Tone bars and thickness for western cedar

[joehendrick]

Hi All- I'm Starting an A shape western cedar top with F-holes and was wondering what the best choice for tone bars would be. I have red spruce sitka spruce and western cedar as choices.

Also everything I've read says add "a little" to the thicknesses. Anyone have a number to add to thicknesses

Thanks for your help

Joe

[HoGo]

Hi All- I'm Starting an A shape western cedar top with F-holes and was wondering what the best choice for tone bars would be. I have red spruce sitka spruce and western cedar as choices.

Also everything I've read says add "a little" to the thicknesses. Anyone have a number to add to thicknesses

Thanks for your help

Joe

I never worked with WRC, but for VERY soft Engelmann I went to 5.6mm in the center and 4mm at recurve while I go for 4.2-4.5 down to 3-3.2 for typical Euro or red spruce.
You should check how stiff the plate is while you are removing wood. I f you worked with spruce before you want to get it to similar stiffness (i.e. the feel when you are trying to bend it)
Good luck.

[Marty Jacobson]

I ruined two redwood mandolins trying the "add a little" approach. Turned out I needed to "add a lot".
For very soft redwood and Alaskan yellow cedar, my center thickness rough carving target is 7.5mm in the center and 3.5mm in the recurve. I have left many instruments at 7-7.5mm in the center and near the neck block, and thinned the recurve out to 3 in the recurve. But that's about as thin as I'll go with yellow cedar. Haven't worked with WRC yet, but yellow cedar is very light and very soft, so I think that's a safe starting point.

Here are some notes from as I was building, and sound clips:
Yellow cedar, Target .130 - .300 parallel. Final 0.120"-0.300", weight 132g. Tap Tone- 244 (B3), 389 (G#4), 577 (D5), 751 (F#5) . Not an impressive top from the tap tone. But should sound great as the specs are very similar to #18, but it is lighter


Straight redwood. 96g, Amazingly resonant, light, stiff top. .125 - .140 on bass side, .300 at crown. .230 at neck and .210 at tailpiece. Tap tones after f-holes were cut: 221 (A3), 359 (F4), 492 (B4), 564 (C#5), 743 (F#5)

[peter.coombe]

Red Spruce or Sitka Spruce would be fine for the tonebars. I would not use Cedar.

[CarlM]

I would not use Cedar.

Why would you recommend against that? Especially if the top is cedar?

[Marty Jacobson]

I agree with that - cedar is soft, and I get the impression (anecdotally, just from playing with it in my hands) that it doesn't spring back from repeated cyclical loading as well as denser spruce does. It can also crack across the grain, which is much, much more difficult to get to happen with spruce. If you made some really tall cedar braces, say 10-15mm tall, it would probably be fine. But spruce is a known quantity, known to work in this application. Now I have heard other luthiers say that spruce bracing delaminated from redwood tops due to the differential in hardness, but I can't think of a reason why that would happen other than conditions which would cause problems in any wood instrument (extreme changes in temperature, humidity, etc).
I've used Sitka spruce bracing on all my cedar, redwood, etc. tops without any problems so far.
Most of the time when I try something new and "innovative", I later find out it was a dumb idea. Oh, I think with the benefit of hindsight, that's why nobody does this... because it doesn't work. Not saying it won't, just keep in mind how much thicker the top needs to be when working with softer woods, and add a similar scale factor to the height of the bracing. Should work... in theory.

[Spruce]

Why would you recommend against that? Especially if the top is cedar?

Cedar is lousy bracewood...
You can easily break it over your knee when making kindling for the stove...
...the first time i did that with Red Spruce, i had a bruise on my thigh for a month....not kidding.

cedar is soft....

Not necessarily...
But even the stuff that is as hard as spruce will easily break across the grain...
That's it's weakness, and Red Spruce's strong point...