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There's some request for discussing neck straightening and neck bending of vintage guitar necks. Basically the same procedure as with any neck including new guitars but this might be focused on vintage necks in particular. These are quotations taken from the ongoing thread Gibson Nick Lucas fans here is your Christmas gift, get out your wallet! .

What would you do with a bowed neck on a guitar that couldn't be relieved with truss rod adjustments?

Rich,

Neck straightening by heat bending - works great. Nearly as easy as adjusting the truss rod. In the worst case loosening the fretboard glue joint and regluing again with requested back or forward bow or twist.

Wouldn't planeing the neck be in order?

No, bad solution since this weakens the neck even more. Planing recommended or allowed only very slightly to level raised places.

If so, wouldn't you feel that greatly reduced the value of the instrument? Once neck material is gone...it's gone. Thoughts?

That's true for my understanding although hard to figure in $$. For this reason I really like original frets no matter in what condition ...


Willi

Could you explain the heat bending process a bit more?

The basics are simple although not easy to believe. The entire neck is heated up to about 60 degrees C ~ 140 degrees F. After reading an article by Roger Siminoff in Frets 1981 I started experimenting. First with air heaters, later with air heaters and red light. Nothing worked until I came across a heating clamp/device obtained from a German supplier. I checked for it again recently and it seems it's not available any more.

Basically this is a heavy duty metal block that will clamped on as the warped neck is requesting with the usage of shims, cauls and wedges. The neck will be over-bent using the cauls and the wedges are needed to fix the fretboard edges. Then the device will be heated up for about 1/2 an hour. The metal will be heated up as well and holds the warmth over a couple of hours that the entire neck will be heated through slowly. But the back of the neck is about 40 degrees C ~ 104 degrees F. Binding won't be burned but the edges of the fretboard need to be fixed, otherwise they will become loose. In this fixture the neck will be left and cooled down for 12 to 24 h.

Mainly the glue joints will be shifted but I think also the wood fibers similar to heat bending the sides (although the heat here is much higher). But the fibers must be shifted as well since it works with solid wood as well. The method is very safe, nothing will be damaged and nothing burned. Finally a neck treated this way is solid and holds its structure for years (I didn't notice any sign of weakness on those necks I have bent years back and still have under control).

The device and the procedure is shown here at Paul Hostetter's site
And pics shown how to make one here.


Willi

Here we go:

I'm a bit concerned by Paul Hostsetter's statemement, "In many instances, this works like a charm. Martins work well, as do many Asian instruments glued with epoxy. Gibsons and Guilds were iffy. Older guitars of any make don't usually respond well because their glue is no longer softenable. Water-based glues in general do best if they still contain a bit of water or if the wood around them does. " If the NL had a bowed neck it seems "iffy" on both counts. It's a Gibson and it's an "older" guitar.

John Arnold's expertise:

I haven't noticed a difference when heat pressing the various makes, nor has the age been a factor. Paul seems to have the notion that old wood continues to dry out, but that is just not true. The moisture content of the wood tends toward equilibrium with the humidity in the air.

The basic process of neck bending by heat is shifting the glue joint but since it works also with solid wood (without any glue joint) there has to be something going on with the wood fibers, too. It might be a similar process we have learned from side bending techniques but the big difference is that the heat needed for side bending is much bigger. The heat applied by using a neck bending/heating device as shown at Paul Hostetter's site only applies heat of about 60 degrees C or 140 degrees F when used correctly.

But I understand that one important fact is that the entire neck will be heated up slowly and remains clamped in this condition over 12 h minimum while the device is cooling down. Also the way the heat will be applied is special since it is radiation heat that differs from air heat for example. The radiation heat penetrates wood pores much deeper.

So I sum up that neck bending depends partially on glue joint shifting but also on wood fiber shifting. Hard to figure out the relation between both conditions. The fascinating result is that the heat applied is quite low without any other or none-welcome follow up to be noticed except slightly raised fret ends (what means slightly shrunken fret board). But this is very minor. Celluloid binding won't be affected in any way but the fretboard has to be fixed while heating/bending since the joint can come loose (hide glue joints).

