Leveling frets on a singe radius board is counter-intuitive?

[Peckhammer]

I was reading an article about fret leveling, and the author was pointing out the differences in technique for single radius vs. compound radius. This quote made me wonder if I missed something in the training I received from some notable repair folks:

"On a single radius fingerboard, we’re trying to keep that radius consistent. To do this, we have to keep our levelling beam parallel to the neck’s centreline. That means that, at times, the levelling beam ‘overhangs’ into thin air (see image below)."

Source: https://hazeguitars.com/blog/compound-radius-setup (see the Fretwork Differences for Compound Radius section)

I've never seen anyone use a leveling beam this way. Is this the way you are supposed to level frets on single radius fingerboard?

 

[TimTam]

He's theoretically correct. If you forget about the fretboard drawn under his single radius diagram, and replace it with the cylinder - of which a single radius board is a section - then it's clear that maintaining a flat fret levelling beam on the tangent to that cylinder requires strokes parallel to the midline of the fretboard, not strokes along the line of the strings.

But you're right that few people do it this way. Doing it by following the line of the strings is more common, and probably easier. And just how much the frets ends up wrongly radiused in practice with the line-of-the-strings approach is questionable. Few people implement either approach perfectly.

However, the theoretical objections that one hears to using a radius block for fret levelling of single radius boards do begin to look less valid. A radius block will impose the same radius as the fretboard on the frets, as if both were sections of cylinders of the same radius. The fact that the frets are actually at a (very) slighty greater radius (~ 1mm) from the centre of the imaginary circle is probably a small consideration.

Of course it's easier to have a single flat fret levelling beam, that will handle all radii - single and compound - if used correctly. Otherwise you need a (long) radius block for every single-radius you need to fret level.

 

[TRexF16]

Doing it by following the line of the strings is more common, and probably easier. And just how much the frets ends up wrongly radiused in practice with the line-of-the-strings approach is questionable. Few people implement either approach perfectly.

I concur it's questionable, and this is the question:
"How can the leveling of the frets possibly be 'wrongly radiused' if it is made perfectly level along the axis of each string?"
IMO you can level the frets identically on a fixed or compound radiused neck and get not just acceptable, but optimum results. My thinking is the goal is not to have a fixed radius fretboard perfectly radiused along the plane of the frets. This would be OK, but the b-string doesn't care that the a-string is enjoying this "advantage." Rather, doesn't each string want the frets below it perfectly level along the entire length of the string? (obviously this is the starting point for the set-up, where we will allow a little front bow to the neck.) I've only built about 15 necks but I have never done anything but run the beam along the line of the strings, nor heard of this being wrong.

But then again I could be full of beans. Somebody 'splain, please.

Rex

 

[schmee]

I concur it's questionable, and this is the question:
"How can the leveling of the frets possibly be 'wrongly radiused' if it is made perfectly level along the axis of each string?"
IMO you can level the frets identically on a fixed or compound radiused neck and get not just acceptable, but optimum results. My thinking is the goal is not to have a fixed radius fretboard perfectly radiused along the plane of the frets. This would be OK, but the b-string doesn't care that the a-string is enjoying this "advantage." Rather, doesn't each string want the frets below it perfectly level along the entire length of the string? (obviously this is the starting point for the set-up, where we will allow a little front bow to the neck.) I've only built about 15 necks but I have never done anything but run the beam along the line of the strings, nor heard of this being wrong.

But then again I could be full of beans. Somebody 'splain, please.

Rex

Yep, it's a conundrum. People say "just use a beam to do a compound radius board/frets." Then I think:"OK, then why worry about getting a straight radius board right then?" Also, What happens when you bend a string?

 

[TimTam]

I concur it's questionable, and this is the question:
"How can the leveling of the frets possibly be 'wrongly radiused' if it is made perfectly level along the axis of each string?"
IMO you can level the frets identically on a fixed or compound radiused neck and get not just acceptable, but optimum results. My thinking is the goal is not to have a fixed radius fretboard perfectly radiused along the plane of the frets. This would be OK, but the b-string doesn't care that the a-string is enjoying this "advantage." Rather, doesn't each string want the frets below it perfectly level along the entire length of the string? (obviously this is the starting point for the set-up, where we will allow a little front bow to the neck.) I've only built about 15 necks but I have never done anything but run the beam along the line of the strings, nor heard of this being wrong.

