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I glued the back on my classical last weekend, off of the solera, and in a rush. I was following Dave Schramm's method of setting the neck angle by locking the foot with the back center strip. That's not really important. What matters is that in my rush I tweaked the neck and now my angle is off and I need to remove the back and clean up and reglue properly. Fillippo had done the same thing and had posted abut how he and Todd had fixed it easily, but unfortunately his posts seem to be gone, or I can't find it. I hope to remove the back on Saturday and any advice on how to proceed would be appreciated. It was glued with Titebond. I have a small tacking iron about 2" long and I thought I could heat it in sections and work a knife in. Is it best to heat the wood or the knife? I've heard both ways.
Thanks for any advice. Wendy

The difficult part is under the slipper foot, if you've used that joint method. I don't have much experience with Titebond but it can't hurt to glue a number of Back off cuts/scrap pieces and practice a bit. It doesn't have to be on an actual side but make sure the glue is well and truly dry before heating, otherwise it might appear a lot easier than on the real Back.
The other thing to bear in mind is not to heat over the centre joint too much, you don't want that releasing. I once had the centre joint open up and it wouldn't close again, no matter how much I tried to rehumidify.

Thanks Michael...ye it does have the Spanish foot. I hadn't thought about the center joint opening. It has a center back joint reinforcement on the inside, and a decorative strip inlaid on the outside of the joint. Don't you think that would help? You've got me nervous now. I had thought about working out the neck angle by tapering the fingerboard when I get there, but I don't want to end up changing my mind and deciding the back has to come off after the binding is done. Better to do it now and do it right. I figured the foot would be the hardest part, but I hadn't thought about the center seam!

Wendy, I've no experience removing a back, but recently had to remove a bridge on a classical. After trying to heat the bridge (which didn't work well), I found that heating a palette knife and working it between the bridge and top worked better than I anticipated. I actually used two knives; I followed the heated knife with an unheated one just to keep things from reattaching (if that makes sense). I had glued the bridge on with Titebond Original, and it was on a few days before I decided to remove it. I heated the knife up on my wife's iron and began working the knife under a corner of the bridge. I think this would work under the foot and tail block as well.

I have removed 2 backs from old guitars,
I used this method of heating the blade or knife, but also heated with the iron the edge of the back. In adition I put a wet cloth to keep the temperature not so high and avoid burning the wood.
It goes pretty quick but taking steps of no more than 2 o 3 inch long. each time wet the cloth and the blade, and so on.
The foot was a lot more dificult.. like the the guys said.

I removed the back on a dulcimer about a month ago. I used an oscillating saw from harbor freight with a thin blade. In the past I have used a heated knife, thin sawblades, vinegar (to soften the glue) and various other methods. The oscillating saw was the quickest and most painless. It does require you to think about where the saw blade is at all times.

Just place the heat right next to the centre joint and not over it. Most important is to take it slow and not become too impatient. I actually find PVA glues release easier than HHG, especially over larger areas like the slipper foot.
Just make sure that the Back really does need to come off and that you can't get the Neck angle by tapering the fretboard.

Hesh,

Does your heat lamp method work on backs, too?

I've thought a lot about tapering the fretboard to get the neck angle and honestly am having trouble making up my mind. Part of the problem is that the guitar face down in the solera now is not sitting perfectly flat and I must have tweaked some tension into everything when pressing the neck into what I thought was the correct angle. I could probably leave it and, without putting it face down in the solera, you would never know. The guitar is for me and I hate to end up later wishing I had taken the back off. Much better to do it now before binding. Originally the neck was supposed to have a little over 1mm forward set and I ended up with 1mm back set. Still undecided though.

Wish I could find Fillipo's post about his. I think he and Todd simply released the back from the foot and linings for a few inches on either side of the foot and then reglued that area. There is enough flex to correct the angle with just releasing that much area. Problem is, I don't know what kind of glue he used. With Titebond, if I release just that area I will not be able to get in and clean out the old glue before regluing. Thanks for the advice so far.

Wendy, before resetting the neck I think you should lay a straight edge between the nut position on the neck and the saddle position on the dome. Use shims under the straight edge if needed. This should tell you how much taper will be needed in the fingerboard, saddle height, etc, to get to your target action at the 12th. You can then decide whether the amount of taper is acceptable.

Joe

Releasing the Back partially and cranking the Neck is referred to as slipping the neck/block. 1 mm back set does sound all wrong the 'usual' classical Guitar.
Perhaps the best way is to work out the saddle height that you require. Usually for a Classical this will be in the region of 11 mm's off the soundboard at bridge position. Then plane a few scrap blocks of wood, one for the Nut end ( fretboard + fret height + Nut action), one for 12 th fret position (fretboard thickness + fret height + action) and one at 11 mm's to represent the bridge + saddle height combined.
Lay a straightedge on these and work out how far you are from the ideal.
On a modern Classical I factor in 6.5 mm for fretboard, 1 mm for fret height, 0.5 mm Nut action. So 8 mm at Nut end, 11.5 mm at 12 th fret.

I have already used a dummy fingerboard including fret height with shims for action height and I end up at the saddle location with 12mm treble string height and 13mm bass string height. Tapering the fingerboard is doable, but I also think I may have induced a twist in the guitar when I tweaked the neck. Everything was laying perfectly flat face down on the solera before and now the lower outside edge of the treble lower bout is raised by 1mm off the solera. I need to release any tension I induced and get everything flat again. Maybe I am overreacting and over thinking all of this.

