Special Tools: Stone Bar For Leveling Frets

[Bruce Johnson]

Here's a special Luthier tool that I'm experimenting with.

I'm not really interested in making or selling these. I built this for my own use, and I may make up a few more for the other guys here in the Lab. Any of you are welcome to grab the basic idea and make your own.

I like leveling my frets using a flat sharpening stone. There are various reasons, but mostly because the stone is very precise, lasts approximately forever, and it minimizes scratches on the frets. I particularly like the stone method on stainless frets, which are what I mostly use these days. My favorite stone is an 8" x 2" Medium Grit Norton Sharpening Stone. I have one that I've been using on frets for many years. An 8" long stone does a fine job leveling frets, as long as you are careful to work the surface evenly, and keep checking with a straightedge. We've talked about the technique on some other threads.

So, I got to thinking: Wouldn't it be nice to have a long, narrow, accurate sharpening stone, just for this purpose? In a flash of brilliance (I get headaches when that happens..) I thought of the small narrow stones that are used on automotive engine cylinder hones. They are available as replacements, in sets of three, in various grits.

I bought two sets of three for $7 each on Amazon. They are Lisle brand, and I chose 3" stones in 320 grit. The stones are about 3" long x 3/8" wide x 5/16" high. They are epoxied onto a steel channel bracket. They are fairly consistent in height, not to high precision, but these six measured within a range of 0.020".

The inside width of the brackets measured 0.360", a little less than 3/8". There were some stamping burrs on the brackets that I took down with a small square file.

I pulled out a chunk of 1/2" x 2" 6061 aluminum bar stock and sawed it off to 18" long, to use as a backbone for the stones. I used one of my small horizontal milling machines to cut rabbits on one edge of the bar, for a nice fit on the stones' brackets.

I epoxied the row of stones along the bar with West Systems, making sure that they were seated solidly. There are small cotter pin holes in the sides of the brackets, but I didn't see any need for extra mechanical reinforcement. Here's what the bar looks like:

There are some gaps between the stones, from the stones being somewhat unevenly glued onto the brackets. I don't think they are going to cause any problems, but on the next one, I'll grind the ends of the brackets a bit to make the stones fit tighter together.

After gluing, there was a small amount of unevenness in the surfaces of the stones. I clamped the beam in the vise of my big mill, and used a small 1/4" shaft-mounted grinding stone to level off the stones. Gently, in light passes, until it was cleaning the surface of all of them. It's probably flat within +/- 0.001". Good as a starting point.

I may make up one or two more of them. One way to increase the flatness accuracy is to grind them against each other. An old Machinist's trick is to use three straightedges to flatten each other out. In rotation, rub A against B, B against C, and A against C, and eventually all three become flat.

I haven't tried any fret leveling with this beam yet, but it feels like about the right size and weight. I have two fretted necks coming up this week to test it on. I may add some wood handles on the top edge at the ends to make it more comfortable.

 

[Beej]

Fantastic as usual Bruce!

 

[charlie monroe]

This is a great idea

 

[mapleglo]

Very cool!

 

[J.D. Detroit]

Great idea. Thank you for sharing this.

 

[Arie X]

yep, stones are cool. i tend to favor fine diamond laps these days. if you have a surface grinder you can mount an sc, cbn, or diamond wheel and dress those stones pretty quick.

holy crap! that's a horizontal mill. i haven't used one of those since i was 14!

thanks for sharing!

 

[Bruce Johnson]

Update:

I tested the Stone Bar out this afternoon, leveling the stainless frets on one of my AMB-2 necks. It worked very well. The 320 stones were a good choice. They cut the stainless quickly without scratching it much. I slid it in straight line stokes, about 4" strokes, right down the string paths and in between. It leveled the frets in maybe a dozen strokes. The weight of the beam was about all that was needed; I wasn't really pushing down on it much.

I like the 18" length. That works well for a 34" scale bass neck. I had debated making it 21" or 24" long, but after trying this one, I think that would just be clumsy and unnecessary.

I haven't added the wood handles yet, but I'm still planning to do that. It was okay using it holding it by the aluminum beam. There wasn't much force or time involved.

