How do I know when to stop sanding?

[funky_chavalo]

Hey, all! I have a custom wishbass coming in unfinished. It’s sanded to 100 now and I plan to take it down maybe to 12000 mesh pad or so before bringing it to a luthier to oil it. It’s an ash body with a walnut top and lead wood fingerboard. I’ve never done this before so my questions are, what should I know going in and how do I know when to move on to the next grit? I’m told this is all fairly straight forward but I don’t want to mess anything up if possible. Thanks, everybody!

 

[thabassmon]

Ok my opinion is the next grade should remove the mark of the previous grade.

Good luck.

 

[Sailfish]

To start, be careful with the lower grit sandpaper (like lower than 220), because it can cause hard to get out scratch marks, but don't be overly cautious. But anyways, for me, the easiest way to know how to move on is just by feeling the smoothness of the wood. So, at every step, feel the wood, and if it uniformly smooth, move on. Also, another important thing, which I had problems with begging wood finishing, is not to press too hard, just let the grit of the paper do the work. Good Luck.

Also, what you can do, is dampen a soft cloth or paper towel, wipe the wood and inspect the grain to see if it is suitable for what you want.

 

[Scoops]

IHMO....

I think you may have the work you want you luthier to do backwards
If you are new to this, have the luthier do the sanding.
You can do the oiling because it's pretty easy to do

 

[Gilmourisgod]

Get a REALLY bright light, or better yet bright sunlight, and look at it carefully between each grade of paper looking for scratches. If you miss any, the oil will pop them nicely later. Move the bass around and Look at it from all angles in direct, indirect, and raking light. Scratches you miss in one light will pop in another. Wetting it with Naptha won't raise the grain, but may make scratches visible. Make sure you blow off the whole thing with compressed air or careful vacuum job between grits, you have to get all the dust and grit off between passes. Look for tiny dings and dents too, it just happens. You can steam those back up to flush with a soldering iron and wet rag. Don't try sanding them out, you'll just sand a divot.

 

[dwizum]

Down to 1200 grit mesh on bare wood?

What types of wood have been used in this bass?

For most finish work I stop at either 320 or 400 on the raw wood - i.e. for a wipe on oil based poly finish on a maple neck I'd stop at 320. If you've got a wood that takes polish really well (i.e. colobolo, ebony, etc) and you're going for a totally "bare" look - like, for an oiled fretboard - then it makes sense to go further (but still, I usually stop at 800 or 1000) but otherwise you're chasing a difference that won't show in the final result.

I think you've gotten good advice above about finding scratches. Progressing through grits is helpful because it spreads the work out. Ultimately, if you're thorough, you really only need a few passes with each grit. The trick that is it's hard to be thorough and even. Make sure you're treating every inch of the wood the same - the nooks between the upper horns and the neck joint are a great place for scratches to hide. Or up close to the edges of the fretboard - it takes careful sanding to get that spot even because you've got a sharp inside corner there. Having a few different hard but flexible sanding pads or blocks will help, plus a soft one for the edges with the final fine grits. Use a hard block or pad for any areas you need to keep square (places like the sides of the headstock) - if you use a soft pad in those spots you'll end up with an uneven rounded off shape that won't be pleasant.

Be methodical - don't use more pressure in some areas and less in others, and try to take the same number of passes everywhere. I find that when I get scratches that persist, or divots, or other sanding problems, it's because I wasn't methodical about it - too much sanding in one spot, or I pressed too hard because I was trying to jam the sandpaper into a hard to reach spot, things like that.

Also - I agree with @Scoops regarding difficulty levels. If you can successfully sand a bass and prep it for finish on your own, then you are more than capable of wiping on an oil finish. Products like tru oil are totally idiot proof and very, very easy - it just takes a lot of time since you'll need a lot of coats, but the actual work is dirt simple and less challenging than doing a good job of prepping the bass. I don't want to scare you off sanding it yourself though, because it's not really THAT hard - but it is harder than the actual wiping on the finish part!

 

[Gilmourisgod]

I love Tru Oil, you can get any level of sheen you want. Too shiny? Knock it back to satin with a grey or white scotchbrite, stupid easy. It will NOT hide or fill scratches or dings though, the opposite actually, they will pop out. I found that out the hard way. I greatly appreciate the skills of Pro Luthiers, but there's no real trick to putting on Tru Oil. They have it at Wal-Mart last I checked, Birchwood Casey, sometimes its in the gun section because people use it for gunstocks. Prick a pinhole in the foil top and put a piece of tape over it under the cap or it will dry out and gum up. Some people keep the bottle upside down, I haven't bothered, but maybe that keeps the top layer of oil from getting oxidized. Sprinkle it on the bass in drops and then rub it in with a clean rag. The first few coats get sucked right up, mostly at end grain, so keep going with coats once a day until it looks like it's building up. Put the oily rags In water or spread them out In the sun to dry, that spontaneous combustion thing is real. In my case it took about 5 coats to start getting shiny. After the first few coats, go all with the grain. Plenty of YT tutorials on how to use it.

