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Sanding advice needed

Discussion in 'Luthier's Corner' started by brstma, Oct 23, 2013.

  1. brstma

    brstma my dog is an awesome dog Supporting Member

    Nov 20, 2008
    I am refinishing a neck thru bass with a redwood top. There were quite a few deep scratches on the top so I took it down at least 1/16". I got it looking really good but when applying the first coat of "tung oil finish" I accidentally scratched the top with my fingernail (which I clipped before starting :rolleyes: ) so I had to take the top down some more.

    Now I am having trouble rounding over the edges on the inside of the horns near the neck / fretboard. It is impossible to get it with a finish sander and sanding by hand is going against the end grain and leaving scratches, but I need to use a grit that's coarse enough to shape the wood.

    Do you have any advice or tricks for getting into those hard to reach places? Should I use finer grit and more elbow grease?

    I was looking at some rubber contour sanding pads but I'm not sure they will help much in the tightest spots.
  2. suraj


    Oct 1, 2008
    Mumbai, India
    Use files to get almost exactly the shape you want, then use sandpapers. Thats what I did on my neck through build when I had to shape the inside of the horns where they meet the neck/fretboard. I used a round course file and a half round course file alternating with smooth files to see the progress I was making. Lastly I used a very smooth round needle file to get it perfect. Like this -

    Read post #215


    Post #245
  3. Projectile


    Feb 5, 2009
    Elbow grease is the only way that ever worked for me.

    I'm surprised that some people use redwood for guitar tops. It's such a soft wood and so easy to dent and scratch! Are you sure a tung oil finish is going to offer enough protection?
  4. Tdog


    May 18, 2004
    Here is a quick trick for you guys.......

    You can eliminate surface scratches along with minor dings and dents by first wetting the area with a damp cloth, small sponge, or water soaked Q-Tip. Don't flood the surface, but get a few drops of water on the effected area. Let the wood fibers absorb the water......Take a heating iron of some sort ( I use an old photographic slide iron, but a clothes iron would work too) and gently heat the wet area and this will cause the grain fibers to swell and expand.....Let it dry and sand back!

    I've remove serious dings from many bodies and necks with this method. It works better(quicker) on softer hardwoods like Koa, Limba/Korina, Mahogany, and Maple

    Don't use a soldering gun!!!!! You can guess what will happen. You could use a small iron like the ones that are used to burn in lacquer sticks...... Take your time. You may have to repeat this action several times because when the wood cools, it will contract slightly.....On more serious scratches and dings, you may have to raise the grain by using this method over the course of a day or so with many applications.

    Obviously this works on raw, unfinished wood.

  5. lbridenstine


    Jun 25, 2012
    I agree with suraj. Files/rasps, then sand. Maybe a scraper too.
  6. brstma

    brstma my dog is an awesome dog Supporting Member

    Nov 20, 2008
    Thanks. After suraj recommended files I remembered that I have a set of fine needle files that did the trick. Now it's just a matter of patiently sanding by hand.

    When Peavey made the production line redwood Cirrus models they all a had lacquer finish. This one is a custom ordered model with an oil finish, presumably tung oil. I knew little about redwood but it was obvious that the factory oil finish was not enough to protect it by how many scratches and dings there were. I am using the Minwax tung oil finish which is a mix of boiled linseed oil, varnish and mineral spirits. I can already tell it will protect better than the original finish. I considered Formby's tung oil finish, which is just varnish and thinner with no oil, but it's not much different that polyeurethane and doesn't look as nice IMO.
  7. Hopkins

    Hopkins Supporting Member Commercial User

    Nov 17, 2010
    Houston Tx
    Owner/Builder @Hopkins Guitars

    Formby's is a tung oil and varnish blend and is nothing like a polyurethane finish. I prefer it over anything else as far as an oil finish goes.

    This bass was finished with Formby's low gloss tung oil and paste wax

  8. brstma

    brstma my dog is an awesome dog Supporting Member

    Nov 20, 2008
    Are you sure? I read the following on the minwax forum that listed some ingredients of "tung oil finishes" and Formby's was listed as having little or no oil at all. I've used the Formby's before and thought it was OK, but I decided to give the Minwax a try after reading this. Most "tung oil finish" products have no tung oil at all.

    There are two types of "tung oil finishes". One is mixture of varnish, boiled linseed oil and mineral spirits (called an oil/varnish mixture). The exact mixtures are proprietary (more oil means a softer finish. More varnish means more protection and durability). Some manufacturers add a dollop of drier to speed up the drying. If you want make your own, mix equal parts of boiled linseed oil, varnish and mineral spirits which will make a nice finish. This same mixture is frequently also called "Danish Oil". It closely mimics a true oil finish but the addition of the varnish resins gives it more durability and protection. These finishes are designed to be a complete finishing system. They are not intended to be overcoated with a film finish. When you do so, you are destroying the look and feel of the finish. For the most part, "Tung Oil Finsih" and "Danish Oil" are identical. They are both oil/varnish mixtures.

    Here are some oil/varnish mixtures:

    Deft Danish Oil
    General Finishes' Seal a Cell
    Behlen Danish Oil
    Maloof Finish (contains pure tung oil and linseed oil)
    Behr Scandinavian Tung Oil Finish
    Minwax Tung Oil Finish
    Minwax Antique Oil Finish
    Velvit Oil
    Watco Danish Oil
    Liberon Finishing Oil ((contains pure tung oil and linseed oil)
    McCloskey Tung Oil Finish (contains pure tung oil, no linseed oil)

    The second "tung oil finish" is one made from varnish and mineral spirits. The approximate ratio is 1:1. This is really just a thinned varnish just like the stuff sold as "wiping varnish". When one two or three coats are applied, it also mimics the finish produced by a true oil but it is harder than the oil/varnish above because it does not have as much oil. It is slightly more protective than the oil/varnish type or tung oil finish. For all intents and purposes it is a varnish finish.

