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trey

Bass Bar Telegraphing Through Top

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Hello,

 

After applying the second coat of varnish on my viola, I noticed that the bass bar is telegraphing through the top in the lower bout.  It was definitely not there after the first coat of varnish.  It's not really visible, but I can definitely feel a raised ridge where the bass bar is.

 

What did I do wrong?

 

Thanks,

 

Trey

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Usually it's from too much water used in clean up and/or too much clamping force. But since you only noticed it after varnishing I wonder what the temperature/humidity is like in your lightbox?

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Thanks, I'll check on the temperature and humidity in my box -- I should be monitoring that anyway.  This my 6th instrument and this the first time this has happened.

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Usually it's from too much water used in clean up and/or too much clamping force. 

 

Or from too much glue not cleaned up to either side of the bass bar?

 

I would think that external varnish might cause some of the problem.  Water-based sizing or ground (like hide glue) seems to me like it could cause trouble, expanding the grain when applied.  Maybe the varnish too could shrink.

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I do not think varnishing causes this. The varnish reveals the defect. After I put in the bassbar I scrape and smooth the top surface. Moisture from the glue swells the spruce. Well, that's my theory FWIW.

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Hello,

 

After applying the second coat of varnish on my viola, I noticed that the bass bar is telegraphing through the top in the lower bout.  It was definitely not there after the first coat of varnish.  It's not really visible, but I can definitely feel a raised ridge where the bass bar is.

 

What did I do wrong?

 

Thanks,

 

Trey

I remember now running into something similar.  I decided back then it was a humidity/temperature issue with wood and finishing supplies. [classical guitar}  But I couldn't feel anything wrong.  Just observable like the glue was making it's way thru the wood high-lighting bracing patterns when finish was applied.

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When varnishing and cutting back you'll notice any lighter spots that you might not have detected before. 
As said above, using too much clamping pressure or too much water can make the ends pop up in the arching. 
You can correct all that before varnishing by re-scraping the arches a little, then re-sizing before the ground. 


 

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I wonder about the wisdom of scraping the little bump out. The chances are that it will reappear to some degree and if you've already varnished or even grounded the belly, unless you're extremely skilled at retouch, you'll make it a lot worse.

 

Fiddles get all sorts of lumps and bumps, and they scream out at you when you're making them, but often fade into insignificance a few months later.

 

I don't cut varnish back myself, although I only use one or two coats,  and think it's often much overdone, and kills the varnish. So perhaps avoid that area so that you don't get a pale spot, and live with it. You may not even remember it in a years time.

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Hard to tell without seeing it but I'm guessing that there was a problem with the way the bar fit and or too much clamp pressure. Whether you spring the bar or not the bar must fit with finger tip tightening of your clamps and it's best to clean up excess glue with a wooden stick and then very lightly with minimum water. Also helps to remove all but the two end clamps after about an hour. This is  even more critical when replacing bars on already varnished instruments.  

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BTW, was anyone else taught that clamps should only bring the work (pieces) together, and NOT force them into each other?  I have a feeling that clamping is more of an art than we might think.

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Most people who were 'taught' use studs for fitting and gluing. 
The clamping...I've always used the open wedge type clamps getting the end ones on first. 
Not too tight, I find it faster than screw thread repair clamps.

 

 

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BTW, was anyone else taught that clamps should only bring the work (pieces) together, and NOT force them into each other?  I have a feeling that clamping is more of an art than we might think.

I agree with the minimal clamping pressure school of thought and it works well with an attitude of using an appropriate, but not excessive, amount of glue. This sounds simple but getting away from the "I want this to be strong so I'll put lots of glue on" attitude is difficult. It's the same with the clamping pressure. There is also a compulsion to further tighten the clamps after everything is clamped up to "make sure", especially if it was a stressful glue-up. I've seen some guys work and they are like zen masters, I'm the opposite but aspire to be like that.

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Thanks to everyone for the insightful comments.  I now know that clamping pressure is most likely what caused the problem.  I'm new at this -- this is my 6th instrument so I am so grateful for your help.

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I did this on one of my early projects.  Heavy clamping, sprung bar, old varnished plate, water cleanup.  Not a valuable instrument ($25!), and not somebody else's.

 

lplate.gif

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