Why level frets under tension?

[coldfingers]

I have never really understood the thinking behind using something like the Erlewine jig to put the neck under tension while leveling the frets. Not saying it's wrong, I just don't understand it.

It seems to me you should start with a perfectly level fretboard, then make the frets perfectly level and parallel with the board, then put the strings on and adjust the neck to the preferred relief. In the guitars I've built, the slight amount of relief resulting from putting on strings after leveling the frets is about perfect. I almost never have to touch the truss rod.

I would think that if you induced that amount of relief with simulated string tension and then leveled the frets, you would end up with frets that are different heights (taller in the middle of the fretboard), and not parallel with the fretboard, and then you would need to crank the truss rod backward (up-bow) to artificially reintroduce the desired amount of relief. I just don't get it.

What am I missing?

[ChrisN]

If I'm not mistaken, PLEK machines also dress the frets under simulated tension. Looking forward to responses to your query.

[Wozer]

I'm gonna go way out on a limb and theorize about this.

PLEK can ultimately set up frets to compensate for various issues in neck geometry...probably the most profound being twist, and at a lower order the actual effect of setting a truss rod to a desired point of "tension" to get a point of relief. since a truss rod is "limited" in its effect on the neck, PLEK can take it a step further and dial in a more suitable relief based upon actual vibrations of the strings and how that relates to the actual playing surface.

with what knowledge I have of the rather arcane math that can describe the details of a plucked string I'm in the camp that a master tech can perhaps do better than a machine (which won't be able to "feel" variables such as what tonewoods are used and their effects upon the actual waveform).

[mirwa]

PLEK

I was almost a Plek owner 7 years ago, we entered into discussion with the manufacturer, finalised prices and so forth, organised the payment and then they dropped one last condition on the sale, all guitars plek'd have to be remotley authorised vee the manufacturer / machine is connected via the internet and each plek job done on said machine incurs an ongoing bill.

So not only do you purchase the machine for 160,000 dollars Australian, you also have an ongoing monthly fee based around how many guitars you Plek, so that is when we bowed out of the purchase.

Steve

[mirwa]

To the question at hand.

In a perfect world, we have a neck with straight grain cut on the quarter, thick enough to withstand the tension applied from the strings, its also fitted with a smooth operating dual action truss rod which adjusts in both directions smoothly.

Now back to reality and not fairy tails.

In the real world, necks are not cut on the perfect quarter, hell some are evn flat sawn, the wood is not thick enough to withstand string tension so the truss rod is cranked right up to combat the strings.

Majority of the time (90 percent IMO), its not too bad, you can do something on your bench like a refret or fret level and when you apply strings the neck bends just a little and gives a nice amount of relief.

10 percent of the time, when you put the strings back on, the neck twists with the grain, the neck twists when truss rod is applied, the neck bows badly when strings are applied, in these situations you want to simulate the neck strung up and then do your work, example refret / fret level and so forth, this combats and minimises the issues from some design flaws or wood flaws.

I have a walk through on my website showing a bad neck and using a jig to simulate, I can PM you the link if you wish

Steve

[coldfingers]

Steve, thanks. I guess I can see that as a way of dealing with problem necks. So I would assume in that situation, you put the strings on, then adjust the truss rod to get the neck as flat as possible, due your leveling, then readjust for relief - is that right?

Sure, PM me the link.

Thanks,
John