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Brad Dorsey

Clamping and Gluing Method for Broken Top

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I have a violin in for repair now with a top that came off in two pieces, due to a long crack along the finger board and a wing crack.

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To glue and clamp the pieces back together, I used a method that I devised and that I have used several times.

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I set the top on a flat piece of plywood to maintain the plane of the rim.  I immobilized the larger piece by cutting three counterparts from scrap wood to fit the bouts and screwing them to the plywood.  I cut a movable counterpart to fit the smaller piece and made two small wedges to provide gentle clamping force.  I cut a hole in the plywood under the crack to be glued so that I could have access from below to push the sides of the crack into alignment if necessary.  I am pleased with the result.  The sides of the crack are perfectly aligned, and I had good control of the procedure.

Is this a standard method for dealing with this type of broken top?  Does anyone have any suggestions or refinements that might be useful the next time I do this?

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48 minutes ago, Brad Dorsey said:

Is this a standard method for dealing with this type of broken top?  Does anyone have any suggestions or refinements that might be useful the next time I do this?

I have a cracked top for which I'm planning the glue & clamp and I was think of this exact same setup. 
The questions I had:

  • Wouldn't pressure from the side tend to raise the middle? Seems you didn't have this problem. If it did, maybe a top clamp should be on standby?
  • I've wondered if clamps are always necessary for cracks that go back together well. Since HHG sets up fast after cooling, why not just hold it together on a flat surface until it bonds? Maybe 10 minutes? 

I'm doing mine this week as soon as I settle on the right plan. I like this setup. Interested in what the guru's have to observe.

 

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37 minutes ago, i8bugs said:

...Wouldn't pressure from the side tend to raise the middle? Seems you didn't have this problem. If it did, maybe a top clamp should be on standby?...

This is a good point that I left out.  In my trial clamping I found that the edge did tend to rise off the plywood right at the neck cut-out.  So I put one clamp there to hold it down when I glued it..

37 minutes ago, i8bugs said:

...I've wondered if clamps are always necessary for cracks that go back together well. Since HHG sets up fast after cooling, why not just hold it together on a flat surface until it bonds? Maybe 10 minutes?...

You probably could do this, but I decided I'd rather clamp it quickly with the wedges, set it aside for the glue to dry and move on to something else.

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1 hour ago, Brad Dorsey said:

I am pleased with the result.  The sides of the crack are perfectly aligned, and I had good control of the procedure.

I think I'm building this jig this week for my crack repair. Hopefully, victory picts to follow. But now I remember my Colonel telling me "hope is not a plan". 

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17 hours ago, Brad Dorsey said:

I have a violin in for repair now with a top that came off in two pieces, due to a long crack along the finger board and a wing crack.

I take it this belongs to a customer, but man I love these war torn fiddles being restored and given another chance. This one looks like it's been in a bar fight, which makes me like it that much more. Be sure to post the final victory pict.

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An alternative to consider: This kind of setup works well for me. I've used it for repairs to the top (similar damage as illustrated in Brad's photos) as well, but the photos of the type of jig I have handy are for the repair of a back where one of the flanks broke away. In this case I used the jig to align the outer ends of the crack (matching the purfling lines) as the fractured "sprung" a bit after it broke away.  I glued those two areas in the jig, then did fine adjustments to the center of the crack using pillars & wedges.  For less obstinate cracks, I've used the jig to glue in one go.

The larger portion of the plate is glued down to the jig around the perimeter with paper squares (so it can be easily removed).

Hope this helps.

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Jeffrey,

When gluing cracks a bit at a time I think there must be a difference in strength of the glue joint depending on how much glue I am able to get into the crack. I can imagine that there are areas which  really aren't glued at all but just held in tight contact by adjacent areas. Obviously the cleats help hold the whole thing together structurally but is there any reason to think that a non homogenous glue joint has acoustic ramifications?

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11 minutes ago, nathan slobodkin said:

I can imagine that there are areas which  really aren't glued at all but just held in tight contact by adjacent areas. 

My Horace Petherick repair story book says to run a bead of water first to get an idea of how far the crack runs. 

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3 hours ago, nathan slobodkin said:

Jeffrey,

When gluing cracks a bit at a time I think there must be a difference in strength of the glue joint depending on how much glue I am able to get into the crack. I can imagine that there are areas which  really aren't glued at all but just held in tight contact by adjacent areas. Obviously the cleats help hold the whole thing together structurally but is there any reason to think that a non homogenous glue joint has acoustic ramifications?

I haven't found this to be a problem, Nate.  When appropriate (as in the situation above), I find that performing partial, or staged, gluing improves the alignment (and therefore the glue surface contact).  I don't see this as non-homogenous.

