Big John's Guitars
Fretboard Contouring is a technique John developed over the years to get better sounding and playing guitars period.
It is applied in fret level and crowns to overcome high action and buzzing chords.
The most pronounced use is in (fret jobs) fretboard preparation before adding new frets.
The main gist of "Fretboard Contouring" is...
Your guitar strings do not vibrate in a perfectly straight line.
It is common practice (for the other guys) to make fretboards as perfectly straight and level as possible. This helps, but is not ideal.
We shape your neck to bow only where it needs to.
This allows low fast action with minimal fret buzz.
Go ahead...hit that G chord hard if you want.
Need to work on really fast scales? NO Problem!
Below was taken from an email where John explained this technique to a customer:
(And for all you DIY types...beware! this has taken us years of trial and error to develop!)
Something I have discovered over the years are certain flaws in guitar MFG:
Companies have to be able to make necks consistent, fast and profitable. And, therefore, cannot afford to pay highly skilled craftsmen to hand radius the necks.
So, all necks get made totally straight and level, with whatever radius is specified, which renders a consistent product - This is in contrast to the physics at work in every guitar, and causes a problem:
The lower notes vibrate wider than the higher notes, which causes the lower notes to buzz on the straight surface of the neck.
Therefore, you get your guitar and you set the truss rod tension to allow enough relief (or bow) to play open chords without buzzing.
Then, you fiddle with the saddle height and get them as low as they will go so that the strings will not buzz too bad up past the the 12th fret.This is difficult since the relief has turned the neck into a little ski ramp.
So, you go back and forth compromising between the two.
The end result is chords that buzz more than you want and action higher than you want for solos.
Now to really answer your question: the radius stays the same down the length of the neck...the treble side of the neck gets a slight horizon or a hump the full length of the neck...the bass side gets this hump from the xxx to the xxx fret then drops slightly to a bowl shape with the highest point behind the xxx fret of the bass side.
When string tension is applied the hump becomes as straight as a laser beam and the bowl more pronounced.
This allows the lowest notes to breathe with the amount of relief they need, without raising the other notes off the neck!!