MIMF

Last week i have been asked if i could reset the neck of a Wishbass which needs to be straightened. That's a low cost fretless bass made for the lovers of an "anti design". The neck gets its stability only from its thickness. There is no truss rod or any stiffening, not even by the use of woods with a large Young's modulus (the latter approach works perfectly in a bass i built 13 Years ago).

The owner wants to retain the rough character of the instrument - i could not convince him to have the fingerboard removed and some stiffenting inserted, eg. some aluminum profile. In other words, no reinforcement of the neck is wanted, just straightening. My idea is to heat it up and to clamp it into a slight backbow.
30 years ago i did that on a guitar - the red problem child thinline - and the neck is still ok. At that time i used the oven in my kithen set to 60° C - but that is not possible with the (really!) long neck of that bass.

So my question: how to heat up a long an thick bass neck? Would a heat gun be a possibility? A strong hair dryer? Anything else?

Thanks for any hints.

maybe you could build a heating box out of plywood just big enough to contain the neck. then use a heat source like light bulbs or something to heat the inside

i straightened a classical neck (made in Mexico) that way a few years ago - used a hair dryer for about 1/2 hour over the neck (mostly fretboard side) and left it clamped over night.

I've ruined finish with a hair dryer before. I don't like to leave it on for a long time. But you could probably just as easily scorch it with light bulbs in a plywood box.
Maybe go down to your local pizzeria and ask to use their oven after closing. It'll add a wonderful calzone scent to the neck too.

I use a 2" x 18" electric heat blanket from the fingerboard side. If you use an oven be careful of delamination at other joints.

Beate,
I would just plane the fingerboard level.

I agree with David. A heat set should only be used when the warping is too severe to plane out.

I saw it already. It is.

Planing it out has the disadvantage to weaken the structure. In this case it is actually too weak - that's why i originally suggested not only to straighten but also to strengthen it - but that will affect the tone

For the good, but, as already said, the Wishbass is more or less the opposite of what at least the professionals her are achieving. Something like this tiny little German car compared to modern cars:

If you put the neck under tension (back bow) using clamps you might be able to use a cloths iron as a heat source on the fingerboard side, heating an area then moving it up to the next area, until you have done the whole neck.

using a wet cloth on the fingerboard? It is a light wood, not a dark one, so care needs to be taken when using an iron. Despite of that i have an old cloth iron exclusively dedicated for heating wood.

My assumption is that the reason heating the neck works is not that you are bending the wood (as in guitar sides) but that you are softening the glue between the fingerboard and the neck, and having it re-bond in a different configuration. For this to work I think you have to heat the whole neck and fingerboard as a unit along its whole length, not piecemeal working along up the neck.

I'd use a light coloured dry cloth I think. Light coloured so that it will show scorch marks before the fingerboard does.

I don't think a dry cloth will accomplish anything.

Yes, this process works by softening the fingerboard glue joint to the neck. Since the fingerboard is thinner and flatter than the back of the neck, it's best to apply heat from the fingerboard side. This lessens the issue of neck laminations coming apart, if they exist.

The times that I have done it made it very apparent that the key to success is having some way to hold the neck in the proper alignment while the glue resets after heating. You want to go a little past where you want the neck to end up. And then hold it there for several hours while the joint hardens.

You don't need that much heat at the glue joint to slip aliphatic (Titebond), only about 170ºF or 80ºC so no need to scorch the wood (+400ºF) You just need to be patient. A moist towel will help conduct the heat into the neck, but set your iron at or under 100ºC. I'd examine the neck under tension to see where the straightening needs to happen, often at the 12th fret and above. You can use a longer heavy aluminum bar to heat the whole fingerboard with a smaller heating element like your cloths iron as the alu will conduct the heat very well. Brass and copper also work but alu is the cheapest.

David King wrote:You don't need that much heat at the glue joint to slip aliphatic (Titebond)

That's why a hair dryer works OK (or for HHG) - you just have to be patient. Here's how I clamped the classical neck, allowing the heat to get to the fretboard. In this case, the center of the bend was at about the 4th fret.

http://www.mimf.com/phpbb/download/file ... &mode=view

I would use Infra Red lamps in clamp light fixtures for this, at least two of them. The finger board will stay clear of encumbrances allowing you to configure your clamps while simultaneously heating. I use Infra Red lamps regularly when using hot hide glue. They really heat things up and are easy to control by moving them closer or further away from the work. Areas that you want to protect from heat can be covered with White paper or tin foil, the Infra Red light won't heat reflective surfaces.

I'm lucky enough to have inherited a neck heating element that St Louis Music put out in the 70s (I believe, don't quote me). It's a very heavy chunk of steel that covers the full fingerboard with a heating element built into it. I've only used it a couple times, but it does get quite hot, well over 170 and seemed to do a good job. I've also tried a variety of smaller scale heat elements from various light bulbs to pro level heat guns with less effective results. I think the key is deep, even heat, a fair amount but it doesn't need to be too hot. The longer the heat can work on the wood, the more you can re-align things. Time is your friend. I add a bit of back bow, if I can, then let it sit for a full day before unclamping. (cooled off, of course).

Thanks.

Not seen: LMI controller.

The heating blankets are from ebay, as are the chunks of aluminum. I'd previously cooked out the skijump, you can sorta see the fallaway.