Official Luthiers Forum!
http://mowrystrings.luthiersforum.com/forum/

Bridge design
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=50432		 Page 1 of 1
Author:  bcombs510 [ Sun Mar 18, 2018 1:16 pm ]
Post subject:  Bridge design
Hello,

I’m working on trying to pull together a more complete design theme for my current builds. Attempting to tie together design elements for the headstock, Fretboard and bridge.

I made the layout in illustrator and made some templates from 1/4” MDF.

Below are two pics of bridge possibilities. For the offset pinholes, am I asking for trouble by moving the low E back toward the back edge? Maybe I should flip flop the offset so low E is normal and A is set back?

Also, any feedback on the design? Is it something already used a lot to have the curves reversed on the headstock / Fretboard and the end of the bridge? I searched on google / bing images and didn’t see anything exactly like it. There is only so much you can do with the design until it starts to look gaudy. :)

Image

Image

Brad


Sent from my iPhone using Tapatalk
Author:  Mark Mc [ Sun Mar 18, 2018 1:47 pm ]
Post subject:  Re: Bridge design
Make sure you draw out the path that each string is going to take from the nut to its tuner post. Will they have a big angle to bend at the nut (more friction and strings sticking or breaking), and will there be crowding. I always appreciate a headstock design that gives a straight pull across the nut. At the bridge end, have you drawn in the full amount of slope that the saddle needs to do for compensation? Your saddle looks a bit slanted, but maybe not as much as I would have expected? But it is hard to tell from these pics. The staggered pins idea looks nice, to me. It has the advantage of more room for your fingers when changing strings, and less chance of cracking along the line of the pins. Disadvantage will be varying break angle of the strings, which might look a bit messy, and the whole bridge size needs to be bigger.
Author:  bcombs510 [ Sun Mar 18, 2018 2:33 pm ]
Post subject:  Re: Bridge design
It might be the skew of the pic, the slot is for standard compensation.

The footprint is based off the design info in the Gore book. It’s 160x30. Is the footprint too small for a typical steel string?

Good point about the string angle with the offset pins. I hadn’t considered that.

Brad


Sent from my iPhone using Tapatalk
Author:  Alan Carruth [ Sun Mar 18, 2018 2:47 pm ]
Post subject:  Re: Bridge design
The footprint is not too small, but I would not go smaller, either. The early Martin 'bar' or 'pyramid' bridges were about that size, and they had problems with them coming up. That's why they went to the 'belly' bridge: the added depth from front to back reduces the maximum stress on the glue line at the back edge, and helps keep the bridge down. Mario Proulx maintains that they had that problem because they 'toothed' the under surface of the bridge (which they certainly did). This actually reduces the strength of the glue joint. Makes sense.

I like to run the pin hole line parallel to the saddle. It helps keep the pins off the same grain line, and avoids the problem of too sharp a break angle over the saddle on the low E, which adds a lot of splitting stress on the saddle slot. It also helps avoid the issue of the double wound part of the low E coming up over the saddle top as the bridge plate wears.
Author:  Terence Kennedy [ Sun Mar 18, 2018 7:44 pm ]
Post subject:  Re: Bridge design
+1 for pin holes being parallel to the saddle slot for all the reasons mentioned.
Author:  bcombs510 [ Sun Mar 18, 2018 9:31 pm ]
Post subject:  Re: Bridge design
Thanks, all.

I’m not necessarily looking to change the hole pattern, but was curious if doing the alternating hole pattern was just asking for trouble. :)

As I mentioned, I’m following the design recommendations in the Gore book. The bridge weight was recommended in the 20 - 30 grams range. So far I cannot get this one below 36.

The specs:

160x30mm. The wings come in 35mm from the edge and are 3mm thick. The height is .360 with a target of .350 after final sanding and radiusing the bottom.

Perhaps the targets in the Gore book include the saddle slot already being cut? I would think a 3/32 wide slot would maybe take enough out to put it close to or below 30.

Below is a barrage of pics showing the weight at various stages.

Drilled and routed to the template:
Image

Wings cut in to 30mm:
Image

Countersunk holes:
Image

Wings brought in to 35mm:
Image

Soften the back edge:
Image

Brad




Sent from my iPhone using Tapatalk
Author:  Joe Beaver [ Sun Mar 18, 2018 9:50 pm ]
Post subject:  Re: Bridge design
If that is Ebony, or even worse, African Blackwood, getting it anywhere close to 30g will take a lot of shaving.