I wiped a little bit of mineral oil on the stones, as a cleaner and lubricant, like I do with the Norton stone.

After the frets were leveled with the Stone Bar, I went over them quickly with a Stew-Mac diamond crowning file, to narrow down the flat stripes across the crowns. Then I rubbed them quickly with the Norton stone, in a side-to-side motion. That made the scratches finer, and all in the crosswise direction. If the Stone Bar is 320 grit, I'd estimate the Norton Medium stone to be about 800 grit, in the scratches it leaves. The last step was a quick polish with a Stew-Mac black (coarse) rubber abrasive wheel in a Foredom flex shaft tool.

That's my whole process for leveling, crowning and polishing stainless frets. Leveling with the Stone Bar was definitely faster than with the Norton stone. So, I can declare this tool successful and in service! Keith and Mike and the other guys here have all been watching with curiosity. I'll probably build a couple more of these Stone Bars for them.

 

[Bruce Johnson]

yep, stones are cool. i tend to favor fine diamond laps these days. if you have a surface grinder you can mount an sc, cbn, or diamond wheel and dress those stones pretty quick.

holy crap! that's a horizontal mill. i haven't used one of those since i was 14!

thanks for sharing!

Arie X;

I don't have have a surface grinder, although I do have an old 1930's LeBlond Tool & Cutter Grinder. With the whole table assembly turned sideways, it will work about like a surface grinder. I was debating using it to dress these stones, but it would have been too much hassle to rotate the table in the location where I have that machine parked. So I dressed the stones in my big Kondia turret mill, using a small arbor mounted drum stone in the spindle. The Kondia has about 22" of X travel, so I could dress the whole bar at once. Not the ideal setup, but it worked okay. I went in light passes of a few thousandths each. The stones were fairly uniform, so I didn't have to take off much.

I actually have 5 horizontal mills here in my shop, although only two of them are currently operational. That one is a 1950's Diamond M20, a small but sturdy and precise little machine. They were made here in Los Angeles and mostly sold to movie projector manufacturing industry of that time. Small footprint, about 700 lbs. Pretty rare these days. I have three of them, which I've acquired for almost nothing. That particular one was headed to the scrap yard. A small machine shop in North Hollywood was downsizing and didn't have room for it. They used it for decades for one particular slotting job. The owner was thrilled that I knew what it was and appreciated it, and gave it to me with all the tooling. A fine little machine for my kind of work. I've been keeping it set up with that 4" x 1/2" straight cutter, just for quickly straightening edges of blocks and cutting rabbits like here.

 

[Arie X]

Arie X;

I don't have have a surface grinder, although I do have an old 1930's LeBlond Tool & Cutter Grinder. With the whole table assembly turned sideways, it will work about like a surface grinder. I was debating using it to dress these stones, but it would have been too much hassle to rotate the table in the location where I have that machine parked. So I dressed the stones in my big Kondia turret mill, using a small arbor mounted drum stone in the spindle. The Kondia has about 22" of X travel, so I could dress the whole bar at once. Not the ideal setup, but it worked okay. I went in light passes of a few thousandths each. The stones were fairly uniform, so I didn't have to take off much.

I actually have 5 horizontal mills here in my shop, although only two of them are currently operational. That one is a 1950's Diamond M20, a small but sturdy and precise little machine. They were made here in Los Angeles and mostly sold to movie projector manufacturing industry of that time. Small footprint, about 700 lbs. Pretty rare these days. I have three of them, which I've acquired for almost nothing. That particular one was headed to the scrap yard. A small machine shop in North Hollywood was downsizing and didn't have room for it. They used it for decades for one particular slotting job. The owner was thrilled that I knew what it was and appreciated it, and gave it to me with all the tooling. A fine little machine for my kind of work. I've been keeping it set up with that 4" x 1/2" straight cutter, just for quickly straightening edges of blocks and cutting rabbits like here.

right on! that sound good. i've got a small table top cnc mill and a micromark mill as well. i would really like a small lathe one day.

have you thought about arraying the stones side by side to increase the width as well?

thanks for sharing and keep up the good work!