The necks are bending with different result or in different grades: easiest or showing the strongest bending effect are the multiple laminated necks without metal truss rod like war time necks or wooden reinforced necks in general. A lower grade of effected bending can be noticed with necks without any other lamination besides the fretboard joint. The lowest grade are steel reinforced necks such as T-bar Martin necks since the bar is withstanding the bending process. Gibson '30s necks can be bent quite well since the truss rod isn't that stiff. Of course the glue used might have a major effect on the result.

I don't have any experience with Asian necks, epoxied necks or necks with white glue fretboard joints as I'm not interested to work on such necks.

Like John I don't share Paul Hostetter's observation on "dried out" neck wood and such. Paul might refer to "dried up" or oxidated oils and resins inside the wood cells and cell walls and perhaps to the slower reaction of seasoned wood in absorbing humid air. But I'm not aware I ever have seen a "dried out" neck. Maybe some brittle fretboards or especially pear wood boards. But I have been bending "dried out" banjo necks of 100 years old and it works so well that one can use such necks either as a bow or a straight edge - what you like better and how the necks were bent.

During the neck heating process, I have always assumed that I am just heating the neck fibers and reforming the neck; similar to a bow maker that heats the pernambuco over the little oil lamp until it hits the magic temp and all of the sudden, the bow just "bends"

I think this is valid for true heat-bent woods or items such as bent sides. Sides usually are (hand) bent with about 150 degrees C ~ 300 degrees F and more. I'm not sure how much heat will be applied by the commonly used bending devices used by many makers. Here actually the fibers will be shifted and remain in this condition (almost). The big difference to the neck bending process is the amount, the grade and the duration of heat applied.

I have always heard that when heating the neck, we are softening the fingerboard glue so that it can all slide. My problem with that theory is that the fingerboard glue didn't have to be softened for the neck to develop the bow, did it?

I would name that shifting as I don't think it's really softened when clamped right. Softening might be true also in some way because when we look at a younger glue joint that will be treated this way, the fingerboard sides can come loose when not being fixed. In the beginning I experimented with much more heat applied by air heaters and red light lamps almost burning the wood and for sure the finish and all plastic parts but this doesn't work well finally for the bending procedure. Actually the shifted glue joint has a big part here while heated up slowly but all through the entire neck rather than high heat applied at the surface only. But again, the heat applied by the device is a fairly low grade but it penetrates the entire neck.

Also, for anyone wanting to learn to do this neck forming process, my best caution to everyone is that this heating can also cook the fret markers right out of the neck and turn them into a little gray, foamy looking glob.

That's correct but then I would understand it's too much heat applied. I use less heat: I switch on the device and let it heat for about 1/2 an h until it as warm or hot I nearly burn my fingers when I touch it. So it hardly will reach 70 degrees C ~ 158 degrees F. Then I switch it off. No plastic will crumble or react in any way. But depending on the neck construction and condition I use different cauls and wedges with different grades of bending while heating.

I emailed my luthier and his feeling is that heat treating necks is a temporary fix and that the neck will gradually creep back into a bow.

That's correct and also the experience I made when using other heat/bending techniques, especially when much heat will be applied and/or the neck will be over-bent using a false technique. The really surprising affect of necks bent this way is:

1. The necks remain in this condition after being bent. They spring back a considered amount right after bending until the next or the next two days but remain in this condition for years. Insofar I presume that there's no weakening under string tension and very little danger of creeping back. Additionally I perform a pressure fretting usually after neck bending. The necks stay straight in the long run and even with higher action in my experience and I used it on some of my own guitars as well without any doubt.
2. The necks can be bent in every direction pretty well as intended and no damage has to be expected presuming the device will be turned off in time.


Willi