My recommendation is if you want a light bridge? Start with a light wood. Then you will be able to hit your goal without sacrificing footprint.
Author:  bcombs510 [ Sun Mar 18, 2018 9:55 pm ]
Post subject:  Re: Bridge design
Joe Beaver wrote:
If that is Ebony, or even worse, African Blackwood, getting it anywhere close to 30g will take a lot of shaving.

My recommendation is if you want a light bridge? Start with a light wood. Then you will be able to hit your goal without sacrificing footprint.


Yep, it’s ebony.

Perhaps I’ll just go with what I have!

Thanks, Joe.

Brad


Sent from my iPhone using Tapatalk
Author:  Joe Beaver [ Sun Mar 18, 2018 11:25 pm ]
Post subject:  Re: Bridge design
I would. 36g bridges work well for me.
Author:  Pmaj7 [ Sun Mar 18, 2018 11:32 pm ]
Post subject:  Re: Bridge design
Looks like you've got a lot of room to bring the wings in more. Probably 1/8" on either side of the saddle. And if you haven't arched the top of the bridge yet that will push the wings out further too.
Author:  Casey Cochran [ Mon Mar 19, 2018 9:33 am ]
Post subject:  Re: Bridge design
The bass strings have a few more pounds of tension, so if you have any problems with lifting perhaps you could flip your footprint to have more material on the rear edge of the bridge on the bass side.
Author:  bcombs510 [ Mon Mar 19, 2018 9:53 am ]
Post subject:  Re: Bridge design
Casey Cochran wrote:
The bass strings have a few more pounds of tension, so if you have any problems with lifting perhaps you could flip your footprint to have more material on the rear edge of the bridge on the bass side.


That's a good idea, I may go that route as well.

I literally lost sleep over this last night. I'm considering adding a belly to the bridge. I'm going to be putting the bridge on with 315g hide glue.

I have this idea that titebond will creep and is therefore more forgiving where hide, if it's going to come off, it's going to go flying. Is that at all true? Or will hide glued bridges also slowly lift and give an indication of needing a repair before it flings across the room?
Author:  Alan Carruth [ Mon Mar 19, 2018 11:37 am ]
Post subject:  Re: Bridge design
Taper the thickness back from the saddle.

Titebond creeps less than some other glues of the same sort, and should not pose a problem in that sense if you glue the bridge on properly, with a thin glue line. The more elastic nature of it is actually a problem in contrast to the more brittle hide glue. Once the hide glue joint starts to fracture it does tend to keep going, and the bridge is thus more likely to fly off and kill the cat. With Titebond the tougher glue line means it's more likely to tear out wood from the top. It's easier to keep the cat away from the face of the guitar than to fix a torn up top.
Author:  jac68984 [ Mon Mar 19, 2018 11:51 am ]
Post subject:  Re: Bridge design
bcombs510 wrote:
Casey Cochran wrote:
The bass strings have a few more pounds of tension, so if you have any problems with lifting perhaps you could flip your footprint to have more material on the rear edge of the bridge on the bass side.


That's a good idea, I may go that route as well.

I literally lost sleep over this last night. I'm considering adding a belly to the bridge. I'm going to be putting the bridge on with 315g hide glue.

I have this idea that titebond will creep and is therefore more forgiving where hide, if it's going to come off, it's going to go flying. Is that at all true? Or will hide glued bridges also slowly lift and give an indication of needing a repair before it flings across the room?


Pin-through bridges (excluding Greenfield-like pin-less bridges) attached with hide glue don’t “go flying” when they let go. The pins will continue to hold the force. I once had a 12 string come back to me after the owner left the guitar in a very hot car on a very humid Missouri day. The owner was complaining the action was extremely high. When I received the guitar, the action was indeed very high. The bridge had lifted to the point only a very small (maybe 1/4 in. at best) portion of the front of the bridge was still glued down. The twelve string was still tuned to pitch, and only 6 pins were present (two strings per pin). It had been that way for weeks. Wish I had taken pictures, but of course I didn’t.

That said, you are correct about Titebond’s and other similar glue’s susceptibility to cold creep.


Sent from my iPhone using Tapatalk Pro
Author:  Terence Kennedy [ Mon Mar 19, 2018 12:05 pm ]
Post subject:  Re: Bridge design
Consider arching the top as well, if you make it a little asymmetric like Martin you will have a constant amount of saddle showing and combined with pins parallel to the saddle slot have a more constant break angle. Might save a little weight as well.

