cello broken neck

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cello broken neck

Postby Steven Wilson » Thu Jun 14, 2012 6:35 pm

I mainly build/repair guitars but lately alot of different instuments keep showing up. I have this cello in with neck snapped off at the heel. The break is clean and goes togather perfectly. Is there any reason not to glue it back togather (hhg) while the neck and and heel are still on the body? The owner's teacher warned against that. I've had very good luck with hide glue and don't believe cello strings would have much more tension then guitar strings.
Thanks
Steven
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cellojoint.jpg
cellofull.jpg
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Re: cello broken neck

Postby Chuck Tweedy » Thu Jun 14, 2012 11:50 pm

I'm certainly no expert in this area, but that looks like a straight glue-up situation to me. Make sure there are no stray slivers of wood, warm the parts, and glue it up. A couple cam clamps on the button and the FB and Bob's-your-uncle.
Likes to drink Rosewood Juice
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Re: cello broken neck

Postby Fred Marcuson » Fri Jun 15, 2012 9:06 am

simple glue up may or may not hold ....
personally , i wouldn't want a simple glue up ( just gluing the neck back in ) come back to haunt me .
i'd remove the rest of the neck from the body and re-glue it.
i'd drill and run a dowel up through the break .
then re-set the neck ...
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Re: cello broken neck

Postby Bill Raymond » Fri Jun 15, 2012 5:32 pm

I'm waiting for some wag to suggest this might be a candidate for conversion to a bolt-on neck.
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Re: cello broken neck

Postby Ryan Mazzocco » Fri Jun 15, 2012 5:41 pm

I'd suggest this might be a candidate for conversion to a bolt-on neck.
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Re: cello broken neck

Postby Stephen Bacon » Sat Jun 16, 2012 1:16 am

You can just glue the neck w/HHG and might have luck, as long as it never gets bumped . One method in this case is to remove the fingerboard , glue the neck as is with HHG , then pin it with a tapered pin, angled against the pull, the bigger the pin the better. For added security a small bamboo skewer is embedded close and parallel to the outside of the heel where the most stress is. My experience in repairing repairs leads me away from metal fasteners in this instance. As it appears to be a repair that should not effect reversibility of removing the neck at a later time the type of glue is not so important. The only essential place for HHG is at the junction to the heel block.
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Re: cello broken neck

Postby Steven Wilson » Sat Jun 16, 2012 1:51 pm

Thanks for the replies. This is a recent china made cello so I'm worried about what type glue was used if I remove the rest of the neck. The reason I am leaning toward HHG is i believe it doesn't show a glue line as much as other glues. I believe this is a factory defect because there is signs of finish inside the crack. The owners son has been taking the heat on this one and denying any wrong doing. at least I can let him off the hook.
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Re: cello broken neck

Postby Mark Swanson » Sat Jun 16, 2012 4:26 pm

I get a lot of chinese guitars to repair that have necks made out of that same wood. The necks break very easily at the peghead, i can't tell you how many I've seen! I glue them up and send 'em back out, and I never get any back.
    Mark Swanson, guitarist, MIMForum Staff
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Re: cello broken neck

Postby Greg Steil » Sat Jun 16, 2012 4:36 pm

I had an Asian Bass in for a crack just the same. Loose as a goose, but would NOT come apart. So I had my neighbor/partner in crime hold the body down. I pulled on the neck. Split the neck from stem to stern!. Reason? A 6" long Allen head Machine screw down through the heel. Metric no less. We both said WHOA! at the same time. I have the hardware stuck to a magnet on the basement fridge. Machine screw....sheesh
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Re: cello broken neck

Postby Stephen Bacon » Sat Jun 16, 2012 7:43 pm

Steven, You are calling it right , it came from the factory with a defect. I have encountered this before. The question is wether that defect will except hide glue. That grade instrument is usually sprayed with a catalyzed lacquer, something very hard to remove as well as glue to, no mater what the glue. Even pinning the joint will not guarantee a return visit as the location of the flaw is where a great deal of stress is. Personally , especially in this case I would use a bamboo skewer but if the client wasn't into looks you could , with less effort, inlay a butterfly over it, very Asian. There are specialty hide glues that will outperform most when it comes to neck repair. The 300 series is incredibly strong. However the glue must adhere to the surface.
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Re: cello broken neck

Postby Steve Senseney » Sat Jun 16, 2012 10:39 pm

I am not an expert on cello repairs, and I can't see exactly how much of the joint has the finish in the joint.

