MIMF

Thank you for trying to help me out. I am making electric guitars now and would like to move into acoustic instruments later.
The bodies are no real big deal, except that I need to make some good templates to route the cavities.
The neck though. I have tried a couple. I try to get the maple neck straight and flat, rout a channel for the truss rod, glue on fretboard. But
after it sets the neck seems to have backbow. Even with string tension I dont get any upbow like I thought I would. I dont have any adjustment
in the rod. What am I doing wrong?
Any help would be appreciated

Michael Huff

Hi Michael. When you rout the truss rod channel, is it flat bottomed or curved?

Do you get back bow before you install the frets, or afterwards? If the frets fit very tightly in their slots, they can cause the neck to bow.

What kind of truss rod are you using? If it's a single action Fender type, it won't correct back bow - it adds back bow to counteract string tension. You need a double action rod for back bow.

the truss rod channel is flat bottomed.
It is a single action truss rod. So either get a dual action, or ... if using a single action, do you make the neck with up bow before installing a truss rod?

thank you for your help

Michael

Fender type truss rods sit in a curved track with one end anchored at the heel and the adjuster (usually) at the he head. Double acting rods sit in a flat cavity and apply upward pressure to the underside of the fretboard and downward at the nut and heel. Totally different concepts. A double acting rod can take out back bow and introduce relief if necessary.

Melvyn Hiscock has a pretty good description of making a fender style neck (you should have his book), I've been using strictly double acting rods for quite a while (LMII) but there was a good article in American Lutherie not too long ago about different rods and how effective they are.

I make my necks dead flat and with a double acting rod I make sure its neutral when I put it in the neck. Fretting might add a hair of back bow, I take that out before starting my fret work. Normally if the neck is dead flat with no strings once up to tension I get the 4 or 5 thousands of relief that I want.

If you use water based glue to attach the fretboard that can cause wood swelling and backbow. Switching to epoxy will fix that.

Are you gluing on the fretboard before or after shaping the back of the neck? What kind of clamping are you using? I glue on my fretboards while the back of the neck is still square and before pressing in the frets, and I use a Stewmac radiused sanding beam with a layer of cork under it as a clamping caul, and leave it clamped until the glue is good and dry. This ensures the neck at least starts off straight.

http://www.stewmac.com/Luthier_Tools/To ... _Beam.html

Unlike John, I fret my boards before gluing them on (I mostly build acoustics and think I can deal with the extension and heel much better). I usually bind my fretboards and I think that is easier off the neck and I do most of the neck shaping before the f/b is glued on. The boards take a back bow but most of that straightens out when I glue it on.







Like I said earlier, I used dual acting rods set neutral, the f/b is almost always flat when I'm done gluing but if not I can take that out with the truss rod before leveling. I end up doing very little fret leveling because its pretty flat to start with.

Different ways to skin this cat

Like other people have said instead of using Titebond use an epoxy glue, also if you're not fussed about vintage accuracy do use a bi flex truss rod, I've had the same happen with Titebond but it isn't consistent, I've not had it happen with a mahogany neck just maple...

thank you to all who have responded. this was more than i expected.
i think i will switch to an epoxy and using dual action truss rods.
i have maple enough for another neck but need fretboard, so back to lumber store.

thanks again.
until next problem

Michael Huff

Hi Michael,
Just know that this is an extremely common problem and one that I fought with for a few years before I figured it out. All the advice so far is spot-on. I'd only add a couple of things. You might find that urethane aka "Gorilla Glue" is a little easier to work with than epoxy though it has a very short shelf life so don't buy it in big bottles.
I've found that I have to clamp my fingerboards to the necks using a curved caul (a rock maple 2x4 that I cut about 1/8" of up-bow into on the bandsaw and cleaned up with a sanding stick. Even with the 1/8" of relief glued into the necks they come out dead straight when I release the clamps. I tighten the trussrod to introduce a little backbow and then sand the radius into them so that when the truss is released the necks end up with a little built-in relief. Once I get the frets in they end up straight again. Carving the neck after the fingerboard is glued on can also result in a backbowed neck if the neck wood has any tension in it. Best to carve close to final dimensions and flatten the fingerboard side just before gluing the fingerboard. This can obviously mess with your truss rod slot if you did that before carving the neck.

I don't want to hijack this post but I'm glad I'm not alone in having experienced this problem, know that Fender had this problem with their slab-board necks in the early '60's, I've had a couple of these necks through my workshop that have had quite severe back bows and similar on some JV reissue Strats.

I've actually started doing the veneer board with the fb/neck joint carved to a 7.25" radius, I used to steam bend the fb's to the radius but that was unreliable so now I carve the fb with a concave face and I have never had one of these develop a back bow, perhaps this is why Fender went to a curved/veneer board.

No one has mentioned slab-sawn wood vs quarter sawn wood. I would expect quarter sawn wood to be more resistant to bowing than flat/slab sawn wood. This is also why I tend to only use three piece maple necks - I don't really expect a one piece flat-sawn neck to be very stable.

Brian

Brian,
This might be true with some kinds of wood but maple has been tested and has been shown on average to be equally strong in both the quarter-sawn and flat-sawn orientations. The benefits of quarter sawn wood are it's improved stability across the grain as it's moisture content changes over time. Since the quarter-sawn/flat-sawn myth is one of the most pervasive on the internet -I bought into it 30 year ago and haven't been able to shake it completely myself, I think everyone who cares about it should conduct a few tests for themselves and come to their own conclusions.
Here's a good primer on the subject from a reliable source: http://www.liutaiomottola.com/myth/quartersawn.htm

I have a couple of beginner and intermediate builders near me who bring me their projects for final fret leveling and setup. I've seen the backbow from using water based glue under a fretboard quite a few times. Its a heartbreak.

Interesting. I've always used titebond to attach fretboards and have never had an issue with a back-bowed neck.

Andy Bounsall wrote:Interesting. I've always used titebond to attach fretboards and have never had an issue with a back-bowed neck.

Me too. Must be blind luck. FWIW Cumpiano recommends PVA glue so you can get it apart (which fortunately I've never needed to do either). Does anyone know what the manufacturers use?

Epoxy fretboard joints release with heat easier and more cleanly than Titebond.

Despite what I posted earlier, I also use original Titebond. The problem has actually happened to my own necks but it was minimal and addressed via fret leveling. I just don't trust epoxy and Titebond is always available. I now always use dual action trussrods but I feel its valuable to achieve a neck that requires a little positive trussrod influence -- in my head I believe that it makes for a more stable neck requiring fewer seasonal changes. I don't like necks that are in the sweet spot without any trussrod influence or are forcing forward movement -- ...nothing to back this up - its just a personal belief.

If you are comfortable using Titebond for this joint then carry on. I try to emphasize the epoxy approach mainly for the people out there that can't deal with any neck movement in their building process. I know epoxy is messy and smelly, and maybe even toxic. But it sure doesn't move. And I can verify that West Systems releases with heat very cleanly. Most marine supply stores carry a selection of West Systems glues and additives.