Plek: The Machine That Keeps it Original

Story by Preston L. Gratiot

Those of us that have experienced the thrill of finding a holy grail of guitars have also learned that our quest will usually bring us a vintage guitar that is far from perfect. In fact, many times, the guitar you finally find may be so worn out that you have to back away from the purchase ­ just when you thought you had finally found it.

Vintage collectables can come with a number of disfiguring maladies. Some are fixable without devaluing the originality of the guitar, such as new strings. A little farther up the scale you might find sticky tuners in need of a clean and lube. Still farther, some wood cracks ­ a major problem to be sure, but not one to shy away from if they are basically cosmetic and easily rendered stable.

The ones that can really affect your judgment in the final acquisition of the guitar are usually related to playability. Here, you find defects such as the warped neck, bellied bridge, worn nut or saddle or - one of the worst when it comes to originality ­ worn frets.

Unless your prospective prize has been a closeted case dweller, fret wear is your most likely problem when it comes to originality, unless you just want a wall-hanger that you can brag about.

The Test Case

I have a 1969 Martin D-28 that was bought in place of a wedding ring. The marriage is still together some 30-plus years later, but the guitar is starting to show its age. It's a daily player and rarely sees the case unless it's going to leave the house, so the top has achieved that nice pumpkin orange patina. Unfortunately, the frets under the E and B strings (#1 & #2) were developing some pretty drastic grooves due to excessive string bends and constant use.

Primarily a finger-picker, the top on this D-28 only has two scratches (pick induced by a clumsy friend), and replacement pickguard installed under warranty because of the dreaded edge curl. So the thought of ruining the originality of the guitar by ripping out and replacing the worn frets had me living with the increasingly chunky action.

That was my situation until I heard about a new process at the Winter NAMM show in Anaheim. There is a new computer-numerically-controlled (CNC) machine, the Plek, just over from Germany, that can read the height of the frets, the twist of the neck and the overall action/condition of your guitar-while the guitar is still strung and tuned to concert pitch!

Just the Facts

The Plek CNC fret dressing system was designed and developed in Berlin by Gerd Anke. As a computer-controlled alternative to traditional methods of manual fret dressing, the Plek records the fret height in relation to the fretboard surface beneath each string with a mechanical finger (touch probe) guided by a computer-controlled arm.

Again, this is done with the guitar tuned to concert pitch! The scan generates a number of graphic images, complete with extensive dimensional data regarding the neck, fingerboard, frets, strings, nut and bridge. The data is displayed in graphic form on the Plek monitor. The graphs illustrate cross-sectional views and pertinent measurements for the frets under each of the string paths as well as individual fret curvature (radius). This original fret path is indicated on screen in red and makes the fret-height anomalies quite evident.

Plek then superimposes a "target line" in green on the neck graph to represent the ideal fret height and neck-relief curve for each string. Because a guitar's larger-gauge strings vibrate in a wider oscillating arc than the thinner high strings, Plek accounts for this using intricate calculations to provide the optimum relief curve for each string. More relief is automatically allocated for the larger-gauge strings.

The graphic readout can also indicate if a trussrod adjustment is required to true the neck itself. The Plek operator can then manipulate the graphic to perform a "virtual fret dress." This allows for custom modeling and personalized action settings. It also gives the operator a chance to observe how the target relief contour reacts to each change in action.

When the "virtual" fret-dress parameters are verified, the Plek system is ready to perform the dressing procedure and the strings are now loosened and moved to the side of the neck.

The computer guides a mildly abrasive rubberized wheel over each fret, and gently removes a small amount of fret material with a series of passes. It's a precise, computer-controlled process, and the fret height is re-measured after each pass. To finish the dressing procedure, the abrasive wheel applies a precisely calibrated crown contour to each fret, followed by a soft polishing to buff the frets for a silky-smooth feel.

When restrung, the fret plane is level, the relief is ideal and the finished fret shape is very consistent. All of this is done to tolerances as tight as .0004 inch, far more accurate than manual work and consistent every time.

Back to the D-28

Being able to accurately plot the fret height in relation to the top of the fingerboard as it sits directly under the string, and to read any twists, bulges or deformities while at full string tension allows the technician running the Plek to accurately plot the optimum fret dressing job while removing the minimal amount of metal.

In the case of my D-28, the deepest groove on the fret most worn established the amount of machining required to save the original frets, while also allowing the tech to program specific machining amounts for EACH fret on EACH string. Thus, delivering a perfect fret dressing that will remain perfect when the guitar is tuned up to pitch.

