I can't explain this

[Dave W]

I was asked privately about how the minimum string height of the Hipshot 2-point bridge compared to the original nylon saddle 2-point (evertilt) on my EB-0. So I measured relief and string height above the fretboard, reinstalled the original 2-point, and measured that. String heights were the same with both bridges, but the relief increased with the original, from .010 to .017". Exact same strings (LaBella 43-104 DTB flats), exact same tuning. How could that be? Reinstalled the Hipshot, relief went back to where it was. I can't figure it out.

[Basvarken]

Did it tilt?

[Pilgrim]

Tilt or break angle, possibly.

[Dave W]

It didn't tilt, I used the same shim under it that I used when I bought it. Tilt, break angle, saddle height, length of string beyond the saddles etc. affect the feel of the string. IIRC the word for that is compliance. None of that affects the number of pounds of string tension. Only the string itself, the pitch it's tuned to, and the scale length can affect the actual tension, but none of that changed in this case. Since the actual tension didn't change, I can't figure out why the relief changed.

[Basvarken]

When you took off the strings, did you touch the trussrod? Or did you leave it untouched?
If you did not loosen it, the neck may have gotten an up-bow. If you put strings on it may be necessary to loosen it before you put tension on the strings. So you start with a hollow neck. And then you bring back the trussrod tension to straighten it back.

[Dave W]

No, I didn't touch the truss rod.

Keeping in mind how the slothead tuners work, removing the Hipshot didn't even unwind the strings. Also, the ball end anchors on the Hipshot are farther away from the headstock than with the evertilt. I just unscrewed the Hipshot's two studs, screwed in the evertilt studs down to the flange, dropped the bridge over the unthreaded top portion, hooked the strings into the ball end anchors (didn't need to unwind them more because of the shorter distance), stuck the shim underneath and tuned to pitch. Took all of about 4 minutes.

[uwe]

I can only (attempt to) theorize it with the higher angle the evertilt must have had - not necessarily visibly. If the strings pull at a higher angle at the headstock, that creates more relief - I would think! (Just imagine what a string pull at a 90 degree angle - i.e. with strings not nearly parallel to the fretboard, but projecting away from the bass at a right angle - would do to a neck!)

"Evertilt affects relief." A new finding. I never trusted those darn things in the first place.

[Basvarken]

No, I didn't touch the truss rod.

Keeping in mind how the slothead tuners work, removing the Hipshot didn't even unwind the strings. Also, the ball end anchors on the Hipshot are farther away from the headstock than with the evertilt. I just unscrewed the Hipshot's two studs, screwed in the evertilt studs down to the flange, dropped the bridge over the unthreaded top portion, hooked the strings into the ball end anchors (didn't need to unwind them more because of the shorter distance), stuck the shim underneath and tuned to pitch. Took all of about 4 minutes.

Okay so you didn't touch the trussrod. But obviously the string tension wasn't there when you took the Hipshot bridge away, since there was no bridge to hold on to.
At that point the trussrod was still working against a temporarily non-existant string pull. Giving the neck an upward bow.
You put strings back on, but did not put the neck back to dead straight (by loosening the truss rod).
I can imagine that maybe the neck stayed in the upward bow, even when the strings were hooked to the replacing bridge and brought back to pitch.

[Dave W]

Okay so you didn't touch the trussrod. But obviously the string tension wasn't there when you took the Hipshot bridge away, since there was no bridge to hold on to.
At that point the trussrod was still working against a temporarily non-existant string pull. Giving the neck an upward bow.
You put strings back on, but did not put the neck back to dead straight (by loosening the truss rod).
I can imagine that maybe the neck stayed in the upward bow, even when the strings were hooked to the replacing bridge and brought back to pitch.

In theory, that's possible. In my case, though, the relief immediately reverted to .010" as soon as I reinstalled the Hipshot.

I can only (attempt to) theorize it with the higher angle the evertilt must have had - not necessarily visibly. If the strings pull at a higher angle at the headstock, that creates more relief - I would think! (Just imagine what a string pull at a 90 degree angle - i.e. with strings not nearly parallel to the fretboard, but projecting away from the bass at a right angle - would do to a neck!)

"Evertilt affects relief." A new finding. I never trusted those darn things in the first place.

I'm shocked to hear that you never trusted them.    But you must be right. The bridge must be what affected the relief. I just don't understand how.

[Basvarken]

Were the saddles of the two bridges set at exactly the same height? (By means of the bridge posts?)

[uwe]

The string pull is the same irrespective of bridge, but is the resistance of the neck to that pull the same irrespective from which direction or from which angle the strings exert their pull? 

[slinkp]

Basvarken's theory sounds plausible to me. Angle would definitely matter. But this would be a very small difference in angle!  The question would be, is it enough to explain the difference in relief?  .... I have no idea!

[Granny Gremlin]

No, I didn't touch the truss rod.

Keeping in mind how the slothead tuners work, removing the Hipshot didn't even unwind the strings. Also, the ball end anchors on the Hipshot are farther away from the headstock than with the evertilt. I just unscrewed the Hipshot's two studs, screwed in the evertilt studs down to the flange, dropped the bridge over the unthreaded top portion, hooked the strings into the ball end anchors (didn't need to unwind them more because of the shorter distance), stuck the shim underneath and tuned to pitch. Took all of about 4 minutes.

I think you just disproved your own thesis that the length of string beyond both nut anmd saddles has no affect on overall tension.

Either that or what Rob said, but I've taken string off and put back before without haveing to do that (all hardware same) and not had a change in action so I dunno; maybe one of them things that can happen but not always.

[Dave W]

Were the saddles of the two bridges set at exactly the same height? (By means of the bridge posts?)

Yes.

The string pull is the same irrespective of bridge, but is the resistance of the neck to that pull the same irrespective from which direction or from which angle the strings exert their pull? 

I'm beginning to think not.

Basvarken's theory sounds plausible to me. Angle would definitely matter. But this would be a very small difference in angle!  The question would be, is it enough to explain the difference in relief?  .... I have no idea!

Angle and direction of force matter in how the strings feel. They don't affect the scale length, and tension on the neck is determined by the scale length, the pitch, and the weight of the string. In my case, nothing changed, yet relief was different.

I think you just disproved your own thesis that the length of string beyond both nut anmd saddles has no affect on overall tension.

Either that or what Rob said, but I've taken string off and put back before without haveing to do that (all hardware same) and not had a change in action so I dunno; maybe one of them things that can happen but not always.

It's not my thesis, it's well-established physics. For example, see pages 4 and 5 of the D'addario family tension chart (.pdf) for an explanation. What I can't explain is how the relief changed when the tension didn't.