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FDP Forum / Guitar Mods, Repairs, and Projects / Fret skim, neck not behaving with truss rod adjust.

vomer
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Broke Down

in the Brassicas
Oct 18th, 2017 02:57 AM   Edit   Profile   Print Topic   Search Topic

The neck of the MJT strat that I posted about in the thread in Miscellaneous is behaving a little oddly. The frets are 6100 (huge!) and the owner wants them lower for comfort. Under string tension it looks OK, with relief of about .015", (at 8th fret, held down at 1st and 18th). Off string tension, trying to straighten the neck with the truss rod leaves about .012" of relief but puts the 1st and 2nd frets into back bow. (The frets look untouched, i.e. uncrowned after fitting, and all measure the same height.) I'm assuming the neck wasn't straight when it was made, or shifted later. It's a quartersawn maple neck with a rosewood board, by Musikraft. I don't have a notched straightedge to check the board, never needed one!

My plan is to skim under string tension. Thanks to Steve Dallman in the thread about files for this idea; I've got a couple of glass pieces being made up for me to use as sanding blocks, and will make a wood block for each end to raise the strings.

I'll report back as to how it goes, but in the meantime does anyone have any thoughts about dealing with a neck like this? I'm not likely to ever buy a Stewmac neck jig, so it seems like doing it under string tension is the way to go.

twangdoodles

michigan usa

Oct 18th, 2017 05:13 AM   Edit   Profile   Print Topic   Search Topic

Leveling under string tension seems unnecessary to me. Get the neck as straight as you can ( if this means that the truss rod is maxed out then I would back it off some to make sure you have adequate adjustment room when you're done ) with the strings off and level.

I believe the neck jig was developed specifically for guitars that don't have truss rods (Martins mainly). If you have one then you might as well use it as it guards against neck-flexing while you're leveling but otherwise isn't usually needed.

vomer
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Broke Down

in the Brassicas
Oct 18th, 2017 05:21 AM   Edit   Profile   Print Topic   Search Topic

I usually would do what you suggest, and in the past have compensated for slight differences between under tension and not by trial and error but this is too extreme. Even with the tall frets, with no string tension there's still too much difference between the relative fret heights and how much I want to remove.

Cal-Woody

USA/California

Why do I keep fixing things that work?
Oct 18th, 2017 06:23 AM   Edit   Profile   Print Topic   Search Topic

This is why you need the notched straight edge for making sure that the fretboard is straight compared to how the frets themselves layout. The notched straight edge goes over the frets and gives you a better visual of the actual wood and then how you should approach and analyze what and how the wood is behaving.
You can just level the top of the frets for a quick job but with the notched straight edge, you'll get a truer sense of what is going on with the wood.

Peegoo
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Oct 18th, 2017 10:58 AM   Edit   Profile   Print Topic   Search Topic

If you have .012" of relief and back-bow at each end with the strings off, you are probably correct to assume the neck was not perfectly straight to start with--or the wood they used for the neck and/or fingerboard was not completely stabilized prior to machining it from a tree into a guitar neck.

The truss rod should be able to pull the neck into a flat or mild back-bow condition with the strings off. If it cannot, it's a warning sign that things are not working as they should.

I've tried fret leveling under string tension, and have not achieved better results than I have with strings off. If there's a high fret that manifests itself under string tension, I level it individually in relation to the frets on either side of it.

I'm also puzzled by the physics behind justification to use a neck jig for leveling frets. First, if the neck is flexing while leveling, too much force is being applied. It takes a very light touch. Second, use of multiple support points behind the neck is overthinking the nature of how wood flexes under tension. I know there are plenty of folks that disagree with me on this, but a neck jig is not necessary to achieve great results.

While it is good practice to have the fingerboard as flat as possible, it's not that critical. What is critical is creation of a flat plane across the fret tops, because that is where the strings make contact with the guitar neck. Leveling the frets is what compensates for imperfectly flat fingerboards and small inconsistencies in fret wire installation.

wrnchbndr
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New Jersey

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Oct 18th, 2017 11:39 AM   Edit   Profile   Print Topic   Search Topic

I look at things maybe a little differently.
I use tension leveling on just about any removable neck that I want a superior result. I never use a notched straight edge because the only way to address a flaw in the level of a fretboard is to pull the all of the frets -- when you have all of the frets out, there's no need for the notches any more. The only exception would be an old guitar that requires compression fretting and I haven't seen one in ten or so years.

What you describe with your neck is something I see often enough. I just call it an "S" shaped neck. (This can also be the result of an elevated first fret -- explained more below)

I have a 8" maple slab that I can bolt to a number of neck heel screw patterns and it gets clamped in my stewmac vise. I have a neck/headstock support that is adjustable via a turnbuckle and I can simulate string tension by elevating the headstock with the heel restrained by the maple slab in the vise.

I start by tuning the guitar to correct pitch and then adjusting the trussrod. I adjust the trussrod using a calibrated straight edge. I adjust with the straight edge checking all six of the string paths until I find the first indication of the straight edge rocking on a high fret between the first and last fret. This would be starting the trussrod adjustment from a condition of relief and tightening. At some point on one of the string paths I'll find the very first indication of a fret going higher than the first and the last fret. I could be anywhere and I'll mark this fret and the position of the fret with a sharpie. I also do a second check to see if the condition remains nearly the same if I use the second fret instead of the first fret. An elevated first fret can cause all kinds of mischief and chasing your tail if it goes unnoticed and it happens a lot. Imagine how a relief measurement would go wrong if your first fret was elevated from the rest.

With the trussrod adjusted under string tension to produce a perfect straight line between the first, the last and one fret between them under string tension, I'll take off the strings, remove the neck, install the neck in my vise and adjust my turnbuckle headstock support (elevate the headstock) to achieve the same level condition with the rocking of the straightedge going away at the position of my sharpie mark.

Now I have the neck in a fairly decent duplication of string tension. I can use feeler gauges along the length of the straightedge to see how deep any valleys are and I can strategize how to achieve a perfectly straight neck with minimal loss of fret meat.

How you proceed from here is up to you but this is my process of setting up for fret leveling.

Over the years I've found that about .018 to .020" is about as low as you can go before a fret becomes uncomfortably too low.



vomer
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Oct 18th, 2017 02:54 PM   Edit   Profile   Print Topic   Search Topic

Thanks for all the replies. I've always wondered if a jig did accurately recreate the same conditions as string tension and wrnch from what you say it sounds like it does. That made a lot of sense to me and I might look into that more in the future.

And yes, an S shaped curve. The 1st fret being way too low (because of the board, not the fret itself) to consider levelling the others to match it. Which is what made me think the neck wasn't right to begin with.

"While it is good practice to have the fingerboard as flat as possible, it's not that critical."

I have found that, and that sometimes it's more about compensating for the quirks of the neck when you see it strung up again, rather than expecting a neck with a *perfect* skim (yeah, I do perfect skims :-)) to behave perfectly when it's back under tension. Which is why I was interested in wrnchbndrs rig, it would take that potential variable out.


Peegoo
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Oct 18th, 2017 04:01 PM   Edit   Profile   Print Topic   Search Topic

As you can see, there are always several different ways to approach these sorts of challenges.

Most techs use a variation of similar techniques because it's something they've developed over years of experience.

FDP Forum / Guitar Mods, Repairs, and Projects / Fret skim, neck not behaving with truss rod adjust.




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