two grits.

[Jay Greer]

For the ulimate smooth surface, my old stand by is an outomotive pneumatic sander known as an air file. This is a reciprocating long board and is especially effective for sanding masts and large flat surfaces as well as topsides. Paper can be purchased in grades ranging from 36 grit to 600 wet & dry. Paper can be purchased in clip on form or sticky back is handy for rapid changing. Harbor Freight has their own brand of air files at more reasonable prices than automotive paint stores. Sticky back paper is also available in roll form.
Jay

[David G]

The bulk of my 30+ years of woodworking experience, I've used electric sanders. Love RO sanders. Really like the Bosch 3725's I have now. I've used pneumatic RO sanders a bit, but am no experts. However, it is my impression that the air sanders in general are designed to be more aggressive than the typical electric. They were developed for the automotive and metal industries - where the coating would be opaque. It doesn't matter if there's a little swirl... it'll be covered by the primer. OTOH, I've seen beautiful sanding jobs done pneumatically.

Technique does matter. As noted, don't move the sander around too fast. Don't skip grits.

You can, as stated, work around the issue by finishing your sanding with a vibrator (as opposed to a RO, eg. Porter Cable Speed Block), or an air file - but you shouldn't have to.

I guess if it was me, I'd talk to my supplier, and see what his thoughts on the problem are. Maybe he'll swap you for one that's better suited to your needs.

Maybe you could finish your sanding with an electric RO. Or a vibrator.

[outofthenorm]

Technique does matter. As noted, don't move the sander around too fast. Don't skip grits.



At the risk of stating the obvious, a light touch matters as well. The last passes with your highest grit should be done with only the weight of the sander - little or no hand pressure at all. It's not really sanding at that stage - more like polishing. Also, don't let the sander slow down while in contact with the surface. But maybe you know that already:D

- Norm

[pipefitter]

Dynabrade is an excellent pneumatic tool. One of the top 3 perhaps. They have sanders for every purpose as has been mentioned. You will find Dynabrade in many high end automotive refinishing shops. What it does do is create a really nice key for primer surfacers, which then need to be block/board sanded (previously mentioned as well) down to very fine grits in all but brush application finishes. Using an RO or any power tool for finish sanding is cheating and as in much of the name, you will get random results. As far as using a RO for finish work(not final prep) on large flat areas, you will find that it's hard to beat the Dynabrade for consistency. There is also different backing discs for different operations as well.

[jgerber]

I have used Dynabrade sanders with a 3/16" orbit in my cabinet shop for at least 15 years. The original two that I bought are still in use. I love the new light weight ones. Recently bought another three for the high school where I now teach. My favorite paper is Mirka gold. I use a light touch, move slowly, work up the grits from 80, 100, 120, 150 and then hand sand lightly with 150 going with the grain. I do not use any finer than 150 do to the M.L Campbell Krystall and Duravar that I top coat with recommends no finer than 120 for a good adhesion.

JG

[pipefitter]

If you use the RO on smaller or narrower pieces of wood, it may not make efficient use of the orbital part of the process and will sand more like a jitterbug sander. Those squiggle marks are more prominent with jitterbugs. An RO allowed to develop full random stroke will not have those pronounced markings.