My experience
Adam Cherubini, NJ
>Hi Bill,
I had to disassemble one of my Wm & Mary pieces many months ago. I had the thing finished but one of the legs was crooked and I just couldn't stand it any longer. The leg was round tenoned into a large glue block in the underside of the case. But because of the lower stretcher, removing one leg meant removing all 4. At the time of disassembly the piece was almost a year old.
I have an espresso machine with the capuccino pipe which I've heard some luthiers use to steam apart instruments. They attach a hose to the steam nozzle. I skipped it. I used hot water instead. Here's what I learned:
Several of my tenon joints were so tight dry that all the hide glue must have extruded out during initial assembly. A little scraping and hot water at the shoulder released the joints nicely. The water was probably no more than 150F. These legs may have taken 5 minutes to free. The water would soften the top layer of glue, I'd scrape it away and apply more hot water. The finish was milk paint oil and wax. The water didn't effect it.
The one loose joint would not release at all. The tenon was 3" long and there was no access to the glued surface. I tried boring holes through the glue block and letting the water soak into the joint. Maybe I didn't wait long enough. Maybe my holes never hit the tenon.
I've sucessfully released test specimens in my shop. I've also reversed things I had just glued up but was way past the open time. (like 30 minutes to 1 hour after gluing). I think the trick is having access to the glue surface. Without that I think you are hosed. If the joint is already loose (like an antique) you're home free. If it was a tight joint, it might be easier or the glue might be somewhere you didn't expect (only on the shoulder). Otherwise, I think you could be looking at 1500 to 3000 psi with no way to stop it.
Oh, that reminds me, Eugene Thordahl once told me alcohol would break the joint. I've never tried that. Speaking of Eugene, he also recommends the lower Molecular Weight glues for us (135). If you have a high MW, reversal is harder. If you added salt or urea or Franklin (which has a ton of Urea) it may be an easier job.
That's all I know. Good Luck with whatever you have in mind.
Adam