Try Brazilian for your bridges sometime, it might surprise you tone wise.
Author:  Freeman [ Mon Mar 19, 2018 2:46 pm ]
Post subject:  Re: Bridge design
I have never bothered to weigh my bridges (i wouldn't know what a good weight was) but inspired by this thread I threw the commercial Martin style ebony belly bridge that I'm using on my current build on a scale. It is6 inches wide, 1-3/8 deep and weighs 35 grams. It could easily have the belly thinned if I wanted it lighter. Don't know why yours are so heavy.

Second, I don't know how much faith you put in the importance of break angle from the saddle to the bridge plate. Obviously with your staggered holes you'll need to do a lot of slotting and ramping to get whatever you decide you want. I build 12 string guitars and it is always tricky to get an acute angle on the back row of pins (there is also some discussion within 12 string circles about which strings you want to have the lesser break angle). I did a little experiment one time and it seems like the strings with lower break angle have less volume - you may want to consider this in your design.
Author:  Alan Carruth [ Tue Mar 20, 2018 11:59 am ]
Post subject:  Re: Bridge design
The testing I've done indicates that break angle is not as important as it's often cracked up to be. I set up a Classical guitar such that I could alter the way the strings tied off at the bridge and change the break angle without changing out the saddle. With the 'normal' 11mm string height off the top the two different string ties gave break angles of 25* and ~6*. I then made a taller saddle, which put the strings 18mm off the top (don't try this at home!) and restored the 25* break angle.

I made very careful recordings of identical mechanical plucks of the open strings, and put together 'synthetic strums' of the three cases. These were played back in random pairs through headphones to listeners, who were asked if the two strums sounded 'the same' or 'different'. For the 'low string' setup cases with different break angles they were guessing. When either of those was compared with the strings raised higher off the top they heard it every time.

The recordings were also analyzed for rise and fall time, maximum amplitude, and harmonic content. Overall there was no difference in the total power output in any case, and the two 'low' setup cases with the different break angles were indistinguishable. The 'high' setup had more energy in the second partials of the notes, and more in a high frequency 'compression wave' tone, both of which act by rocking the bridge: the strings being higher off the top had more leverage. Note that there was no more power output with the higher setup: what was effected was the mix of partials. That's what people were hearing.

I'll note that the plucker I used activates the strings so that they vibrate 'perpendicular' to the plane of the top. Normal plucks have some crosswise component to the string motion, which could cause the strings to roll on the saddle top if the break angle is too low. In real life 6* probably would not be enough break angle, but I think 12* would.

There is no particular reason to expect steel strings to act any differently in this respect than nylon, that I can think of. It's a lot of work to do one of these experiments, and It would be hard to make the time to repeat it with steel strings.

I'll note that break angle does seem to be important in the workings of an under saddle transducer: piezo elements seem to like as much static own load as they can get. That's the only benefit I can see to having more than 'enough' break angle. The greater the break angle the more tipping force there is on the top of the saddle, trying to break out the front of the bridge slot. This can be greatly mitigated by cutting the slot with a back angle. When the saddle bisects the break angle there is no net tipping force, but anything helps. That's how fiddles get by with those tall skinny bridges.
Author:  bcombs510 [ Tue Mar 20, 2018 1:01 pm ]
Post subject:  Re: Bridge design
I noticed that the Isbell signature Martin has a pyramid bridge and the pins are at the same angle as the saddle. I like the look although I didn't think I would like the pins on a slant like that.

https://downhomeguitars.com/wp-content/ ... 00x800.jpg

I'm leaning toward making the whole bridge a little wider (34 mm maybe) and then getting more agressive with the wings to shave the weight. The bridge above has wings that go almost all the way to the saddle, same as Pat recommended.

Thanks for the feedback, Alan. It's fascinating to read.
Author:  Colin North [ Tue Mar 20, 2018 1:12 pm ]
Post subject:  Re: Bridge design
I usually get quite aggressive with the wings.
When the top of the bridge is flat I route the slot the full length of the saddle to the edges of the flat top. Then radiusing the top extends it just enough beyond for me.
Author:  bcombs510 [ Sat Mar 24, 2018 9:50 pm ]
Post subject:  Re: Bridge design
So I decided to heed the advice of the experienced...

I increased the footprint to 160x34 and put the pins on a slant to match the saddle. It’s over 30 grams but after final sanding and putting a radius on the bottom I might be right at it.

