Well Dave,
It would appear that plasterers in the UK also have small tools, HERE you go, now you can have one to
Cheers
Kim
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| Removing a bridge glued with hhg http://www-.luthiersforum.com/forum/viewtopic.php?f=10102&t=8411 |
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| Author: | Dave White [ Mon Sep 11, 2006 8:55 pm ] |
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In about my very first post on the OLF I sought advice on fixing an early 1900's all mahogany parlour guitar. Well "guitar building time" moves in it's own sweet way and I finally have a slot to devote some attention to this lovely guitar. I need to remove the ebony bridge to fix the cracks between the bridge pin holes. Given the guitar's age I guess it will be glued with hhg. To loosen this you need both heat and moisture. The heat bit I can do as I have the lmi bridge heat blanket but how do you go about getting the moisture into the joint? Do you have to get a sharp edge into the bridge joint partly first to give a route for the moisture? Do you mist spray and then apply the heat? Any methods from you repair gurus would be gratefully received. |
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| Author: | Pwoolson [ Mon Sep 11, 2006 10:24 pm ] |
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I've had good luck with just heat on HHG bridges. Might try that first. If you indeed need steam you might try a small espresso maker. Hook a piece of tubing to the steam part and a needle (the kind to pump basketballs) to the end of that. That should give you the desired result. |
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| Author: | crazymanmichael [ Mon Sep 11, 2006 11:38 pm ] |
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i just dip my palette knife in the water to start. then i use a small plastic pipette to introduce a bit more after it is loosened a bit. |
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| Author: | Martin Turner [ Mon Sep 11, 2006 11:47 pm ] |
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A pallette knife heated up using a painters heat gun. Gently work the knife under one end of the bridge and work along length of bridge. |
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| Author: | Kim [ Tue Sep 12, 2006 1:16 am ] |
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Dave, I have a plasterers small tool, no this is not an affliction, rather it is a plasterers pointing tool very similar to a palette knife but duel ended. I am sure you are familiar, but if not, it is about 10" long over all with a thin 3/4" wide rectangular blade at one end, and somewhat the same at the other which has been tapered either side to form a point. Into this pointed blade I have scored a groove down the centre and then, working with a small fine triangular needle file, I have widened the score to a slight valley. Using a diamond honing plate,(thanks Michael) I have thinned both blades to a fine wedge, more so the tapered end than the rectangular. Like others, I heat this tool in hot water and GENTLY work the pointed grooved end into the glue joint. As it makes way deeper into the joint, I then alternate between ends of this tool occasionally wicking the groove with small droplets of hot water via a needle and syringe using the slightly thicker stronger rectangular end to apply a bit more pressure as required. Hope this helps Cheers Kim |
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| Author: | Barry Daniels [ Tue Sep 12, 2006 1:29 am ] |
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On an old guitar like this, the bridge might pop off relatively easily without heat or moisture. I would attempt to insert my putty knife under a corner of the bridge and see what happens. |
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| Author: | Kim [ Tue Sep 12, 2006 1:50 am ] |
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Well Dave, It would appear that plasterers in the UK also have small tools, HERE you go, now you can have one to
Cheers Kim |
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| Author: | Alan Carruth [ Wed Sep 13, 2006 6:49 am ] |
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I, too, learned to disassemble HHG joints dry. The beauty of the stuff is that is brittle and has low peel strength, so that if you can get one edge started a thin knife will generally simply follow the glue line. I use a regular stainless steel table knife that I have ground down into a wedge cross section, with a thin but, not a sharp, edge. The distiction is important: if the edge is sharp it will tend to cut wood fibers and dive into the grain if there's runnout, while a thin edge will be flexible enough to follow the glue line. The important thing about this is that you need to develop the feel for knowing when you're splitting the glue line and not severing wood. I learned by taking apart a lot of cheap fiddles to regraduate them for practice, and that's usually easier than removing a bridge on a guitar. Still, once you 'get it' it's not bad. And there are those times when a little water helps. Usually water weakens the wood grain as well as softening glue, which is why I like to avoid using it. sometimes a better 'wetter' is alcohol, although you have to be careful that it doesn't cut the finish. Of course, there are those times: you can't very well get a knife into a dovetail, which is why you need to use steam there. OTOH, Titebond and such like require heat and/or moisture. If you can't cook the joint to 140 degrees F or better, acetic acid is a better solvent than water. It destroys the glue chemically. Hot vinegar works pretty well, by photographer's stop bath is stronger. The combination of acetic acid and iron is a traditional black stain, which is why I got a stainless steel knife. Lastly, I've always felt that a bridge that was split through the pin holes needed to be replaced rather than repaired. I don't think any glue line will be as strong as the original wood was in rupture strength over time. |
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| Author: | Dave White [ Wed Sep 13, 2006 6:59 am ] |
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Thanks for all of your suggestions. Kim - I like the idea of getting plastered
Alan - thanks for this. I will try it as you suggest. I hear what you say about a new bridge but as this one has hung around for 80 year's or so if I can get it off cleanly and glue it back with hhg, I'd rather give it the chance of a few more years: 
I'm thinking that the mahogany top will behave a lot better than spruce wrt avoiding taking a lot of the top wood as well. |
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