Hi Todd - All good questions.
Todd Rose wrote:
First, to look at the benefits of flattening the area with your wet-and-warm-the-wood method... One benefit is that it helps to close up the crack(s). Another benefit is that it makes the area look better just by making it flatter. Another benefit could be that it helps to re-glue any braces that may have come loose under that area, by creating a flatter gluing surface. Are there any other benefits that you see? A devil's advocate might question the necessity of doing it at all, and just leave the area somewhat concave, so I want to really consider all the benefits and weigh them against costs and any other potential drawbacks.
First - I think you hit them all. Closing up the cracks, bring the top back down to braces it's pulled from, and of course aesthetics have to factor in as well. It's probably not
necessary, but now that I know how to do this I just can't bring myself to lay finish on without first flattening it and possibly loose the chance forever.
Todd Rose wrote:
Second, I'm somewhat amazed that you can apply that much heat for such a long time inside the guitar and not have brace glue joints failing. Do you consider this a risk of this procedure? I realize you don't have the heat gun cranked up way high, but 60 deg C/140 deg F, for an hour... wow, that doesn't cause things to start flying apart in there, or over-dry the wood and cause other problems?
Second - I should have been more clear on my temperatures. I take notes on heat settings for various tools in various circumstances, and for the heat gun I place a thermocouple at 1/2-3/4 from the opening until it stabilizes. This means that if I'm reading 60c as it leaves the gun, I'm probably going to find closer to 40-45c by the point it spreads and hits the top. And to be honest, I did not check my notes before posting so I may be off on temp, though I can tell you that if I hold my hand just past the scoop I can keep it there indefinitely without getting painful hot. The box does warm up during the process, but I'm always feeling around inside and out as a caution. If it started to feel uncomfortably warm I used to blow it out with an air hose or give it a short rest, but not so much anymore. There's no tension on it, and I doubt any joints are exceeding 40-45c (110f), so I stay cautious but have never been alarmed. You could also certainly do it in shorter sessions to keep the box from warming and drying out as a whole, though I've usually done it in one or two sittings.
Todd Rose wrote:
Third, the purpose of the heat, you say, is to "heat the moisture and help swell the wood on top, while keeping the inside relatively dry in comparison to the outside". What if you wet the outer surface but didn't apply the heat, or applied a gentler heat, like, for example, putting a little night light bulb in there for several hours or something? My inner devil's advocate needs convincing that the heat is necessary, since it would seem that the moisture alone would swell the fibers of the outer part of the spruce.
Third - I've wondered this myself, but have never tried it this way. The idea I've had of this has involved keeping a difference, and trying to aggressively swell the exterior more rapidly than the interior. I've thought of trying without the gun, but since the method I was taught seemed to work so reliably I've never had a candidate I felt like trying this on. Like many methods who's originator isn't around to tell the story, I like to assume there are reasons that went in to shaping a technique in to what they have become. My concern would be that without an aggressive drying on the interior, the water may simply swell the in and outside at similar rates. It may work fine, but I just honestly don't know.
Todd Rose wrote:
Fourth, what happens after the wood thoroughly dries out and reaches EMC? I would think that the fibers near the outer surface would have become permanently compressed by the years of force under the shrinking pickguard, and that they will pretty much return to that state and pull the board back into the concave shape. Again, I don't mean to doubt your expertise or experience, but my inner skeptic can't let that question go unasked.
Fourth - It would certainly seem this way, but I haven't found it to be the case in practice. It does take a bit for the wood to start to swell, but once it's flattened out it seems to keep that way quite well. I did this to a 60's D-18 about 10-12 days ago and didn't get a chance to start laying finish down for over a week. They seem to remain fairly stable once they're done, even in the raw, and I've not noticed much change more than a smidge of cupping returning.
Todd Rose wrote:
Fifth, when you apply finish to the pickguard area, are you necessarily trying to level that area with the surrounding area? Or is the purpose of the finish simply to seal the wood and make it so you're not sticking the pickguard back onto the wood itself (so that it will more easily pull itself loose if it continues to shrink, rather than tearing apart the guitar)? Would you consider shellac a reasonable alternative to lacquer for this purpose?
Fifth - I'm not necessarily concerned with bringing the surface flat in finishing, but I think it is nice to have it flush with the lacquer at least around the edges. This way if you're making a new pickguard you have the option of perhaps enlarging it even just 1/16" in spots where you may like to obscure a dirty crack. It's not necessary though, and I'm sure you could leave it low with no problem. I use shellac as a sealer/filler, but switch to lacquer for build coats. I do know people who use shellac for the whole job though and it works great.
Todd Rose wrote:
Finally, do you have a standard charge for this job, or what might be a reasonable estimate of the charge for repairing a situation like this, including the cracks?
Finally, I leave the range pretty broad on my price list at $200-$280, and I don't list the cracks as included. If there are one or two small cracks I will often include them in that price, but larger ones will be charged seperately. With the cracks and the size of the guard I would probably be quoting $320-$360, or 3_1/2 to 4 hours billable labor.
Now the big question to me is, what to do about the pickguard? I usually advocate cutting a replacement when they're really shrinking, but am honestly quite frustrated in not being able to find a good supply of old, thin, flattop style tortoise that looks decent. I've heard of folks heating, boiling, pressing old pickguards to flatten, but never tried it myself. Seems like the finish cracking when you flattened it out would be pretty bad, and I don't know how stable to expect it to be. So there's the part I have no answer for. I suppose if that one wasn't too warped I would just clean it up and stick it back down. I would really prefer to find a replacement material (preferably in a sustainable supply). If anyone could answer point me to a supply that is not too thick, of decent color and grain, and not computer-printed pixilated layers (man I hate that stuff), I would be very appreciative.