Tone bar tension?

[Bluetickhound]

Had a quick question about tone bars that I didn't see addressed in the archives... Now that I have a few builds under the belt something has been bugging me so I thought I'd bring to you all.

Should tone bars have any "springiness" to them as they are attached or should they lay in place tension free before glue up? I have somehow been unable to get the bars to sit in place without there being a slight bit of spring to them. When I clamp them down they are flush with no gaps (that I can see, even with a flashlight) so I'm good there but I'm concerned over the long haul that even a little stress could lead to trouble with cracks.

Am I worried about nothing or should I keep futzing with them until they set in place freely?

[sunburst]

Any "spring" will go away pretty quickly, so as long as the joint is good, in the long run it makes no particular difference if the braces lie in place or if they need a little push. Wood has enough plasticity that the bars (and to a much lesser extent the top) will permanently conform to the shape they are glued in. I prefer for them to lie in place, but I don't worry is they need a little help.

[Bluetickhound]

Thanks John! I'm going to spend more time on my next build (an A5) to get them to lie in place but it's good to know I'm not going to have trouble in the future with these bars, at least not because of a bit of spring... Each of my builds have gotten better (all 3 of them, lol!) and I'm starting to see things on my own instead of asking 50 jillion questions here. Mostly I'm seeing which tools are "must haves" vs. "would be really nice to have".... I had considered the tabletop CNC deal but after a bit of soul searching, have decided I like carving my plates by hand. A thickness sander, on the other hand, has been deemed a "must have".

[Spruce]

Had a quick question about tone bars that I didn't see addressed in the archives...

Go search violin making forums, and you'll be reading threads for weeks... ;)
It's an infamously touchy subject in the violin world, and advocates for both sides are quite vocal on their reasons for springing the bar...
...or not.

[Bluetickhound]

Go search violin making forums, and you'll be reading threads for weeks... ;)
It's an infamously touchy subject in the violin world, and advocates for both sides are quite vocal on their reasons for springing the bar...
...or not.

Wow! Thanks for the heads up Bruce! On the surface, it seems like it would add a bit of stiffness to the top but I'm not experienced enough to know... What John said about the bracing "relaxing" kind of shoots that theory down. Been keeping an eye on your site for some nice quilted back/side wood for an A model that's in the works... Do you have stuff other than what's listed online?

[Spruce]

Been keeping an eye on your site for some nice quilted back/side wood for an A model that's in the works... Do you have stuff other than what's listed online?

We're not allowed to discuss that here, so I'll drop you a PM...

[amowry]

I'm with John-- I think any tension will tend to relax pretty quickly, but I tend to avoid "built-in" stress wherever I can. Of course once you string it up there's gonna be stress everywhere, so who knows?

[Charles E.]

In the violin (and mandolin) world I like to fit the bar (s) with out tension. I chalk fit them with placement studs so that the fit is perfect.

I have had to deal with replaced bass bars in violins that were fit with tension built in and over time distorted the top. I don't think it is a good idea.

[Bluetickhound]

My plan going forward is to not have any spring in my tone bars. Part of my issue is bad technique drawing the line to cut. I have trouble getting the pencil to follow along at the ends (the middle is fine) so there's where my spring is coming from. I went out and got one of those contour gauges (the type with 70,000 little wires that slide to form the shape) and in a test piece I was able to get a really good fit right off the bat. A little work with the chalk and planer and I think I'll be able to get it close to perfect.

[sunburst]

You might find that how you hold the brace stock while chalk fitting can make a difference. If you hold the brace in the middle while you press/rub to transfer the chalk, the ends will be tight and the middle will be loose. In other words, the middle must spring down to fit. If, on the other hand, you hold the brace at the ends, the middle will be tight and the ends will need to spring down. I've learned to vary the position where I hold the brace to chalk fit it. That way I can get the braces to lie in place with a very close fit. They still need to be clamped though; no rubbed joint for braces for me.

[Bluetickhound]

That's a great tip, thanks!! I would normally hold a brace At the ends and have to press down the middle. I hadn't even thought to vary the grip.