fret levling - radius block or straight edge

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fret levling - radius block or straight edge

Postby Steve Kelfer » Wed Nov 14, 2018 5:46 pm

Greetings, I am new to this forum. Before I ask for assistance I would like to thank the administrators of this forum for allowing me the privilege of posting. It is appreciated.

I'm not a professional Luthier, but rather an avid guitar player with numerous instruments to maintain and I am endeavoring to become better informed about aspects of maintenance and minor repair. Today my question involves fret leveling tools and techniques.

My goal is to make my guitars more playable with lower action being taken as a considerable target goal. I have small hands and need help at times in this department.

I have watched many hours of film and done a fair amount of reading on the subject of fret leveling. After investing in some professional fret leveling tools, namely notched straight edges and leveling 'bars', etc., I was having a discussion with someone about the difference between radius blocks and the leveling straight block as they relate to the radius of the neck. My own common sense tells me that to properly level the frets to an exacting standard on a neck that has a radius, even a slight one, that the leveling tool would need to have a matching radius. But many of the videos I have watched seem to suggest that radius blocks are used to create the radius on a fretboard itself (no frets) and that a leveling bar can be used for the fret leveling.

So can someone please explain to me the pros/cons of using a radial sanding block as opposed to a straight level edge when leveling frets? Are people using leveling bars as a matter of convenience? For the most exacting leveling job the frets need to be levels with the exact same radius as the neck? Or is intonation only affected by fret to fret height? And not the height of the fingerboard between frets on either side of the neck as opposed to the centerpoint? (The latter statement seems absurd to me). But then what do I know? I'm an amateur :)

Thanks again in advance for any input.
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Re: fret levling - radius block or straight edge

Postby Bryan Bear » Wed Nov 14, 2018 6:27 pm

I have never used a radius block to level frets. I don't know if people do this successfully or not but it seems like a bad plan to me. The radius of the fretboard is not the same as the radius of the fret tops. By that I mean that the offset of the height of the frets slightly widens the radius. Think of drawing concentric circles offset by the height of a fret; those two circles have different radii since one is smaller than the other. I would think that leveling with a radius block would tend to take more material off the outside of the frets. In practice, this difference may be negligible, like I said, I have never done it. Also, you would want to know the actual radius from guitar to guitar and compound radii may throw that all off too.

Using a straight beam makes berfect sense when you consider that the strings are straight and you want the tops of the frets in the string paths to match. This is why you can have a radius and not have to have the whole board flat. When I level frets (with a straight beam) I am keeping the string paths and fretboard taper in mind.
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Re: fret levling - radius block or straight edge

Postby Bob Gramann » Wed Nov 14, 2018 7:45 pm

To say what Bryan said in a different way: I use a 12” long beam to level frets. I sand the fret tops along the lines of the strings which are not parallel. My beam is an inch square steel tube (from home Depot). I sanded one side exactly level on a piece of sandpaper glued to a quarter inch glass plate. I put a piece of self-adhesive sandpaper on that leveled surface of the tube. I replace that sandpaper when I wear it out.

Using a radius block to level the frets would assume that the strings are parallel. Usually, they are not. Each string needs a straight path.
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Re: fret levling - radius block or straight edge

Postby Steve Kelfer » Wed Nov 14, 2018 8:24 pm

So I think what you are saying is that the string path on most guitars goes from the nut to the bridge in a straight line and you want your frets to be perfectly level down this straight-line matching the string path. When I say it like that it makes perfect sense. But then I think about places on the fretboard where the distance from the fret top to the fretboard would be a sufficiently different travel distance to alter intonation, no? Put another way, should the distance between the top of the fret and the fretboard itself need to be also identical everywhere on the fretboard?

I'm not a math or physics expert so I'm hoping someone else is. So is the ideal fretboard, at least theoretically, one where the tops of the frets are all equal parallel to the string path, AND the distance between the top of each fret and the fretboard is identical across all frets?

