Help create an FAQ for nut files

[Bob Gramann]

The bonding resin and the composite fill each require curing and have the cure time listed in the directions (20 and 40 seconds, respectively). The curing light has a selectable timer. I don’t understand why the light was so inexpensive. My light came with an orange eyeshield which I understand is necessary as exposure to the intense blue light will eventually harm the eyes.

After, we’ve done this enough times to be confident in it, and if we are confident in it, we might talk to StewMac about how to make it easily available to everyone. I will report back positive or negative after I have some experience.

[Barry Daniels]

Thanks for taking the lead on this Bob. I am right behind you on this.

Yep, the lights are very inexpensive. Being a simple LED is probably part of the economics. The deal with Stew-Mac is they would probably be a bit more expensive than eBay, to put it subtly.

[Barry Daniels]

Bob, is it necessary to have the nut free of the guitar to apply the materials?

I just ordered the necessary components except for the acid. Do I need a certain strength of phosphoric acid?

[Barry Daniels]

It looks like Frank Ford uses this same technology for clear finish repairs also.

http://www.frets.com/FretsPages/Luthier ... inish.html

[Bob Gramann]

The Optibond instructions specify 37.5%. The gallon I bought says that it’s 35 to 45% in the MSDS. It seems to work.

The bonding agent and the fill are very easy to handle and would not require the removal of the nut. The acid needs to be washed off and the surface needs to be completely dry. When I experimented, I used an unattached nut, applied the acid (it likes to spread-some might be available in a gel), washed it in the sink, and completely dried it with a paper towel although the instruction specify blowing it dry with compressed air. I haven’t run the experiment on how the acid reacts with the finish I use. I will probably remove the nuts I am working on until I figure a process for the acid that won’t endanger the guitar—I wouldn’t want to get acid on the truss rod threads or even on the wood. My next research quest is to find out what material the smaller container needs to be to safely hold the phosphoric acid. I don’t plan to keep working with the gallon jug.

This Wikipedia article explains the function of the acid https://en.m.wikipedia.org/wiki/Dental_composite


StewMac would be considerably more expensive but a lot more reliable. The Optibond that I bought advertised on the ebay page that it was in Florida. It was shipped from India (and came in just over a week). I would think that StewMac might be able to work a deal with the manufacturers so we wouldn’t be buying medical grade stuff. A couple of the sites I ordered from had disclaimers that I must be licensed and that they would check. They didn’t.

The CA fix for quick finish repairs is easy enough that I don’t think I will use the dental materials for that.

[Barry Daniels]

I bought some gelled 37% phosphoric acid in small hypodermic needles that is intended for dental use. Might be controllable enough to use on an attached nut. The biggest issue will probably washing the acid off with water and not ruining adjacent surfaces. Judicious use of paper towels and minimizing the water may work.

[Bryan Bear]

I bought some gelled 37% phosphoric acid in small hypodermic needles that is intended for dental use. Might be controllable enough to use on an attached nut. The biggest issue will probably washing the acid off with water and not ruining adjacent surfaces. Judicious use of paper towels and minimizing the water may work.

I'm pretty sure Dave and Hesh in Ann Arbor use this stuff in their repair shop. You might want to ask them if/how they are doing it on attached nuts.

[Bob Gramann]

Barry, I left a drop of the acid on some raw rosewood. It flowed out over a large surface area as if it had no surface tension. It considerably roughened and discolored the surface after it dried vs. no change for an adjacent drop of water (which stayed in a drop). But, not having to remove the nut is so inviting that I plan to do the next one in place with thorough masking and extreme care. The gelled acid seems like a good solution and I may order some after I get some experience.

[Barry Daniels]

If dentists can do this in someone's mouth, surely we can do it on a guitar neck!

[Peter Wilcox]

Just thought I'd add a few pics of my cheapskate nut slotting tools, since I'm making some nuts (from soup bones, of course). I'd like to afford gauged nut files, but a couple hundred bucks are not in my lutherie picture. I mark, then cut all the slots to depth using a jewelers' saw.

For the slots under 0.015" I've selected some jewelers' saw blades of the appropriate kerf. For slots around 0.020 to 0.026 I use welding tip cleaning files in the jewelers' saw.

For slots up to about 0.060 I use a bead reamer in a rotary tool. I measure the fit using the appropriate guitar string.

For larger slots (basses) I can get needle files into the above slots to enlarge them. I only make 5 or 6 nuts a year, so this method is not too egregious.

[Bob Francis]

That's a great idea!