Official Luthiers Forum!

I have noticed in a number of posts that some use random orbital sanders (let's call 'em ROS's to save some typing) for sanding guitar backs and tops. I have done a bit of commercial woodworking, and have even used hand belt sanders on some cabinetry and furniture, but for the finest woodworking projects, I always tried to avoid ROSs, due to the swirling cross-grain scratches they leave. Based on the fact that at least some of you using ROSs are professional luthiers, you must have found a balance somehow.

Obviously, higher grits and lower pressure are keys to getting less distinct cross-grain scratches, but they are still there. Do you always follow your ROS work with a final "with the grain" hand sanding, or have some of you found ROSs to be acceptable for the final pass?

I'm also inclined to use a flat, hard, block to prevent divots - which sometimes are undetectable until a gloss finish is applied. Even 220 grit can leave small divots, so how do you avoid them? (Or, do you take them out with a final hand sanding, using a block?)

Thanks!

Dennis

_________________
Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

Random orbit should varry the the orbit enough to not leave swirls. Now an orbital sander uses a consistant repeating orbit and would leave swirls. But a good ROS will varry the orbit enought to eliminate this issue.

I do heavy sanding if powered with my palm finishing sander. I don't use my ROS till 220 grit or higher normally. but even 120 grit will leave no noticable swrils and finer grits leave the wood like glass.MichaelP38799.421087963

You should check out the Festool RO sanders. Dang....I saw one with a fairly course grit, and I couldn't see any scratches after it had sanded some wood. It was amazing, and tons of torque, but you wouldn't know it by the way it felt in the hands. Gonna get me one someday...and one of their chordless drills...wow!

_________________
"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

I should have said an good ROS varies the orbit often enough. That is the key to no swrils

I suspect Dennis that what you had used was a pneumatic or electric orbital sander. These are often used in body shops to shape and smooth sheet metal, bondo and rough finish work. They have a cam that causes a rotary sander to vary it orbit a couple times a cycle. This is not enough to prevent swirl marks. The are great for rough shaping and smoothing but not for finish work.

Yes, it is good to make the distinction between "orbital" and "random orbital." I know some of the shop tools I used in the past in cabinet and furniture work were orbital sanders (electric and air), and, (in addition to the swirls), they may have left a lasting negative impression that I am unduly carrying over to random orbital sanders.

Thanks for the input, Hesh, Michael, and Don!

Dennis

{edit} My DeWalt ROS fell apart after being overworked on a house deck and railings, so I will have to get out my Porter Cable ROS and put it to the test.DennisLeahy38799.4477662037

_________________
Dennis Leahy
Duluth, MN, USA
7th Sense Multimedia

I just started to use a ROS on tops, backs and sides both before and after the box is glued up. I have a drum sander to thickness my wood and I have to leave it a little thick because I always end up with a few deep scratches from the drum sander. The ROS has been a real time saver and I find what ever scratches are left behind are easyly removed by hand sanding.
Don't forget to wear that reporator though!

Wade

_________________
Wade
Nashua, NH
http://www.wadefx.com

I'll use the ROS with grits over 120. Lower than that and you're asking for trouble, IMHO. I find it's better to look over the guitar with Naphtha and a good sharp scraper. After that it's 120, 180, 220 on the ROS and then 220 with my trusty Lee Valley sanding block followed by 340 and 400 (by hand)... Hope this helps.

_________________
I'd like to be able to prove, just for once, that money wouldn't make me happy...

I had an old Makita ROS which would spin very fast when run free. I had to make sure the pad was in firm contact with the wood before flipping the on switch, or nasty divots were inevitable.
My new Makita doesn't do this & is a joy to use. I go straight to 220 grit after the thicknessing sander. Works quick & smooth.
I now avoid using finer than 220 anywhere where there is dark & pale wood side by side, The finer dust grinds into the pale wood & is very difficult to get out. A good sealer coat on the light wood before sanding helps a lot.
It takes care & a bit of technique when levelling hard & soft woods together (ie. rosettes). If you aren't careful, you'll end up with the rosette proud of the top surface in some places.
If you are trying to sand dried glue off a wood surface with a ROS, you will usually end up removing a bunch of material around the glue before the harder material is gone... Much better to use a scraper till the glue is removed, & then sand.
I use my ROS constantly... It even works well (with very fine paper) for final sanding the neck shaft... as long as you keep it moving at all times.

Daniel, Great tips about rosettes and dried glue. I've only used my ROS for the last few builds and had not noticed those issues yet.
Thanks,

Wade

_________________
Wade
Nashua, NH
http://www.wadefx.com

I bought the festool 5" rotex a few weeks back, in orbital mode it eats wood, in ROS it leaves a fantastic smooth and dust free finish. With the vac attached the surface is clean and so is the air. Pricey, but I really got 2 sanders in one and it had better last forever. I bought the 5" because I'm working on an archtop and figured it would get into the curves better then the 6", plus I saved $5.. For flat tops I might have gone with the 6".

I have a Dewalt ROS and use it the same way as Wade, its a great time saver. Recently I have been using Abranet discs fom 120 to 240 I find them much better than standard ones.
Well back into work shop to cut some kerfed linings!

    Rick218

   I use ROS in the roughing stages but all finish work is done with sanding blocks.
john hall
blues creek guitars