Restoring the inside of an upper joint tenon

Gheorghe

My taragot is the type where the upper joint ends with the "male" tenon onto which the female MPC goes.

The first thing I noticed when I bought the instrument is that someone was a little overzealous with the reamer perhaps, or file/drill bit. Whatever the tool was, it wondered off to 1 side a bit, so the hole is not regular, but rather oval, and thus part of the wall is dangerously thin. It has not gotten any worse in the 1 year of playing I do, but I do keep an eye on it. What is the best way to approach this?

In the order of least-invasive to most, here is how I see it:

1. Leave it alone (I've been pretty good at that).
2. Use dust+glue to build up that wall from the inside, then re-drill to correct diameter. (John's restoration post made me consider this)
3. Make a plug, drill out the tenon (making the walls really thin, glue in the plug, and re-drill to proper diameter (about 9mm in my case).
4. Cut off the tenon entirely, make a new one, drill into the upper joint to glue in the brand new tenon, then re-ream it.

Clearly I'd like to avoid or postpone #3 and hopefully never have go to #4, but if I plan on ever implementing method 2, should I take it easy with oiling that part of the instrument, so as to make any future glue adhesion easier? Any other options I have not thought of?

I'll post a picture of what I'm talking about in the next few days.

George
 
If you're good at the lathe, you can start with an entirely new delrin tenon (learn how to obtain a conical bore and a cylindrical outer circumference), then, if your new tenon stump looks promising, cut and ream the joint (cylindrically) and glue in the new tenon.

Just filling alone is probably more for peace of mind, unless you do this as preparing the grounds for a new tenon.

Another option might be filling plus a metal tenon sleeve.
 
Thank you Ben. 2 very useful things I picked up, that I didn't even consider:

1. Delrin can be used - I had no idea
2. I can make the tenon first, without getting invasive, and only do the surgery if things turn out well.

Yes, I'm pretty good on the lathe, and getting a conical bore should be absolutely no problem. At that short length, nothing will wonder off on the lathe. But I believe in that portion of the instrument, the bore is cylindrical - at about 9mm. The taper doesn't begin until a few cm into the upper joint. I think. Toby covered this in a separate post, and I can double check.

Thanks for the tips! Good to know there is a solid approach to this in the future, should I feel the need to do something about it.

Is good quality CA glue typically the glue of choice for these repairs? That's what I keep reading. I come from a luthier end, and there CA glue is usually frowned upon. But there are different goals there, mostly reversibility and the ease of future repairs to the area.

One thing I forgot to mention: When I recorked the instrument, I first wrapped that mouthpiece tenon with strong thread, and then saturated the thread with superglue. Then the cork was glued on top of it, using contact cement ("Barge"). I took that idea from a repair person who suggested it for fixing a tenon crack in another part of the instrument. So that MPC tenon should have plenty of strength for some time.

George
 
Gheorghe said:
Is good quality CA glue typically the glue of choice for these repairs? That's what I keep reading. I come from a luthier end, and there CA glue is usually frowned upon. But there are different goals there, mostly reversibility and the ease of future repairs to the area.
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Unfortunately delrin resists most glues including CA. There are a few specialized adhesives that are supposed to work, but they are a bit expensive.

Gheorghe said:
One thing I forgot to mention: When I recorked the instrument, I first wrapped that mouthpiece tenon with strong thread, and then saturated the thread with superglue. Then the cork was glued on top of it, using contact cement ("Barge"). I took that idea from a repair person who suggested it for fixing a tenon crack in another part of the instrument. So that MPC tenon should have plenty of strength for some time.
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That is an excellent technique to provide strength to a surface. I have seen "banding" done with carbon fiber thread to repair a crack where pining is impractical. First a small channel is cut into the body by turning on a lathe. Then the carbon fiber is wrapped tightly around the joint adding CA to each couple of layers. It is built up slightly above the surface so that when the glue sets it can be turned on the lathe and sanded flush with the surface. On dark grenadilla it makes an attractive---almost invisible repair.
 
