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classical bridge design....wings
http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=29954		 Page 1 of 1
Author:  Doug Powdrell [ Wed Nov 17, 2010 4:28 pm ]
Post subject:  classical bridge design....wings
I'm doing a 'run' of honduran rw classical bridges ala Courtnall, Bogdanovich, Somogyi, and OLF inputs....

Seems that weight, geometry and wing thickness are recommended....but as I file, shape and profile these, the term wing deflection keeps coming to mind....wings seem crucial to drive vibration to the top bracing.

Wing Thickness; seems 3mm-4.0mm are used...grain orientation would come into play, no? Should wings deflect at the hinge or along its length (tapered thickness)....assuming load goes through saddle-wings-bracing-soundboard....should bass or treble differ in stiffness?

Is the curved cross section in wings for looks....could the wings be made thinner/flatter with similar section modulus?

In my mind, classical bridge wings play a critical part in transferring vibration...more so than steel string due to lower driving energy.

Would a 'looser' bridge underpower a stiffer soundboard bracing?...and vise versa

How do we maximize energy transfer from bridge wings to top bracing and in regards to treble and bass response? We modify top bracing for treble and bass response....why not wings??

Are we looking for a certain note (B, G,D?) when properly profiled????

Never really thought much about it 'til I studied and built 2 classicals and began building classical bridges....previous bridges were pre-made......thanks.
Author:  Alexandru Marian [ Wed Nov 17, 2010 5:41 pm ]
Post subject:  Re: classical bridge design....wings
Yeah but well, now you seem to be thinking too much about it :D First of all just make sure it is not too heavy. 25 grams is heaviest I would use. I would not put it on a floppy soundboard. At the other extreme, light soundboards with extremely light and flexible bridges make flamenco guitars and yo don't want to get too close to that with a classical either. A good bridge will have a bit of wing flex, but if it too much, it would not hurt to have an internal bridge patch. A too flexy bridge comes from both very dense (your Honduras RW choice is not the best) and very light wood. In the first case you need to thin the wing to even under 3mm to get rid of the weight. In the second you need to stay under 5mm so it doesn't look like a China factory clunker. Both result in too much flex for my taste, but which can be easily fixed from inside. As a result I always pick the bridge and measure the density before deciding on the bracing detail. Or one could always pick bridges that are not too heavy and not too light but I don't have this luxury yet.
Author:  Doug Powdrell [ Wed Nov 17, 2010 6:31 pm ]
Post subject:  Re: classical bridge design....wings
Thanks for the input Alexandru..

Yeah, maybe overthinking (I like to build mostly right brain, but now and then that darn left brain gets going again (engr. by trade)...I like to 'get lost' in my hand carving...thinking about each cut as I near the end....kinda like a painting....when is it done and when is it overdone....kinda like bracing.

Best wood for bridge??? I thought hon.rw. was up near the top....? idunno

I prefer no bridge patch...

Currently, these bridges are stiff at 3.5mm wings (+/-)...and I will work 'em down when the soundboard/bracing is determined.

'A good bridge will have a bit of wing flex'....I need more experience to determine...'a bit of'...wings have a ring/glassy tap (good)....guess I'll go for the 'build 2 identical except for wing modifications'.

thanks again. appreciate your input (and your guitars).
Author:  Alexandru Marian [ Wed Nov 17, 2010 6:45 pm ]
Post subject:  Re: classical bridge design....wings
I've been through engineering school too but I never practiced it laughing6-hehe

I guess a bit of flex is just that. When it is too clunky it can barely be bent. It needs to move a little without flexing your muscles. But more important, I repeat, don't make it too heavy. When dealing with dense material there are many tricks to use besides thinning the wings. You can make a narrow center block, width, everything. Don't make the tieblock too tall. Slope the tieblock face towards the saddle. Round off and carve the saddle block well. Dig a trench between the blocks, saves weight and could make changing strings easier. Carve off the back of the tieblock. Not only it reduces weight, also seems to be taking away some of the stress in the glue line. That is where bridges start to fail.

