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Andreas Preuss

How much glue is needed on the top block facing the top?

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2 years ago I had a commercial violin coming in the shop which needed a raise pitch. 

Opening the upper bouts of the body turned out to be a nightmare because instead of animal glue some synthetic very resistant bond was used in the factory. 

When I glued the top back on the edge this made me think, do we really need glue on the top block in the area which is under the fingerboard? 

At times it can be very hard to get an opening knife through this area and then no matter how patiently you try to do it the surface looks 'scattered' after opening.

So I didn't apply glue on the cheap violin I the red zone. When it came back last week for a minor readjustment of the pitch, I could slice it open in 5 minutes put a shaving at the neck heel and close it again, all in less than 30 minutes, mostly because I didn't have to work the opening blade through the entire surface of the top block. 

Do we really need glue there?

 

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Any two surfaces not glued has the potential to buzz or really screw up the sound. I could see your un-glued upper block area turning into a buzzing kazoo very easily. So yes, any two wooden surfaces that "interact" need to be glued. Do they need to be glued super hard so that they will never, ever come apart? No, but they do need to be glued.

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Consider the violin body as a box girder under stress from the strings, which is trying to bend it into a "U" around the bridge.  Firmly gluing the top block to the belly gives the lever arm of the neck resistance from the belly where the notch is.  Otherwise, it's going to rotate the top block (and ribs) against the back alone, and bow the belly upward.at the top, leading to a neck failure more quickly than one might expect.  In some cases it will encourage belly cracks in the upper bouts, as well.  Any time you leave part of the "box" free to move, it weakens it.

I've had problems due to loosened blocks in the past.  This isn't some theoretical thing.

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A year or so ago a new customer brought me a viola to adjust. She'd bought it new about four years previously, and then after less than a year it had "gone bad". She'd had it to two or three other shops, and they'd cut her new bridges and posts, and adjusted the heck out of it and it still sounded the same.. it was just OK, but she assured me that it had been much better when she'd bought it.

I took it back into the shop and started probing round with an opening knife and discovered that the bottom block was virtually unglued to the top, except for the rib. The top block was the same. I kept the instrument overnight, glued the blocks back to the top. The next day she said it was back to the way it had been, and yes, it was a much better sounding instrument.

I knew to do this because I have had the same experience more than a few times, to the point where it's something I now check right away. So I'm going to say it's necessary..

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11 minutes ago, arglebargle said:

Anything two surfaces not glued has the potential to buzz or really screw up the sound. I could see your un-glued upper block area turning into a buzzing kazoo very easily. So yes, any two wooden surfaces that "interact" need to be glued. Do they need to be glued super hard so that they will never, ever come apart? No, but they do need to be glued.

So far the experiment showed over the past two years on this cheap instrument no complaint. 

Otherwise we should be reminded that an opening at the seams of the same length (3cm) often stays unnoticed for longer times BECAUSE it doesn't buzz. 

 

 

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4 minutes ago, Violadamore said:

Consider the violin body as a box girder under stress from the strings, which is trying to bend it into a "U" around the bridge.  Firmly gluing the top block to the belly gives the lever arm of the neck resistance from the belly where the notch is.  Otherwise, it's going to rotate the top block (and ribs) against the back alone, and bow the belly upward.at the top, leading to a neck failure more quickly than one might expect.  Any time you leave part of the "box" free to move, it weakens it.

This leverage is still done by the portions of top block glued to the top right and left to the fingerboard.

in any case I have to add, if the top block is very narrow, o would certainly glue it more to the inside.

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7 minutes ago, Michael Darnton said:

A year or so ago a new customer brought me a viola to adjust. She'd bought it new about four years previously, and then after less than a year it had "gone bad". She'd had it to two or three other shops, and they'd cut her new bridges and posts, and adjusted the heck out of it and it still sounded the same.. it was just OK, but she assured me that it had been much better when she'd bought it.

I took it back into the shop and started probing round with an opening knife and discovered that the bottom block was virtually unglued to the top, except for the rib. The top block was the same. I kept the instrument overnight, glued the blocks back to the top. The next day she said it was back to the way it had been, and yes, it was a much better sounding instrument.

I knew to do this because I have had the same experience more than a few times, to the point where it's something I now check right away. So I'm going to say it's necessary..

Well, if top AND bottom block are a kind of entirely loose there is certainly something wrong. 

I am not saying it should not be glued, just leave the center area unglued to make operations like raise pitch easier and less damaging to the instrument. 

