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Nick Allen

Possible plate shrinkage.

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So I'm in the midst of completing a new two piece flat sawn back for a violin I started for a customer. It's a DG model of the Plowden variety.

So my problem here is the ambient humidity here. I'm in Pittsburgh, and the humidity wave has been eternal, and crushing. Like that kind that makes you feel like you need a shower 24/7.

So I bought some curly maple to make a back with. It started life at 6% moisture content. But now, since it's been so humid, and I have no means to control that, I'm pretty sure that it's much higher now.

I already have the outline finished, and the final arching, and am working on graduating it. My biggest fear is that after all of this work, I'll end up with a plate that is too narrow for the rib garland.

Is there anything I can do at this point other than just pray? I have considered the possibility of trimming the upper and lower bout ribs a bit in the event that my worst fears come to be.

Has anyone been in this situation? Any advice would be appreciated.

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Are you keeping the rib garland in the same room as the back?

I am wondering if the ribs and back are in the same environment there will be any problems?

Maybe wait until the humidity drops before gluing the back on.

How's the top?

Sorry for all the questions.

Pete

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Can you buy a dehumidifier? Even a small one will work if you store the wood in a small room except while working on it. Like a closet or bath room. I have a basement workshop that I keep near 50% rh. Without the dehumidifier the rh can climb to 80%.

-Jim

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So I'm in the midst of completing a new two piece flat sawn back for a violin I started for a customer. It's a DG model of the Plowden variety.

So my problem here is the ambient humidity here. I'm in Pittsburgh, and the humidity wave has been eternal, and crushing. Like that kind that makes you feel like you need a shower 24/7.

So I bought some curly maple to make a back with. It started life at 6% moisture content. But now, since it's been so humid, and I have no means to control that, I'm pretty sure that it's much higher now.

I already have the outline finished, and the final arching, and am working on graduating it. My biggest fear is that after all of this work, I'll end up with a plate that is too narrow for the rib garland.

Is there anything I can do at this point other than just pray? I have considered the possibility of trimming the upper and lower bout ribs a bit in the event that my worst fears come to be.

Has anyone been in this situation? Any advice would be appreciated.

My son lived in Pittsburgh for several years and didn't like the summer humidity either. He has since moved to Denver and recently to Salt Lake City Utah and seems happier.

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Unless you plan to glue the garland on the back while the garland is still glued to the form, you'll be able to push it around a little to get a reasonable fit.  I'd just want to make sure the back plate was not too high in moisture when it's glued on, otherwise it might want to shrink and split.

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I plan on removing the ribs from the mould just before glueing. I don't have a fancy collapsible mould. So I suppose I can fidget it around a little bit.

I was at my girlfriend's house where she has a table with a breadboard end. Over winter, the ends were about a centimeter wider on each side, now they are narrower than the perpendicular middle section. How'd that for seasonal swelling?

I just wonder how much the plate will shrink? Maybe it'll be negligible?

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I just wonder how much the plate will shrink? Maybe it'll be negligible?

 

I'd guess no more than .5mm across the widest part.  

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The ribs are in the same room (basement). But regardless, the ribs will only shrink depth wise, which may require me to plane them flat again lol.

If they're still in the mold then you can count on the mold retracting too.  I'm running into a similar problem with a plate bolted to particle board so that I can route purfling channels.  What starts out in the morning as flat surfaces end up with me taping and holding down plates while routering before the end of the day is up.  

  My best results while gluing anything violin related are with a humidity reading of 27-30%  on it's way up.  Haven't seen those low readings in a while - been dealing with high 40's to 60%  readings of late.  

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I plan on removing the ribs from the mould just before glueing. I don't have a fancy collapsible mould. So I suppose I can fidget it around a little bit.

I was at my girlfriend's house where she has a table with a breadboard end. Over winter, the ends were about a centimeter wider on each side, now they are narrower than the perpendicular middle section. How'd that for seasonal swelling?

I just wonder how much the plate will shrink? Maybe it'll be negligible?

I use an outside mold. To hold the ribs in shape, I temporarily glue internal bracing between the blocks made from wood scraps. Once it's glued to the top plate, I remove the bracing.

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Unless you leave a front in the UVA room for 6 months it won't shrink much, even then....when you leave it in normal humidity it will get fatter again. 

1/4 inch in some cases. 

Try it. 

 

You can also see:  http://www.popularwoodworking.com/tricks/how-to-calculate-wood-shrinkage-and-expansion

 

According to the tables, that might happen for a difference of ~10% moisture content, which could happen between exceptionally dry and fairly humid conditions... for flatsawn wood.  It is also about the level of shrinkage I get (tangentially) after hydrothermal processing, which ends in a high-temperature vacuum bake. (about half of change comes back).

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I think this will prove to be a tempest in a teapot. Keep us informed nevertheless.

I totally agree with Mike. Wood moves that's a fact. Most air dried wood which is what tone wood is supposed to be will only ever reach 9 to 13% emc by it self. Many tone wood suppliers are using vacuum systems to help speed the drying process these days. Like Don said above the garland will be flexible enough to move around. After all once the fiddle leaves your shop it will be exposed to all sorts of environments.

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On 9/2/2016 at 6:31 PM, Nick Allen said:

So I'm in the midst of completing a new two piece flat sawn back for a DG model of the Plowden variety.

How did that turn out for a back plate?  Any problems?

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