Also laying in the solera face down the neck is raised by 2mm at the nut end, which means I have lost my forward set on the neck and actually induced about a 1mm backset.

Check and recheck everything, including the solera. If you have induced a 1 mm back set there is no way you can get the correct geometry, even with tapering the fretboard. Here I'm referring to your average Classical Guitar. There's all sorts of weird and wonderful construction methods that are outside of the norm.

Michael, Is it possible to do this if it was glued with Titebond? Wouldn't the old glue need to be cleaned out before regluing? I can see how it could easily be done with hide glue.

On a new build I think it advisable to remove the Back. As you crank the Neck it moves the slipper foot inside the guitar, resulting in either a gap or a slight hump.

I am going to try to remove the back today, after avoiding it for the last 2 days. Yesterday I spent the entire day cleaning out the storage under my deck and scrubbing the deck and side of the house and windows, just to avoid taking off the back. Probably would have been an easier more enjoyable day just taking the back off.

I am confused about measuring neck angle. I use a dummy fingerboard with 1st and 12th frets. I use an action shim at the 12th fret and I rest the straight edge on the first fret and on the action shim at the 12th fret. Then I measure the height off the soundboard at the saddle location. I have never used an action shim for nut action. Am I doing it wrong?

CallyRox,
I can't tell from your descriptions whether you have ended up with a positive or negative neck angle.
First off, the actual surfaces of the neck and top without the fretboard can be off (not flat or a bit twisted) and it doesn't mean much as long as you can achieve a good clean glue joint when you glue the fingerboard on, seeing that you can true the board after everything is together.
You should be seeing a "lift" of about 2mm between the level of the top and the nut. I.E. the necks rises up slightly from the plane of the top (opposite from steel string set up).
If you can maintain a bridge + saddle height of around 11-13 mm with around 3.5-4mm height above the 12th fret (plus the fret height) and do so by adjusting the taper on the fret board, you may not have to take your back off at all.

Thanks David. There is actually no lift right now from my top to my nut. My upper bout is flat and my dummy fingerboard lays nice and flat on the upper bout to the soundhole so I should be able to get a good joint and maybe what I have ended up with is no neck set, which would be ok if I just taper the fretboard to compensate. My lower bout has a dome of I think between 1-1.5mm. Last time I checked with a straightedge I think the string height was 13mm at the saddle. I am not removing the back today. I am spending some time with a straightedge and measurements and giving it some thought. I'll come back on here later with exact measurements.

I had to walk away from this for a couple of weeks because I was too frustrated by it. I spent some time measuring today and what I have ended up with is no neck set, the nut end of the neck is in the same plane as the perimeter of the guitar and the flat area above the soundhole, so a clean joint with the fingerboard should be fine. It would have been nice to get the angle I was aiming for but I didn't and learned what not to do next time.

My measurements show that a 6.5 mm fretboard at the nut + 1mm fret crown + .5mm nut action and a 5.75mm fretboard at the 12th fret + 1mm fret crown + 3.8 mm bass action gives me 12mm string height at the saddle. I assume this is an acceptable amount of taper?
I have never tapered my fingerboards from nut to 19th fret before. I have tapered the thickness from treble side to bass by running it through the thickness sander with a shim, before gluing, and taking it off the back as shown by Robbie O'Brien. This is a pre-slotted board. What are your methods for tapering the length and does it have to come off the top of the board after it is glued? I'm sure there must be different methods so please share what works for you.
Thanks for all your help, Wendy

I have used Campiano and Natelson as my guide in classical guitar construction, and they recommend tapering the fretboard for classicals. While I slot my own fretboards, the method I use would work with pre-sloted boards since I taper them after they are slotted, but before they are glued to the neck. I simply determine how much taper I want from nut end to the 12 fret, and then apply sucessive layers of masking tape to the slotted side of the fretboard. I begin at about the 3rd fret and lay a length of 2 inch wide masking tape down the remaining lenght of the fretboard. I lay increasing layers of tape as I move down a few frets each time. The length of each layer of tape gets progressively shorter as I move down the length of the fretboard, but the total thickness of tape (i.e., the tape wedge) increases down the length of fretboard until I've built up the correct tickness of tape at the 12th fret thickness gage. In this way, I build a wedge (slightly stair-stepped by each layer of tape) of tape down the length of the fretboard. I run the fretboard (taped and slotted side face down) through my thickness sander to achieve the taper. Doesn't sound much different from the way you taper your board from bass to treble side. Although, Cumpiano and Natelson mention that you can also taper from bass to treble side, I have not done this; I just file my treble side nut slots a little deeper to lower the treble strings. Hope this makes sense, and that I understood your question correctly.

Thanks Martin, that makes perfect sense. I was hoping there was a way to do it without having to plane it by hand.

It's easy to do with a sharp Plane and the use of a straightedge to check progress.

Very glad to hear that you will be able to get a good result without having to pull the back (grimace). All your measurements sound very good indeed.
I put the basic taper in my fretboard by running it through my 16-32 Jet sander and cranking down the height adjustment steadily as it goes through.
It takes some practice to match the speed of the belt-table and crank rotation but works well once you get the hang of it.
The tape "shim" method sounds very clever and an excellent alternative ........plus you'll want to do a final leveling once the board is attached as well.