 

[Bruce Johnson]

have you thought about arraying the stones side by side to increase the width as well?

Why would I want it wider? They are grinding a narrow line path on a convex surface (because of the radius of the frets). I don't see what wider stones would gain in function. I specifically wanted a long narrow stone, to make it easier to grind following right on the string paths.

 

[Arie X]

hand holding stability was my thought

 

[Bruce Johnson]

hand holding stability was my thought

Oh, okay. That's why I'm thinking of adding some wooden handles along the top. Larger grip and stability. Although using as it is wasn't bad at all. It was doing most of the grinding by the weight of the bar itself. I was just lightly holding it at both ends and sliding it up and down the neck in about 4" strokes.

 

[WardEarth]

Good thread, A plus!

 

[Bruce Johnson]

An update:

Last week, I helped my buddy Randy Robinson, down the hall, make up one of these stone bars for himself. He bought two sets of stones, 220 grit and 320 grit, and made his double sided. It works well, but having the second set of stones on the top side makes it less comfortable to use. Now that he's tried it, he thinks he should have just made them two separate beams.

On mine, I used a 1/2" x 2" aluminum bar, and used a milling machine to cut the one edge down to 3/8" thickness. We also used 1/2" bar for his, and I milled the one edge for the 320 stones. However, the 220 stones were a little wider than 1/2". He epoxied them on the back edge of the beam using some veneer shims to center the stone brackets on the beam. It worked fine. So, if I build another one of these, I'd probably use thinner bar stock and not bother having to mill it. 1/4" x 2" would work.

One other thing I found is that it's real easy to flatten the stone bars by rubbing two of them against each other. I clamped mine in a vise, stones up, and slid his along over the top of mine. It only took a couple of strokes to true the two against each other. Fast and easy. That's a good reason to make two of the bars for yourself. I may make myself a 220 bar, for occasional coarser cut jobs, and to use to keep the 320 bar true.

 

[dwizum]

I came here from the other thread you posted this in. I'm wondering - how often do you have to re-true those stones?

I've thought about leveling with a stone but I've been afraid that it would go out of true too quickly. I know that the stone I use to sharpen my kitchen knives needs flattening every few uses.

 

[Bruce Johnson]

I came here from the other thread you posted this in. I'm wondering - how often do you have to re-true those stones?

I've thought about leveling with a stone but I've been afraid that it would go out of true too quickly. I know that the stone I use to sharpen my kitchen knives needs flattening every few uses.

Well, since I made this stone bar, Keith and I have used it to level frets on maybe 20 necks. And it didn't seem to show any wear. I slide it down the string paths in 4" to 6" strokes, and it doesn't take very many strokes to level the frets. I think on the last Scroll Bass neck I leveled, it was maybe two strokes per string path. The stones cut the stainless quickly, and don't get much wear. Remember that even stainless frets are a lot softer than a hardened knife blade.

I was checking a little while ago, and I see that they sell those stones in grits from 40 (!) up to 600. I might make up a 600 beam too.

 

[bobdabilder]

Thanks for this.

 

[Means2nEnd]

Thank you this is a fantastic idea and as usual and excellent thread.

 

[Grinderman]

Yes, I'm chiming in belatedly, but I have to say this is impressive.

 

[Bruce Johnson]

An update:

The original Stone Leveling Bar that I made back in 2018 is now showing some significant wear on the stones. I only use it occasionally, because I don't build that many fretted basses. But Jeremy has been using it a lot, on every neck he builds.

So, now the stones are worn down to about half thickness at one end of the bar. It's interesting, though, that the stones are still straight and flat along the length. The wear is straight and even, not dips or hills. That's good news. When we use it, we're always using stroke lengths of 4-6". I think Jeremy was pressing harder on it, which is why he wore it more. I just lightly hold on to it, using the weight of the bar as the pressure. I may eventually rebuild that bar, knocking off the old stones and putting on a new set.

I have a few other ideas on how to build them better, too. I may make up a new set of several of different grits, including one fairly coarse one to use to true up the others.

I'm also thinking of trying to build a similar long leveling bar, but fitting it with several narrow fine tooth files. For the quickest coarse leveling.