Summer Uke Build #16: Cutting Fret Slots

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Blog entry by onoitsmatt posted 02-03-2017 04:34 PM 1090 reads 0 times favorited 0 comments Add to Favorites Watch
« Part 15: Fingerboard and Fret Slotting Miter Box Part 16 of Summer Uke Build series Part 17: Neck Mortise »

With my last entry, I had been attempting to make a template to accurately space the frets. After several failed attempts, I decided to just correct the template with the fewest issues. I had been somehow missing my mark by just a fraction of an inch. You can see below the lines and the cuts. Bear in mind, with the little miter box I made, I couldn’t see what I was doing when cutting, so was relying on feel. I marked each fret on the template and cut a little score on the edge of the template at each mark. Then as I fed the template through the miter box, I would use the saw to feel for those marks. When the saw would catch on a mark. I would cut. Unfortunately I was apparently feeling some marks that weren’t there, or was shifting the template a tiny bit between finding the mark and making the cut. In any case, the result is below:

I decided to just clean up one of the templates that only had 2 slots out of alignment. I filled the bad cuts with CA Glue and decided it would have to do. You can see the CA Glue smeared in a couple of places.

Having had so much trouble with seeing what was going on, I decided to modify the miter box and replace the wood on top with some clear plastic. After cutting the top off, I found that just the front and rear supports with the kerf in them were adequate to guide the saw. So I decided to leave the top off and just use the miter box like this:

You can see the little bit of razor blade (dulled with a file) sticking up to allow the slots in the template to drop in place.

Next it was time to cut the slots. I used two-sided tape to adhere the fingerboard blank to the template. One edge of the fingerboard blank was planed perfectly straight/flat as a reference edge to ensure the frets all aligned parallel to each other. I had read that Harbor Freight has a cheap ($8) japanese pull saw that is exactly the right kerf for the width of a fret slot. So I picked up one of those the other day. The blade is extremely flimsy, which I had also read.

When finished with the first try at all 18 fret slots, they looked good. However they were too shallow to allow the “tang” of the fret to go all the way down. This means the fret itself will stick up too far and won’t seat properly. So I went back to deepen the slots. But in doing this, the kerfs widened as well. So a few of the slots were too wide to allow the fret to grab.

Here you can see the fret wire. The top is the surface that sits above the fretboard. The lower portion is the tang. The tang has little barbs on it. The barbs grab the wood to hold the fret in place. The tang width is 20/1000ths of an inch. With the barbs it is about 32/1000ths of an inch. So the goal is to get the fret slot as close to 20/1000ths of an inch as possible to allow the tang to go in and allow the barbs to grab. If the slot is close to or greater than 32/1000ths of an inch, the fret will just be loose in the slot which does no good.

Since I had essentially made this fingerboard unusable, I decided to use it as a practice board to figure out how to ensure consistently deep cuts that were deep enough to allow the depth of the tang but not so deep as to cut through the fingerboard entirely. The fingerboard is only marginally thicker than the depth of the tang.

Ultimately, I decided to add a spine to the japanese pull saw. I cut the blade off the stock handle and had a small Freud gents saw that I picked up at a yard sale a couple of years ago that I never liked/used. The spine on it was just about the exact length of the blad of the pull saw, so I pulled the blade out of the gents saw spine and shoved the pull saw blade in instead.

This helped with the rigidity of the blade and also gave me a reference for depth. As luck would have it, when cutting slots with the template in place, the spine hits the guides at pretty much exactly the depth I need. Got lucky here.

Here is the wrecked fingerboard after having cut all the slots too shallow, then doing a lot of practice cuts to ensure the depth and width of the slot is just right for holding fret wire securely.

After being satisfied that I can get consistent cuts with the saw and template, I made a few more fingerboard blanks from the mesquite log I salvaged from the firewood pile. I got two decent blanks out of what was left, but both have knots in them that may or may not wind up being a bit of a blemish. I’ll put the knots face-down and hope for the best.

Here is the finished fret board slotted and ready to go.

There are two or three slots that are a shade wider than I would like. All the slots seem a bit wider than my practice board. I’ll likely drop some CA glue in each of the slots to ensure the frets hold ok. Next time I’ll probably run a sharpening stone along both sides of the saw blade to get the kerf width a shade narrower.

-- Matt - Phoenix, AZ

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