bridge thickness & neck angle

[peter havriluk]

Dancing between two measurements, neck angle and bridge thickness, at some point after setting the neck angle, it seems as if controlling the amount of saddle exposed on a finished guitar is much the child of bridge thickness. So....are there any commonly accepted minimum and maximum thickness dimensions on bridges? I've been putting my caliper's jaws on bridges smack in the middle, between the 3rd and 4th pin locations.

It seems reasonable to adjust bridge thickness to get to a desired straightedge-atop-the-frets condition after the neck angle geometry is deemed acceptable and the neck and fretboard seem cosmetically happy where they are. But I don't have an idea of what minimum and maximum values are for bridge thickness.

Thanks, folks, for indulging my many questions.

[John Parchem]

I do not use bridge thickness min and max rather I have an acceptable range of the strings off of the top when strung up with my desired action. Sorry I use mm, but I am OK with 12-14 mm of string height. I get this by taking the measurement of the projecting straight edge off of the top and adding 2 times the action. A .340" bridge works for me. Maybe if my string height was on the high side I would go to .4"

[peter havriluk]

John thanks for your explanation. It helps.

Let's see, now: Nut slot height, string relief, neck angle, fretboard taper and thickness, action height, bridge thickness, get them all decent and the geometry is under control. Piece of cake!

Getting all these variables to dance together...

[Dave Bagwill]

Following a good set of plans should help a bit, and then following them religiously. But still, no piece of cake I agree.
Even with their careful CAD programs and lots of experience, the Martin factory keeps a box of bridges, all the same except for their thickness, next to the people doing the bridge gluing. There are too many variables involved, even with CAD, so that making something fit is always a big factor.
Cake? Hmm...I wonder if there is a cookie in kitchen?......

[peter havriluk]

Plans? What plans? Anybody got a drawing for a 14-fret dreadnought that's 93% of a Martin Herringbone with a 23.92" scale length? You mean the sketches I made with the bracing layouts and bridge plate location?

I DID do a drawing of the side projection, to get an idea that my neck angle made sense. Provided I actually achieved the same neck angle in wood as on paper and the top had the same radius as planned.

[Dave Bagwill]

It wasn't a criticism Peter. My point was that even following plans, using pieces cut out by a cnc machine, a calculated bridge height will seldom be perfect. I don't know why - wood is like that, I guess. Of course most of us (all?) don't have a number of pre-made bridges of different heights to choose from.

[Hans Mattes]

FWIW, I'm a member of the same school of lutherie as Peter -- "Plans? What Plans?" Each guitar I've built (around a dozen so far) has been different -- most of them better than their predecessors, except for a couple of real duds.

For the last four, I've taken an approach to fitting the neck that makes neck angle and bridge/saddle height separate issues so each can be dealt with individually and rather easily.

I'm using a bolt-on neck having a heel with parallel sides morticed into the headblock. (I've used mortices ranging from the thickness of the sides up to ½", but I don't think it really matters much.) And I've been using a "floating" extension of the neck/fretboard with no contact to the top of the soundboard. I slot the headblock a bit so that the bolts holding the neck can be adjusted to allow the fretboard to be positioned anywhere from ⅜" to ½" above the soundboard. Thin wedges (ala Taylor) can be used to adjust the angle of the neck so that low action is available all along the fretboard. (For the record, I've been using a 90 degree neck heel angle and a 30' soundboard dome.)

I've built several guitars this way and see no downside. They're easy to set up and play well.

As an aside, in addition to keeping the fretboard off of the top of the soundboard, I've kept the UTB clear of the underside of the soundboard. That lets the entire soundboard participate in making music. I've taken two approaches to managing the structural requirements of string tension: the simplest has been to run two structural members inside the box, between the headstock and the tailstock, one on either side of the soundhole. The other approach involves bracing the headstock with a strong (carbon fibre or steel) transverse brace mounted ⅛" clear of the bottom of any soundboard braces in the area and anchored into wooden blocks fitted to the sides of the upper bout. Both approaches seem to work fine with no obvious downsides (though some folks might object to structural members being visible through the soundhole).