I would like to hear from members who have used cyanoacrylate (Super/Krazy glue) to repair head-joint cracks: how have you applied the material and what results have you obtained?
Hi,
The problem with just filling the crack, is this: The wood shrinks around the liner and causes it to crack. The crack will continue to open if it is still under pressure from the liner. I remove the liner and ream the head, and re-glue the liner into the head joint. But this is more of a advanced repair job.
I use a commercial form of super glue, combined with fine blackwood dust.
I mask off the area around the crack, I use scotch tape, and remove it right away, but masking tape will work also. I get the tape as close to the crack as possible, say 1 mm away, fill the crack with blackwood dust, mounding it slightly in the crack and apply the super glue. Make sure you don’t breath the fumes! Then i scrape off the mounded glue, carful not to dig into the wood. Sand the area with 400 Grit and then I finish with 2000 grit. Then, buff the area, using a tripoli. That is pretty much it…
Thanks, Jon.
Dick Abrams
I’ve done similar to Jon’s description, save that after removing any metal liner tubing I first glue the crack itself shut with cyanoacrylate by using the bottle nozzle to squirt the glue into the open crack - it also migrates quite well by capillary action… (hold the crack open a little to insert the glue if it isn’t standing open by carefully inserting something like a knife blade as a wedge - but don’t overdo it and crack the wooden tube elsewhere!) and then clamp it or bind it to hold it shut. This will inevitably squeeze out surplus glue, which you will need to remove once the job has set by careful scraping and rubbing off with acetone on a cloth. You need to get the now-glued-closed crack glue surface slightly below the wood surface in order to top-dress it to disguise it as well as possible. Then proceed as Jon says - ream the bore to re-admit the liner without stress and glue it back in (if you haven’t got a lathe, like me, dowel wrapped in sandpaper will serve to expand the bore, but be careful to do it evenly around the bore and not to “hour-glass” the tube. Then top-dress the crack with the glue/dust mixture and clean it down flush according to Jon’s instructions. Surplus glue may again be removed with acetone on a cloth, but don’t overdo use of that on your top-dressing or you’ll take too much off and have to re-do it. I’ve successfully made some cracks nearly invisible this way - looking like part of the grain unless you catch the light in a certain way that shows the superglue+dust in the crack-line up as slightly shinier than the wood.
Having acetone to hand when using superglue is always a good idea!
I’m grateful for this excellent information on using cyanoacrylate for major repairs–many thanks! Has anyone tried instilling cyanoacrylate into a hairline crack to keep it from opening further?
Dick Abrams
It can also be mentioned that super-glue/blackwood/ebony dust can be used to fill a ding as well as to glue a crack. I use this method to build-up an ebony nut when string grooves have been worn down by wear or excessive filing. Once the glue/dust mixture has hardened, you can work it just like new wood. This saves you from having to replace the whole nut on a stringed instrument.
Dick, please re-read Jon C’s first response. Simply filling any crack, with anything, is NEVER a good idea! It may seal up any air-leak - temporarily, but when the crack re-asserts itself, there will then be a residue of glue/filler to be cleaned off/out to add to the difficulties of the ultimate repair. The crack must be seen as the symptom of the problem, not as the problem itself. Ignore that and do as you suggest - your crack will either re-open despite the glue, maybe splintering off it, or the tube will crack elsewhere to relieve its stress. If you want a temporary air-seal to a crack and don’t want to tape over it, filling it inside and out with pure beeswax will usually do the trick, won’t add to the stress/will move with it, and is relatively easy to remove before a final repair.
If you have a crack in an un-lined section, say on a joint mortice or tenon, sure, very carefully levering the crack open a little, squirting/capillary drifting glue into it and clamping it up may fix the problem, depending on whether it was clumsy putting together or a knock that caused it - a temporary trauma, or whether it was an integral stress in the wood, in which case once again that stress will probably re-assert itself and cause another crack. I have used superglue in this way, but I emphasise, to glue the crack shut, NOT to fill it. The only filling that should ever be done is top-dressing the repair to give a good finish.
Doug makes a good point re the other potential uses of the wood-dust/superglue mix - I’ve repaired the edges/chimney surfaces of embouchure holes and the edges of tone-holes thus.
Jon and Jem, thanks for the detailed info. Yours are the voices of long experience and I don’t mean to belabor this, but I’m unclear on the concept. Understand that I’m mostly thinking of antique flutes here, and cracks associated with lined heads, barrels and tenon sockets.
I was under the impression that the cracks on metal-lined sections were primarily caused by shrinkage of the wood over time around the metal lining, which is inherently stable. At some point, under some stress like a temperature or humidity change or a physical shock, the wood finally gives way and cracks to relieve the stress.
What I don’t understand is this: once the wood has cracked, why is there further movement (beyond what the flute tolerated without cracking for, say, its first 50-100 years) other than due to the fact that the wooden tube has lost its structural integrity? I would think that if the crack were filled with something as strong as super glue/wood dust in its “final” open position, the stress would be relieved and the integrity returned so everything would be stable from that point on.
My only direct experience has been with cracks on the head and foot sockets (which are all lined) of old wooden Haynes flutes. They’re all more than 85 yrs. old now and I’ve never seen one without these cracks. Cyanoacrylate and wood dust seems to stabilize these cracks perfectly and I’ve not seen problems return, even though the sockets are subject to continuing physical stress. Granted, they may not be subject to the extreme thermal changes of a lined head.
Obviously, your experience with lined headjoints indicates otherwise. So what don’t I understand?
Herb
The hairline crack I referred to occurred in the lined head-joint of an antique R&R and was stable for years. Then it suddenly opened up to about 1 mm despite controlled room humidification and storage in a sealed plastic container. I put a wet sponge in the container with the head-joint and re-sealed it–48 hr later the crack was completely closed again, nicely demonstrating the unstable nature of such cracks and prompting my thought that drizzling in some cyanoacrylate might prevent recurrence.
From the various comments I’d say the field was in need of a controlled test of the method under varying conditions of heat & humidity.
Dick Abrams
What I have found to be the case much of the time, the wood will expand and contract depending on the humidity the flute is subjected to. This all depends on the type of wood. Ebony or boxwood expands and contracts a lot more then Cocuswood or Blackwood. If you were to be very careful and always keep the flute in a controlled environment, the repair may hold, but players like to take there flutes out and play them in adverse conditions. I don’t rely on the CA glue to hold the crack, I mostly rely on the gorilla glue that I glue the liner in with to keep the crack from moving. I will ream it a little loose except by the embouchure hole. The gorilla glue foams up and acts like a cushion, or expansion joint, that gives the wood room to expand and contract.
The barrels are even more of a challenge, especially when they sandwich the wood in the female slide. I usually have to bore out and replace the sockets with new wood.
Hope this answers your questions. don’t know if it is just weird science, but this is what I have found when repairing the flutes.