Yeah, here's where the old-school players and collectors might argue that a trusted luthier/tech could do just as well, but it just ain't so. Even the relatively new technique that straps your guitar down to a jig designed to bend the neck into the shape it would take if strung to pitch isn't as accurate as having the actual strings doing that job. You can't just bow the neck up and say, "That's about right," unless you want to underline ABOUT!!! The Plek machines the frets to the nearest .001mm (1/100mm) or .00039 inch. Work done by hand has a precision of approximately .1mm. Just for the sake of reference, differences in fret height of 0.03-0.04mm or more can be felt by a guitarist.

Face it, even the best of techs can only approximate the bow and twist of what your guitars neck actually looks like under string-induced tension, and that's one area where the Plek system shines. It is absolute! No guesses here. This is computerized accuracy and there is no guesswork ­ it is exactly what it is. This precision also allows minimal material removal because it is so accurate.

And that, my fellow guitar fanatics, is the baseline that the Plek begins with. In fact, you can even request a print out of each fret's height under each string with a red line plotting the existing string action, compared to a green line that indicates the computer-selected optimum action profile with the amount of material to be removed from each fret and the number of passes the grinding wheel will make to attain this optimum result.

The Plek system even checks the radius of each fret to make sure that the side-to-side curvature of the fretboard and frets are perfect. Here again, the traditional tech can do this based on templates and the "magical" feel, but not to the accuracy of a CNC machine.

So will the Plek put luthiers out of business? No way. For the typical setup on the daily player, I have no reason to doubt that my trusted tech will almost always deliver a playable guitar. But herein lays the proverbial rub, if I am going to be placing one of my prized "grails" on the workbench, I don't want anything done to that guitar that doesn't need doing!

Back to my '69 D-28. I was told that the worst of the frets would need to be replaced at the minimum, the maximum preferred for playability being a total refret. The thought of removing the original frets sounded like a guaranteed devaluation of collectability and guitar value to me, even if the guitar would once again be a smooth player.

But the thought of minor chinks in the fretboard and the incalculable effects to the straightness of the neck caused by the insertion of new frets left even more doubts about the operation. Luckily, I heard about the Plek machine and its ability to machine frets with an accuracy way beyond that of any human hand. Thus the worst of the frets could dictate the amount of machining required to bring the rest of the frets into perfect accord with each other. So, I packed up the D-28 and rolled down to Fret Tek in Los Angeles where Plek tech Rodney Millar worked his magic.

It turns out that I was to be doubly blessed as fellow luthier Joe Glaser, the Plek tech from Nashville was visiting to check out one of Rodney's new tool finds and he joined in on the fret dressing.

Did it work? Yes, the D-28 still has the original frets and the action and playability has been improved to a level I have yet to find on another Martin. Of course I am running Martin Silk and Steel strings, but the guitar was dressed specifically for the related tension and string size. Different string gauges can also be programmed into the computer and the optimum computer curve modified by the Plek tech to fit your playing style and needs.
The cost for a typical Plek dressing? A little over $200. But this includes setting the truss rod, cutting the nut and adjusting the bridge as well, so if you really care about your collectable vintage guitar, it can be quite a bargain.

When I worked at Haas Automation, builder of high-tech CNC machining centers in use by NASA, numerous NASCAR, CART and Formula One racing teams ­ and the Fender Custom Shop - I could see the future uses of CNC machines in the guitar-builder's workplace. Granted, you don't have to machine a solid-wood guitar body to the same tolerances as a CART racing engine that is so precise that it doesn't even use gaskets, but if you can do it at an affordable price, why not?

Time has proven that technology will not be stopped and at the recent Healdsburg Guitar Festival for Luthiers, I was pleased to hear how many of the world's best luthiers were extolling the virtues of the CNC machine.

However, you might ask if you can trust your instrument to a machine. What happens if the computer malfunctions or the electricity fails? Because this is so critically important, the Plek system has a zero-mistake tolerance built in. It will only act on information that has positive proof. Before the first scan begins, the instrument is located or indexed to the machine and measurements are taken that are then checked by the Plek. If there is a discrepancy, it stops and requires the operator to recheck the data entered. At every step of the way, it checks itself, and if there are any anomalies, it stops. There are additional layers of checks to prevent damage due to power failure or computer problems.

So was I pleased with the playability of the guitar? Very much so. In fact, I offered up one of my Fender Custom Shop Strats and it is now my favorite electric.

But what really makes me plan to use the Plek system again is the fact that it maintained the originality of my prized D-28. It is still sporting the original frets and it plays better than any other Martin I've had the pleasure to play - and I've literally played hundreds!

Plek Locations:

Fret Tek
1748 Westwood Boulevard
Los Angeles, CA 90024
(310) 474-2238

Glaser Instruments
434 E. Iris Drive
Nashville, TN 37204
(615) 298-1139