    Here are some thinned varnishes:

    Minway Wiping Varnish
    Watco Wiping Varnish
    Formby's Tung Oil Finish
    Zar Wipe-on Tung Oil
    Hope's Tung Oil Varnish
    Gillespie Tung Oil
    Waterlox Original Sealer/Finish
    General Finishes' Arm R Seal
    Jasco Tung Oil
  9. Hopkins

    Hopkins Supporting Member Commercial User

    Nov 17, 2010
    Houston Tx
    Owner/Builder @Hopkins Guitars
    It says on the can that its a tung oil/penetrating oil/varnish blend. Formby's has always worked very well for me, especially when finished off with a good coat of wax when finished with the oil. Formby's low gloss with a good coat of paste wax makes for a nice luster.
  10. brstma

    brstma my dog is an awesome dog Supporting Member

    Nov 20, 2008
    I does say that on the can.

    I am finding that the Minwax doesn't build up as easily as the Formby's, and when a medium to heavy coat is applied it dries with a gloss, where the Formby's stays low gloss.

    What paste wax do you use? Does the wax offer extra protection or is ot for appearance only?
  11. Hopkins

    Hopkins Supporting Member Commercial User

    Nov 17, 2010
    Houston Tx
    Owner/Builder @Hopkins Guitars
    I have a can of Minwax paste wax that I have had for the better part of 3 years. It basically gives the low gloss oil finish a little luster. I use an oil finish when I want a low gloss finish that feels like bare wood, so I don't want it to build up to a high gloss hard shell finish, I have a spray gun and urethane clear for that.
  12. brstma

    brstma my dog is an awesome dog Supporting Member

    Nov 20, 2008
    I applied a couple coats of the Minwax tung oil finish but it was coming out way too glossy, so I decided to sand again and use the Formby's instead.

    Now I'm having trouble with sanding marks I can't get rid of. I let the bass sit for a week to dry, then sanded down to wood again. I was having trouble with the marks so I let it sit for another week in case it was the fresh oil finish causing the trouble. I am still getting sanding marks I can't get out. I'm using 400 and 600, and have tried 1000, 1500 and 2000 grit papers and all of them leave marks I can see when holding the bass at an angle in the light. I didn't have this problem the first time around, but maybe I just didn't notice. I'm using a quality finish sander and hand sanding in the tighter places. I have done quite a bit of cabinet ind furniture finishing and haven't had this happen before.

    Any advice or suggestions?
  13. brstma

    brstma my dog is an awesome dog Supporting Member

    Nov 20, 2008
    Any help to offer on this? ^^^
  14. Joedog


    Jan 28, 2010
    Pensacola FL
    I have a few pieces of teak furniture I've sanded and re-oiled a couple of times. The key is to use wet/dry sandpaper WITH SOME OIL AT THE SAME TIME. It also works on my walnut and maple bass. Works great for me.....YMMV.
  15. brstma

    brstma my dog is an awesome dog Supporting Member

    Nov 20, 2008

    I did try using mineral spirits but it didn't help. I'm not ready to apply any finish yet, just trying to get the fine scratch marks from sanding out first.
  16. lbridenstine


    Jun 25, 2012
    Is it redwood burl or regular redwood? If it's burl, maybe you're getting scratch marks because it's kind of like sanding against the grain no matter which way you go? I used a random orbital sander on buckeye burl from 80-220 grit and it worked great and didn't leave scratch marks, then I did the finer grits by hand.

    Or, maybe the scratch marks you have are from a lower grit and you just need to go back to a lower grit to get those marks out, then work your way back up again.

    One other thought is, the first time I used high grit finishing paper, I used it dry and it clogged a lot with sawdust and created these hard spots on the paper that ended up scratching up the wood that I was sanding. So, I guess check your paper and make sure it's clear, if that's not it, then maybe go back to one of the other ideas.
  17. sowilson


    Jul 5, 2013
    sometimes for soft wood I'll hit it with a 1lb cut of shellac to stiffen the fibers so that it will sand easily.
  18. brstma

    brstma my dog is an awesome dog Supporting Member

    Nov 20, 2008
    Right now I'm just working on the alder back of the bass, but I am getting the same thing on the redwood. I need to get the alder back done first because once the redwood is good it can hardly be looked at without it scratching.

    I am using clean paper and changing frequently.

    I thinking the first oil finish I applied is the culprit since I didn't have this happen the first time through. Even though I've sanded it down to wood with 220 then 400 there is still a shine to the wood surface when looking at an angle in the right light. Sanding by hand with these grits leaves large scratches and using 600+ grits look more like scratches in a finish.

    I ordered a mini , variable speed orbital sander for my Proxon 12 v system so I'm hoping that will help. The marks show the worst when sanding by hand and this will get into some spot I can't with my palm sander. Maybe more time for the oil finish to cure will help, but it's been almost 3 weeks.
  19. brstma

    brstma my dog is an awesome dog Supporting Member

    Nov 20, 2008
    I finally got the sanding done. The variable speed on the new sander helped a lot, as well as the smaller size base (2" x 3") What helped the most was I used some fine sanding sponges I had laying around. I didn't expect them to work so well so I didn't even consider using them until nothing else worked.

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