But then again I could be full of beans. Somebody 'splain, please.

Rex

I don't want to push any of these notions too hard, because as I said I think there's theory here and then there's what can be achieved in practice with manual tools. And I was only responding to what the OP's link (from which the pic below is taken) explained about neck geometry and its implications for fret levelling. But it's an interesting, mostly academic (IMHO) exercise to see if we think it is correct .....

Re your question "How can the leveling of the frets possibly be 'wrongly radiused' if it is made perfectly level along the axis of each string?"

If you think about neck geometry, a single string running along a single-radius neck does not have all the frets under it at the same angle ('level') along its length. The strings diverge as they get further from the nut. So the frets under them should become more angled. If you take the B string for example; the 3nd fret under it will be flatter (more level) than the 12th fret under it, as the fretboard has become more angled as the string has moved closer to the outer edge of the imaginary cylinder.

So that is the way things are, geometrically, with perfectly installed frets ... at least prior to any levelling. But is it optimal ? And what does fret levelling in different ways achieve ?

The direct implication of the OP link's theory is that 'line of the strings' levelling of a single-radius neck takes more metal off some frets than others ('incorrectly'). This takes some mental gymnastics, but first imagine the relatively narrow, flat levelling beam, running diagonally on the surface of a cylinder (of which a single-radius fretboard is a section) - ie along the lines of the diverging strings. When starting levelling, the undersurface of the flat beam will only be tangent to that cylinder along a line from near the top corner of the beam to near the bottom opposite corner - essentially a line parallel to the fretboard midline. If it continues to sand down the frets along that diagonal string line, it will lower the middle-neck frets more than those at either end of the neck - basically by flattening the 'walls' of the cylinder to make the frets tangential to the whole beam's flat surface along the beam's diagonal line of action.

It will thus achieve frets whose angle under each string no longer changes along each string's line (as it did in the starting geometry before levelling) - the frets will be at the same angle under each string along their entire length. In effect, the radius of the frets will be flatter than the radius of the fretboard.

Is this good ('optimum') or bad ? Up to you.

And if you do exactly the same thing on a compund radius neck - ie 'line of the strings' leveling - you will get a different result ... frets that change angle under each string to match the (change in) fretboard radius. This is a result of a compound board being a conic section rather than a cylinder section (like a single-radius board).

To be clear again, I am not advocating changing the way levelling beams are used on single-radius necks. I am just responding to the fundamental geometry expounded in the OP's link to the opinions of a very experienced tech / luthier. And I think that source's implied criticism of line-of-the-strings levelling of single-radius necks is mostly theoretical, and unlikely to matter for most of us in practice with manual tools, viz. tilting at windmills.

 

[kingvox]

Understring fret leveling addresses all these issues, especially when you use a tool narrow enough to level the frets under one or two strings at a time.

Very, very long story short: I've been doing fretwork for over 10 years and after dozens upon dozens of refrets and level and recrowns, I have not once had a need to use a leveling tool longer than 7 inches, and have had exactly zero negative results from simply leveling where the problem areas are and leaving everything else alone, without any regard for the radius of the fret tops.

It's important to note that my goal is ALWAYS taking off the absolute least amount of fret possible. With an understring leveling tool this becomes much easier, as you can actually hear the problematic frets in real time, and IMMEDIATELY check your leveling work by playing immediately after you do it.

Fret radius is EXTREMELY secondary to fingerboard radius. This is why on new aftermarket necks I get, I just pull the frets, radius the board the way I like (6" to 15" compound radius), and re-fret it. The really important part is how careful you are with radiusing the fingerboard and prepping the slots before the frets are installed. I use a long straightedge to check the fretboard for level when I'm radiusing. And I simply use the short wooden Stewmac blocks to do this, though I do the 6" radius by hand.

If the slots are carefully prepared and every fret is seated (ideally with a clamp or press) firmly against the board, which was prepared as perfectly as possible, there should be little or absolutely no buzzing with low action without any leveling whatsoever.