And I would think that the physical cut of the nut and bridge would play into it as well. The cut/shape of where the strings sits in the nut grooves and bridges varies depending upon the design. So in a perfect world you'd want the nut and bridge leveling the strings with the same radii as the fretboard.
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Re: fret levling - radius block or straight edge

Postby Bob Gramann » Wed Nov 14, 2018 9:55 pm

The difference in fret height caused by leveling along the string path is pretty small--big enough to make a difference in buzzing, but pretty small. What's important is the top of the fret. Theoretically, if the fret height above the board varied, you could stretch the string on some frets more than on shallower frets by pushing harder. Intonation on a guitar is not perfect. This effect is likely to be much smaller than the effects of many of the other causes for imperfect intonation. Don't worry about that. Get your frets even and crowned properly so that the guitar plays without buzzing at a comfortable action height at the intensity that you want to play. Remember that after you get the frets even, you are going to dial in some relief (a forward bow of the neck) balancing string tension with the truss rod. Relief can be a whole 'nother topic.
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Re: fret levling - radius block or straight edge

Postby Bryan Bear » Thu Nov 15, 2018 1:22 am

Bob summed it up pretty well there. Don't worry about small variations in fret height from the board as long as the tops are even relative to each other. The nut slots should be along that same line or very slightly above. After you get the frets level and the nut slots the proper depth then you can dial in relief and set the action by adjusting the saddle height. Another related topic is fallaway. Some (myself included) like to add a little fallaway to the frets beyond the body joint by making those frets slightly lower. I put a couple layers of masking tape over the fret at the body joint and use my beam to level the upper frets. The beam rides on that masking tape which makes the upper frets a little bit lower than the plane of the rest of the frets.
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Re: fret levling - radius block or straight edge

Postby Steve Kelfer » Thu Nov 15, 2018 8:33 am

Thanks for all the replies. I'm learning that this work is part science, part art. Now how does one become proficient at being scientifically artful? Or maybe artistically scientific? :lol:
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Re: fret levling - radius block or straight edge

Postby Gordon Bellerose » Thu Nov 15, 2018 2:17 pm

I will add another point of view to this discussion, as I do use a radius block to level frets.
If you rout or sand a consistent radius into your fret board, does it not make sense that the frets can be the same radius and height from the board, right across the neck?

I have measured the radius on many necks that have come in for repair, and find that they are pretty consistent from one end of the neck to the other.
If the board is flat end to end, the frets can follow the same profile with no undesired effects.
I get my actions pretty low and playable using the radius block.
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Re: fret levling - radius block or straight edge

Postby Bryan Bear » Thu Nov 15, 2018 2:49 pm

First let me say that this probably doesn't make much difference in practice since we are using such a small section of a large radius. Using a radius block to level all the frets at once will work well since (if using a constant radius) you want them all to be the same radius on the tops. My point was that if you use the same block to level the frets that you used to radius the board, the height of the frets will induce some degree of mismatch since the radius of the tops of the frets will need to be flatter than the board (assuming relatively consistent fret height across the frets. Again, the actual effect might be too small to matter.

I don't use a constant radius so I don't know the answer to this question. Since the board is tapered, if you use a sanding block to sand in a constant radius, won't the edges of the nut end of the board be thicker than the other end. Or I suppose you could sand so that the edges are a consistent thickness but then wouldn't the center of the board be thinner than the other end? Would that be enough to affect the string projection over the bridge?

I do what is basically a compound radius though I don't really measure. I use a hand plane and plane the radius in, similar to how you might round over an edge with a block plane. As I am taking shavings off, I pay attention to the radius at the nut and get that where I want it. I make my plane strokes following the taper of the board (and imaginary string paths) and since I am taking full length passes the edges of the board end up a consistent thickness and the lines along the string paths are flat. Essentially the taper of the board determines the radius at the bottom end of the fretboard. If I plane in, say, a 16" radius at the nut, the other end will be flatter by whatever amount the fretboard taper dictates. I never measure that end because I don't really care what it is. I use a long straight edge along the fret tops to mark out the radius on the saddle blank (which will be an even flatter radius).
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Re: fret levling - radius block or straight edge

Postby Alan Carruth » Sun Nov 18, 2018 8:37 pm

Like Bryan, I use a hand plane to shape the fretboard surface to a more-or-less compound radius, so a radius block won't work.

