First back sound post crack repair attempt!

[polkat]

Well, over the years I've done a lot of front plate crack repairs, and a few slightly open back seam repairs, but (oddly) for the first time I'm looking at a back with a sound post crack. Not a valuable instrument and it belongs to me, so I'm not worried about trying to fix it.

The crack is about 3" long and the post sat right in the middle of it. It is slightly open on top, and closed (but visable) inside. I figure on doing a post patch, but want to get the crack closed before working on the patch. Gently bending the plate to see if I can close the crack on top, it just barely doesn't quite get there.

I can't find my curved plate clamp. Anyone have any suggestions about approaching this?

[Jeffrey Holmes]

I can't find my curved plate clamp. Anyone have any suggestions about approaching this?

My suggestion is to find your strap clamps and try them in combination with pillars and wedges (you can use the search function for "pillars" to find more information).

[lyndon]

correct me if im wrong jefferey, but doesnt hans weisshaar say not to worry about the crack staying glued until after the patch bed is carved out and you're ready to glue the patch in, im obviously not an expert on this topic, but i know it can be very difficult to keep the crack glued while youre carving the patch bed, eliminating that wood on the inside might make it much easier to clamp the outside of the crack together.

[polkat]

Can't find those clamps dang it! So, let me ask this; as I said, this fiddle is a cheapo, and my primary interest in it is as a backup instrument in the event something happens to my good one(s). I play as well as work on them.

I got the crack glued up today with a jimmy rigged setup. It closed up okay, but I would never trust that alone. While I know this might sound bad, I'm thinking about just gluing in a flat piece of maple (bent of course to the curvature of the plate in that area), perhaps a piece of old rib, sort of like a big cleat, but without counter sinking it into the plate, other then smoothing the edges. This plate is only about 3-1/2 to 4mm thick.

Yea, a hack job, but would it work?

[lyndon]

no, not for long at least, there is practically no tension trying to draw the crack apart on the inside,(where youre wanting to support it), and lots of pressure tension trying to break it apart on the outside, thats how a back post crack works, on the other hand ive seen people still playing violins with open cracks on the back, wouldnt reccomend it but they still make noise!!!!

[Jerry Lynn]

... doesnt hans weisshaar say not to worry about the crack staying glued until after the patch bed is carved out and you're ready to glue the patch in, im obviously not an expert on this topic, but i know it can be very difficult to keep the crack glued while youre carving the patch bed, eliminating that wood on the inside might make it much easier to clamp the outside of the crack together.

That sounds like a horror story in the making. The split needs to be well registered before you do any of the next steps (cast, plan the size and location, excavate, etc).

Jerry (pre coffee, post early morning infant waking)

[Jeffrey Holmes]

correct me if im wrong jefferey, but doesnt hans weisshaar say not to worry about the crack staying glued until after the patch bed is carved out and you're ready to glue the patch in....

Hi Lyndon;

Jerry's correct. The crack needs to be registered, glued & stable before making the cast, etc. In the final stages of excavating the patch bed or fitting the patch, it's not completely unheard of that a crack may open slightly, but at that point you have support from both sides (cast and patch) to register it's position.

[jacobsaunders]

While I know this might sound bad, I'm thinking about just gluing in a flat piece of maple (bent of course to the curvature of the plate in that area), perhaps a piece of old rib, sort of like a big cleat, but without counter sinking it into the plate, other then smoothing the edges.

Yea, a hack job, but would it work?

I think I would rather throw it away and buy a new violin.

[Stephen Byrne]

Hack job? It sounds like you´re going to preform this particular task with a hatchet which is not a tool most reputable violin makers use and if they did they would certainly keep it to themselves.

Yea, a hack job, but would it work?

[Craig Tucker]

Can't find those clamps dang it! So, let me ask this; as I said, this fiddle is a cheapo, and my primary interest in it is as a backup instrument in the event something happens to my good one(s). I play as well as work on them.

I got the crack glued up today with a jimmy rigged setup. It closed up okay, but I would never trust that alone. While I know this might sound bad, I'm thinking about just gluing in a flat piece of maple (bent of course to the curvature of the plate in that area), perhaps a piece of old rib, sort of like a big cleat, but without counter sinking it into the plate, other then smoothing the edges. This plate is only about 3-1/2 to 4mm thick.

