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FoxMitchell

Advice Needed for Cello Repair

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Hey folks! So inspired by the so-far success with my first complete violin rebuild, and my cosmetic repairs on others, I decided to undertake the restoration of this cello I posted about here:

 

I opened it up today to find the damage was a lot less severe than I feared, only two major cracks on the top, buuuut there's some oddities in it as well that I figured I better ask for advice from the folks here who know what they're doing.

 

20171208_232447.thumb.jpg.0bad58c20c38c6babd6835a387155ae4.jpg 

Those two enormous things at the top and the bottom, they seem to be 'cleats' someone put there to hold back a pair of cracks on the neck notch and the saddle respectively, and they seem to be doing their job, keeping the cracks from going into the center of the plate, but on the edges the cracks are open.

Should I take those things out and close the cracks and put small cleats there, or leave the large things and just slip some glue into the cracks as they are?

 

And on the bottom ribs...

20171208_232755.thumb.jpg.e925043848bb0e687660ce6b7d593f38.jpg

These monster cracks have been filled with some sort of wood putty or something. The cracks stop at the lower block, so I'm thinking it might be possible to close it without dismantling the whole thing down there, the Weisshaar & Shipman book seems to have a chapter on fixing that type of crack with a jig and linen strips. Would anybody have any specific advice on how to approach this damage?

 

Thanks!  :)

 

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I would get rid of those silly long cleats at the top and bottom of the top plate,they look to have actually caused cracks rather than preventing them:) or are those lines at the end of each pencil lines?

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The crack(s) either side of the bottom block are fairly typical, and result from the fact that ribs, over time shrink slightly in height, whereas the block doesn't. In order to open the cracks and clean the grime out, and to force them together with a cramp, it will be necessary to remove the bottom block, and make a new one after you have repaired the cracks. Making a new bottom block is fraught with difficulty should you be inexperienced, due to the necessity to have the rib outline and the belly outline coordinate afterwards.

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Hi FoxMitchell - my compliments with your top removal. Neatly done.

The rib cracks at the bottom and taking into account what Jacob has just written...

- trim the top of the block down by 5mm or so.

-  take a piece of 3mm thick spruce about 100mm wide and glue it across the bottom of the corpus - a "faux belly" to coin a descriptive term for it. This should hold the ribs in position while also protecting the edge of the corpus from tool-dings.

- chisel a trench across the block centred on line with the cracks on either side - about 25mm wide. This will give support to the ribs while you fiddle with cleaning out the cracks and clamping/gluing  them back together. When clamping time comes, insert a 25mm spacer at the top of the block  - the clamping forces will tend to bring the outside of the cracks together. Helps make a near invisible joint.

-  Carve the block away until within 0.2mm of the ribs/back and use warm water (only on the block) to loosen the glue join.

- carve and fit a replacement block

- pilot drill and ream the end-pin hole

- remove the "faux belly"

- refit belly.

Cheers edi

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I don't really do much with cellos, so I'm just "upsizing" for this. Considering the type of instrument, I would have a tendency to not try to do too much with the rib cracks. First option: Clean out the cracks some, and overlay that whole rib area with some linen. I would use a archival PVA glue for that, as it is reversible, and remains flexible after drying. Lineco adhesive is a good one used for museum restorations. http://www.lineco.com/cart.php?m=product_list&c=1118

Second option: Clean out the cracks, and overlay some veneer, or some very thin plywood. I have some model making plywood, used for model aircraft, that is 0.8mm thick https://www.dickblick.com/items/33305-2132/ This plywood can also be found in good hobby shops. If using the plywood, you should probably make some counter forms to maintain the rib profile.

In both cases, the moisture from cleaning, may help to swell the wood a little perhaps even closing the crack some. Both of these options are reversible if needed.

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Aside from your other problems with this cello, it looks as if the bass bar is parallel to the center seam. Can you measure from the center seam to the bar at the widest point of the upper bout, and again at the widest part of the lower bout? 

