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Matthew Noykos

Edge overhang and rib shortening in new instruments.

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I had a conversation with a colleague and we talked about how she likes to leave the edge a little big on her new instruments in anticipation for the plates to shrink over time.  

I never thought about doing this even though I think it might be a good idea, since I’m often addressing this issue in restoration by shortening the ribs.  

If I did this, it would make sense to me to gradually bulge the overhang as I approach the widest point in the upper and lower bouts.  I also have heard of maker’s throwing their plates in a dry light box before doing the final edge shape.  

Are there any of you makers out there who have experience with this and would you like to share some thoughts?  

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Thinking back on it, this mostly happens at the lower block. As in, I've never had to shorten  c-bout or bass side upper bout. It makes me wonder if the plates are shrinking, or are the ribs expanding from neck sweat and hand grease. I know that plates shrink sometimes, but it seems to be rare enough that compensating for it at the start would be a bit of overkill. I mean, you can see a lot of weird distortions on older instruments, but it doesn't necessarily indicate a problem that needs to be prevented from the start.

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53 minutes ago, Matthew Noykos said:

...If I did this, it would make sense to me to gradually bulge the overhang as I approach the widest point in the upper and lower bouts...

That makes sense to me, too, because the plates shrink narrower, not shorter.  I'm not a maker, but I have shortened a lot of ribs.

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1 minute ago, arglebargle said:

...this mostly happens at the lower block...

I think it happens more in the lower bout simply because the lower bout is wider, so it experiences more plate shrinkage.

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Maybe I'm wrong, but plate shrinkage never struck me as a problem that modern makers needed to address. I've seen many older instruments with fine, intact margins. Why would you assume that your plates are going to shrink? Rib distortion seems a much more likely scenario. I would venture to guess that rib expansion and shrinkage is the more likely culprit of plate changes than the actual plates themselves. 

 

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49 minutes ago, arglebargle said:

..plate shrinkage never struck me as a problem that modern makers needed to address...

Plate shrinkage can obviously be minimized by using well-seasoned wood.

49 minutes ago, arglebargle said:

...rib expansion and shrinkage is the more likely culprit of plate changes than the actual plates themselves.

That doesn't make any sense to me, since the ribs shrink and expand across their width, not along their length.

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This is definitely a problem with new viols where there is no edge overhang. I have several instruments where this is a problem, always at the area adjacent to the bottom block.

 

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The bulge in the ribs is invariably adjacent to the bottom block, which would leave you with a funny outline if you were to anticipate this:)

I would though urge anyone making a gamba to give it edges that protrude beyond the rib outline (similar to violin)

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7 hours ago, Matthew Noykos said:

I also have heard of maker’s throwing their plates in a dry light box before doing the final edge shape. 

That''s roughly what I do... put the plates in an environment with 15% lower humidity than ambient overnight, prior to gluing them on. The outline is already adjusted for this shrinkage. I also think this reduces the likelihood of cracking if the instrument is later subjected to very low humidity.

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8 minutes ago, David Burgess said:

That''s roughly what I do... put the plates in an environment with 15% lower humidity than ambient overnight, prior to gluing them on. The outline is already adjusted for this shrinkage. I also think this reduces the likelihood of cracking if the instrument is later subjected to very low humidity.

Martin co. did this to their guitars back before WW2. They kept tops in room with elevated temperature (that was their way of lowering humidity before modern technology) to prevent top cracks.

I think that the tops don't shrink all that much (especially if the wood is well seasoned) but the changes in arching caused by string tension will pull the edges in...

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41 minutes ago, David Burgess said:

but I do like to err on the side of caution/overkill

Your avatar shows you as braver man :lol:

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Do you purfle before gluing the plates on? Or do you just estimate the final shape after drying?

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I am definitely aware of making instruments that may be around for along time.