Of course it's important to make sure the glue gets into the crack as evenly as possible, but working time can be reduced if doing a smaller area... and therefore a dilute (thinned) form of a stronger gram strength glue can be used (which I see as pretty much of "a wash" in terms of bond strength).  It's pretty easy to tell where the glue "runs" and where it stops when pumping the glue by plate manipulation or use of a suction cup.  Cleating as you go can ensure that you don't weaken the previously glued portion when manipulating the next...and that you get the glue to run in to meet the last section successfully.

I also don't see cleats as holding things together as much as stabilizing the flex of the plate in the crack area. If a crack is going to open, it often seems to do so even when cleats are present.

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14 minutes ago, GeorgeH said:

Can you share what caused that crack?

The quote above refers to top cracks which I've also used variations of the jig for... but I'm assuming your asking about the one I illustrated?

The violin illustrated, made in 2005 by a friend and colleague with a rather good reputation, was dropped onto a CIM studio floor from a standing position in 2006.  He, the owner and the teacher asked me to repair it.

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15 minutes ago, Jeffrey Holmes said:

The violin illustrated, made in 2005 by a friend and colleague with a rather good reputation, was dropped onto a CIM studio floor from a standing position in 2006.  He, the owner and the teacher asked me to repair it.

Ouch! It looks like a remarkably clean back crack which is why I asked. Thanks.

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17 minutes ago, GeorgeH said:

Ouch! It looks like a remarkably clean back crack which is why I asked. Thanks.

As clean as they get, except for some small bits of chipped out wood at the surface.  I was a hard impact.

 

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4 hours ago, Jeffrey Holmes said:

As clean as they get, except for some small bits of chipped out wood at the surface.  I was a hard impact.

 

Thanks for the photos Jeffery. Of course now I want to know what's in that bottle on the final touch up.

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1 hour ago, i8bugs said:

Thanks for the photos Jeffery. Of course now I want to know what's in that bottle on the final touch up.

It's chameleon varnish, which automatically changes color to match its surroundings. ;)

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Without wishing to always be the killjoy, a few thoughts on closing cracks.

 

I think there are two main considerations when glueing cracks. One is to get the two sides of the crack together across the width, the other to get the crack in register i.e. both sides at the same sea-level, that there be no step when one runs ones finger across it afterwards. I’m ignoring any longitudinal aspect for the moment.

 

As far as I understand the approach demonstrated here correctly, the second aspect here seems to have been relatively neglected. Also, the strength of any widthwise pushing together needs to be judicious, since one will be in danger of distorting (particularly thin) plates. With exceptions, I have the experience that the width-wise shoving together is not the difficult part, I often just shove the plate with my beer-belly against the table edge, leaving me with two free hands, and clamp cramping blocks on the outside holding the crack flat and cardboard on the inside, the principal being that the outside cramping block should be slightly harder than the inside cardboard, that in difficult cases, the outside will come out flat. The other worry I would have, is that one should apply glue and cramp fairly quickly, before the glue starts any gelling process. I wonder if I would achieve the necessary speed, were I to faff about with all sorts of cams and wedges. Also I assume a “Universal” jig would be difficult to invent, since not all violins are the same shape. (not to mention D'Amores and other stuff)

 

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I've had success with temporary alternating blocks that overhang the crack and keep the surface edges in register. They can be also used as the pillars for clamping (like on Jeffrey's pics) as I do in very long cracks or center seam separations. I prefer thick wire C-clamps that can be applied swiftly and aplly pressure right next to the plate surface (but I use wedges - prepared and marked for each pillar as well to prevent opening on oposite side of crack).

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Jacob,  Thank you for your thoughtful response.  Based on my experience with this fixture, I think that your reservations are unwarranted:

 

4 hours ago, jacobsaunders said:

...As far as I understand the approach demonstrated here correctly, the second aspect here seems to have been relatively neglected...

Not entirely neglected.  As I said, there was a hole in the plywood under the crack being glued so that I could push the two sides up or down with my fingers while feeling the outside to see if the sides of the crack were in register.

 

4 hours ago, jacobsaunders said:

...Also, the strength of any widthwise pushing together needs to be judicious, since one will be in danger of distorting (particularly thin) plates...

I was able to control the pushing together quite precisely by how far in I pushed the wedges.  I pushed the two sides of the crack together with my hands, and then I inserted the wedges only far enough to hold the movable clamping block in the same position.

 

4 hours ago, jacobsaunders said:

...The other worry I would have, is that one should apply glue and cramp fairly quickly, before the glue starts any gelling process. I wonder if I would achieve the necessary speed, were I to faff about with all sorts of cams and wedges...

I always worry about gluing time with hot glue.  I had both pieces of the top on the clamping fixture with the crack separated by about a quarter inch when I applied the glue.  I estimate that I had the crack together and aligned and the clamping wedges in place about ten seconds later.

