"Reasonable" tone bar height for F5?

**HogTime** · Feb-11-2009, 1:55pm

I know this is subject to many variables, not to mention "trade secrets", however ..... What is a "ballpark" height for the finished tone bars on an F5 with a Sitka spruce top?

I started around 0.5" height and a thickness of about 0.25" for the bass and 0.20" for the treble. I've worked the bars down to where they are highest in the middle and tapered down to the ends (quickly the last 1" or so).

Both my bass and treble bars are now at around 0.35" height in the middle. About right? Hopefully not too short, or I'll have to find all the shavings and glue them back on.

Thanks,
Ralph

**Michael Lewis** · Feb-12-2009, 1:17am

How stiff is your top? How thick? What is your long arch like? These concerns are what I use to determine the size of the braces (tone bars). Are you going for the traditional Loar mystique, or something else? I have seen successful tops with braces as large as 3/4" high and as low as less than 1/4" in the center. If your top is overly flexible you may want to use larger bars to resist the down pressure. If your top is stiff you may not need much at all.

**HoGo** · Feb-12-2009, 6:00am

If your top is close to Loar specs and arching shape (very important) then you can use Loar style bars that are: treble approx. 1/4" high, bass bar a tiny bit lower at its center gradually tapering towards kerfing.

**Rick Turner** · Feb-12-2009, 8:28am

"top close to Loar specs" would have to include stiffness as one of the specs...forget dimensional measurements alone...deflection specs would be important as Michael indicates.

**HoGo** · Feb-12-2009, 4:21pm

Originally Posted by Rick Turner

"top close to Loar specs" would have to include stiffness as one of the specs...forget dimensional measurements alone...deflection specs would be important as Michael indicates.

Well, I'd bet my salary that Loars were not made to deflection specs. The wood was graded mostly by cosmetics (gpi and degrees off-quarter) and carved to predetermined thicknesses (plus minus some random deviations) and often some of the wood got sanded away from outside (much of it unintentionally), but no deflection was measured.... If you use similar woods and carve very close to the specs you are in the ballpark. Unless you want make exact copy of one given Loar. They are not all equal. Some Loar tops are quite deformed/distorted while others are not at all. Deflection all over the place.
I don't want to tell that this is what SHOULD be done. Just that it may be REASONABLE (re: OP) to use those numbers if the other specs fit the Loar scheme.

**HogTime** · Feb-12-2009, 4:58pm

I'm a first time builder and building a Siminoff F5 kit, which came with the top and back carved to his specs (which I think are Loar-like). Roger said the top had very tight grain, so I assume that means it would be stiffer than his normal tops.

Sounds like I'm at least "in the window" now. I don't have any way to measure deflection or I would try to. Also don't know enough about wood to say whether my top would be considered stiff. As far as desired sound - good for bluegrass and not necessarily like a Loar (which I've never heard).

Thanks for the input,

**Rick Turner** · Feb-12-2009, 5:53pm

Do we know if Loar tap tested mandos before they were varnished? Did he then say, "Take a little bit more off here."? Did he flex tops and make suggestions re just how much to carve? If not, then what's the big deal? Was he simply signing pieces of paper for a marketing ploy or was he really in charge of how the instruments were individually made? If he was simply signing the work of others, then perhaps those others should be receiving some credit...