Bridge design question

[Mike Sandor]

I have a couple of questions regarding the bridge design I am using on my acoustic builds.
1. If the saddle slot is angled towards the rear, say 4 degrees, should the pins follow suite? Is 4 degrees enough? I believe I read here that some use upwards of 8 degrees.
2. If it is advisable to have them the same, would it not be easier to do the machining of the saddle slot and the pin holes on one plane and get the angle by machining the bottom of the entire bridge?
3. Does the distance from the saddle to the pins stay the same for all strings, or is this dimension altered string to string to change the angle of the string over the saddle?
The reason for these questions are that I am making fixtures to build these on a cnc router, and the cutting sequence will dictated fixture design.
Thanks, Mike

[Rodger Knox]

I believe the saddle should have between 4° and 8° tilt back (ideally just a little less than half the break angle), but the pins don't need to be tilted.
Question two goes away.
Three is a personal choice, all the same distance, all the same break angle, straight line, curved line, they all work as long as there's enough break angle (about 10°)

[Alan Carruth]

I've been using a nine degree back tilt on the saddle. Rick Turner came up with this: it's something like half the break angle, which should come close to eliminating the tipping force on the saddle top that splits out bridge fronts. It's also just enough so that the added length when you raise the saddle height is just enough to correct the string compensation without your having to check it. Smart guy...

[Joel Nowland]

I think the bridge pin hole being tilted can give better rap around contact between guitar string and bridge and perhaps better energy transfer.

The more concentration on elements that produce more energy transfer form the strings, to bridge,to guitar top the better. If small details actually help or not can sometimes be difficult to determine.

Joel Nowland

[Barry Daniels]

From an engineering perspective, a tilted saddle makes sense, but bridge pins don't really gain from this approach. The forces at the pin are all concentrated on the ball end being anchored under the bridge plate and tilting the pins does not change this in the least.

[Mario Proulx]

But from a practical perspective....

I set my bridge pins back at about the same as the saddle(8°) to lessen the (strings')break angle, which the angled-back saddle increased.

In other words, if you do nothing else to your bridge design and decide to set the saddle at an 8° angle, the pins will be much closer to the saddle than they were previously. To rectify, you can move the pins further back, or angle them.

[Barry Daniels]

I agree with you, Mario.

[Joel Nowland]

Mario

I respectfully disagree with the idea that the forces are all concentrated at the ball end. It depends on how your bridge is designed.

Using unslotted pins is important and if your bridge holes and string slots are made in such a way that the strings are making firm contact with the bridge pin shaft and the wood of the bridge the string can and should, "from an engineering perspective," transfer energy all the way from bridge plate and ball end to the top of the bridge and then of course to the saddle.

Each string slot is cut with a special nut file/saw to match the string diameter. The unslotted bridge pins make contact with the string along the length of the pin shaft firmly anchoring each string from ball end to the top of the bridge.

Joel

[Alan Carruth]

Joel Knowland wrote:
"I respectfully disagree with the idea that the forces are all concentrated at the ball end. It depends on how your bridge is designed."

I can't for the life of me see where you got that out of Mario's post above. Maybe it's from something he said in some other thread?

What I saw in Mario's post made perfect sense. Assuming for the moment you drill the pin holes a certain distance back from the saddle slot, if the saddle is angled back, then the top of the saddle is a little closer to the pin holes than it would have been had the slot been vertical. Moving the saddle top back increases the break angle, so you need to move the pins back to reduce that. One way of doing that would be to angle the pin holes back, if you're drilling them up from the bottom of the bridge so that the locator is at the bridge bottom rather than the top.

Anyway, the bridge pins are toggles: they will effectively hold the strings in place even if they're somewhat loose in their holes because the ball end will push back against the front of the pin and wedge it in place. The loads on a pin bridge and bridge plate seem to be fairly complicated; far more so than on the tie bridge of a Classical, and I suspect that there's a lot of variation in the way the loads are taken up depending on some of the details. I'm not at all convinced that pins 'transmit sound' in any useful way; if the string vibration doesn't stop at the top of the saddle you've got a problem, as far as I can see.

That's the function of the break angle: to see that the end of the string is in reasonably firm contact with the saddle top. So long as that's the case all of the force generated by the string vibration should be transmitted to the saddle and the bridge. More than 'enough' break angle (and I think that six degrees is probably 'enough') won't transmit more force or produce more sound.

That said, more than the minimum break angle does two things:
1) it puts more tipping force on the top of the saddle, UNLESS the saddle is back angled so that it bisects the break angle.
2) it does subtly alter the loading on the top (not increase, alter). I was surprised to see this in the experiments I did (on a Classical with a tie bridge), but it seems real enough. It's a small effect, and does not seem to alter the sound of the instrument very much: nobody could hear a change in break angle if the string height off the top was not altered. This assumes that in altering the break angle you have not changed the height of the strings off the top.

In sum, then, increasing the break angle beyond the minimum does nothing to help the guitar, and may hurt it. Why do it?

[Jeff Highland]

In sum, then, increasing the break angle beyond the minimum does nothing to help the guitar, and may hurt it. Why do it?

Only to give you some margin for future saddle lowering

I agree, too much is a bad idea and the typical Martin arrangement is excessive

[Joel Nowland]

Alan

I don't know why I wrote Mario's name.

I was commenting on Barry Daniels post where he wrote, " a tilted saddle makes sense, but bridge pins don't really gain from this approach."

I am in the middle of a batch of four guitars and at the same time machining a batch of 36 truss rods and just took a brief pause to read a few posts on the MIMF.

Sorry!

[Barry Daniels]

Joel, my opinion on the tilting issue being somewhat moot to bridge pins is that since they are tapered, a tilt is not as relevant. Also, since the string is anchored by the ball pulling against the bottom of the bridge plate, a tilted pin does not gain much. A non-tilted pin is not more likely to pull out under its own accord. Also, if you ramp your string slot with a round-over, then a tilted pin is rather meaningless. There really is nothing wrong with tilting a pin, but I don't think there is much to gain either. Just my opinion.

[Phil Walsh]

Where the heck have I been? This is the first I've heard of angling the saddle slot. How do you cut it?

[Alan Carruth]

I use my drill press as a stand in for a milling machine to rout the slot. I just stick a nine degree wedge to the table with double stick tape, and proceed normally. If you're routing the slot in a bridge that's already on the guitar then the wedge goes under the router.