 

[Dirk Diggler]

Great advice so far, go by feel. Start working at feeling the surface, and as thebassmon said, stop when the lower grade marks disappear. You also don't want big jumps in grit, like don't go from 80 to 300, plenty of grits in between.

And indeed you can handle the oil part, sanding is much more difficult. If you mess up with the oil, you can easily just sand it off.

Take your time, I used to hate sanding and finishing, I've learned to embrace it, and surprising actually enjoy that part of the process now.

Good luck,
Dirk

 

[Paulabass]

I would stop the 100 grit right now. It's for removing/reshaping wood. Go to 320 now, and keep inspecting under good light till all the sanding marks from the 100 are gone. This may take some work, cause the 100 is like dragging it down the driveway. For tru-oil finish no need to go past 800.
Save the money and do the oil finish yourself, it's the easy part.

 

[byacey]

A sharp scraper will smooth it out after the coarse sandpaper faster than moving on to 320 grit paper. You may have to resharpen the scraper a few times, because sandpaper leaves abrasive particles in the wood.

 

[dwizum]

One more tip - wash your hands! The normal moisture and oils on skin can interfere with finishing. No one wants a faint fingerprint sealed forever under their bass's finish.

 

[funky_chavalo]

There is an insane amount of incredible and helpful information on here. Thank you everybody for the help and guidance! It’s well appreciated and I’ll post pics up when I’m done

 

[Rôckhewer]

REALLY bright light, or better yet bright sunlight,

I also like to check with a flashlight...with beam pointing across at a very low angle. (Scratches cast shadows... sorta)

For tru-oil finish no need to go past 800

I don't think I would even go that far.
You don't want to polish the surface. Even oil that penetrates needs a little "tooth".

 

[bolophonic]

I agree that the sanding doesn’t need to go anywhere near 12000 grit mesh. I would start at 220 until the rough marks are gone and work my way up.

 

[Ggaa]

When I was doing a little bit of finish work years ago....to tell if it's time for next grit of paper, clean the piece thoroughly of sanding mud, let/wipe dry. I had to hold the piece at a certain angle to the light to see the surface clearly(shiny spots, scratches etc).

 

[Gilmourisgod]

I think I went up to 400 grit on this one, which was probably overkill. Once it's soaked in good, subsequent oil layers go on very thin, so it does take a while to build up any thickness. I lost count, maybe something like 20 coats?

 

[JRA]

beautiful, Gilmourisgod .

 

[micguy]

The higher you go in grits, depending on the wood, the less the wood will take oil. It's even more pronounced with regular stains, but I rarely go past 320. Much of the time, I'll do end grain a grit or two higher (say 320) than the face grain (say, 220), to try to make the stain or oil more consistent across the different parts of the instrument.

 

[7dollarbologna]

I got me a wish bass!

 

[Plain Old Barry]

I make antique reproduction furniture, not instruments, so this is where the following comes from...

- With an oil finish, there's no need to go above 800, many stop way before, as low as 320 or 400. You can actually rub the oil in with higher grits which will fill grain. Sanding too finely burnishes the grain, closing the pores, retarding the penetration of early finish coats.
- Card scrapers are fantastic, faster and and more efficient than sanding, but the sharpening and learning curve can be steep. Stick with paper if you haven't really learned to scrape. There have been demo after demo where pros can't tell the difference between a properly sanded and scraped surface once a finish has been applied. Lots of folklore there...
- Always sand with the grain.
- Use naptha or denatured alcohol and raking light to see scratches. Each grit should remove all previous scratches.
- Always use a padded backer block, such as cork, felt, or rubber behind sandpaper, not your hand. Blocks can be dowels or curved surfaces for some areas, but they still should be padded. Rubber mouse pads can be cut up for great backing material.

** The best way to learn finishing is with decent sized scraps of the original wood, prepared (sanded, scraped, oiled, or film finished) with the same steps as the project! Write every step in a notebook or on the back of the scrap. Make your mistakes on the test pieces. Once you like it, follow the same steps on the project. Save the notes and/or the successful test piece for next time. **

Have fun!