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, so any pointers on how to make a clean 'de-joint' on the back plates, titebond used.lesson learned: never rush the jointing(or anything else for that matter)
Thanks,
Frank
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| undoing a back glue-up http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=18745 |
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| Author: | Frank Aarre [ Wed Sep 10, 2008 4:11 pm ] |
| Post subject: | undoing a back glue-up |
| , so any pointers on how to make a clean 'de-joint' on the back plates, titebond used. lesson learned: never rush the jointing(or anything else for that matter) Thanks, Frank |
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| Author: | Michael Dale Payne [ Wed Sep 10, 2008 4:16 pm ] |
| Post subject: | Re: undoing a back glue-up |
Do you have the joint reinforcement on yet? Do you have a center seam purfling or wedge? If you can answer no to both questions then heat the joint and seperate with a seam knife or use a razor knife and a clamped in place straight edge as a guide and score through. Either case you will need to re-candel the seam. removing all old glue and truing up the seam. |
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| Author: | Frank Aarre [ Wed Sep 10, 2008 4:19 pm ] |
| Post subject: | Re: undoing a back glue-up |
just raw plates, so just a heat gun and razor knife then. |
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| Author: | Rod True [ Wed Sep 10, 2008 4:23 pm ] |
| Post subject: | Re: undoing a back glue-up |
Frank, I had to do that on my first guitar and I've done it on a repaired 12 string too. Some will say put some vinegar along the seam to soften the glue. I tried that, left it for 2-3 hours and nothing happened at all. What I did do was this, get a moist cloth and hold it over the back along the seam, it doesn't have to be any more than 1-2" wide at the most. Using a clothes iron on high, hold it on top of the cloth moving it slowly back and forth along the edge of the back. What this does is heats up the glue joint and introduces some moisture into the wood to help with the heat but more importantly it helps so the wood doesn't dry out and crack. So work in small sections. Take a thin putty knife (get one from home depot and thin it down and round the corners on the sander or use a sanding block) and work the knife in between the back plate and the side. When the glue has softened enough from the heat, this will be easy to do. DON'T FORCE THE KNIFE or you can split the back wood than you have another repair to do. Work your way around the edge, wetting the cloth when it drys out and working the knife along to separate the back from the rims. It will be a bit more difficult at the head and tail block as these are larger surfaces which have more glue on them. Just be patient with the iron and the knife and you'll get it off. Also you may find that the brace ends will separate from the back when your doing this. If you don't have the top on, you can press on the brace end when you've heated that area to try and keep the brace down. Don't work the knife under the brace or it will separate at the ends. If the brace does separate at the ends it's ok as when the back is off you'll be able to clean out the dried glue and re-glue the brace down. Once you've got the back off, clean up the rim edge with the sanding disk (or what ever other method you choose) and make sure the inside of the back plate is cleaned up too (no glue residue or dried on glue) and glue it back on (aligning it right) when you're ready. |
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| Author: | Rod True [ Wed Sep 10, 2008 4:24 pm ] |
| Post subject: | Re: undoing a back glue-up |
OH my did I ever read your post wrong. I thought you had the back plate glued to the rim.  Heat gun or clothes iron will do. A putty knife with a thin edge will work to separate too. |
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| Author: | Michael Dale Payne [ Wed Sep 10, 2008 4:25 pm ] |
| Post subject: | Re: undoing a back glue-up |
I would not use a heat gun and a razor knife. If you use heat use a seam knife (thin flexable pudy knife). If you are concerned with using heat. use a straight edge and razor knife and score throuth the at the joint. no matter how you disassemble you will have to re-candel the joint. You will not get it to seperate clean enough to glue back to gather without re-fitting the (candeling) the joint because you need to remove all glue and have the plates joint edges fit perfect. |
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| Author: | Rod True [ Wed Sep 10, 2008 4:27 pm ] |
| Post subject: | Re: undoing a back glue-up |
