bridge types and stress on CB top vs......um, alternatives?

Thinking about different kind of general types of bridges...

I visualize some as causing compression on the top of a CBG (trapeze tailpiece and floating bridge)

and some causing what I assume is tension (typical acoustic guitar glued on with bridge pins). I don't know what's under a 'tune-o-matic' type, and probably wouldn't use one on a CBG, but it looks similar to an acoustic top-mounted one under tension...unless they have solid/semi-solid support underneath...

Are there common sense general rules of thumb that certain constructions need to be beefed up or they'll pull apart vs. others being squashed?

I get that a solid body or fairly-well filled hollow one solves some of this, if that's the direction one heads in...

Thanks

Murray

Replies

carverman November 8, 2010 at 10:34pm

Mark Werner said:
I've used a "Red Henry" type bridge on several instruments, and they work well:

http://www.murphymethod.com/index.cfm?event=pages.content&conte...

I've built the mandola that's my avatar, and at least two others. This style does require a bit of neck angle, and does put more stress on the top. I braced the mandola, and no problems, even with the full 8 strings.
I found the thin plywood top of another instrument bending a bit under the pressure, but again a bit of bracing corrected that.
Generally, a higher bridge will put more stress on the top and require the appropriate neck angle as well.

Flatter bridges work very well too... But I don't think cigar-box construction would be strong enough to handle a conventional bridge-pin type arrangement such as found on your typical steel string.

Yes, that is a good example of the bridge that I've custom made for myself out of maple with a
bone saddle. On a 6 string build, string pressure is even more critical. but a flatter or lower bridge
takes quite a bit of the stress off the top. Another builder mentioned a sound post method that
didn't work out..I guess your mileage will vary as they say, but I'm going to try a reverse mirror
style of support bridge under the top because the weak plywood top of the CB will "give" more
under 6 string tension over time. Flat bridges with pins on full size guitars have bridge plates
underneath to even out the stress on the top in the area of string pull as well as bracing
done in tried and true fashion depending on the type and make. Bracing if done correctly
can enhance the sound of the top.
carverman November 8, 2010 at 10:20pm

Some hollow bodies are semi-hollow if using the Gibson style tune-o-matic (t-o-m) as the
support posts on the t-o-m are fairly large, and need to be anchored into a solid wood
neck-tone block. The tone block being either a neck thru design or a separate neck
joining the body via tenon, which adds to the string sustain on a solid body
or semi-hollow.
On the CBG, it is very difficult to use a t-o-m, if you want the lid to open.
I'm also doing my first CBG build and I rhink what I will be doing on mine is to use an
"acoustic bridge-support rib" underneath the top so that when the top is closed,
it contacts this support bridge right underneath where the string bridge would be
set for intonation. If the support bridge is added, once the CB is glued to the neck,
and made slightly higher (no air gap), then the closed lid and string bridge should
apply enough pressure for it to work correctly..much like a sound post that is
necessary on a violin to achieve full resonance between the top and back.
Ben November 8, 2010 at 8:28pm

Hey Murray, I build mostly floating bridges (although I did one glued, but with nylon strings so there wasn't much tension). I've only had one box top that has significantly bowed under the pressure...and it sounds great! I tried a sound post under the bridge (like violin construction) but this completely killed it. I knocked it right out and it has been great ever since. It hasn't deteriorated or anything. It's got a ton of Mid-range frequencies but its a traditional tenor guitar so it really bites nicely. I don't know if this helped at all...probably not, now that I reread of it...
Mark Werner November 8, 2010 at 8:14pm

I've used a "Red Henry" type bridge on several instruments, and they work well:

http://www.murphymethod.com/index.cfm?event=pages.content&conte...

I've built the mandola that's my avatar, and at least two others. This style does require a bit of neck angle, and does put more stress on the top. I braced the mandola, and no problems, even with the full 8 strings.
I found the thin plywood top of another instrument bending a bit under the pressure, but again a bit of bracing corrected that.
Generally, a higher bridge will put more stress on the top and require the appropriate neck angle as well.

Flatter bridges work very well too... But I don't think cigar-box construction would be strong enough to handle a conventional bridge-pin type arrangement such as found on your typical steel string.