I could probably take the wings in a little further too, now that the radius is on the top.

Image


Sent from my iPhone using Tapatalk
Author:  Alan Carruth [ Sun Mar 25, 2018 10:17 am ]
Post subject:  Re: Bridge design
Keep in mind that the 'ideal' bridge weight is, as with much else on the guitar, a moving target. Thirty one grams might be just what you need.

The basic function of the bridge is to tell the string how long it is, so it will know what note to make. It does this by presenting the string with a large impedance mismatch; the effective mass and stiffness combination of the bridge and top is larger than that of the string. This causes the wave traveling down the string from the pluck to reflect from saddle, only passing some energy on to the top to produce sound. You're looking for a balance here: too much reflection and you don't get any power, too little and you lose sustain.

Impedance is sort of a tricky concept. Technically it's the ratio of force over velocity at the driving point at a given frequency: it's a measure of how hard it is to drive something with an alternating force. Impedance is low at a resonant frequency: that's almost a definition. It's easy to drive the low A string at 110 Hz, and multiples of that, and hard at other frequencies. Strings are simple structures, and the resonance and impedance are relatively easy to calculate if you have the math skill. Guitar tops are 'way more complicated, and very difficult to compute. It's usually easier just to build the thing and check it out.

There are three variables in the impedance equation; mass, stiffness (or tension in a string), and loss (resistance). Losses always add to impedance. Mass has very little effect on impedance at low frequencies, and the effect rises as the frequency goes up. Stiffness adds a lot to impedance at low frequencies, and the effect declines as you go up in pitch. Either mass or stiffness impedance can go negative at some frequencies. 'Resonance' is the frequency where the mass and stiffness effects cancel out, leaving you with only the loss term.

This becomes clearer if you think of a string vibrating in it's fundamental mode: it makes one 'hump' that curves up or down in the middle from fixed end points. When the string is at it's highest an lowest points the velocity is zero, and all of the energy is stored at tension, which is a little higher than it was when the string was at rest. When the string reaches the mid-point of the vibration, so that it's straight from the nut to the saddle, the tension is back to the minimum, but it's moving fast, so the energy is stored as the momentum of the string's mass. All you'd need to do to keep it going would be to feed in enough energy to replace what's lost to friction within the string, and from the string to the air.

So, you can get the necessary impedance in the bridge to define the string length either from mass or from stiffness. Making the top stiff at the bridge, say by using 'tapered' bracing or a thick top, means that you can reduce the bridge mass and still have enough impedance to get decent sustain. Stiffness moves the resonant pitch, the lowest impedance of the top, up, so the string energy will tend to 'leak' out into the top better at high frequencies: the treble is enhanced. If you use 'scalloped' bracing you might well need that 31 gram bridge to avoid having the impedance of the top go too low at the 'top' or 'air' resonant pitches, usually around G on the lo E for the 'air' and the open G string for the 'top'. The low G resonance is the common 'guitar wolf'. The energy from the string gets 'dumped' into the top so fast that the note is twice as powerful for half as long. Because of the way your hearing works, you notice the lack of sustain but not the extra volume. The remedy is to use added mass at the bridge to make up for the relatively low stiffness and get the impedance back up.

In short, the bridge mass has to be seen as one piece of the system puzzle. Different makers balance things in different ways, and get different sounds. If you're going for that Martin 'thump' then scalloped bracing and a heavy ebony bridge is the place to start. When the goal is a more 'responsive' fingerstyle instrument with more treble, you might move to tapered bracing and a lighter bar bridge. You can even mix and match, but that's riskier.

Sorry for the long post. Hope this helps.
Author:  Colin North [ Sun Mar 25, 2018 12:00 pm ]
Post subject:  Re: Bridge design
bcombs510 wrote:
So I decided to heed the advice of the experienced...

I increased the footprint to 160x34 and put the pins on a slant to match the saddle. It’s over 30 grams but after final sanding and putting a radius on the bottom I might be right at it.

I could probably take the wings in a little further too, now that the radius is on the top.

Image


Sent from my iPhone using Tapatalk

If you taper the back of the bridge you could probably lose at least another 3-4 grammes if you want too..
I normally do this after gluing now to make clamping/cauls easier.
Page 1 of 1 All times are UTC - 5 hours
Powered by phpBB® Forum Software © phpBB Group
http://www.phpbb.com/