jbtsax said:
Unfortunately delrin resists most glues including CA. There are a few specialized adhesives that are supposed to work, but they are a bit expensive.
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jbtsax is right - Delrin is attractive but isn't really fond of glueing. It's one of those self-lubricating synthetics, and in your case, something like plain old ABS (if obtainable in billets) might be better, or some local hardwood like cherry or walnut?
 
tictactux said:
jbtsax is right - Delrin is attractive but isn't really fond of glueing. It's one of those self-lubricating synthetics, and in your case, something like plain old ABS (if obtainable in billets) might be better, or some local hardwood like cherry or walnut?
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If I were to re-do the tenon entirely, I'd probably go with the same wood as the instrument - rosewood I believe. I also still have a small chunk of ebony - it would make an interesting match.

George
 
if you redo the tenon be careful of light and porous rosewoods, There are higher density rosewoods out there.

When I was fiddling with barrels I tried a few rosewoods - can't recall which ones but the lighter more porous ones were not very good for barrels. When I thinned one from a "fat" barrel to one that would fit in the case the tone went with it.

I'd stick with high density woods - such as African Blackwood, ebonies, Mopani, etc.

as for a repair the carbon banded technique is a great one and the carbon strips, if I recall, can be obtained from JL Smith Company.

But to unovalize it at least temporary (and cheap home fix) I recommend a glue that is stronger and more reliable (I think) for a structure. That of epoxy. Clear epoxy could be used or even black epoxy (Ferree's I think sells some). I think epoxy (though varies) would be a better strength structure than CA. I'm not sure what is available at a local store.

If you use a CAs though I would use only industrial strength CAs, not the "normal" type you buy from a local store. Just look at the labeling, there are a few industrial strength ones sold too.

here's some basic research info I accumulated on woods
http://clarinetperfection.com//wood.htm

Also, about woods, I recall two 3x3x8 inch blocks I had of african blackwood. One was about 1 lb heavier than the other ... talk about density differences !!
 
SteveSklar said:
If you use a CAs though I would use only industrial strength CAs, not the "normal" type you buy from a local store. Just look at the labeling, there are a few industrial strength ones sold too.
!!
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I think the tenon has plenty of strength at this point, so most likely the only thing I'd do in the near future is fill in the gouged out part with dust and glue. But maybe I'll change my mind on that.

The glue I used for crack repairs was Loctite 406 CA glue. I read about it some place as being the most forgiving when it comes to oily woods. It was about 15 bucks for a few ounces on amazon.

George
 
Gheorghe said:
I think the tenon has plenty of strength at this point, so most likely the only thing I'd do in the near future is fill in the gouged out part with dust and glue. But maybe I'll change my mind on that.

The glue I used for crack repairs was Loctite 406 CA glue. I read about it some place as being the most forgiving when it comes to oily woods. It was about 15 bucks for a few ounces on amazon.

George
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Here is a picture of what I'm talking about. Most likely it's no big deal. The wood is nicely saturated with oil now, so it's kinda dark.

George
IMG_20120131_202052.jpg
 
The only problem I see really is that the mpc doesn't line up with the bore. This creates both a contraction and leave exposed edge, neither of which is desirable acoustically. I suggest you use either epoxy wood putty or car body putty to build up the off-center part and redrill. We use this stuff to make shakuhachi bores. It will outlast the wood. You can mix acrylic paint into the epoxy putty to get the correct color; I'm not sure about body putty.
 
kymarto said:
The only problem I see really is that the mpc doesn't line up with the bore. This creates both a contraction and leave exposed edge, neither of which is desirable acoustically. I suggest you use either epoxy wood putty or car body putty to build up the off-center part and redrill. We use this stuff to make shakuhachi bores. It will outlast the wood. You can mix acrylic paint into the epoxy putty to get the correct color; I'm not sure about body putty.
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I thought about the mpc alignment thing also, you're right. I'll give it some time before I do anything, since the wood has tons of almond oil in it at this point. When it dries out some, I will take care of it. A little alcohol cleaning should help adhesion also. I am, however, leaning toward ebony dust and ca glue, I must admit. I have a good amount of it from making a mpc for my other taragot.
With all these substances, I do think about toxicity - ca, epoxy, putty, etc.