In practice, unless a neck is really f***ed up or the board was extremely carelessly radiused before fretting, you're only gonna be removing a couple thousandths of an inch off SOME of the frets when doing a level and recrown. That amount is essentially imperceptible. You would have to really do a hack job to mess up the radius of the fret tops so much that someone would notice, or to affect the feel or playability in any actually perceivable way. I know because I did it to my own guitars in the early days

Sometimes after leveling, I would just kiss the tops of the frets with one of those Stewmac radius blocks to restore some of the radius. If you wanna go that route, I think that's the most practical way to get there. I did that many times with no ill effects, but I also didn't obsessively check the fret tops to see if they were back to a "true" radius.

Digital calipers are your friend. The Stewmac ones. To me, consistent fret height is far more important than whatever radius they end up at. If the fret is about .050" across the whole length, you're good. If you've got it .050" on one side and .030" on the other, mistakes were made, and that is gonna be super noticeable.

That's also why fretboard radiusing is first in line compared to fret radius: you can "compound radius" by leveling out the middle of some frets, but then you're gonna have the frets much lower in the middle. If you take it out of the board instead, your frets will be a uniform height all the way through, which is a much more noticeable variable than fret top radius, in my experience.

 

[Backbeat8]

I think the whole idea of needing to do fret-levelling in the first place is misguided. Because most people think they need it, so "strings won't choke out when I bend", on steep radius like 7.25", but if you have played that radius, you don't encounter any "choking" out. I can bend a Minor 3rd with no problems. I could see if you are trying to use a steep radius fingerboard and then combining that with massively tall frets, then maybe the could be a problem....

But if the frets are following the same curve as the radius, then it shouldnt be a problem.

I was playing a 7.25" radius a couple days ago, with 6105s and there were no problems bending it at all.

Enlighten me, on why anyone really feels they are gaining anything from "fret-levelling", if as you say, it's only a 1/1000 of an inch anyway.

 

[RLee77]

Great posts here. To the OP’s question, I agree with the theory that he states regarding compound vs single radius, cone vs cylinder, parallel for the cylinder to match fret heights, and for the cone you need to align the vectors to pass through the center of the nut (tip of the cone). It makes sense. Timtam’s posts are excellent and make good sense to me also.
To kingvox’s point, I’ve mentioned before on other threads that I felt it was better to use a 8” to 10” beam, rather than a beam nearly the length of the fretboard, for compound radius boards, to avoid mucking with the radius as much as possible. A shorter beam reduces the discrepancy of going the full fretboard length all at once. And I totally agree with the point that one should strive to remove as little material as possible.
But I also think that the amount of variance we’re talking about here is very small; the diagrams exaggerate things to more clearly show the theory.

 

[Greenstreet]

I think the whole idea of needing to do fret-levelling in the first place is misguided. Because most people think they need it, so "strings won't choke out when I bend", on steep radius like 7.25", but if you have played that radius, you don't encounter any "choking" out...
Enlighten me, on why anyone really feels they are gaining anything from "fret-levelling", if as you say, it's only a 1/1000 of an inch anyway.

If the frets aren't level, the guitar can have issues with fret buzz and/or dead spots, and can force a higher action than what many players prefer.

The radius of the fretboard has no bearing on whether or not the frets need to be leveled.

If the frets have high spots, low spots, or divots, there is nothing "misguided" about doing a level and crown.

 

[Backbeat8]

The radius of the fretboard has no bearing on whether or not the frets need to be leveled.

That makes sense!

 

[highwaycat]

Kingvox what under-string leveling tool do you use?

 

[highwaycat]

I recently did a fret leveling experiment, where after I did a refret and leveled the fingerboard with an aluminum radius beam with a fence, and frets installed, I leveled the fret tops with a flat beam.(First picture, 'single radius style' how I normally do it.) Now the frets were very level. So I started the experiment:
I re-marked the fret tops and checked the radius with the leveling beam and 2" radius block. Made sure everything was perfect. It was, maybe the last frets were very slightly flatter, but not as flat as most people get em, I'm very good at not changing the radius and naturally flattening out the last frets. I corrected everything with block.

I re-marked the fret tops and tried leveling in the lay of the strings, second picture style.

The results were extremely similar. There is literally barely a difference. There is though, but if done carefully, some frets were just 'scratched'. And just barely removed any marker.

I re-marked and went at it again and again, straight leveling, lay of strings, radius beam/block strokes, long story short: as long as your technique is good, it don't matter.

Just don't level the frets with the neck too straight...better not straight enough than too straight..
I've done a lil more than 200 fret levels.

