Okay, this is a new task that I have never taken on before, and I'm finding it to be a real toughy. I stopped my attempt today until I could get some better knowledge and be ready to take another shot at this.
So, I have a trashed Favilla Baritone Uke that I am working on, for my own pleasure and experience. It is not a valuable instrument - the family that owned it let their kids drag it around until they shattered the dovetail, and the back has cracked wide open as well. I am repairing and refinishing it, but I have lots of time and no need to to crazy getting it done quickly.
This morning, I spent some time with a heat lamp, trying to get the back to come loose. There is no binding on this guitar, so I need to do this pretty neatly. I heated the thing until it felt hot to the touch inside, and tried some palette knives from the inside. They proceeded to follow some grain and come out about a 1/16" below the actual joint, and it was tough going the whole way. I had been adding moisture to the joint, and nothing seemed to be giving. I figured I needed to stop before I made the situation worse, and I did so.
I suspect that there is an easier way of doing this, and I also suspect that there is going to be some sanding involved afterward, to re-establish the kerfing joints and all that good stuff.
As you will be refinishing the instrument I see no reason to remove the back from the inside.
I would remove the back by using hot palette knives from the outside. Start by using a gramil to score the seam between the back and sides, then start in a bout area, or somewhere that looks like it may be loose, and work your way around to the neck/tail blocks.
Use hot knives to separate and a cold knife to hold the seam apart till any old glue drys, check to see if any of the back braces are tucked into the lining so that you can work carefully around those.
My thoughts on how to approach this, I'm sure you'll get a few different suggestions, but this has worked OK for me.
I agree with Cal. That's how I remove them. It's not so hard if you take your time. I actually keep a Bunsen burner to heat my "knives" and I usually add a bit of moisture to the seam as I work. The "knife" I use most is one and a half inch wide and has been thinned so that it is very flexible. It's actually bent from use and has been very handy because of it. I am able to use the knife with the bend up or down as I need it to avoid following runout. It's not foolproof but it helps a lot.
Make the separation as clean as you can but don't get in a big hurry to sand anything. it's possible that you may end up with some bits of the sides that stick to the back and it's easier, in my opinion, to just leave them there to be glued back into place when the back is replaced. One of the guitars I'm working on has some of the side material and a thin layer of the neck block still attached. It all lines back up just fine and actually helps align the back. Your'e going to want to get rid of the old glue but I wouldn't do wholesale sanding.
That gives me hope. There is no way to avoid losing a few splinters, I guess, but then I can fill any spaces up with dust or pore filler, and it should turn out fine. I shall make another attempt, this time with a hot water pot, an alcohol lamp, and lots of different tools and knives.
Pictures at 11.
Mark, this is one of the many jobs that takes LOTS of time. Do NOT rush! Slow and steady steers the course!
Well, it came off, I was surprised how easy some of it was, and really dang difficult other parts were. Live and learn.
I can't seem to get the picture to upload right now, I'll try again later.
So, my next problem is that the wood has warped like crazy, the back should be dead flat, but is instead crazily arched. The long crack on the back seems to be curved too, meeting at then ends, and not in the middle. How can I flatten this piece?
I have a mahogany Favilla that had 5 or 6 splits in the face that were all cupped. I had to remove the existing braces and dampen the inside then clamp it down between two sheets of thick plate glass. I left it setting on the bench with some moist papertowels so it had a chance to get flexable before I clamped it up. I was afraid that I would make more splits if I forced it flat too quiclky. I did have to spline a couple of them and of course they will need cross grain splints on the inside but the top ended up very flat when I finished. I re-braced and is that everything is fine.
I happen to have had some plate glass that I could use ( makes a great sanding surface too) but I don't think that it would be hard to find something else flat enough to do the job and, to be honest, sheets of plywood or particle board may have helped draw moisture from the wood faster. I left it clamped up for about 24 hours and it was flat when I opened it up. I did take care to leave it flat on one of the sheets of glass and layed some sticks across the grain of the top with some weight on them for a fews days, turning the top every day. It dried nicely while being better humidified in the process. Most of the cracks closed up pretty nicely. The two I had to spline had been "fixed" before with some kind of gray epoxy so I wasn't surprised that picking that out left a gap.
What is with these Favilla instruments anyways? They really seem to love to curl up.
I have a friend who visited the Favilla shop in the 60's, and he says that they did hand select their wood, but somehow they seem to be the most curl-prone brand I've seen.
My thought for today is to heat up my granite surfacing block, and clamp the moist wood to that. Or perhaps just wet, heat, and clamp in my go-bar deck with some acrylic holding it in place.
Sounds like a plan, Mark.
I think my guitar face curled because it was not really well quartered. It's like they chose tops with straight grain but didn't pay attention to runout.
It's clamped in the go bar deck now, and to absorb moisture, I included one of those "Sham-Wow" microfiber cloths in the clamping sandwich. We'll see how it is tomorrow.
Okay, the go-bar clamping didn't work, but taking a granite surface plate, heating it on the barbecue, and then clamping the piece down on there very wet did work a treat. The granite block was pretty warm, and it took a long time to release its heat - a few hours of steady cooking. I left it clamped up for two days, and took it apart this morning.
I now have it clamped flat on another piece of wood, because I know it is just ready to go back to curling up if let loose. I'll flatten the other half of the piece, then glue the two together along with the braces and some reinforcement, and this should be good to go back together!
Thanks for the thoughts and inspiration, as always.