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11 hours ago, jacobsaunders said:

The crack(s) either side of the bottom block are fairly typical, and result from the fact that ribs, over time shrink slightly in height, whereas the block doesn't. In order to open the cracks and clean the grime out, and to force them together with a cramp, it will be necessary to remove the bottom block, and make a new one after you have repaired the cracks. Making a new bottom block is fraught with difficulty should you be inexperienced, due to the necessity to have the rib outline and the belly outline coordinate afterwards.

I assume even though the crack stops at the block I'd still have to carve the bottom block out to fix this?

20171209_172210.thumb.jpg.6c86b858f308c3f19eb7b8dd676689dc.jpg

 

4 hours ago, Barry J. Griffiths said:

Aside from your other problems with this cello, it looks as if the bass bar is parallel to the center seam. Can you measure from the center seam to the bar at the widest point of the upper bout, and again at the widest part of the lower bout? 

It's approximately 35mm at the lower bout and 31mm at the upper bout.

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14 hours ago, fiddlecollector said:

I would get rid of those silly long cleats at the top and bottom of the top plate,they look to have actually caused cracks rather than preventing them:) or are those lines at the end of each pencil lines?

The lines are pencil marks. The cracks are right at the neck and saddle notches.

I just hope those are cleats, not some sort of inlaid patch or something!

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16 hours ago, FoxMitchell said:

I assume even though the crack stops at the block I'd still have to carve the bottom block out to fix this?

20171209_172210.thumb.jpg.6c86b858f308c3f19eb7b8dd676689dc.jpg

 

 

If you study old Celli, you will find a great many cracks, particularly where slab cut ribs have been used, that appear to “stop” at blocks. This is due to the universal “shrinkage question” because ribs have shrunk slightly in the height, but the blocks have not. This creates tensions, which give in the form of cracks. To durably resolve this. One will have to remove the block in order to get the crack clean and together An alternative in your case would be to gingerly take the block out using dampness; You fold up and lay a soaking wet paper piece of kitchen roll on either side of the block, and cover the area with cling-film, so that the water cannot evaporate and stand the cello up in some corner overnight and do something else. The next day you can attempt to get an opening knife between the block and the ribs. If you do not immediately have success (quite possible) you should not get violent, and risk breaking anything, but reapply re-wettened paper kitchen towel & cling film for a further overnight stint. When you have the block out in one piece, you will be able to repair the crack, and then re-use the original block. Afterwards you will have to plane the 1mm-ish end grain part of the block that protrudes over the shrunk rib. This way you will have an enduring repair, as opposed to a violent one, which will go open again within a foreseeable time frame, and avoid frantic customers coming around to complain about the crack every couple of years

 

 

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I have started work on this cello, and I have a question!

How do I fix this apparently simple crack?

20180224_203911.thumb.jpg.991f44c895325c61a69a23ea452bb738.jpg

It seems simple, but you have to put a huge amount of force to close it. I fear that that much tension would just cause it to split open again once the closing clamp was removed, or that the wood would split elsewhere nearby if the grain is weak.

Is there any specific technique for cracks that don't want to close?

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First I would remove the cross-grain cleat which might be acting to hold the crack open.  Then perhaps swelling the wood along the crack with water would close the crack.

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14 hours ago, arglebargle said:

Before you proceed further, please do as suggested and remove the useless and potentially damaging huge cleats.

Please.

Not to worry, the giganto-cleats are out!  :) 

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Alright, I got some linen to patch this thing up. I have a question though!

On 12/9/2017 at 1:21 AM, FoxMitchell said:

20171208_232755.thumb.jpg.e925043848bb0e687660ce6b7d593f38.jpg

On these rib cracks, how should I put the linen patches?

 

Just over the cracks all the way from end to end?

Over the entirety of the lower ribs?

Over the entirety of the ribs from end to end of the cracks?

Multiple vertical strips?

Multiple little patches like cleats?

Something else I should know?

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Fox,

$10. dollar cello if I read your OP correct?

I haven't done a cello...yet... but have done several guitars with similar of worse rib damage.

Judging from the photos......

I would not remove the tail block on this [$10] one to deal with those ends of the cracks, unless the tail block is no longer glued tight to the crack area that extends into it.

