Carbon Fiber Bridge Plates / Patches

I was going to add this to the bottom of my other recent bridge plate question, but it had grown long enough. For those of you using carbon fiber bridge plates, is there a preferred source for them? How about a preferred thickness? A quick google search brought up dragonplate.com, where they have several thicknesses. My guess would be to go for either the 1 mm, or the .025".

Matt, we haven't used carbon fiber plates yet - only rods and pipes for neck reinforcement. Anyway, there are people like Marshall Brain out there saying the tensile strength of carbon fiber is five times as much as (or five times more than) steel. So I don't know how thick you make your rosewood or mahogany bridge plates but probably not more than 5 mm thick, so 1 mm of carbon fiber is going to do the job. In fact, if I were going to I would try 0.5 mm or 0.0125".

Just my 0.02 dollars.

erich@muttcrew.net said:

Matt, we haven't used carbon fiber plates yet - only rods and pipes for neck reinforcement. Anyway, there are people like Marshall Brain out there saying the tensile strength of carbon fiber is five times as much as (or five times more than) steel. So I don't know how thick you make your rosewood or mahogany bridge plates but probably not more than 5 mm thick, so 1 mm of carbon fiber is going to do the job. In fact, if I were going to I would try 0.5 mm or 0.0125".

Just my 0.02 dollars.

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Rosewood/Mahogany Bridge plates at 5mm thick who uses them at that thickness???....I use spruce and never more tham 1mm thick.

Timbuck said:

Rosewood/Mahogany Bridge plates at 5mm thick who uses them at that thickness???....I use spruce and never more tham 1mm thick.

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He suggested .5mm or 1/2mm.....I think you missed the decimal. 5mm would be huge!!!

Timbuck said:

Rosewood/Mahogany Bridge plates at 5mm thick who uses them at that thickness???....I use spruce and never more tham 1mm thick.

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Hey Timbuck, add your thoughts to this thread, if you would be so kind. Thanks!

jerickson said:

He suggested .5mm or 1/2mm.....I think you missed the decimal. 5mm would be huge!!!

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The point I was trying to make is that 1.0 mm of carbon fiber would have the tensile strength of 5.0 mm of steel (according to accepted or at least undisputed theory). So no matter how much strength 5.0 mm of rosewood might have (I quote "it's huge"), it's less than 5.0 mm of steel and therefore less than 1.0 mm of CF. So we can most certainly assume that 1.0 mm of CF is strong enough and 0.5 mm of CF is also very likely strong enough to compare to anything anyone out there is making in rosewood bridge plates. I would venture even further down, but the stuff is light enough that 0.5 mm is hardly going to weigh things much.

luvzmocha said:

http://www.ukuleles.com/Technology/bridgesize.html

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From that page:

In all my instruments, I put a bridge plate beneath the bridge, glued to the underside of the top. The bridge plate is made of graphite carbon/epoxy composite bi-axial sheet. I use 0.018" thickness for sopranos and concerts and 0.030" thickness for tenors and baritones. The width of the bridge plate extends 0.5" beyond each end of the soprano and concert bridges and 0.75" beyond the ends of the tenor and baritone bridges. In all cases, the bridge plate extends 0.25" above and below the bridge plate. The ends are rounded into semi-circles. This material is available from Composite Structures Technology as carbon shear webs and may be ordered in a variety of widths. I usually buy the 3" widths of each and cut them to size with metal cutting shears. The part numbers are: C3001 (0.018") and C3011 (0.030"). The prices seem reasonable to me and service is very good.

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Thanks.

All i know about the subject is, that without a bridge plate the thin top will flex under the tension of the strings and the bridge will catapult off tearing the wood as it go's...or so I'm told.

erich@muttcrew.net said:

The point I was trying to make is that 1.0 mm of carbon fiber would have the tensile strength of 5.0 mm of steel (according to accepted or at least undisputed theory). So no matter how much strength 5.0 mm of rosewood might have (I quote "it's huge"), it's less than 5.0 mm of steel and therefore less than 1.0 mm of CF. So we can most certainly assume that 1.0 mm of CF is strong enough and 0.5 mm of CF is also very likely strong enough to compare to anything anyone out there is making in rosewood bridge plates. I would venture even further down, but the stuff is light enough that 0.5 mm is hardly going to weigh things much.

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I don't disagree with you erich. I was pointing out that you were suggesting 1/2 mm not 5mm for the carbon fiber. I'm a huge fan of carbon fiber and am well aware of its strength vs steel properties. Many guitar builders are using it with their lattice bracing designs to allow them to use thinner tops than with traditional fan bracing but still have structural integrity. (greater volume w/thinner top) I was also agreeing with Timbuck that a bridge plate of 5mm would be way too thick and I don't know of anyone using one that thick. I guess I'm guilty of laughing out loud at the thought of a 5mm thick bridge plate.