 

[RLee77]

Just don't level the frets with the neck too straight...better not straight enough than too straight..

Not sure I get this... if the neck isn't flat when you level, don't you end up with a slight hump in the middle frets, compared to the low frets and high frets?

 

[highwaycat]

Not sure I get this... if the neck isn't flat when you level, don't you end up with a slight hump in the middle frets, compared to the low frets and high frets?

It's simple, just be careful to not get the neck in a slight backbow.
That's worse than not getting the neck not straight enough.
You can't eyeball this, and plenty of people make both these mistakes.
So I like the method of marking the fret tops and doing a pass or too and looking at what frets got hit, kinda like ron's tutorial which is a sticky in the tele-technical forum on top. That's the best way to do it. Like he says it's better to tighten up to where you want the neck than loosen down, think of it like you tune up to pitch instead of down.

 

[RLee77]

It's simple, just be careful to not get the neck in a slight backbow.
That's worse than not getting the neck not straight enough.
You can't eyeball this, and plenty of people make both these mistakes.
So I like the method of marking the fret tops and doing a pass or too and looking at what frets got hit, kinda like ron's tutorial which is a sticky in the tele-technical forum on top. That's the best way to do it. Like he says it's better to tighten up to where you want the neck than loosen down, think of it like you tune up to pitch instead of down.

Ok I get it now, you’re saying to err on the side of relief rather than back bow.

 

[moosie]

I level frets the traditional way, with the bar in the lie of the strings, etc etc.

But the luthier I learned a lot of things from, he does what @kingvox calls 'understring leveling'. Amazing really. There's zero setup, except for sticking a pencil sized steel rod in front of the nut - like you're setting up for dobro. Then he takes a milled-flat piece of 1.5 inch angle iron, about 7-8 inches long, with sandpaper attached, and starts rubbing 'problem areas' that he's identified not with a fret rocker, but just by running a 6" Starrett ruler up and down the frets.

I wish I had paid more attention. I've tried to do this, and I'm missing some key aspects, I'm sure. With the 'dobro rod' in place, you can't check actual playability. I think he checks progress by sliding that rule back and forth. Thing is, it's a very tricky business to hear / feel the slight 'nick' the front or tail of the ruler makes as it meets, or leaves, a high or low fret.

The main benefit, as I understood it, is you're not working on a flattened neck. You're working on a neck under playing tension. There's relief, and there's even some compression. My friend always felt that the StewMac jig wasn't as good as his method, not just because of the setup time, cost, clumsiness, etc, but because it doesn't introduce compression. He maintained that with a difficult, perhaps twisted neck, it could make all the difference.

@kingvox, I'd be greatly in your debt if you could show us what you do.

 

[Vizcaster]

I'm not concerned with where the lines go on a diagram, I'm concerned with whether the fret is at the same height compared to the frets above and below it where the string is going to be vibrating. The problem with the article is that the diagram greatly exaggerates the taper from nut to heel, and all it does is justify the author's solution-in-search-of-a-problem.

 

[kingvox]

The tool I use is one of my own design, and is thin enough to fit under the strings tuned to pitch without needing to jack them up anywhere. I would gladly share the design but I don't have a patent yet and haven't applied for one, and have been wondering what to do with it. Perhaps once I get a mechanical drawing done I'll upload it into the public domain. Not sure yet.

It was inspired by Rectify Master though. Check those tools out. The idea is the same as his "RM Lite" but I just think my design is more elegant and I also believe in using shorter levelers. 7" to me is perfect. 4" for spot leveling. I never had a need for a longer fret leveler.

I get the neck as straight as possible under string tension, then play every single note and start working on the problem areas. Being able to play immediately after leveling is a huge advantage and generally with the neck completely straight, the action is lower.

So if you have little or no buzz at 2/64" action you're not gonna have buzz at higher action. By the time you add some relief back to the neck you'll be good to go.

Important side note: the low strings need more room to vibrate. Putting the neck in a slight backbow and THEN leveling around frets 4 to 11, just a bit, will carve some relief into the frets themselves. Doesn't need much.

So then the low strings will have a bit more room to vibrate, which they need to avoid buzzing. I've always had a harder time getting rid of buzz on the Low E compared to the high E and this seems to do the trick.