Another option--Glue with the hot hide glue, let this set up a day, and then saw where the finish filled crack causes a weak joint. Then you can fill the saw kerf with a small shim, and hot glue this in place.
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Re: cello broken neck

Postby Stephen Bacon » Sun Jun 17, 2012 1:18 am

Good save, I have done that and it works. Just make sure that your shim fits quite well.
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Re: cello broken neck

Postby Steven Wilson » Tue Jun 19, 2012 6:32 pm

Thanks for the advice
I'm not sure I understand the skewer. Are you talking about a hardwood dowel on the center of the heel and then a smaller bamboo dowel closer to the point of the heel?
Steve-if you click on the pic it gets pretty big. I like that about this new forum software.
Thanks
Steven
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Re: cello broken neck

Postby Steve Senseney » Tue Jun 19, 2012 7:13 pm

OOOOH!! BIG!!!
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Re: cello broken neck

Postby Steven Wilson » Tue Jun 19, 2012 7:22 pm

Hey Steve
Since I'm not sure how easy it would be to remove the rest of the neck I'm thinking about your shim idea. The crack line is not straight so I'm wondering about so other method then a saw kerf. Ideas?
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Re: cello broken neck

Postby Steve Senseney » Tue Jun 19, 2012 7:49 pm

By saw kerf, I mean with a hand saw, just to the depth of the finish that leaked into the crack.

I can't really see by the picture whether this is a straight surface or a curved surface.

With that much of the neck joint exposed, do you think you could steam and heat the rest of the joint and get it removed?
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Re: cello broken neck

Postby Stephen Bacon » Wed Jun 20, 2012 2:04 am

I use to use a 1/2 hardwood dowel in the center of the neck angled slightly toward the block, and yes a bamboo skewer or two closer to the outside of the heel. Now I use a tapered hardwood dowel as well as screwer. If your adding a kerf spline do it before you skewer. Just hand saw a bit into the heal over the glued up neck. Then via scraper or sander make a snug fit spline
.
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Re: cello broken neck

Postby Edi Malinaric » Mon Jul 09, 2012 1:33 pm

I find that, for cellos, a 5/8" dowel works just fine :-)

Hi All - I have recovered several broken cello necks and a 5/8" diameter maple dowel works just fine.

After cleaning the broken faces of any loose fibres to get the best fit possible, I glue everything together using instant glue. It's thin and you can feel the break "register". I hold it together while slowly counting to 60. Then put it aside it until the next day. Because the instant glue is almost water thin you usually have a repair that is near-to-invisble. Masking tape either side of the break prevents excess glue running over the varnish.

Next one drills the dowel hole so that it runs parallel to and 3-4mm in from, the rear surface of the heel. I have a lathe so it's simple thing for me to turn my maple dowels to be a slip fit into the drilled hole.

I file a flat along the full length of the dowel to avoid the twin perils of hydraulic lock and pneumatic ejection. No prizes for guessing how I discovered those :-(

I use structural epoxy glue to glue in the dowel. If you spin the dowel as you press it home the epoxy is smeared into and over every square mm of the gluing surface and all the air bubbles "splat" out - rather obscenely.

The new grain direction, glueing area and the epoxy result in a repair that far exceeds the strength of the original wood. The epoxy also seals the dowel against moisture affecting the wood in any way.

Some of the breaks came that were mechanical threaded repairs that had re-failed. Being a mechanical engineer it bothered me. What I would have thought was an absolutely sure-fire, far-too-strong, over-the-top fix had not lasted. Both failures occured under the end of the bolt i.e. outside the area of the steel fixing.

After mulling over those failures I realised that tightening the bolt introduced a tensile stress beyond its end - and a tensile stress in the heel is exactly what caused the original failure!

A glued in maple dowel with the grain running vertically through the heel introduces no residual stresses into the neck and replaces "wrong", easily split grain with "right" grain. The neck is returned to a stronger state than the original just-strong-enough condition.

A similar situation exists at the tip of bows. There a carbon fibre dowel is less intrusive than the traditional spline and is much quicker to do. The last bow tip repair only took me 35 minutes - mainly because I was able to leave a little carbon black dot in the tip face. Even on the 2mm dowel I file a flat.

cheers edi
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Re: cello broken neck

Postby Steven Wilson » Thu Nov 08, 2012 12:40 am

OK, The simple glue up failed. I explained to the the owner it might so he is OK. My Question is how to remove the rest of the neck. On a guitar I would use pressure(clamps) from the bottom of the heel, but the back covers that so what is the best way? The glue softens with heat, I was able to get a hot knife between the heel and the back, I'm just wondering the best way to get some pulling pressure once I get some heat/steam in the joint without pulling the whole thing apart.

Thanks
Steven
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Re: cello broken neck

Postby Michael Lewis » Thu Nov 08, 2012 3:00 am

You need steam to soften the glue around the heel stuck in the mortise. First you must separate the button of the back from the heel, only after it is free should you try to remove the rest of the heel. When you get the heel out glue it to the neck. When the glue is dry then saw a slot from the end of the neck/heel and glue in a spline with the grain running perpendicular to the neck grain. Once dried and trimmed, you reset the neck.

In the process of gluing the broken surfaces together make sure they fit well and clamp them so they close completely. Use fresh hot hide glue.

You should request a book at your local library by Margaret Shipman and Hans Weisshaar regarding violin restoration. It will have drawings, photos, and explanations of just about any repair for a violin family instrument. I would suggest you buy the book but it costs over $300.
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