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Robert Renick
06-01-2013, 07:28 AM
What are the reasons for choosing to build with one over another? Do these reasons change from size to size?
Thanks

Allen
06-01-2013, 10:36 AM
String through and tie bridges can be made smaller and lighter than a pinned bridge.

With a tie bridge, the string tension is trying to rotate and peel up the bridge relying on a glue joint only. With a string through and pinned bridge some of that same tension (how much I couldn't say for sure) is moved to the bridge plate where the knot or bead that is on the end of the string bears up against the bridge plate. With a well made and fitted pinned bridge, the pins can be pulled out after the string is up to tension. The string will stay in place.

And finally aesthetics. What looks good for your application. For my taste, I'm not a fan of tied bridges most times. Pinned bridges are my first choice, but they don't work well in all applications. String through is my choice on sopranos.

ProfChris
06-01-2013, 10:37 AM
This is too general a question to give a comparative answer. I can think of 7 or 8 quite different designs off the top of my head, and I'd guess there are quite a few more, each with a number of variations.

As a general answer, a bridge must achieve a number of things:

1. It must stay attached. If it's glued to the top this means a minimum glueing area. But a floating bridge can be tiny if the tailpiece is fixed.

2. It musn't be too heavy, or too light, or taake up too much of the top. Too heavy can damp the top, making it quiet and dull. Too light might not transfer energey efficiently (I think, but others will know better - certainly it can affect tone adversely). The more top it occupies, the less there is to vibrate and make music.

3. It must be strong enough not to fall apart under string tension.

4. It must put the terminations of the strings in (approximately) the right places.

5. It must transmit the energy of the strings to the top as efficiently as possible.

All bridges make compromises between these. As an example, a floating bridge is light and occupies very little of the top surface area. But it's less effeicient than a fixed bridge in transferring string energy. I'm just finishing a sopranino with a floating bridge, and to compensate the top is very lightly braced with no bridge plate. As a different example, if you use a pinned bridge you need a robust bridge plate to stop the strings pulling through, but the plate takes a lot of the load so the bridge footprint could be smaller (except you need the space to fit the pins). And so it goes.

Then you start making aesthetic choices, which give you different shapes, and choosing your wood for a combination of its appearance and mechanical properties, and on it goes again.

Really, it's remarkable that any builder ever decides what kind of bridge to use.

coolkayaker1
06-01-2013, 11:07 AM
I like string through bridges on all my ukes if I can have them that way.

Beau Hannam Ukuleles
06-01-2013, 02:02 PM
You can also have a through bridge without pins.
They look very neat..
Eric devine uses this system

It is arguable that with a through/pin bridge, the strings transmit the vibrations towards/into the top in a slightly more effective manner. Most of this energy already goes down the saddle into the top though.

Robert Renick
06-02-2013, 05:09 AM
Thanks for the help. One of my main concerns is simply reliability. The classical tie block style looks like it has so much material removed that it could get fragile, the Martin style looks to have more support around the saddle, but the string slots could be a weak point. The pinned bridge looks to be the most durable, but the largest and adds more parts.
Thanks Prof Chris, for the answers, and yes it is a wonder some of us can get anything done.
I will proceed with a Martin style bridge. One perspective I am building from is using local or domestic wood. The instrument is a 18 3/8 scale, all POC large tenor which will be set up low G with the baritone tuning option. It is all light color wood, so to stay in theme, I have some various maples in the shop, and some light colored pecan, so those are my choices at the moment. I am thinking rift to flat sawn will be the best grain orientation.
What are the preferred hole sizes for the knots? Is there a difference for baritone vs. tenor for the hole sizes? 1/8" looks too small, 3/16 looks a bit big, but those are my brad point options in the shop now.

I live in the town of Mount Shasta, wonderful place, but limited in stores and such, so to go look and measure some basics requires a 60 mile drive, thanks for the help on these basic questions.
Rob

Rick Turner
06-02-2013, 07:14 AM
I have to disagree with the theory that string vibrations travel through the bridge to the top. There is not some mysterious pathway down, through, and into the instrument.

String vibrations move the entire bridge which thus moves the top. Yes, the saddle affects tone, but I think of it as a tonal filter and also that the hardness directly affects the string at the contact point...it's like a selective shock absorber on a micro level. The saddle is the interface between string and bridge which is what moves the top.

Also, the bridge is the single biggest and most important brace on the entire top.

There are practical issues...glue surface, mass, tying knots or using beads, etc...which can affect your choice of bridge design

There is also the issue of whether the bridge is torquing the top as with any bridge that is the terminus of the string or whether it's a floating bridge as per archtop guitar or violin. That's a major difference in how the top is driven.

We usually use the knot in a hole with a slot in the back of the bridge style, but also do some string through bridge with beads for smaller bridges and also pin bridges if the customer wants that. I do not hear much difference among those three types.

One (well two) interesting issues are bridge weight and the resonant Q of the bridge material. There is a reason why almost ALL classical guitars have ebony fingerboards but rosewood bridges. Think on that one a bit...

Robert Renick
06-02-2013, 09:06 AM
Thanks Rick, I have just been surfing around a bit to understand your post better. It seems that for a bridge the balance between weight, impedance, and flexibility are all fine lines. Seems the density of the material would be the most encompassing number for these characteristics. With that in mind I am comfortable with pecan as a decent choice as it sits close to the rosewoods on the density and hardness charts. I did not find a good chart of the resonant Q of the materials.
I have read some interesting post from Allan Carruth on the topic of material choice for bridges, he recommends trying softer lighter materials with an enlarged footprint, specifically he was suggesting domestic walnut and cherry as viable options.
Maple is used on violin family instruments for bridges, I guess weight being the driving factor there.
Lots to think about, thanks
Rob

Beau Hannam Ukuleles
06-03-2013, 02:39 AM
Rick,
Thanks for your thoughts on the string vibration :)

On bridge weight, and pairing that down- do you think a (newly built) uke would benefit with a classical like neck angle (ie-fingerboard diving into the top, with the top of the FB aimed just above the bridge base) and a low/stiff bridge? This seems to be the end result of what inevitably happens over time with old Spanish heeled ukes compiled with top bellying. The logic seem to say that this would also change (make greater) the degree of angle of the strings over the saddle and thus (lessen) the torque (downward pressure/rotating action) of the bridge to top by a few mm thus reducing the amount of energy able to be transferred into the top? My physics sucks but i'm presuming torque/downward pressure/poundage exerted on strings through break angle can be used as some form of reference point for each other.
Am I just splitting hairs?

resoman
06-03-2013, 05:18 AM
A great read, IMO, is a book by Roger Siminoff called the "Luthier's Handbook where he discusses bridge design in one of the chapters where he discusses the mechanics of different bridge designs. He discusses what happens when strings terminate at the bridge vs strings that terminate at a tailpiece.
The book got pretty good reviews and I liked it. I'll read it again, probably several times.

Rick Turner
06-03-2013, 05:33 AM
I took Roger's "Tap Tuning" seminar a couple of years ago...it was really interesting and helpful, especially in terms of getting consistent results. It's also worth noting that Roger doesn't get stuck in one way of thinking...his concepts have evolved over the years, and he understands that there is more than one way to achieve tonal goals.