Guitar Making and Repair/Cut and Polish
Iím having major issues trying to cut/polishing a custom build. Iíve done like 20 variations of the following process and Iíve had to re-lacquer 3 times nowÖ.It seems like no matter the process I still end up with small hair-thin scratches in the final finish. Iíve read and tried to follow all advice given by tech service and through videos/articles online.
Hereís what Iím currently doing:
I use the nitrocellulose lacquer from STEWMAC, spraying 5-6 light coats 1.5-2 hrs apart. I let this cure for 12-16 days and then level sand:
I use a small wood block and 2000 grit EAGLE micromesh abrasive paper (also from STEWMAC). I let the sandpaper soak in soapy water overnight and then transfer the sandpaper to a new dish in the morning with warm soapy water, using a cup of water and 3 drops of Gain dish-soap. I sand in small circles, about the size of a dime. Every 30 seconds, Iíll wipe off the slurry with pieces of a soft cotton t-shirt. Once level and there are no more shiny spots, I inspect the surface for non-uniform scratches Ė to which there are usually many. While trying to fix those, I usually end up making even more scratches, but eventually I get it to the point where the swirls look mostly uniform.
Iím not sure if my pressure is uneven, the sandpaper is wearing unevenly, or if my block of wood is not flat enough against the body to keep things evenÖor if thereís another issue there. In any case, then I move to the next step:
Once here, I lightly wipe the surface with a wet paper towel to remove the dust. To cut and polish, I use a STEWMAC swirl remover and a dampened STEWMAC 5Ē polishing pad on a hand-drill at maximum speed. For an area like the headstock, Iíll put 3-4 drops of swirl remover on a 3Ē pad, dab the pad on the headstock and then buff, starting in one corner and working my way from the outside in until the compound is not visible on the surface.
At this point there is usually some compound still on the surface, which I try to wipe off with a soft piece of T-Shirt. I canít tell, but it almost seems like the t-shirt is further scratching the surface. Again, Iím not sure if my pressure is too much or too little, if the pad is wearing or still has old compound on it from not being clean enough, is too damp, is too dry, or a number of other things that might induce scratches?
At this step it looks shiny, but there are still small scratches in it. I have tried going over it with a new pad and the FINE polishing compound, and then going back over it once more with the swirl remover, but it just seems to move the scratches to a new location instead of completely removing them.
To clean up, I wash all the rags/t-shirts in a washing machine and let the polishing pads sit in soapy water overnight and then run them through several rinses in hot water until all of the soap is gone. Then dab on a paper towel until damp and let sit out overnight to dry.
I feel like the scratches are being introduced during compounding, because I tried sanding with the grain and then polishing and the scratches that appeared were circularÖbut Iím not sure how to get past this.
Hopefully, Iíve explained this well enough, but if you need more information, just let me know. Iíd really like to be able to put a pro finish on this thing and itís been really frustrating dealing with this process over and over.
Thanks for your help!
While I mostly can't fault your extreme attention to detail, Chris, with all due respect, you're giving yourself way too much work.
By changing your technique, you can get MUCH better results. Some of your procedures need modification, while some materials also should be changed.
1. Get rid of the wood block! It's too hard and it's forcing the paper to trap grit particles, and that's what's causing your scratches and swirls. Use an EPDM rubber block instead. These are sold under the trade name "Dura-Block" in auto body supply stores. You can buy a 2' length of 3/4" X 1 1/2" Dura Block for something like 7 or 8 bucks, then cut it to length. I use 2" lengths mostly. This has just enough "give" to allow you much more efficiency in your wet sanding...you can actually feel the "cutting" action of the paper.
2. 2000 paper is too fine and takes too much time. Use #1000 grit paper.
3. Despite what Stew Mac recommends and says that "the pros" use, foam pads are useless to cut, although they are fine to glaze and apply wax. You should break down and buy one of Stew-Mac's pedestal buffer kits, then build a plywood pedestal for it with a 3/4 horse motor. It'll take a day or two to build and get running, but using flannel buffs and Menzerna abrasive billets, you can take a 1000 grit sanded guitar body to a glasslike shine with none of those annoying scratches, in 20-30 minutes. Period. Following this, use Meguiar's plastic polish or 3M scratch remover, to remove any swirl marks, followed by two applications of Zymol cleaner wax liquid. This is the only water-based liquid on the market, and it is superior to anything else. I can do a black finish that looks WET and stays that way, using these materials and methods.
Every pro shop that I know (save those who specialize in French Polish finishes--and more power to them!) uses pedestal buffers and stick or billet abrasives. Time is money, and pro results wil come from pro techniques, tools, and materials! The couple of hundred bucks you'll spend on the buffer is cheap compared to a shrink @ $150 an hour, when you've gone nuts trying to get those scratches out using your method.