Cello neck joint repair

[Mark Wybierala]

I need some help here. This is a modern student cello made in Germany and sold via Meisel with the Meisel name in it. The neck has cleanly departed the body. I have a few pictures also. The break is totally clean -- its actually not really a break but rather a total failure of the glue to hold the neck in place. I am bothered by the way the neck joint was made. The neck block was never in contact with the sides of the heel. There is no evidence that there was ever any glue on the sides of the heel. All of the contact area was on the butt of the heel and because there was less than 1 square inch of actual contact area between the butt of the heel and the neck block I understand why the joint failed. The heel tab that typically extends from the cello back was not part of the back but rather a separate piece.

Picture of the neck heel. There was no glue on the sides and I have cleaned off the glue from the butt end. There was only a small contact area at the top of the heel and the bottom of the heel as indicated by the circles.

[Mark Wybierala]

Here is the neck joint at the neck block. You can see the small contact areas at the top and the bottom. The neck block itself was never shaped to be in contact with the sides of the neck -- the neck block sits in relief behind the sides.

[Mark Wybierala]

Suggestions for repair??? Should I install shims against the sides of the neck block to get a proper fit? And what should I do about the heel cap? I'm thinking I should carve a vee into the back of the cello over the neck block and make a 1 piece heel cap that will glue and bridge from the neck heel to the block.

[Ryan Mazzocco]

I can't tell, is the tenon dovetailed or just straight? Can you slide the neck straight back in or do you have to drop it in? Cuz I'm thinking, if it's straight and it's inexpensive enough of an instrument you could drill holes in the head block and and heel for dowels, flood the cavity with epoxy and call it good.

[Michael Lewis]

NO, no epoxy, at least not yet. It looks like the "button" was torn out of the back, which is a plywood plate. If it was a good quality instrument the back would come off and a "swallow tail" would be inlaid into the inside surface of the back and the new button would be part of that swallow tail. It's a strong repair but not sure this instrument is worth all that work.

Yes, shim the sides of the mortise so the heel fits snugly. HOT HIDE GLUE.

It is so much easier to work on good quality instruments because they are worth the work and pains we take to make them right, and many of the techniques are well understood.

This one looks like soft Chinese plywood from the pics.

[Mark Wybierala]

Michael: Plywood would make sense for what appears to be a clean break and a separate heel cap or button. I'll do a sort of swallow tail from the outside. Yes hide glue is what I will use after I construct a decent pocket. Our main product that we sell are entry level Chinese manufactured violins and cellos. They've become much better over the years and are suitable for an eleven-year-old but only after they have been properly set up with an average of 35 minutes on the bench . We sample three different vendors each year and pick the best. Typically one out of about sixteen are rejected by us and our supplier has no problem with an exchange. On this particular cello although it says "Made in West Germany" I'm thinking that the materials are probably from China. It has quite a superior external fit and finish but clearly went down an assembly line at very high speed.

Much thanks

[Mark Wybierala]

Damn - the heel block is made from some sort of really awful stringy lumber that even with a good quality chisel, it will not cut cleanly. Its like wet douglas fir. I've got a pair of maple donor pieces about an eighth-inch thick that I'm going to epoxy in place because there is no way I'm going to get a clean joint for hide glue. The maple will make for a decent medium to carve properly. If it were not such a pretty instrument, I'd call off the repair. The fingerboard is actually ebony and the neck is actually maple.

[Michael Lewis]

Like so many products, they are made with only one purpose, to be sold. Whether they actually function is beside the point I guess.

If you resort to using epoxy make sure it is of good quality and make sure you mix it really well and then mix it some more before applying it. I have used West Systems epoxy, available at West Marine boat shops.

[Mark Wybierala]

I'll get some new epoxy for the side shims. I'm going to try and fabricate a dummy heel piece to simulate the neck heel and get the side shims correct. Its the heel block that has a concave flat bottom. I'll try to match the butt of the heel to it and then use hide glue when I attach the neck. The end cap, or button, I'll do last as a separate procedure when the neck is solid -- just because I can. Maybe use a router (dremel in a router fixture) and a template to get a nice clean flat surface.

[Mark Wybierala]

This ended up being quite a learning experience and an adventure. I fabricated a dummy heel that accurately matched the neck. Using a dremel and a new bit, I was able to cut a reasonably consistent relief cut behind the sides attached to the neck block using the clean and straight sides (that meet at the heel) as a guide. It was very tedious but I got the very end of the relief formed cleanly using a very small wood chisel. I created maple shims to fit into the relief on both sides and using carbon paper and a micro-plane adjusted the shims to achieve a tight and consistent joint with the dummy heel. The neck itself needed a couple of light wacks to fully seat and the alignment to the body was nice and straight. I did all of the alignment adjustment without glue and I could pick up the entire instrument by the neck.
I epoxied the shims into place using wax paper under the dummy heel as a caul being careful to not get epoxy on the surface of the shim that would eventually be in contact with the actual neck. I used epoxy here because of the inferior wood of the neck block. Although I did get a fairly clean cut with the dremel, the wood was exceedingly porous and stringy. I judged that the hide glue would not be up to the task of holding due to the larger average of open and soft spongy stringy grain. I used a three hour curing epoxy so I might possibly get a better penetration of the epoxy into this inferior wood. I let the epoxy cure for three days. The dummy heel block was clamped into the vee and after three days, came out cleanly along with the wax paper. The squeeze-out of epoxy was minimal and I cleaned the new mating surface with acetone and q-tips. I used hide glue to attach the neck and made the needed custom cauls to hold the neck in place. The one thing that I over looked and I can't believe I did was the neck angle. Everything about the neck joint was joyously perfect except that in the end I had to lower the bridge height by about a quarter inch. It wasn't terrible but it was one of those things that you kick yourself for. I never once checked the neck angle during the fitting and I should have really known better. I just assumed that the base of the joint was correct. In the end, this was a great and successful adventure and I'll know better next time.