No objection here. I just wanted to clarify my point as it seemed to be causing some misunderstanding. The question is who is going to do the experimenting once we get the formulas figured out.

BTW, the 0.030 inch plate that David Hurd suggests for tenors and baritones would calculate as follows, assuming that our formula (CF = Steel * 5) is correct:

0.030 in x 5 = 0.150 in = 3.8 mm

So if you think you need 3.8 mm of steel, that would be the way to go

I always thought it was pound for pound five times stronger than steel

And yu would be right Ken because that is what happened on my first 2 ukes until Bob Gleason put me right!

here's my view:
It's not how thick the plate is but how much tension and rigidity it puts into the front that is important. Bear in mind also that to put a carbon patch in place (and I think it's a great idea - just not for me) you must introduce the bet noir of adhesives - epoxy.

Let's look at the process: first we have a layer of epoxy, the CF mat and a layer of epoxy and a1mm bridgeplate if I remember correctly. What do you think all of that epoxy is doing? Second point. David finished his instruments with the West System as a grain filler, further stiffening and tensioning the wood with epoxy. Next there was a hard skin of cellulose lacquer (real luthiers use this you know...). It is important to look at the whole picture and wonder because prior to all this fuss, David comprehensively flex tested and thinned his soundboards to some very tight data.

So, is it necessary to quibble and calculate? I am skeptical for the simple reason that there are more processes that follow bridge plate placement that have a final impact on the sound. I find it hard to understand why someone would go to a lot a trouble 'tuning' a front before it was on the instrument... I am also sure that the final 'finish' on these instruments played a significant factor.

If it was straightforward, proven and simple we'd all be doing it wouldn't we. Some of the greatest instruments out there have a simple 2mm spruce or cedar bridgepatch... And if you want to read some balony busting stuff try Jose Romanillos' book on the great builder Antonio de Torres. There is a photograph in there that shows the pencil marks where Torres intended the braces to go and their final resting place - the poor old boy had arthritis and accuracy was not his forte with those second epoch instruments. And do they sound great? You bet they do!

Pete Howlett said:

And yu would be right Ken because that is what happened on my first 2 ukes until Bob Gleason put me right!

here's my view:
It's not how thick the plate is but how much tension and rigidity it puts into the front that is important. Bear in mind also that to put a carbon patch in place (and I think it's a great idea - just not for me) you must introduce the bet noir of adhesives - epoxy.

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I did a little research into gluing CF, and found this interesting bit:update: The post I quoted above is from 2004, so I wrote Mr. Proulx and asked him if he still felt the same way with regards to polyurethane glues and carbon fiber. He wrote back immediately, and here's what he said:

I believe that makes for 17 years of experience with the stuff...

Pete, apparently even David Hurd is confused, as the information in his book and web site conflict regarding the recommended thickness of CF for bridge patches.
And you are correct. Kawika built excellent ukuleles but that doesn't point to one particular thing, but rather a whole cacophony of techniques that he used together.

Gimmee that mojo man...I've had a terrible day!

Don't confuse "strength", as in tensile strength, with "stiffness", which is the main property for which CF is valued. They are different qualities. It's really helpful to get the terminology right when dealing with engineering issues.

Rick, do you know how CF is tested for stiffness? I would imagine it would be some sort of tensile test.

I’m just curious since I test fiber optics for a living. I have an idea on how it would be done, but never tested for stiffness.

Here is a test you can do: Take a piece of whatever you are testing at a defined thickness (weight does not matter at all for this), fix it between two solid points (like two sawing horses), hang a bucket on a hook in the middle and start piling the weight into the bucket: water, sand, lead weights, etc. The more you can pile in before the piece either bends or snaps, the stiffer (or stronger) it is. To compare with other materials, of course, you would need to also use the same length (distance between the sawing horses) and width. If you have ever done this with carbon fiber, and I have, you know it won't likely bend much at all but will snap at some point. But what you will also find out is that the bucket is fuller than when it snapped or bent or otherwise gave with a piece of wood the same length, width and thickness.

BTW: There is also a measure of stiffness (e. modulus?) in a bow. It means the piece returns to its strait (or unbent) shape after you remove the bucket of weights, i.e. it doesn't get bent out of shape and stay bent when you let go. In my experience, CF snaps before it bends all that much. And it resists bending big time. So go figure if we're talking about strength or stiffness. I don't honestly think it matters much, since we are talking about a thin plate comparable (in strength and/or stiffness) to a thin layer of maple or spruce or rosewood.

P.S. Come to think of it, I think that was e. modulus. Sorry folks. As Pete was saying "I had a really bad day". Take it from here and forget whatever I was saying. I gotta go relax and play some guitar to re-humanize.

When they say as strong as steel...what grade of steel do they mean ??...There's a lot to choose from http://en.wikipedia.org/wiki/Steel_grades
With my experience with C/F bike frames that suddenly snap in half with no warning..I'll stick to steel or aluminium....come to think of it whats wrong with aluminium bridge plates.