Yea, a hack job, but would it work?

FWIW,

I've fixed this type of thing before (on more than violins) - but I do meatball, not hack...

Mostly this type of thing is done on a poorly maintained school instrument - something that is barely escaping the round file…

I don't have a problem using a carefully made caul or counter form behind the patch on the outside surface of the back plate - in order to force everything back into place when clamped - with a secondary layer permanently glued on the inside surface like a giant cleat - under where the post sits - providing adequate surface area to provide an adequate platform for it (the post) not to push the crack open again, - and permanently close everything, clamping from the outer surface, directly around to the inside surface, (and where the quality and worth of the instrument will in no way pay for "the proper works"), but when positive/permanent result is still required.

It can be done. But, as I’m sure you realize - it will never sit in the repair hall of fame.

Oh well... and don't go cheap on the glue either - only hot fresh hide glue.

[Joshua Blevins]

My suggestion is to find your strap clamps and try them in combination with pillars and wedges (you can use the search function for "pillars" to find more information).

here are the clamps for the pillers, you can get them from micro mart.

and here is an example from Russel Wagners web sight on how they are used:

here is micro marts web sight:

http://www.micromark.com/solid-brass-miniature-bar-clamps-3-3and4-inches-long-set-of-2,7066.html

[Jeff White]

I really like those clamps, gonna have to get some. jeff

[Jeffrey Holmes]

Yes... those little clamps can be used for a number of things, including pillars, and are pretty easily modified. Handy to have. Thanks for the link, Joshua. I'd not ordered them for a while.

My impression is the OP isn't all that interested at this point, but maybe others are... for pillars, I've been using these for a couple years. I like the design, as you're able to get the jaw close to the plate and still have room to turn the screw. They also "bite" the pillar. Very stable.

[Jeff White]

Ooooh, more toys. Did you make these Jeffrey? If not, where can I get them. jeff

[Jeffrey Holmes]

Ooooh, more toys. Did you make these Jeffrey? If not, where can I get them. jeff

Nope... I bought 'em. They're available at Cremona Tools (and I picked some up when I was there a couple years ago... shipping costs are unreal to the states), but there are a couple people in Boston that occasionally offer them. One (a restorer named Christian Schabbon; has the clamps listed on his website) attended the restoration workshop last summer.. so I bought some more from him.

[polkat]

OP here. Well, I went ahead and did the standard patch. It was my first, and while it won't win any beauty contests, it seems quite functional.

However, while doing the job, the plate split in half at the seam. No glue evidence at the edges, so I'm guessing it was under glued or glued with weak glue. The edges are very clean. I have never reglued the seam of a fully carved plate before.

Any advice on a jig of some kind to hold the plate halves in registration while regluing??

Thanks!

[lyndon]

you were supposed to use some form of plaster(or other) cast to hold the back while you clamped the patch, treat a center join crack just like you would any other crack only it is a little trickier to line up the edges, as you dont have the jigsaw puzzle effect of two pieces mating together just when you get them perfectly aligned like you do with standard cracks, do a couple dry runs with the crack clamps so you know exactly how to position when your glueing, and plan exactly what your going to do if one side ends up higher than the other, how are you going to clamp it flush etc

[polkat]

Yea, my fault. I didn't bother with the mold as I didn't expect the plate to seperate like it did.

Still can't find those clamps so I'll try experimenting. Thanks all!!

[captainhook]

Large number of alternating cleats for alignment is probably the best you can do.

[polkat]

Which is exactly what I ended up doing. It's fairly well aligned.

How's it going Capt? Haven't spoken in a while. Still unemployed, which is why most of my tools are gone now, so I have to do stuff by jimy rigging. Write when you can and let me know what you've been doing.

polkat out.

[Stephen Byrne]

Here´s a UK supplier selling miniature brass clamps for 8.75 euros a pair. http://www.toolman.co.uk/acatalog/mini_tool_kits.html Unfortunately they just have wing knobs.