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Is there a difference between conical and compound radius?

A

allexcosta

Apr 7, 2004
4,721
119
#1
Sorry if this has been said before or if it's a noob question, but is there any difference between compound and conical radius?

I could swear that I've seen someone making compounds with different radiusing blocks, but can't remember where...

That's different from a true cone, right?

Another question, what's you preferred conical radius? I think Fodera's 9.5 to 20" feels great.

Thanks for your kind responses...
 
#2
I'm fairly sure they are the same thing. With bass I'm not sure I get the purpose of it, with a guitar its so you can play chords easily at the nut end, and bend easily at the other. But most bass players dont bend high up, or play chords low down. I have read there are some other small benefits, but nothing that sounded major, or worthwile (if building). Maybe there are other good reasons for one on a bass that I'm unaware of.
 
#3
You can't get the action as low on a cylindrical radius as you can get on a conical one. The strings of a bass form a cone, not a cylinder. If you go too low on a single-radius board the string will keep bumping on the next fret as you go up the neck, causing unwanted buzz...
 
#4
allexcosta said:
You can't get the action as low on a cylindrical radius as you can get on a conical one. The strings of a bass form a cone, not a cylinder. If you go too low on a single-radius board the string will keep bumping on the next fret as you go up the neck, causing unwanted buzz...
Click to expand...

I don't know If I would completely agree with this........ Remember, that there's a radius on the nut and the bridge can be set to radius as well, they do serve a role in this, not just the FB radius.. Perhaps if they were both flat and not matching the closest radius, this could happen.
 
#5
Rickett Customs said:
I don't know If I would completely agree with this........ Remember, that there's a radius on the nut and the bridge can be set to radius as well, they do serve a role in this, not just the FB radius.. Perhaps if they were both flat and not matching the closest radius, this could happen.
Click to expand...

I'm pretty sure this would be true only if the string spacing was even throughout the instrument, but the strings converge to the nut. If you take a bass with a 10" radius nut and a 10" radius bridge the strings will form a cone.

Good article here:

Lutherie Myth/Science: The Strings of a Stringed Musical Instrument Describe a Conical Section
 
#6
I guess you could call them the same thing, just nobody refers to a "conical fretboard". Rather using "conical leveling" to create a more consistent playing surface. This is something I have put forth here for many years but has rarely been commented on. Conical leveling is different from a compound radius in that it varies by instrument. You can have a compound radius but still need to level in a conical manner as the string path will be different for each instrument. A variance of as little as .005 in string path can make a huge difference if the board is leveled in a generic manner. Bridge and nut slotting can fluctuate as much as .05 making conical leveling with the known string paths to be a must for proper action without spending hours touching up after dressing. This holds true for bass as well as guitar, and using a 30 path regimine will equate to much easier set up in the end.
 
#7
The strings do define a conical surface. Note that not all compound radii fit a conical surface so the radii must be chosen to conform to the same conical surface defined by the strings or you lose the setup benefits of the compound radius. The difference manifests in single-radius boards as falloff on the higher frets.

A flat surface is essentially the degenerate case and an idea setup can be performed on a flat fingerboard.
 
#8
There is a subtle difference between a compound radius and a conic. I made a quick model to describe:

Screenshot2011-03-29at121453.png


The one on the left is a true conic, which would be slightly parabolic if it was laid flat. The one on the right, compound radius the way guitar/bass builders do it. The arc is perpendicular to the plane of the fretboard.
 
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