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10 minutes ago, Violadamore said:

Otherwise, it's going to rotate the top block (and ribs) against the back alone, and bow the belly upward.at the top, leading to a neck failure more quickly than one might expect.  In some cases it will encourage belly cracks in the upper bouts, as well.  Any time you leave part of the "box" free to move, it weakens it.

I've had problems due to loosened blocks in the past.  This isn't some theoretical thing.

I still haven't worked on my little project that has this exact problem.  One of these days, I am going to have to make a little patch that strengthens all those little belly cracks right at the block, and I will be going for a precise fit on the top block that will get glued.  This violin has a very sweet sound, but that area of the belly would start slowly sinking with strings tuned up.  At first I thought it was the neck joint, but no.  Everything there is solid except the belly which was sort of suspended above the block. 

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24 minutes ago, palousian said:

I still haven't worked on my little project that has this exact problem.  One of these days, I am going to have to make a little patch that strengthens all those little belly cracks right at the block, and I will be going for a precise fit on the top block that will get glued.  This violin has a very sweet sound, but that area of the belly would start slowly sinking with strings tuned up.  At first I thought it was the neck joint, but no.  Everything there is solid except the belly which was sort of suspended above the block. 

What gave me a major education on these issues was when I bought the "Martian".  Its radical arching, similar to what Dieter Ennemoser does, makes unusually great demands on the upper and lower block attachments to maintain rigidity of the deeply recurved edges.  When it works, it sounds wonderfully resonant, but I had to go through all of the 100+ year old hide glue joints supporting (more "restraining", actually) the belly and reinforce them, as well as seal several propagating linear arch cracks that can't be cleated on the inside.   Looks and sounds cool, though.  :)

I came to realize that the same stresses affect a traditional violin, just not as obviously.

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While I agree that the top block is often extremely problemmatic when removing a top, I also think that a solid connnection there is critical both from sound and structural stability.  If the glue joint fails there, then there can be a cascade failure that damages the top and back plates.  Personally, I try to make sure that the top block glue joint is more solid than any other part of the top, and whoever has to remove the top (which might be me) will just have to suffer with it.

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1 hour ago, arglebargle said:

Anything two surfaces not glued has the potential to buzz or really screw up the sound...

 

49 minutes ago, Violadamore said:

...I've had problems due to loosened blocks in the past.  This isn't some theoretical thing.

 

49 minutes ago, Michael Darnton said:

...I have had the same experience more than a few times, to the point where it's something I now check right away. So I'm going to say it's necessary..

 

7 minutes ago, Don Noon said:

...I...think that a solid connnection there is critical both from sound and structural stability...

OK, you folks have convinced me.  I will glue tops to blocks good and tight.  Have fun getting them off.

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If we properly size the blocks and use thinner glue, it shouldn't  be so difficult to remove the top, should it?

I agree with Don in that I feel that the blocks,  top and tail, should be well fit and attached. 

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When I make new instruments, I do 2 small tricks:

Cut a very small chamfer at the edge of the block.

When I size the block with glue, I don't go quite to the edge.

If I use thin enough glue for the final gluing, it will soak into the wood where it's not sized. So there will not be glue squeezed out at the edge of the block. And the tiny slit from the chamfer will lead the opening knife in position.

kloss.jpg.08e4eca4d8730ae0e7dc464cbc0539c5.jpg

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7 hours ago, duane88 said:

I like that.

I don't... it's a stress concentration at exactly the place where the string forces are doing their best to peel the top plate off.  I think there's a much higher chance of initiating a crack that will make the joint fail.  

Anything that makes it easier to take that glue joint apart will also make it more likely to fail when you don't want it to.  The question is:  how do you want to balance the risks?

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8 hours ago, Salve Håkedal said:

Cut a very small chamfer at the edge of the block.

I just wanted to point out that Jacob Sauder described this as a typical feature of Wildham's instruments in another thread. Just thought it was interesting that it is something that some modern makers do today as well.

On 2/27/2018 at 2:11 PM, jacobsaunders said:

Widhalm's top (no longer existent here) and bottom blocks are quite large, almost semi-circular from the plan view, and he always bevelled the top corner of the top and bottom blocks off at roughly 45°, reducing the glueing area to the belly. I do not know why he did this, but it is another Widhalm authentication box that needs to be ticked.

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Many of the better repairers/restorers I have run across, who have done a lot more repair than I have, have stressed the importance of a good bond between the top and the upper block. When sound goes downhill, separation between these parts is one of the things they look for.

