Re: Regluing a loose back
Hi--am reviving this old thread. It has been very useful. I am a hobby luthier and and helping out a friend who had the back of his mandolin at the tailpiece separate from the rim. The sides "bulged" out from the back---pulling some of the kerning loose. Since the kerfing was loose -- I decided to remove the back and reglue the kerfing (with HHG). I built a jig as shown by Sunburst (thanks John!) and its going well so far. I have sanded the surfaces (with a large sanding board on both the back and the rim surfaces) The surfaces are clean and there are no traces of the old glue. with some pressure applied using the "Sunburst jig" in the tailpiece area--about a .10 inch needs be pushed in to achieve good alignment in the tailpiece area.
A couple of questions/thoughts:
This is an Eastman 305...it had no locating pins in the headblock or tailblock. Would you put some in locating pins?
In terms of the glue up--would it be best to glue the back to the rims in one section at time. that is glue the part that mates without pressure, wait until that is secure and then glue the part that needs pressure . I understand that this would be similar to how violins are reglued using a pallet knife and HHG.
The back does not have any binding. I have thought of gluing it back together with minimal pressure to correct the bulging and leaving something of a mismatch at the tailpiece and then installing binding to deal with the mismatch of the rim to the edge of the back---thoughts on that?
Since you have to wrangle the rims inward with the jig.....are the chances good that this will delaminate again-- but I read (Frank Ford's test) this technique works pretty well.
Thanks for any advice--and thanks again Sunburst for sharing info on the jig you made.
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Re: Regluing a loose back
Here is a picture of the back and rim---and showing the mismatch. This is not glued up--the back is just resting on the rims here.
Attachment 181375
Re: Regluing a loose back
I usually glue the neck and tail block first, lining them up into their original position. Then I glue the ribs, lining them up as best as I can. So far as I know, this has always been the standard practice in both the fretted instrument world and the violin world. If the tailblock is glued last, the neck angle will probably be reduced considerably from its original position. The decision to add binding waits until after the glueing has been completed.
Re: Regluing a loose back
If the back is shrunken and will no longer align all the way around the rim, I normally "average it out" so that there is a small amount of misalignment all the way around. It is usually not very noticeable at all when done.
You shouldn't need to add binding, and I wouldn't advise it. That is a big job and gets bigger when you have to touch up the finish.
Re: Regluing a loose back
I will add that each job of this type needs to be evaluated individually, and there are no hard and fast rules about the "right" way to do it. You are looking for whatever will produce the best end result. I have just edited my previous post to say "usually" rather than "always."
You might try dry-clamping the instrument a couple of different ways, and see what technique that suggests in this particular case.
I have found that it is harder to pull sides in than it is to push them out.
Re: Regluing a loose back
Yes thanks. everyone for the advice. Very helpful!!
I built a jig similar to John's to add moderated pressure to bring the rims into alignment with the back and glued the area near the tail piece. Checking after the glue dried--the other areas seem to align pretty well with a small amount of misalignment but the main area near the tailpiece looks pretty good - Now that I know that the other areas besides the tailpiece are aligned pretty well--I will hot knife in hide glue (as violin luthiers describe) one section at time for the rest of the instrument (the entire instrument will be clamped, but the sections to be glued are unclamped for gluing and then clamped for the glue to harden).
Andy
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Re: Regluing a loose back
Here are some pictures of the jig (similar to the "Sunburst Jig" -- thanks John) I built to push the sides in to align better with the back:
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Re: Regluing a loose back
Here is my variation on the rib-o-matic. It is so common for teens and 20's A models that I have a dedicated jig that gets a lot of use. Also shown is a larger guitar sized model for a Collings that got left in a hot car last summer....
j.
Re: Regluing a loose back
You guys are making me feel so inadequate. Great thread.