To that end I allow  the humidity and temperature in my wood storage rooms to cycle naturally with the seasons, keep all wood for an absolute minimum of five years before use regardless of when the dealer says it was cut and do leave the edges slightly wide in general and shaded slightly wider yet at the outer bouts. I also leave a significantly wider margin at the upper block to allow for at least one "New York neck set" once the neck drops (it will). Finally all edges should retain a flat gluing surface showing on the under side or none of the above does any good. The line between the glue surface and where the edge starts to round off provides another place to camouflage the discrepancies and all the  discrepancies in edge width can be faded out so that they are not noticeable to the average eye and at least inoffensive to the discerning one.

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10 hours ago, arglebargle said:

Maybe I'm wrong, but plate shrinkage never struck me as a problem that modern makers needed to address. I've seen many older instruments with fine, intact margins. Why would you assume that your plates are going to shrink? Rib distortion seems a much more likely scenario. I would venture to guess that rib expansion and shrinkage is the more likely culprit of plate changes than the actual plates themselves. 

 

The reason why you have seen plenty of old instruments with intact margins is because the ribs have been shortened at some point.  It happens to all of them at some point it seems.  It’s due to the way wood shrinks.  You get negligeble movement lengthwise in the tree but the width moves a lot in comparison.  Over time you will have shrinkage in that direction.  Since the length of a rib will not move, but the top and back will across the grain, the rib bulges.  Usually at the bottom block because that’s where it gives.  It also happens in the upper bouts too, but that can be addressed during a neck reset or graft.  Restorers will remove the top and release the rib from the block and shorten that joint a touch and redistribute the rib.

I had talked to a wood scientist about this and she gave me a chart listing the average shrinkage in every direction for various woods.  It confirmed all the things I had known from experience.  If I can find that chart I’ll post it.

I have seen new instruments need a rib shortening too fairly soon after they were made, hence the original post.  I think you can mitigate some of that by using well seasoned wood and pre-shriking like David mentioned but I think the problem of the rib bulge will happen eventually.

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Also, I’m not talking about a large amount of extra overhang.  It may not even be noticeable to the casual observer.  And I’m thinking the gradual increase as it gets to the outer bouts would make it more subtle too.  

I also like Nathan’s idea of leaving room for a later NY neckset.  

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1 hour ago, HoGo said:

Your avatar shows you as braver man :lol:

You don't think my avatar suggests overkill? :D

1 hour ago, HoGo said:

Do you purfle before gluing the plates on? Or do you just estimate the final shape after drying?

Purfling is done prior to gluing the plates on. I have a pretty good idea of what shape change to expect.

26 minutes ago, Michael_Molnar said:

I think this is a solution looking for a problem.

Nathan and I have been making and repairing instruments for a very long time....

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I’ve seen a lot of plate shrinkage on old instruments at my bench. Quite often when the ribs are bulging out of shape at the bottom block, it’s happening because the plates shrank and the bout opened up, but someone tried to force the rib in to get the overhang right. Like some others have said, it happens on newer instruments sometimes. Sometimes you can open the whole bout and redistribute the overhang, but the only real solution is to just trim the ribs. 

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For new instruments, dare I suggest you could dry the wood to 4 percent MC or so to minimize shrinkage (the hysteresis effect).

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6 hours ago, David Burgess said:

Nathan and I have been making and repairing instruments for a very long time....

Oops. My remark was not about accommodating a NY neck set, but to the earlier posts. I should have been specific. 

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I don't worry about any of this apart from being careful to use very stable wood. The old greats were not thinking this far ahead but although I agree it is right that we should think ahead from the experience over history my approach is to let future restorers hopefully deal with this...It's not too big a job if the instrument turns out to be worth the effort.

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How long before these kind of problem would possible start, 50+ years?

My oldest are 22 years old and I haven't seen any visible shrinking. I can't imagen this would be a problem. After 50-100 years they probably need some fixing anyway.

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13 hours ago, Michael_Molnar said:

Oops. My remark was not about accommodating a NY neck set, but to the earlier posts. I should have been specific. 

My remarks were about both.

12 hours ago, Peter K-G said:

How long before these kind of problem would possible start, 50+ years?

My oldest are 22 years old and I haven't seen any visible shrinking. I can't imagen this would be a problem. After 50-100 years they probably need some fixing anyway.

"Visible" shrinking? I guess the level of caring about how much eventually goes wrong with a fiddle is a personal decision. ;)

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