Bob,
A lot of guitar repair techs use a hot knife to work under the edge of  the glue joint.  The "knife" needs to be very thin.  A wide, thin artist spatula heated by a torch or perhaps boiling water is a good choice. I have a couple that are 1.5 inches wide with a rounded tip. I thinned the edge of one a bit without making it very sharp. I heat this one and  use it to work the separation  while the other can be used as a wedge. You need to work carefully and give the heat a chance to melt the glue.  You may also want something like Popsicle sticks to keep the back separated from the sides while you work.  Take your time and you will be OK.

ZZ

Bob,
I  don't know how big your tail block is.  If it's fairly wide and thick, it may be easier to start a little higher up the side and be able to get to  one of the sides of the end block as well as it's back edge. If it's fairly narrow just start where you said.  You'll have to make that call.

I don't know how thick your finish is but careful use of an exacto knife may be needed to cut through part of the finish before you start.  If your finish is thick you may need to cut through the finish all the way around the body to help avoid chipping.  

You might try heating an area of the seam with a blow dryer or even a good old fashion Hot water bottle  to help you get started.

Your mention of pulling the back off of a mandolin makes me think to caution against leaving thing apart too long. If you have a mold for the uke you may want to put it back into that while you work. This will help keep everything better aligned. Things can "move around" when you remove a top or back and getting it all back straight  can be a bit of a problem.  If the mandolin is old, you should be particularly aware of this.  If you can rig some way to hold it while working, it would probably be easier to reassemble it without some overhangs.

The skewers are a good idea. The bambo skewers I find around here may be long enough to span the width of the body.  I should also clarify a point in my post earlier.  I said I use a "torch" to heat my knife but I actually use a Bunsen burner.  You don't need a blasting flame like a propane torch gives you but a candle really won't work either. You may be able to do it with a sterno can but I haven't tried this. The idea is to be able to reheat the blade fairly quickly but you don't really want to be burning the wood either. You want the blade hot, not red hot.  I don't know what kind of glue you used but a little moisture in the joint as you work can help too. Just  don't overdo it. Take you time and don't force anything.

ZZ

Thanks for the help.

I ended up using an iron to heat it. The butt-joint separated at the tail block. I finally got started on the side and worked around to the heel and to the tail block last. The back may be reuseable. I would hate to do all the sanding again.

Next task is to remove the existing brace and make the new brace and glue it in place.

I should have checked the board before I started.

Bob

Mark:
I had no scorching but mine was already finished in truoil.
The razor knife that I used cut up to the surface over the tail block so I am seriously thinking of replacing the whole back. Mine is a three piece back because I have good access to three inch mahogany but my saw won't cut larger pieces. Both butt joints separated at the tail block.

Next time:
I will dull the razor knife on a sharpening stone before I use it. I want it thin but dull.
I will start on the side and work to the heel and tail-block.
I will only use the iron on the outer 3/4 of an inch at 3/4 heat.

Bob

ZZ:
What shape of pallet knife do you use?
I picked up two different styles yesterday at the dollar store (my favourite emporium) but I don't know which to use. One is rectangular and three inches by3/4 while the other one is trowel shaped and 2 1/4 inches.
TIA

Bob

Sorry, Bob, I can't figure out how to get the images on this post. Follow the URl and you will find a picture of my two favorites for this.
http://www.zooomr.com/photos/zippyzingo/

The top one is dark from heating it over a flame. It is very thin but not sharp.  Technically, it is something called  an"Alginage spatula", used in the dental trade to mix some of the materials used in moldmaking.  It's thin and very flexible. You can see that it is also a bit curved. It didn't come that way but it works very well like this, particularly when working under a bridge or finger board.
               
The bottom one is a plaster knife from a dental supply house that is made just a bit thicker so not quite so flexible.  Either one could be made from a putty knife. The hardest part would be thinning them out must a bit without ruining their flexibility and temper.  (just don't overheat them if you grind them down a bit. )

I found a link to a dental lab supply company that carries examples of these sorts of spatulas.  http://www.pearsondental.com/catalog/product.asp?majcatid=614&catid=4753&pid=178...

I forget to take a picture of a small square putty knife that I sometimes use, heated in a flame, along with the round headed spatulas. Is just a wooden handled putty knife with the corners rounded a little so they won't dig in, and the edge thinned down a bit.  Sometimes you need a straight edge but I think the round knife is easier to handle, particularly when just starting.

ZZ

Actually, Don, it seems to me that a hot Xacto knife blade wouldn't be bad for a small instrument because it focuses the heat where you want it.  I wouldn't want to try prying anything loose with it but a flexible putty knife could follow the Xacto blade. You don't want to pry too much anyway.     

I've got a couple of low wattage soldering irons laying around and I've got a mandolin that I need to open up. I've been dragging my feet on doing it because... well because it's going to be a complicated repair and I never see to get my ducks in a row on it.  Maybe I'll rig a blade for one of the irons and try it on this sometime.

ZZ