Last night I suffered the dreaded peghead scroll break when the mandolin fell off a stand during a rehearsal. Of course, I looked up Frank's article in frets.com [http://www.frets.com/FretsPages/Luthier/Technique/Mandolin/BrokenSc...] and lo and behold, his article is on a Unicorn and Mustang--same builder as mine. The only difference is that on mine the binding didn't break, although the part from the scroll to the top point came loose from the channel. Clean break in the wood, no missing chunks--nearly invisible when hand fitted back together. I even have some of Taku's stain and varnish--he sent some to me some years ago so I could repair a ding on the peghead point.
I emailed Frank with three questions but I know he's busy and I thought I'd run it by this group for thoughts on alternatives:
1. What viscosity of ACC Should I use to initially reattach the part--thin or "gap filling?" [And if I were not to reinforce the repair as Frank did, should I use ACC or hide glue?]
2. [I don't have the tools Frank Used so...] Instead of routing a channel and insetting a piece of maple as Frank did, I'm thinking of drilling a diagonal hole through the scroll into the main part of the peghead and gluing a length of dowel in the hole, for reinforcement. Do you think that would work? It seems like starting the hole at such an odd angle might be the spoiler, but otherwise, it might be nearly as strong.
3. There's also the issue of how to get glue into the hole, once drilled.
Another thought: Frank's article was written in 2001. I've seen a couple of negative comments on the longevity of ACC here and elsewhere. Is it the right stuff 12 years later?
I need to at least stabilize this before tomorrow because I have a gig and no backup mandolin... . I've had this mando for 13 years before this happened. Should I take a chance and reglue and not worry about it for the next 13?
Thoughts, ideas, alternatives? Talk amongst yourselves. Discuss.
Pictures to follow when I get back from an errand I need to run now.
I think Frank only uses CA to hold the scroll long enough to complete his spline repair. The spline is glued with hide glue.
I understand that, but it if the ACC fails, will the surface joint open up in the future?
My implied point was that it's the spline joint holding it together not the CA. I think the spline (or dowel) would have to slip for the joint to open up.
If you have an invisible fit why would you need to fill gaps?
Dowels work but they allow rotation, but because you have a clean break the fit would probably serve to lock the piece in position.
If you're worried about the CA why not use hide glue and make custom cauls to allow clamping while gluing?
My two cents.
Maybe you can get it glued up well enough to use your mandolin this weekend and then return to it for a stronger repair later. I would recommend HHG for a clean tight break.
I always have misgivings about doweling repairs. I've seen and used them for years in instruments and, mostly, in furniture repair. They never seem to last over the long term. I think the dowels often shrink over time and weaken the glue joint.
Frank's patch repair is something that I've seen several builders use on new instruments to help reinforce this particular weakness. I think it probably insures that the scroll won't break off again better than any other method I've seen. If you can't do it this way I think you should consider taking it to someone who can do it for you.
I appreciate the concern, Ned, and I agree in general. If the break weren't so hard to clamp (as Frank points out) I'd go for HHG--something he dispensed with in the same situation. However, the deed is done with ACC (gap filling) and it is very tight. I'm letting the initial cure age for a while and it's a good enough joint for the gig tonight.
I emailed with Frank and he thought the dowel might be a good idea and could make the amount of touch up much less. Why would shrinkage be any more of an issue than with Frank's insert, anyway? In either case, I'd want to make sure both the instrument and the dowel were well stabilized in the same humidity environment (it's about 44% today in the house with my whole house humidifier) to avoid big differences in expansion or contraction.
My thought is that a dowel would be a bad solution for any joint that had a lot of continuing or repetitive shear or twisting force, e.g. rungs in a wood stool. In this location, however, it's there to provide cross grain reinforcement in case the scroll gets bumped again and would otherwise separate along the weak grain line. The force here was not enough to break the binding (although it did pull off cleanly) even with a pretty hard fall on a hard floor and I don't think a big bump is likely to happen much in the future--it went 13 years so far without a problem and it's been down before.
If I do use the dowel, I'll probably use LMI luthier's glue instead of hide glue. Again, because there's no constant or frequent load on the part, it probably won't suffer from the same issues that PV glue usually has problems with--creep under load, heat issues, etc. Putting the glue in the dowel hole might also spread it to any voids that remain nearby in the crack, as well. Heck, I saw Lynn Dudenbostel use the LMI glue to mount a bridge on a new guitar in one of his DIY videos. I asked him about it and he said that the loads were such that it wasn't a problem in that location.
Keep the comments coming--I'm in no rush to jump into the reinforcement stage and if I didn't need the ax for frequent use I'd probably have sent it out already. But I'm 30 miles from the nearest guy I trust and he's usually backed up for weeks.
BTW, I retired the offending stand, effective immediately. If I kept firearms, I might permanently prevent it's use by others.<G>
I just use C.A and it never came apart again after 10 years thats my exp. Bill.............
That's my next question. If I just leave it alone, joined with CA, is a much more difficult fix in store if it happens to get whacked again? It's now joined, nearly invisible, stable. Maybe the reinforcement is overkill in the real world.
Someone mentioned twisting forces and a dowel reinforcement as maybe incompatible. Any comment on two smaller, parallel dowels (3/32") instead of one (3/16")?
I don't beleve it will ever brake again in the same place . And I don't like to use dowels to fix anything.... Bill..........
Well, revisiting this again as last night the mando was knocked over by a band mate during a gig. It was glued with CA (medium viscosity) before and it broke in exactly the same place. A dry fit shows that it fits as well as the first time. My theory is that the raw wood absorbed most of the glue so there wasn't much to hold it together. As soon as I get my hands off the guy's throat (<G>) I'm going to go again with CA unless someone can suggest a better adhesive.
I think it needs to be reinforced or it will always be delicate.
Precisely - that's why I use the spline despite its obvious cosmetic downside.