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kittykatjaz

Best way to approach or run away from cello repairs

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Hello,

I have been asked to look at repairing an old beaten up cello with many numerous cracks on the belly which a few of them are old that have been repaired and reopened. By looking over the cello it has already had a lot of repairs which many have not been well done, especially a sound post crack on the back which has been poorly patched but stable.

The main concerns are not hiding the cracks but repairing and stabilizing them and making the instrument structurally sound. I explained to the lady that owns the cello that taking the top off could be opening a big can of worms and it is a job that I am reluctant to take on.

Please have a look at the photos at the link below and any ideas on how best to approach would be very appreciated.

http://www.jasminedavis.com/boardphotos/eliz_cello/

Thanks

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Hello!

I would say that the top would have to come off.  A few of

those have the potential for bass bar cracks. Yes, a can of worms.

And a bad S.P. crack in the back is a deal breaker for me. Is this

a job or a favor? A job? No. A favor? Let's see what we can do.

In my opinion, you have to be enthusiastic about both cellos AND

restoration to successfully restore a cello. You are clearly

enthusiastic about cellos. If not so much about restoration, I

would let it pass and maybe start on a smaller cello, like maybe a

violin. Celli of a certain age tend to have all sorts of fancy,

special, hidden problems not easily spied from without.

If you are not excited about taking on a job, then that is a good

sign that you shouldn't do it. If you are only nervous, then think

a bit, have a drink or two, and either jump in or don't.

From you past posts it is clear you could do this kind of repair.

 So drink up .

Good luck.

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Jasmine, you have built two cellos from scratch. You know you can do this. Will it be fun? probably not.

Replcing missing wood along the edge can actually be sort of satisfying, when the end results are good.

Make yourself a set of clamps before you ever begin...get some 5/16 allthread (don't know what they call it there), wingnuts, and 5/16 clear flexible tubing, to pad the clamps.

celloclamp1resize-1.jpg

You can cut them to the length you want, and shape the heads the way you want...bend them to the curve appropriate for the job.

celloclamp2resize-1.jpg

It would be a good idea to glue some leather to the wooden clamp heads, to avoid scratching the cello...the ones in the photos don't have it yet.

These only took a few minutes to make: I drilled a series of holes in a strip of wood--one set to be the holes through which the clamp rods would go, the other set, rotated 90 degrees from the first set, to be sawn through the middle, making matching halves--each half making a single clamp head.

I made enough heads for eight clamps, but only needed four right away. You probably will only need four, I would guess. Plan the job, make the clamps, then begin. And if you can get Jeff Holmes on your side from the beginning, do it. :-)

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These cracks are all close to the sides, meaning that the long clamps as shown by COB3 though needed, will not be sufficient. You need an edge clamp and several pillar clamps. You can get a commercial edge clamp from International Violin Co. for about $25, but I know no commercial source for the pillar clamps--you will have to make them. The pillar clamps are not the calimari clamps of Oded, you need to exert much higher forces that they are capable of. I made mine out of a 3" PVC pipe cap (get two per cap). Do a search on "pillar clamps" and look for the red colored clamps (of apartment luthier?) which have a long bolt going through the center.

You will have to wash out each crack to clean it and see how well it closes. I would use the rare earth magnets across the crack to insure that the crack lines up during the gluing. You can do maybe one crack per day because you also have to glue in the blocks for the pillar clamps; so it will take you a few days. Clets will be needed. A lot of work but also good practice.

Mike D

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I get a little jumpy when someone mentions the
phrase “much higher forces” in regards to crack
clamping. Pillar clamps, while they can pull a split together;
really shine in keeping arching in check. Clamping should only be
thought of as means of keeping two surfaces together. 
Squeezing the bejesus out of a crack can cause more frustration
later on by distorting something you didn’t intend to
distort. 



 



Putting a split (new or old) back together is
an exercise in creative thinking.  No one solution is
perfect.  Often multiple methods are required to put a crack
back together – jigs, partial gluing, strap clamps etc. 
There is a lot of info in the archives.



 



Sorry if this came off a little cold. 
It’s been a long day, and I have a four month old kitten
helping me type.

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Well... if you can't be convinced to run for high ground...

I think Mike is correct about the edge clamp. That tool would come in handy for this particular job.

I agree with H. L. concerning the pillar approach, however. Too much clamping force on a pillar & wedge system will tend to distort the arching. They don't require much pressure to do what they do. The system is very useful for adjusting alignment, fine tuning the joint and helping to hold things in place... not squeezing a gap closed. Used correctly, pillars will help negate much of the requirement of magnets and top-to-bottom clamping.

Working carefully, you should be able to get those cracks pretty close during your cleaning process. I'd make sure if you wet the crack surfaces during the cleaning process, that you don't allow them to dry "open" (unclamped).

If you have difficulty in completely closing the crack, you might consider employing a jig (I believe I illustrated one type of clamping jig in a "back crack repair" thread some time ago). It was a pin and wedge affair. A jig will allow you to apply just a bit of pressure in a specific area, areas, or direction that would be awkward to access or control with a strap clamp.

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My thoughts would go along with arglebargle. Is it a paying job or a favor. How much time and effort are you willing to spend. It looks a lot like a violin that I'm working on now. I got it for a class that I'll be taking in a couple of months. It came to me with several cracks, loose seams, and other problems. I'll end up gluing and cleating the cracks, removing the carved in bass bar (yep, bass bar crack), putting in a new bass bar, new end blocks (lower one cracked, upper one to reset the neck in a class), and re-gluing loose seams. Lots of work for an old German fiddle!