If the plate is still squarish you can also just cut the seam with the table saw, bandsaw, jigsaw... Because as Michael has said, you'll have to joint the seam again anyway. |
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| Author: | Frank Aarre [ Wed Sep 10, 2008 4:43 pm ] |
| Post subject: | Re: undoing a back glue-up |
thanks, sure, i could just cut it, but i just wondered if i'd be easier to do something to make the glue loose it's grip. Frank |
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| Author: | wbergman [ Wed Sep 10, 2008 4:52 pm ] |
| Post subject: | Re: undoing a back glue-up |
Some people put a center strip in after gluing, by routing a channel and inlaying the strip. I think they first glue the interior reinforcement strip, so the inlayed strip can go all the way through. In this type of construction, the accuracy of the initial center joint is irrelevant, because it is cut away. If your boards are still wide enough to saw open, they are wide enough to try an inlayed strip, and still start over if you mess up the inlay. |
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| Author: | Michael Dale Payne [ Wed Sep 10, 2008 4:52 pm ] |
| Post subject: | Re: undoing a back glue-up |
frank777 wrote: thanks, sure, i could just cut it, but i just wondered if i'd be easier to do something to make the glue loose it's grip. Frank The two things that will soften titebond are heat and moisture. With moisture being pretty much out of the question that leaves heat. That said it will take linger than cutting it and saves no work if score cut with a razor knife. If you do use heat keep in mind that the titebond will seperate at 120-140 no more heat than that is needed. let the heat and the seam knife do the work do not push woth any force on the seam knife or you will have a grain split. |
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| Author: | Rod True [ Wed Sep 10, 2008 5:03 pm ] |
| Post subject: | Re: undoing a back glue-up |
MichaelP wrote: frank777 wrote: thanks, sure, i could just cut it, but i just wondered if i'd be easier to do something to make the glue loose it's grip. Frank The two things that will soften titebond are heat and moisture. With moisture being pretty much out of the question that leaves heat. That said it will take linger than cutting it and saves no work if score cut with a razor knife. If you do use heat keep in mind that the titebond will seperate at 120-140 no more heat than that is needed. let the heat and the seam knife do the work do not push woth any force on the seam knife or you will have a grain split. Why would moisture be out of the question? A thin strip of moist piece of paper towel or cloth over the seam and a clothes iron would be pretty quick to soften the glue. Moisture isn't a bad thing if it's used right, and actually it really helps depending on the glue used. I know he said titebond so it's not as important as say HHG or fishglue. |
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| Author: | Howard Klepper [ Wed Sep 10, 2008 5:29 pm ] |
| Post subject: | Re: undoing a back glue-up |
What Rod said (first). If the plates are squarish, and you can lose 1/8" or so of wood, and there is nothing magical about the exact grain pattern you get from joining again on the same lines (which won't be exactly the same anyway after rejointing), then what could work better than sawing? |
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| Author: | Brock Poling [ Wed Sep 10, 2008 5:43 pm ] |
| Post subject: | Re: undoing a back glue-up |
You can also put it in the oven for a few minutes at 200. you can pull it out and just pull the plates apart. |
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| Author: | LuthierSupplier [ Wed Sep 10, 2008 6:24 pm ] |
| Post subject: | Re: undoing a back glue-up |
I agree with Howard on this. Just saw it and recandle and glue. |
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| Author: | Frank Aarre [ Wed Sep 10, 2008 6:51 pm ] |
| Post subject: | Re: undoing a back glue-up |
so i took the razor knife to it and it really was very quick and easy this way. i resharpened the plane to a kind of sharp it has never seen before, and did the shooting board thing, it comes out dead straight, but no matter which way i plane it i get a tiny bump in at least one spot over the lenght of the back. because of the figure of the wood i suppose. now this wouldn't bother me if i was using a centerstrip, but i really like the look of a strip-free back, especially with this wood. so with this kind of wood would it be better to use the sandpaper approach, or am i doing something wrong when planing? Frank |
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| Author: | Arnt Rian [ Thu Sep 11, 2008 3:17 am ] |