I would drill small holes [1/16- 3/32] at the extreme ends of the cracks and insert wood pins [think belly/back locating pins] and finish the pins flush inside and out [except where the block covers the bottom ends of the crack, flush outside only]. this will help prevent the crack from "running" at a later date from knocks, humidity etc.

Then I'd align and glue the cracks with inside and outside cauls/clamps covered in cling wrap to get the best closure possible under the circumstances.

Believe that having that done I'd do "full patches" with the fabric full width of the ribs [inside the linings] and out just past the length of the cracks and my "stop pins".

I've done it through a guitar soundholes in the past a couple of times.... you will obviously do a much neater job having the access with the belly off.

Have fun

sorry steps out of order: crack glue up first ... then the "stop pins.... then fabric. :)

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19 minutes ago, Michael Jennings said:

Fox,

$10. dollar cello if I read your OP correct?

I haven't done a cello...yet... but have done several guitars with similar of worse rib damage.

Judging from the photos......

I would not remove the tail block on this [$10] one to deal with those ends of the cracks, unless the tail block is no longer glued tight to the crack area that extends into it.

I would drill small holes [1/16- 3/32] at the extreme ends of the cracks and insert wood pins [think belly/back locating pins] and finish the pins flush inside and out [except where the block covers the bottom ends of the crack, flush outside only]. this will help prevent the crack from "running" at a later date from knocks, humidity etc.

Then I'd align and glue the cracks with inside and outside cauls/clamps covered in cling wrap to get the best closure possible under the circumstances.

Believe that having that done I'd do "full patches" with the fabric full width of the ribs [inside the linings] and out just past the length of the cracks and my "stop pins".

I've done it through a guitar soundholes in the past a couple of times.... you will obviously do a much neater job having the access with the belly off.

Have fun

sorry steps out of order: crack glue up first ... then the "stop pins.... then fabric. :)

 

 

1-No pins, please. They will cause cracks of their own and will not keep the crack from "running".

2-He paid 10 bucks for the cello, but it is a decent, student grade Mirecourt cello. Properly repaired, worth a good bit more than $10.

3-As Jacob said above, remove the block, do it right. 

4-"Full patches", as you call them, will make the ribs much too stiff and will most likely cause the rib to distort further. These aren't guitars.

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Yeah I paid $10 for the cello, but it's likely going to be worth more if I fix it properly. And if it sounds good I might take up to playing the cello too, who knows!  ;)

This is the current project status:

-The lower block is already removed. Soaked it out without problems. And like Jacob predicted, there's 1mm-ish of overhang that will need planing.

-The giganto-cleats on the belly have been removed and the cracks were cleaned, all glued and clamped, to be cleated in a couple of days when I have the time for it.

-The rib cracks have been thoroughly cleaned and are now awaiting to be glued shut. I'm overjoyed that they actually close perfectly with a little bit of persuasion from a clamp. I just need to figure out what kind of patching to do with the linen.

I don't like working on cellos because of the size! That thing is occupying an excessive amount of realestate in my workshop. But I'm really happy it's actually not given me any trouble with the repairs that need to be done! It's like a good dog that sits still at the vet while being treated. I wish the same could be said about a violin I'm working on; the violin is like an angry cat clawing and biting and refusing to hold still!   :P

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As stated never done a cello...... 

I use linen strips for side/re-enforcment when building guitars as Martin did in earlier days...

One such repair I did on a 19teens Martin that had suffered a similar rib crack.... has lasted 40 years now since the repair without mishap or any negative effect on the tone or response...that said, I suspect that the ribs on a cello may have much more acoustic influence than those on a guitar.

I'm here to learn. 

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Weee! Cleats time!

I got the X and the Z sizes for the cleats, but I'm not entirely sure about the Y axis. How tall/high/thick should they be?

I've been following the instructions from Triangle Strings on cleats, and they have cello sizes listed all the way up to before the last step. It says then to make the cleats 1.5mm high. Is that for both violin and cello or just violin?

 

IMG_20180309_233115_510.jpg

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Cleat thickness is part of the function of immobilizing flexibility of the crack.  If you examine successful cleats you'll find thicknesses vary, as does other variables. For your cleats, 1.5 mm after doming them is probably fine.  In the future I'd suggest being tidier with cleaning up glue after install. 

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