Sanding advice before refinishing

[CPike]

Hello all luthiers,

I am fixing up a bass and was wondering if anyone has some tips on what the finest grade of sandpaper I should use in preparing the wood for revarnishing. Any other advice and warnings would be welcome and appreciated.

Thanks, Chris

[mpm]

Which wood? Spruce and maple are two decidely different animals when it comes to sanding...

[CPike]

Both! I've stripped the entire bass and I'm ready to sand the whole shebang...

[mpm]

Well, be careful sanding the spruce. If it is a wide grain pattern, the wood between the grains sands out way faster than the darker grain wood. Consider using cabinet scrapers, they leave a much nicer finish anyway.

[CPike]

Great, thanks for the info - I've read warnings about using too fine a grade of sandpaper as it will cause the finish to not adhere to the wood as well. Do you (or anyone else) think 220 is fine enough?

[Martin Sheridan]

I usually sand down to 220 with a random orbital sander.

[robobass]

Wait, I'm no luthier, but I would think that powersanding any part of a double bass would be somewhat outside of standard practice! Comments from the experts? Also, scraping is an ancient art which requires some real training, or at least practice. I would recommend further research before attempting either of these procedures.
Robobass

[Bob Branstetter]

Originally Posted by CPike

Great, thanks for the info - I've read warnings about using too fine a grade of sandpaper as it will cause the finish to not adhere to the wood as well. Do you (or anyone else) think 220 is fine enough?

You didn't say if the bass is carved or ply. If it is ply, don't use a power sander. I've had dozen's of basses come into my shop where the DIYer had sanded through the top layer. It ain't pretty when that happens.

I prefer scrapers, but I've been using them for 40 years. If you insist on using a power sander on a carved bass, I would start with 220 and work your way up to 600. Varnish has a tendency to magnifying any sandpaper scrathes, so the finer the scratches (from the sandpaper), the less they will show. I've never had a problem with the wood being too smooth for the varnish to adhere. Actually, the better the wood is prepared, the better the varnish will look when you're done.

[CPike]

Thanks for all the advice, folks - it's been very helpful. Keep the comments coming! Bob, to answer your question, the bass is carved. I don't have a power sander, so it will all be by hand. I'm pretty good with a scraper on a fingerboard, but I've never tried it on maple or spruce.

Chris

[Martin Sheridan]

Bob,
You're answer is right on. Acutally, I use the sander and scrapers, but a sander will do.

If you're doing it by hand try using a thick rubber erasure as a sanding blockand possibly a cork from a whine bottle for the recurve, just make sure it's not to big.

[Michael Case]

Originally Posted by Bob Branstetter

You didn't say if the bass is carved or ply. If it is ply, don't use a power sander. I've had dozen's of basses come into my shop where the DIYer had sanded through the top layer. It ain't pretty when that happens.

I prefer scrapers, but I've been using them for 40 years. If you insist on using a power sander on a carved bass, I would start with 220 and work your way up to 600. Varnish has a tendency to magnifying any sandpaper scrathes, so the finer the scratches (from the sandpaper), the less they will show. I've never had a problem with the wood being too smooth for the varnish to adhere. Actually, the better the wood is prepared, the better the varnish will look when you're done.

Bob,

Other than cosmetic, what happens if the top layer is sanded through in small spots?

[Bob Branstetter]

Originally Posted by Michael Case

Bob,

Other than cosmetic, what happens if the top layer is sanded through in small spots?

The damage is mainly cosmetic, but there may or may not also be a structural issue here. I purchased a replacement back from Englehardt last year. The top veneer layer was literally paper thin and peeled back where I cut the outline and had to be re-glued before I could finish the outside edges. Then the glue made the thin veneer bubble. The older Englehardt backs had much thicker veneer.

Even if the damage is only cosmetic, it tells everyone who looks at it that the person who did the work was not a very good craftsman no matter how well the varnish is applied. A little more time and care is the difference between a good job and one that looks amateur with a capital "A".

[Michael Case]

I see, thanks Bob.