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Yes, the edge clamp goes on the endgrain edge of the plate to help align the ends of the crack and pull them together. The clamp can also push apart, so I usually give it a tiny push apart when putting the glue in the crack, and then pull them together. Please note that you have to make sure that the crack is aligned along the entire length. The edge clamp won't do that.

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It looks like many of you guys have never made calimari clamps from PVC tubing. They are very weak and would be unsuited for substitution as a pillar clamp. I like the idea of calimari clamps, and I have made some of them, but they are not useful for this repair. As far as clamping forces are concerned, well, you have to use good sense. My pillar clamps are made from 3" PVC tubing with a 1/4-20 bolt going through the center----they are not nearly as strong as an all metal pillar clamp.

Mike D

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I was initially confused by H.L. and Jeffrey's comments, and then I found this year 2005 post:

http://www.maestronet.com/foru...R_FORUMVIEWTMP=Linear

Jeffrey is shown repairing a cello crack in which the crack has sunk inwards--the pictures show the pillars being compressed near their top so that the crack closes on the inside, first, and compensates for the inwards sinking. With this mechanical advantage, it would take very little clamping force to close the crack on the inside and bow the sunken region slightly outwards.

I was thinking of a crack which did not suffer from inwards sinking; therefore, the clamping force would be applied as close to the bottom of the pillar as possible (adjacent to the top). For this particular repair, you would need those specialty clamps.

Mike D

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Thanks guys for all your words of wisdom.

This cello repair is a bit of a favor and an opportunity for some experience building so I am not trying to edge away from it. It is more of a cautious/nervous worry about taking on such a big repair. Since the beginning of the year when cello #2 was completed there has been a steady stream of locals asking for repairs which has been quite exciting and challenging in various degrees but this cello certainly tops them all.

The techniques that have been explained here are very easy to understand which will make the repair more straightforward and approachable which is what makes this forum so great.

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I think that a key for doing restorations is patience. Deal with each crack and problem one at a time. The violin that I'm working on has quite a few cracks and open seams. It's a long process- Clean the crack- let it dry. Get all the clamps pre-set - glue the crack - clamp the crack- let it dry. Go on to the next crack. It will take several days at an hour or two per session. After I get things stabilized, them I'm back to re-assembly, where a maker might be more comfortable. Retouching after putting things together is a whole separate matter! Have fun!

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"Deal with each crack and problem one at a time."

That's good advice. But sometimes, when you have several open cracks in the same area, it is helpful to stabilize all but one of them with temporary cleats.

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quote:


Originally posted by: Mike_Danielson

>It looks like many of you guys have never made calimari clamps from PVC tubing. They are very weak >and would be unsuited for substitution as a pillar clamp.<

The strength of the small pvc clamps depends on the type of pipe it's made of. If it's made of heavier guage pipe, the small clamps, originally intended as lining clamps, can be a challenge to spread open.

>My pillar clamps are made from 3" PVC tubing with a 1/4-20 bolt going through the center----<

When did you come up with this type clamp?

Oded

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With this number of cracks it would also be helpful to hear from experts how they would take the top off to minimize the risk of extending the cracks.

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I sometimes apply drafting tape to vulnerable areas and cracks. I also support the area I'm openng with my hand. Go slow and keep a careful eye (magnifiers) as you're opening the seam for splitting of plate or linings.

Oded

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My pillar clamps are made from a 3 inch schedule 40 PVC pipe cap. The wall thickness is 0.22 inches. I use a hacksaw to get two c- ring clamps from each cap. A 1/4-20 bolt goes through the center with a wing nut. A chunk is cut out of the PVC ring and the edge dressed with a file to give an edge contact so it can operate as a clamp.

I got the idea from seeing "apartment luthiers" picture of red-colored c-ring clamps when the subject of Oded's calimari clamps came up and apartment luthier showed his clamps. I could not find a commercial source for pillar clamps; so, I had to make my own. My PVC pillar clamps are not as powerful as all metal ones but they are strong enough.

I am still thinking about how I could make all metal pillar clamps--I lack a metal working lath and mill. Those nice metal ones appear to use square brass stock for one side of the clamp. It is the square hole in the other side of the clamp that gives me a problem unless I cut it by hand with a file. Yah, I suppose I could cut it by hand. Seems more reasonable as I think about it. Then I would have to thread the end of the square stock--hmmm.

Mike D

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I'm not sure I follow your description but your post caused me to go through my archives where I found an exchange I had with (another) MD on March 19, 2002. The post describes a largish section of PVC pipe, a small section cut out, with a bolt and wingnut transveres through the center diameter of the ring so that tightening the wingnut causes the clamp to pinch. The open section sits at the base of the towers and a wedge is placed at the top of the towers. The tool allows you to torque the crack either inward OR outward as needed. I blieve there's a picture of the clamp on the Upton Bass site. ( I don't know if they attribute the design or not)

There is NEVER any need for a great deal of pressure to be applied to a crack. If the edges don't come together then repair wood should be splined into the gap or the wood wetted on either side of the crack to cause it to swell but this technique should be used very judiciously.

Oded

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I won't disagree with Brad. Sometimes dealing with one crack means that you have to do something with some other areas to stabilize them while you're working on the first crack. All part of the planning- figure out what needs to be done first, then next, etc..

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