 

4 hours ago, jacobsaunders said:

...Also I assume a “Universal” jig would be difficult to invent, since not all violins are the same shape. (not to mention D'Amores and other stuff)

This was not an attempt to create a universal fixture.  I can re-use the plywood, but the concave counterparts will have to be custom made for any other instrument I might try this method on.

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29 minutes ago, Brad Dorsey said:

Jacob,  Thank you for your thoughtful response.  Based on my experience with this fixture, I think that your reservations are unwarranted:

 

Not entirely neglected.  As I said, there was a hole in the plywood under the crack being glued so that I could push the two sides up or down with my fingers while feeling the outside to see if the sides of the crack were in register.

 

 

 

I was able to control the pushing together quite precisely by how far in I pushed the wedges.  I pushed the two sides of the crack together with my hands, and then I inserted the wedges only far enough to hold the movable clamping block in the same position.

 

I always worry about gluing time with hot glue.  I had both pieces of the top on the clamping fixture with the crack separated by about a quarter inch when I applied the glue.  I estimate that I had the crack together and aligned and the clamping wedges in place about ten seconds later.

 

 

 

This was not an attempt to create a universal fixture.  I can re-use the plywood, but the concave counterparts will have to be custom made for any other instrument I might try this method on.

Thanks, makes more sense now

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8 hours ago, jacobsaunders said:

Without wishing to always be the killjoy, a few thoughts on closing cracks.

 

I think there are two main considerations when glueing cracks. One is to get the two sides of the crack together across the width, the other to get the crack in register i.e. both sides at the same sea-level, that there be no step when one runs ones finger across it afterwards. I’m ignoring any longitudinal aspect for the moment.

 

As far as I understand the approach demonstrated here correctly, the second aspect here seems to have been relatively neglected. Also, the strength of any widthwise pushing together needs to be judicious, since one will be in danger of distorting (particularly thin) plates. With exceptions, I have the experience that the width-wise shoving together is not the difficult part, I often just shove the plate with my beer-belly against the table edge, leaving me with two free hands, and clamp cramping blocks on the outside holding the crack flat and cardboard on the inside, the principal being that the outside cramping block should be slightly harder than the inside cardboard, that in difficult cases, the outside will come out flat. The other worry I would have, is that one should apply glue and cramp fairly quickly, before the glue starts any gelling process. I wonder if I would achieve the necessary speed, were I to faff about with all sorts of cams and wedges. Also I assume a “Universal” jig would be difficult to invent, since not all violins are the same shape. (not to mention D'Amores and other stuff)

 

Hi Jacob.  

No killjoy.  All good observations.

Concerning the jig I illustrated (Brad already spoke to his):  As I said: This system works well for me. If it doesn't make sense to you, do what does.

I do believe a more-or-less universal jig could be fashioned, though I've never had the desire to do so... some rectangular board with rows of pin holes or something similar, but it doesn't take long to fashion a custom jig when needed.

There are a variety of ways to ensure the alignment of the crack in the jig which I won't go into at the moment, as if you read my description of the process in this case, the crack was left dry (no glue) in the center, and the purpose of the jig was to align the ends at the edges (as the broken piece "sprung" after the impact released it and was actually slightly longer than it originally was).  

The  middle portion aligned very well dry, but in this case I did not risk it remaining that way in the jig with slippery glue applied.  The center of the crack was glued in sections using pillars and wedges (good for signing the crack correctly as well as adjusting thew arch to it's original contour).  I tend not to use pressure from above or below the plate for alignment unless really necessary. A slight gully (caused by the wood swelling from moisture, then shrinking back) sometimes results if the clamp is not removed quickly enough.

The clamping wedges in the jig were numbered and pre-marked for position.  Clamping was very quickly accomplished as only the part broken away was "free".  I'd say it was at least as fast as messing with a bar clamp. Since the perimeter was glued down to the jig platform, and the free piece was held by the cams & wedges, no arch deformation occurred.

The crack was well aligned after gluing.  Touch up, with the exception of the small flakes of wood and varnish that were missing when I received the instrument, was very straight forward and did not require any the the existing varnish to be altered at the boarders of the crack.

 

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On 5/14/2019 at 4:48 AM, jacobsaunders said:

...I often just shove the plate with my beer-belly against the table edge, leaving me with two free hands...

Are you trying to tell me that I need to drink more beer to do this right?

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19 minutes ago, Brad Dorsey said:

Are you trying to tell me that I need to drink more beer to do this right?

a mere question of training

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On 5/14/2019 at 4:48 AM, jacobsaunders said:

 I often just shove the plate with my beer-belly against the table edge, leaving me with two free hands,

I reckon I'm much more suited to doing this sort of procedure than I once was... ;)

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