George
 
Gheorghe said:
I thought about the mpc alignment thing also, you're right. I'll give it some time before I do anything, since the wood has tons of almond oil in it at this point. When it dries out some, I will take care of it. A little alcohol cleaning should help adhesion also. I am, however, leaning toward ebony dust and ca glue, I must admit. I have a good amount of it from making a mpc for my other taragot.
With all these substances, I do think about toxicity - ca, epoxy, putty, etc.

George
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Toby, something like this? http://www.homedepot.com/webapp/wcs...alogId=10053&R=100649628&catEntryId=100649628

Sounds like a better solution that trying to build up superglue and dust.
 
Can't see the page. Superglue and dust would work fine, but it will take time to build it up. Superglue is completely non-toxic and inert after it sets. Most epoxies contain bisphenol alpha, but then so does the epoxy sealant in your canned tomatoes. Not good stuff, but should be no problem without direct oral contact.
 
Gheorghe said:
I thought about the mpc alignment thing also, you're right. I'll give it some time before I do anything, since the wood has tons of almond oil in it at this point. When it dries out some, I will take care of it. A little alcohol cleaning should help adhesion also. I am, however, leaning toward ebony dust and ca glue, I must admit. I have a good amount of it from making a mpc for my other taragot.
With all these substances, I do think about toxicity - ca, epoxy, putty, etc.

George
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I was just about to say, ebony dust and CA! You've got it. It's not that big of a deal acoustically as long as it seals well, and it's really no big deal to fix, either. If it sounds good, it sounds good, and I've ignored things like that, fixed them, with no massive acoustic improvement. If you feel the need to re-build that little "issue", it wouldn't hurt.
I too have a little toxicity paranoia at times but as long as you're careful about where it goes and what it does, it won't kill you.
 
PrincessJ said:
I was just about to say, ebony dust and CA! You've got it. It's not that big of a deal acoustically as long as it seals well, and it's really no big deal to fix, either. If it sounds good, it sounds good, and I've ignored things like that, fixed them, with no massive acoustic improvement. If you feel the need to re-build that little "issue", it wouldn't hurt.
I too have a little toxicity paranoia at times but as long as you're careful about where it goes and what it does, it won't kill you.
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I agree with PrincessJ--if it ain't broke don't fix it. It might well not make any noticeable difference acoustically to center the hole (or it might--hard to predict). I don't think it could hurt, but I don't really see any structural issues if you leave it as it is.

Believe me, CA glue is completely and totally inert when it cures; that is one of the great things about it as compared to epoxies. And anyway, since your mouth doesn't (or at least shouldn't) come in contact with the tenon, there is really no issue with epoxy either.
 
Nice work. Can you explain how you did the repair so others can borrow your ideas? Thanks.
 
jbtsax said:
Nice work. Can you explain how you did the repair so others can borrow your ideas? Thanks.
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First I cleaned everything with rubbing alcohol. Then I filled the chewed out inside with Loctite 406 superglue and ebony dust. I used a wax covered plastic tube inside to keep things in shape. It didn't work so well, since the glue took longer to set than I thought it would. When it did, I sanded the top flat. I then made an ebony extension. I cut off a chunk about 4mm thick, then drilled a hole in it of the same diameter as the instrument's opening (I believe 9 or 10 mm). After that I cut the ebony to size, slightly larger diameter than the tenon. I didn't bother using the lathe, since it could be easily done by hand and needed to be custom-fit to the instrument in the end anyway. I glued it on (again, superglue), let set overnight. The next day I trimmed it flush with the tenon, and sanded it down so that the MPC fits on perfectly. I used a little trick I learned from fitting double bass bridges: I applied lipstick to the top of the tenon, then put the mouthpiece on, and removed it. The lipstick marks on the bottom of the mortise indicated high spots on the tenon, so I sanded it down gently. I'm sure this is overkill, and there are other ways of making sure it's level.

At that point I decided to extend the cork to the near edge of the tenon. That's what you see in the picture. By the way, I use Barge contact cement for the cork - is that what's typically used?

George
 
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