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I've noted physical problems with instruments with a more "swing" to the arch approaching the edge (like Amati family instruments) as well as instruments with less severe arching approaching the neck set. If the joint between the top block and the plate is compromised, it can result in instability in the string height, response, and distortion of the arch under the fingerboard. The condition of the upper block/table joint is therefore included in my standard inspection protocol.

No one likes to wrestle with a stubborn upper block when removing an instrument's top, but there is certainly enough of a difference between adequate and too strong a bond that with some forethought and planning we can help prevent TBDS (top-block distress syndrome).  Using a weaker mix of glue, or a weaker solution of a more brittle glue (like bone glue) and taking care to avoid over application will render a joint with plenty of resistance to failing without a bit of help from your opening knife.

 

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15 minutes ago, Jeffrey Holmes said:

I've noted physical problems with instruments with a more "swing" to the arch approaching the edge (like Amati family instruments) as well as instruments with less severe arching approaching the neck set. If the joint between the top block and the plate is compromised, it can result in instability in the string height, response, and distortion of the arch under the fingerboard. The condition of the upper block/table joint is therefore included in my standard inspection protocol.

No one likes to wrestle with a stubborn upper block when removing an instrument's top, but there is certainly enough of a difference between adequate and too strong a bond that with some forethought and planning we can help prevent TBDS (top block distress syndrome).  Using a weaker mix of glue, or a weaker solution of a more brittle glue (like bone glue) and taking care to avoid over application will render a joint with plenty of resistance to failing without a bit of help from your opening knife.

"TBDS (top block distress syndrome)..."

Too funny, but also very true. The neck just resting against the top will do very different things, both structurally and acoustically, than having a  solid joint there.

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10 hours ago, Salve Håkedal said:

Cut a very small chamfer at the edge of the block.

You often see a very small chamfer on well executed replacement blocks. It’s a nice touch for “the next guy” who has to remove the top.  

In my experience, the top block joint fails most often because of not ensuring good wood to wood contact before reinstalling a top, or from a poorly executed projection raise. 
 

1 hour ago, Jeffrey Holmes said:

we can help prevent TBDS (top-block distress syndrome).  

 

Oh, that’s good.... it’s going on a mug.  

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2 hours ago, Don Noon said:

I don't... it's a stress concentration at exactly the place where the string forces are doing their best to peel the top plate off.

This is one of those areas where a finite element stress model could add some insight. If the glued area just off the chamfer was primarily in a state of compressive stress, then glue failure would not be an issue. 

One can imagine what the stress condition might be by thinking about how the body and plate deforms as the strings are tensioned, but my experience is that intuition is frequently contradicted when the details of the loading conditions are carefully considered.

In this case, intuition would say that the downward force at the bridge would tend to put the block joints in compression against the top. But there might be a rotation of the neck upwards due to the tug of the strings that might offset part of that compression and make the area near the chamfer go into tension: greatly increasing the chance of glue failure.

My intuition is that any bending moment at the blocks is due mostly to the deformation of the plate due to the load at the bridge.  That would tend to make the chamfer edges experience a compressive stress while the rib edges might go into tension, or at least a smaller compressive stress.

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When I was at the late Jean-Frédéric Schmitt in Lyon,  he used to glue one layer of rolling paper on the block, allegedly it would make opening the violin next time easier.

While I'm then done it on a few occasions, taking his word for it, I can't tell if it really helps  getting the fiddle open, as I never hard to reopen or open a violin closed that way

 

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I'll add my vote to the importance of making sure the block areas are well glued, even though I very much share the dislike of contributing to TBDS.

I was lucky to have an experience similar to Michaels, but fortunately decades ago.  Ever since then if there's an instrument that has suddenly changed character or that does not sound as well as I think it should I investigate that area, and that of the lower block, very well with good light, a mirror and through the end button/pin hole.  It's pretty remarkable how much a failed joint between a block and the top can detract from the sound and playing characteristics of an instrument.  I've seen even seen this happen on modern instruments that I know had well prepared joints and were glued well.  It is also one of the areas that I pay a LOT of attention to when I'm doing repair work to any instrument.  I've done a lot of inlaid patches to block areas of tops...
That said, I've seen plenty of good sounding instruments, apparently with distorted archings and or careless top fitting with large gaps between the blocks and top that sound fine.

I've seen the chamfered top block on Perreson instruments (just on the "corners" toward the inside of the instrument of the upper block) and like that idea.

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