| Post subject: | Re: undoing a back glue-up |
Hei Frank, if you get a "bump" somewhere (and not tear out) I would I would suspect it is your technique or setup (or both), not the wood. What is your set up like; type of plane, shooting board style, type of wood etc? Most bench plane sizes will work for this; my preference is a #5 1/2. It is also important that the plane slides on a smooth, level surface, and that the shooting board and work pieces are all firmly held in place during the cut. Take light cuts and shift your pressure on the plane during the cut; on the toe when you start the cut and on the heel at the end. Then, if your plane is sharp and set up well all that is left is some practice… 
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| Author: | Frank Aarre [ Thu Sep 11, 2008 3:29 am ] |
| Post subject: | Re: undoing a back glue-up |
I guess i would call it tear-out. my technique is probably sloppy too, but i feel the plane is riding straight and smooth. shooting board is a couple pieces of mdf, straight and smooth.workpieces and shooting board is all well clamped down. i've got the plane set for a really fine cut, plane is homemade wooden plane with hock steel in it, smoother size. Frank |
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| Author: | Frank Aarre [ Thu Sep 11, 2008 4:01 am ] |
| Post subject: | Re: undoing a back glue-up |
well seing as how i suck at explaining, it's picture time. so for the tearout Attachment: tearout.jpg And a pic of my shooting setup Attachment: shooting board.jpg Arnt, yes that is an old 'høvelbenk' hiding under all that clutter, one i got from my dad that he made himself about 35 yrs ago back when it paid off to make your own furniture. nowadays you can buy most finished furniture cheaper than the cost of raw lumber. Frank |
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| Author: | Frank Aarre [ Thu Sep 11, 2008 5:31 am ] |
| Post subject: | Re: undoing a back glue-up |
nevermind, a smaller cut solved it(thought it was small, but seems it could go even smaller). Thanks Frank |
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| Author: | Arnt Rian [ Thu Sep 11, 2008 5:49 am ] |
| Post subject: | Re: undoing a back glue-up |
Well, there you go! My shooting board is similar, but it also has a second stop, for the long side of the plates. This means one hand can hold the work pieces in position against the stops while the other hand operates the plane. No fiddling with clamps, and the plates always return to the same position after I lift them off the board to check my progress. Your base board (the one that the plane rides on) could be longer so the plane doesn't 'fall off the edge' with each cut. I would expect this to interrupt the flow of the stroke, creating a possible source for unevenness. |
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| Author: | Colin S [ Thu Sep 11, 2008 6:42 am ] |
| Post subject: | Re: undoing a back glue-up |
I usually start shooting the edge with the blade fully retracted, and then gradually dial the balde in so that at the start I'm only taking dust rather than shavings. As I increase the cut, as soon as I take a full length shaving then generally that is the job done. Also I have a third piece of sacrificial wood, slightly longer than the boards I'm shooting underneath them, so that the cut starts and finishes off of the boards. Candle the joint by holding the boards against a window. Colin |
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| Author: | joel Thompson [ Thu Sep 11, 2008 5:39 pm ] |
| Post subject: | Re: undoing a back glue-up |
Colin S wrote: I usually start shooting the edge with the blade fully retracted, and then gradually dial the balde in so that at the start I'm only taking dust rather than shavings. As I increase the cut, as soon as I take a full length shaving then generally that is the job done. Also I have a third piece of sacrificial wood, slightly longer than the boards I'm shooting underneath them, so that the cut starts and finishes off of the boards. Candle the joint by holding the boards against a window. Colin This is exactly how i was taught to do a joint (except i use a light box not a window that way you now exactly where any gaps are) if you take only minimal "dust" to start with you will be able to joint the the back/top much quicker. the main problem i have is making sure the presure is even as i allways take more off at the ends  Joel. |
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| Author: | stan thomison [ Thu Sep 11, 2008 5:45 pm ] |
| Post subject: | Re: undoing a back glue-up |
saw it, clean it, re join it right. |
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