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Special Tools: Stone Bar For Leveling Frets

Discussion in 'Luthier's Corner' started by Bruce Johnson, Aug 8, 2017.


  1. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    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".

    IMG_5048B.
    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.

    IMG_5050B.
    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.

    IMG_5049B.
    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:

    IMG_5058B.

    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.
    IMG_5059B.
    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.

    IMG_5057B.

    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.
     
    Last edited: Aug 8, 2017
  2. Beej

    Beej

    Feb 10, 2007
    Victoria, BC
    Fantastic as usual Bruce! :)
     
    reverendrally likes this.
  3. charlie monroe

    charlie monroe Gold Supporting Member

    Feb 14, 2011
    Buffalo, NY
    This is a great idea
     
  4. mapleglo

    mapleglo Gold Supporting Member

    Sep 7, 2013
    phoenix, az
    Very cool!
     
  5. J.D. Detroit

    J.D. Detroit

    Nov 12, 2015
    Detroit
    Great idea. Thank you for sharing this. :thumbsup:
     
  6. Arie X

    Arie X

    Oct 19, 2015
    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!
     
  7. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    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.

    IMG_5067B. IMG_5068B.
     
  8. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    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.
     
  9. Arie X

    Arie X

    Oct 19, 2015

    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!
     
  10. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    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.
     
  11. Arie X

    Arie X

    Oct 19, 2015
    hand holding stability was my thought
     
  12. Bruce Johnson

    Bruce Johnson Commercial User

    Feb 4, 2011
    Fillmore, CA
    Professional Luthier
    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.
     
  13. WardEarth

    WardEarth Supporting Member

    Feb 18, 2010
    Anchormanville, CA
    Good thread, A plus!
     

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