Tools, techniques and diagnostics

The finishing schedule. 

This is mostly applicable to guitars and banjos.  We have had a lot of success with shellac, both with its own amber color, and tinted.  Maple fretboards and other small pieces look good with beeswax and linseed oil.  We built a buffer / polisher for about $60 out of a used electric motor, two bearings, two pulley wheels, a belt and two x two  cotton buffing wheels.

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A spray booth. 

We use nitrocellulose lacquer routinely, both out of a can and applied with a low pressure spray gun.  Both are great, as long as you use a spray booth, and a good vapor mask.  The booth described here is easily put up and taken down, and makes a great difference to results. The fan in the doorway pulls air and unwanted spray away from the item being sprayed, which hangs from a hook on the inside.  There is also a fan at the far inside end of the garage, pushing air towards the doorway.  This combination, together with spraying on not-too-humid days, has lead to very good results.   

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A drum sander. 

We could not bend guitar sides without this sander.  It cost about $50 to make, out of used parts.  It was important for us that we could control the feed by hand,  so that we could thin instrument sides locally, for example in the small radius regions around a cutaway.  Typically we aim for an approximately uniform 90 thou. (of an inch) sides, thinned to 70 thou. around the cutaway.  Strength is built back into the thinned regions during the kerfing process, using small vertical braces.

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Attaching engraved overlays.  

Once we started using the CNC router for engraving there was no going back: The results are so good.  But for us that meant engraving on thin coupons or templates, because of shipping issues.  Then we had to find a way of accurately aligning and gluing the engraved templates onto the substrate, e.g. a headstock inlayed template onto a guitar neck headstock.  

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The angled headstock start location

If you are using bindings, you can choose the start of the angled headstock so that the bindings along the fingerboad and those around the headstock match in height at the nut face.  

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Making the top and back arched plates.  

As usual, a lot about the process of carving the top and back archtop plates is found in the remarkable book “Making an archtop guitar” and the associated video “Archtop Guitar Design and Construction”, by Robert Benedetto.  There are also plenty of websites that discuss the process.  We picked up a few ideas along the way, and here we document them in case they help.  You need to read the book first. 

We use a pin router to make trenches at specified depths to guide our carving. This took time to set up, but has proved time-saving in the long run.  We also use a carver mounted on a power grinder to speed up wood removal and reduce blistered palms.  Spokeshaves and small "violin planes" are indispensably called into play after this.

We are also now using a home-designed and built CNC router to make the arched plates, and other parts.  Details can be found here.

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Making a neck

Our necks have become pretty standard, and initially we carefully followed Robert Benedetto's detailed instructions in his published book.  With the CNC router capabilities, things changed a bit; mostly on how to attach a headstock overlay.  We have used Hard Maple, Sugar Maple, and one Western Red Cedar.  Use Sugar Maple.  The linked details will get updated as we work through our latest two necks. 

The following assumes a 2 to 3 mm deep, inlayed headstock overlay will be used, and that an exactly matched template for routing the headstock shape is available. We make both on a CNC router.  The overlay has 9 mm diameter holes for the tuning machine bollards while the headstock will be drilled with 10 mm diameter holes.  The routing template includes small holes at the centers of where these 10 mm diameter holes for the tuning machines will be.  See more relevant information at “Making banjo fretboards”, “The headstock overlay”  and “Start location of angled headstock”. 

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Setup: Nut and bridge

We go through the process to make the otherwise-finished instrument playable.  The fretted fingerboard is attached to the body.  After setting the relief, we finish the frets with e.g. 320 grit sand paper and then 500 grit sand paper, using a radius block to match the fingerboard radius. We also re-crown the frets, and finish the ends, before continuing.  Then the order of work is:

1.     Set the relief again (no string tension). This is how much the fingerboard is bowed, away from the strings, usually measured around fret 7 location.  Use a relief straight edge and the truss-rod.

2.     Set the initial nut height and slotting depth or nut action.  The “nut action” is the distance between the bottom of the nut slot, i.e. the bottom of the string, and the projected top of the frets. It will be set differently for each string.  

3.     Set the initial bridge height and slotting

Then under string tension: 

4.     Set the relief   

5.     Set the nut action and nut height  

6.     Set the bridge height and therefore the 12th fret action (the height between the top of the 12th fret and the bottom of the string)

7.     Iterate 5 and 6, checking relief 

8. Set the intonation

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Making the sides

We describe in words and pictures how we bend the sides, make and use an outside mold, and add the blocks and kerfing. 

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Modifications for an acoustic-electric

The tailpiece is modified to ground the strings when we use an inductive pickup.  The internal cable needs to be held in place, and the pickup supported

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Making bridges

We describe how we set the intonation, i.e. make sure the guitar stays in tune as we play up the neck, and that leads us to describe how we make bridges.

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Repairing topcoats

A razor blade can be turned into a small plane to remove topcoat drips, runs or overfills