I level frets with a long, flat file. Files are not always flat, even when they're supposed to be. They can get warped in the hardening process, and since they have to be fully hard they can't be annealed to remove the stress that causes them to warp. When you buy a file take along a straightedge so you can find a flat one.

When I started out I used a sharpening stone to level frets. I happened to find a couple of fret rounding files in a store that sold salvage stuff, and used one of those to round them. It lasted about two years. It occurred to me that grit from the stoner was probably getting embedded in the frets, and that was what wore the file out. I switched to filing them level, and the second file has lasted me for over forty years. Sandpaper makes the same sort of grit.

It's really easy to over think this stuff. The amount of material you remove in a pass or two with sandpaper or a file on the fret tops is not enough to make a substantial difference in the radius, or the action for that matter. If you just try to seat the frets evenly, and dress about the same (minimal) amount off each one before rounding them off, you'll be fine. In that respect the biggest aid is blacking the fret tops with a felt tip pen before you level them.
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Re: fret levling - radius block or straight edge

Postby Bryan Bear » Sun Nov 18, 2018 9:57 pm

Interesting thought about the grit wearing out the files used subsiquently. I hadn’t thought about that. Though I suppose since I don’t make a lot of guitars and I crown with an inexpensive cant saw file I don’t need to worry too much. I’ll keep an eye out for a file that is actually flat though. What type of file do you level with? I assume a fine cut of some sort.
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Re: fret levling - radius block or straight edge

Postby Alan Carruth » Mon Nov 19, 2018 1:16 pm

I have used a number of different ones. One I like is a Nicholson #2 XF double cut. I will say that EVO fret wire sure is hard on files...
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Re: fret levling - radius block or straight edge

Postby Rodger Knox » Mon Nov 19, 2018 1:40 pm

Another alternative is to level the board itself along the string paths, including the desired relief. If the frets are uniformly seated, no fretwork is required.
I usually do have to dress a few frets, but nowhere near a complete leveling.
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Re: fret levling - radius block or straight edge

Postby Bryan Bear » Mon Nov 19, 2018 2:14 pm

After the frets are in, I make sure the fretboard is flat. Usually it is flat without adjusting the truss rod but sometimes it needs a tweak. Once the board is flat, I like to level all the frets to ensure they are in the same plane. That doesn't necessarily mean I am taking off much material (not counting the fallaway I put in below the body joint), just enough to ensure they are all level and any hammer marks are out <G>. With the fretboard and fret tops flat, adding string tension usually puts in about the right amount of relief.

For me, it is easier to slightly flatten all the fret tops then recrown and polish them leaving a thin line of leveled fret on the top than to check and spot dress problematic frets. It probably takes me a little longer that way but I don't really have to do any thinking; I consider myself a cognitive miser <G>
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Re: fret levling - radius block or straight edge

Postby Alan Carruth » Tue Nov 20, 2018 11:46 am

I try to get the relief right with no tension on the strings. The strings pull the neck up, and then I adjust the truss rod to get the neck shape back to where it was without the tension. That way I now that the tension on the rod is exactly balancing the string tension, so there should be no net force causing the neck to creep either way. That's the theory..... ;)
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Re: fret levling - radius block or straight edge

Postby John Clifford » Mon Dec 03, 2018 12:05 am

I use a StewMac aluminum 12" radius sanding beam for both shaping the fretboard and leveling the frets (and also as a clamping caul for glueing the fretboard to the neck, and for shaping the tops of the nut and saddle). I understand all the reasons why that is not a theoretically perfect method, some of which have been mentioned here. But it sure is simple and convenient and produces consistent, dependable results. And I can tell you that if your neck is straight and stable, the frets are level and nicely crowned, and the action is set correctly at the nut and bridge, it will play great. Maybe a handful of players would notice a difference between this and the follow-the-string-paths method, but I haven't run into any of them yet. That said, I wouldn't use this method with anything smaller than a 12" radius.
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