Official Luthiers Forum!

Hi all.

I've just purchased a wireless Ryobi random orbit sander to use for wet sanding my guitars. I'm trying on my first now, did three coats so far. The results seems to be ok, although I do have some questions.

First, I've noticed that some of the water seems to be pushed through the back by the vibrations and pressure applied by the sander, thus generating small drops of water inside the guitar. Is this common when using a randon orbit sander?

Secondly, and most important, the guitar seems to vibrate in resonance with the sander depending on where I'm sending and the sound becomes VERY loud, to a point where I'm wondering if so much vabration is structuraly ok or not... Any known issues about that? I wouldn't want to see the back or top cracking while sanding!

Thanks a lot!

_________________
Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

Alain, I don't wet sand with mine but I would not do anything that resulted in small drops of water inside. I do use the ROS on mine dry and you bet it's noisy, I see no reason why this should be a problem but wear hearing protection.

_________________
David White, Toronto

"All my favourite singers can't sing."

It is NOT a good idea to wet sand with an electric sander, wireless or not. The sander will suck up the water into the tool and it can short out. Also, if water is penetrating your finish and wood, something is very wrong, and your back may soon exhibit separation.

What the others said and in addition besides ear protection stuff a hand towel in the sound hole and that will help with the noise a great deal. I use a Festool, light weight ES 125 and don't press on the sander at all. I only take it to 220 prior to finish and get nice results.

I don't have a lot of experience making guitars, but I have a lot of experience with sanding.

I don't think a ROS or any electric sander could or should be used for wet sanding for several reasons. It's much more aggressive than hand sanding even at the slowest RPM--in finish mode it's imperative you control how much material you're taking off. Wet sanding papers are specially formulated to not deteriorate when wet and to lose abrasive at a steady rate to create a fine slurry with the water. That's what really does the smoothing. And, of course, in general electricity and water don't go together.

Finally, I personally like the tactile sensation of smoothing something with wet sandpaper by hand. You can feel the friction going away as the surface gets smoother. If you carry it beyond that point you risk removing too much material.

In other words, for surface preparation prior to finishing I have no problem with ROS and use it all the time. However, for final finish work wet sanding by hand is the way to go.

_________________
Without music life would be a mistake.

~Friedrich Wilhelm Nietzsche

The pro finishing guys use air powered sanders, I am forgetting the product names right now, and get good results.

Perhaps using a ROS, at least for the general sanding prior to finishing, is not unlike subjecting the guitar top to 24 hours of Smoke on the Water and loosens up the top a bit.......

Hesh is right, the Pros use air powered equip. I mostly w/s by hand with a block, but will use a sander for leveling the large flat surface areas. I use an old Makita 1/4 sheet sander that I converted for wet sanding by replacing the pad with cork. These old finishing sanders do not have any type of dust exhaust and do not pull any air/dust/water into the body of the sander, as do the newer type of ROS and 1/4 sheet units. I first saw this type of sander being used for wet sanding at Jean Larivee's factory in Victoria, BC years ago.

I would not use any sander that has dust extraction for wet sanding.

Cal

_________________
Remember, there are no stupid questions, only stupid answers!

I don't see how water could be pushed thru the guitar .It should be sealed
with pore filler and the nitro. I don't need fast production wet sanding so by hand
works just fine for me even if it can be a pain at times.

_________________
Anderson Guitars
Clearwater,Fl. 33755

Thanks for your comments guys.

Regarding the water going through the wood it seems to be on areas where I sended through the finish. So I'm less worried about that. I understand Barry's point about the top separating: if water gets inside glue joints, that's bad. But you have to understand that the drops of water are really rare, maybe 3 or four on the entire guitar back.

Regarding the elecrtical hazards, correct me if I'm wrong but I assumed that the worst that could happen with a wireless tool is a short circuit that would kill the tool without affecting me. If that's the case, that is a risk I'm willing to take. Specially since the dust extraction system is unfonctional: the holes in the pad are sealed by the extra soft cushion I added. The risk of water going all the way up the electrical unit is really not that great.

I'm not giving up on this just yet. I believe I have not laid down enough coats before sanding, resulting in water going into the wood. And using the towel inside the guitar should reduce the resonance issue (thanks Hesh!)

Oh and by the way, I'm not using nitro, but rather polyurethane. I'll soon switch to varnish though, but the sanding process should be the same.

Once again, thanks for your feedback, and I'll let you know how it goes.

_________________
Alain Moisan
Former full time builder of Acoustics, Classicals and Flamencos.
(Now building just for fun!)

First off I too think that pneumatic ROS is the tool for wet sanding and electricity and water don't mix well.

Another tip I got from a pro finisher is that your guitar is not flat, most electric ROSs have a too firm backing to account for the curvature of the body and neck in my opinion. I have a ¾” thick, a bit more cushioned backing pad I bought from Micro-Surfaces for the ROS I use on finishes. It conforms better to the contour of the body.

When the paper leaves the surface then reengages the surface you are likely to get those spiroghaph of cycle scratches some times left by ROS. If the paper stays in full contact this is far less likely to happen

I too have pretty much gone to dry sanding in most cases. I heavy level with 600, then 800 and 1000 3m hook it pads. I then move to MicroMesh 3200-12000. All done dry.

Another thing is not to add excessive pressure. The ROS is heavy enough to get the job done

Water seeping through finish is a sign of a porous finish and lack of grain filling and sealing