Seperate PU-glued joint with heat, solvent or saw?

[charangohabsburg]

A while back I bought a nicely figured and bookmatched ovangkol e-guitar top off ebay. Unfortunately the top was already joint with that foamy PU stuff, and the joint was poorly made (partly coming apart) which I guess was the reason it got sold. Which do you consider the best way to separate the two halves? Is a reasonably accurate saw cut the best or are there even better ways? (such as "preheat the veneer 20 minutes in the pizza oven" or "send it to me I'll take care of the problem" etc...). Every suggestion is highly welcome even if it is only good for entertainment. If it really serves this would also be great, of course.

Cheers,

[Allen]

Personally, I would be running it through my bandsaw, but I've got a very good carbide tipped blade that would do a great job of the task.

[Nick]

I've never had any experience with PU glue but trying to apply a bit of heat first couldn't hurt, I'm guessing & then if that doesn't work, if you have enough width in the set then run the bandsaw down the joint, You'll only lose 1.5-2mm. That's how I'd approach it anyway but somebody with PU experience might have better ideas Markus.

[nnickusa]

+1 on the saw. I used that stuff alot when I was building, as it makes a strong bond, but if I had to fix a joint, I just sawed it apart and started again...

[charangohabsburg]

Thank you Allen, Nick and Nick!

Even without ever having worked with PU glues my first thought was also the saw, and probably first, as Nick suggested to try with heat. I have a temperature adjustable heat gun and could start with 180 or 200°C and crank it up if nothing happens. Problem is that I know myself too well and am a bit afraid that if I have no known working target temperature I would end up with the maximum heat which, according to the heat gun's data sheet and digital display would be 620 °C which would make me the privileged one to build for the first time in history a guitar with birdseye charcoal

Thanks a lot for your input, the top will make a trip through the bandsaw. I am not really concerned about loosing a bit of width, I have not yet planned to use it for something specific. It only would have been nice to only lose the absolute minimum of the nice figure. Here some pics of it, just for fun:



The bad joint:


Cheers,

[Nick]

The bad joint

No such ting mon


Irie

[kiwigeo]

Personally, I would be running it through my bandsaw, but I've got a very good carbide tipped blade that would do a great job of the task.

+1. Dont muck around...if losing a few mm's isnt an issue then go straight to the bandsaw.

[charangohabsburg]

Will do so Martin. It seems that the let-it-in-a-parked-car-in-the-sun trick won't do it.

[Trevor Gore]

Funny (as in strange). I've just had a PU joint fail in a non-guitar related project. It's not like I don't know how to make a joint! I thought this stuff was supposed to be idiot proof! I did some rough-and-ready testing (butt jointing 18mm ply) and disassembly with a mallet. I'm back to using Titebond. I had to belt it a lot harder before it failed.

As for your problem Markus: bandsaw.

[rocket]

excuse my ignorance people but what is PU glue ?
Rod.

[kiwigeo]

excuse my ignorance people but what is PU glue ?
Rod.

Polyurethane

[Nick]

excuse my ignorance people but what is PU glue ?
Rod.

Polyurethane

& it foams at the mouth just like a rabid dog apparently.

[rocket]

Thanks.
Rod

[nnickusa]

Markus,

in that photo, it looks as though you'll lose a mm or two anyway, given that void. Guess that was one of those ideas that the "glue will fill it, as it foams and expands."

Nice looking bit of timber tho....

[Nick Payne]

Guess that was one of those ideas that the "glue will fill it, as it foams and expands."

Yes, PU glue might fill gaps but it isn't gap filling...

[charangohabsburg]

Markus,

in that photo, it looks as though you'll lose a mm or two anyway, given that void. [...]

Nick, there was no void. What you see in the right picture in my former post was the step I created by pressing with my fingers one half upwards and the other one downwards.

Fortunately I had a close look at the symmetry before I made the cut. It seems that the first owner struggled quite a bit with getting the surfaces straight, so the centre line of symmetry was not exactly identical with the joint, e.g. there was no perfect symmetry, even if this was hardly detectable because the wild figure made a good job on camouflage. Anyway I took advantage of this and made the cut slightly off the joint line:

Nice looking bit of timber tho....

Thank you.

And thank you all for your input. I still think it would have been stupid not having asked before running it through the saw. Maybe there would have popped up an even easier solution to this.

Cheers,

[charangohabsburg]

The bad joint

No such ting mon

Irie

[Kim]

PU glue has a place in lutherie but that is really restricted to neck blank laminations where there is no potential for reversal.

Urethane glue sticks like ......urethane glue. In a building construction environment it really is wonderful stuff. The claim about gap filling properties is valid in that circumstance because even when there's a few mm between components, that famous foam will bridge the gap and this does add to the overall bond strength.

That said I must confess to being confused as to why the f&%k anyone would consider using the stuff to joint a bookmatch if they had 'any' understanding whatsoever about what it is instrument makers do with bits of wood.

Nice look'in set you have there Murkus and I'm glad it ended up with someone who knows what to do with it...

Cheers

Kim

[kiwigeo]

Nice look'in set you have there Murkus and I'm glad it ended up with someone who knows what to do with it...

That's exactly what I was thinking. Very often a really nice piece of wood like this one escapes the clutches of an idiot and ends up in the hands of a gifted craftsman.

[charangohabsburg]

Nice look'in set you have there Murkus and I'm glad it ended up with someone who knows what to do with it...

That's exactly what I was thinking. Very often a really nice piece of wood like this one escapes the clutches of an idiot and ends up in the hands of a gifted craftsman.

Thank you. I hope I'll do justice to your opinion regarding my skills, and I will do my best to not be the next idiot with this nice set.

Maybe I'll search a colour matching set of ovangkol sides to make a parlour guitar or something similar, but I am not sure yet. It is not high up on my priority list. At least it fits now in my standardised room divider elements!