I forgot, don't fully carve your wings without considering the doming too. Probably around 1mm for medium depth.
Author:  Alexandru Marian [ Wed Nov 17, 2010 7:19 pm ]
Post subject:  Re: classical bridge design....wings
Better wood choices: Brazilian and Madagascar, and Indian if you are cheap or the the trim asks for it. But the real factor is the density of each piece. Lightest Madagascar I measured was only 650 Kg/m3. Brazilian, 780. Indian, something under 800 too can't recall. All three can reach 1000Kg/m3 though, same as Honduras and coco. I think 800-850 is a nice medium density.
Author:  Peter J [ Wed Nov 17, 2010 7:35 pm ]
Post subject:  Re: classical bridge design....wings
[quote="Doug Powdrell"
....wings seem crucial to drive vibration to the top bracing.

Is the curved cross section in wings for looks....could the wings be made thinner/flatter with similar section modulus?

In my mind, classical bridge wings play a critical part in transferring vibration...more so than steel string due to lower driving energy.

We modify top bracing for treble and bass response....why not wings??
[/quote]

1. Yes, absolutely. There is only a finite amount of string energy to transmit to the top. The bridge is the biggest brace in your 'system' and only differs from the others in that it is fastened to the exterior surface of the top. I usually aim for a bridge between 17 - 21 grams; 17 - 19 g. for a flamenco and 19 -21 for a classical. The height of the strings off of the top varies for each style also. ~ 10 mm. for a flamenco and ~ 12 mm. for a classical. Exceeding that height puts too large of a moment on the saddle/bridge slot. The height of the saddle block itself should be about 7 mm. for a flamenco and about 9 mm. for a classical. The height of the tie-block can vary a bit based upon the attachment strategy you are using; a 12 hole or 18 hole attachment may require some additional height based upon the hole spacing/sizes you are comfortable with.

2. The shape of the wings is not sacrosanct. Take a look at a Sergei DeJonge bridge and you'll see what I mean.

3. The transfer of energy into and across the top is the critical factor. A steel string uses the bridge, bridge plate and the sizeable x-bracing to accomplish this. A classical / nylon string instrument with it's lesser energy is at the mercy of the overall stiffness of the top/bracing system. A bridge patch is not absolutely necessary depending upon the response you are looking for. Many are successful in the application of a 'Bouchet bar' rather than the bridge patch.

4. Wings can be truncated for a 'brighter, less sustaining, quicker response' sound. The width of the bridge is also not sacred. YMMV...

With the many variables we deal with in each build the bridge and how it affects the response, sustain, tonal characteristics, playability in regards to string height and action (some players call this "feel") and loudness of the guitar can vary within its own set of requirements quite a bit. The three primary rules are: 1. don't make it too heavy 2. Don't make it too wide 3. Don't make it too tall :lol:

The rest is up to you.....

As an afterthought, there is an excellent article in American Lutherie #97, Spring 2009; What is the Flamenco Guitar." A panel of very experienced luthiers speak to the the differences and there is some excellent discussion about bridge design and guitar responsiveness.
Author:  Doug Powdrell [ Wed Nov 17, 2010 8:42 pm ]
Post subject:  Re: classical bridge design....wings
PeterJ-Thanks...will re-read GAL article tonight....and will check Sergio DeJonge,too.

I'm designing for 6 hole, 12mm height strings...backsloped tieblock. Similar to fig 24.2 pg. 290, bottom design Courtnall.

Note-I do not have a scale..will purchase one before another guitar is built (documentation, comparison,etc.). (completed 19 ss, 2 class., 5 ukus....what was I thinking???) idunno. More feel than numerical data, I guess.....

I build guitars to relax and let the right brain have fun!! laughing6-hehe

It's all about 'feel'...from a players perspective and from a builders perspective....gotta surpress left brain more? [headinwall] ..it's easy really....but when is a painting done???

thanks guys. As you see, I'm not asking 'how to'...but rather intuitive guidelines....your advise is well taken. thanks again.
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