MIMF

i have an aluminum neck bass guitar that i built, actually im building a bunch of them. i am finding that i have succeeded in making the neck totally flat. i know this becasue i use a granite surface plate to check the flatness. so after building two or three instruments ever in my life, i have discovered that no matter what i dothese things are 'buzzy' at the fifth through twelth frets, even though all the frets are the level with one another and with the fretboard. i then cam across an article that stated that some front bow is a good thing and so i used some shims under the fret board on a flat surface plate and clamped either end to produce about 1/32 of front bow from the 5th-12 th frets, lo and behold the buzzing ceased and the action is approaching a decent height. my question is this:
how much front bow shoudl i be building into these ? am i righ in determining that front bow is needed? please help! thanks!

Yes, front bow is good, although there are a few dissenting voices. The forward bow is called relief. It allows setting the strings as low as possible (action) and minimizing buzzing.

Normally, anywhere from .007 to .010 of an inch is the desired range of relief in guitars and basses. A truss rod allows adjustment of this setting so you may think about adding one on future necks.

Also, leveling and polishing frets helps in getting low action.

barry thanks for the reply, is that range .007-.010 from the nut to the bridge? or just from the nut to where the neck meets the body? thanks

i also forgot to mention that i put 1.5º of pitch to the neck as well.

I always try to get the neck as straight as possible, but in most cases end up with from .004, to .010 of relief on a 6 string electric.

I place a machinist grade straight edge on top of the frets and measure the largest gap between the top of a fret and the bottom of the straight edge. This usually occurs around the 5th or 6th fret.

My theory is that you want the neck to take on a bit of a parabola since that's the shape a vibrating string takes. It can be nearly straight from the 12 fret up but getting gradually more relief curvature as you head towards the nut. It's hard to control this shape via the truss rod alone but relatively easy to control with static neck stiffeners in conjunction with the truss rod.

I use a curved bottom truss rod slot to sort of accomplish the same thing.

Somogyi does an magnified demonstration of a guitar string vibrating path using a 50 foot bungie cord and two anchor men. Plucking the tightened bungie cord about 5 feet from one end sends a large wave to the other end where it bounces across the string to the other side before coming back. The wave traveled the length of the string several times until the motion dissipated. It looked like the maximum wave came close to the anchor point when bouncing back, so of the apex of the relief should be as close to the nut as possible to prevent fret buzz.

My setups go like this.
I use a double action truss rod.

Relief is from .004, to .010.
Measurement under the string at the first fret goes from .025 at the Bass E string, to .012 at the Treble E string.

For bridge height, the measurement at the 12th fret goes from .065 under the Bass E string, to .030 under the Treble E string. (measured with capo on 1st fret)

If my fret work is done properly, (no high spots, or humps, proper fallaway in the upper frets) I can get the low action with no buzz.

Not really pertinent to a bass, but interesting reading.

http://www.stewmac.com/How-To/Online_Re ... itars.html

Peter Wilcox wrote:Not really pertinent to a bass, but interesting reading.

http://www.stewmac.com/How-To/Online_Re ... itars.html

You're quite correct Peter! I did not fully read the original post.
My bass specs are a bit different for sure.

Relief is usually .014 - .016
Under string at 1st fret = .25 Bass E, - .020 at G string.
Bass E, Height at 15th = 5/32 "
Treb G, Height at 15th = 1/8 "

gordon,
that looks more like what i needed to know thank you for posting that! the good news baout my neck design is that once i set the relief i then bind the fretboard to its surface and it wont move unless its bent. then you can bend it back no truss rod but still flexible ,gotta love metal.

gordon,
.015? as in 1/64th? that seems too small but .14 is way too big...hm..

Gregory,
I set the relief on a bass guitar neck at: .014, to .016.
Others may try to get the neck a bit straighter than that, but I find that I can get the nut action a bit lower if I use those measurements.
One other thing top remember is fall away.
That, is the slight ramping down of the higher frets. That helps get the bridge height down a bit lower with less buzz.

My experience with "fall away" on a bass is that it just causes fret buzzes in the middle of the fingerboard. No free lunch there in my experience.
It might be a sort of preemptive strike on bolt-on instruments that have a tendency to form a ski ramp where the neck attaches to the body?

my buzzing was limited to the middle /higher frets, when i put the relief on the neck this went away almost entirely. the relief is mostly between the 5-6 fret to the 12-14 fret. my relief is about .05 so maybe that is too much i am building another one now and i will be putting the relief in first before bonding my fret board this time. i will post the results, the good news is that i am making the same bass guitar over and over so thats good,thanks guys!

David King wrote:My experience with "fall away" on a bass is that it just causes fret buzzes in the middle of the fingerboard. No free lunch there in my experience.
It might be a sort of preemptive strike on bolt-on instruments that have a tendency to form a ski ramp where the neck attaches to the body?

David, I find that I have to start the "fall away" at about the 13th fret, and slowly ramp down from there.
It seems like the truss rod allows the neck to move the most around the 9th or 10th fret. This causes the ski ramp you speak of.
If I don't use fall away, I find that there will be buzz up around the 13th or 14th fret by the time I get my bridge height where I want it.

Do you do differently? If so, I would sure like to learn what it is that you do. Might save me some work.

Gordon,
I use a taller section of carbon fiber and it's embedded into the bottom of the fingerboard. The result is a very stiff neck that stays pretty flat from the 12th fret up regardless of how the truss rod is set. You might try doubling up the CF between the 12th and the heel end of the neck. I've been wanting to try tapering the CF spars I use from 1/2" tall at the 12th fret to maybe a 1/4" or an 1/8th at the 1st fret. I'd need to make an equivalent wood filler wedge to backfill the slot. Reliably cutting a tapered depth slot seems overly complicated to me.