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Hello luthiers,

I know this topic has been discussed many times but I screwed this up on my last build and I want to make sure I get it right this time. So I'm trying to figure out what should be the optimal clearance above the saddle slot. Right now I have 3/64 inches (1.2 mm).

Thanks
Dominic

For me, I like my unfretted board to be coplanar with the top of the bridge. So my value for how much gap as shown in your photo after fretting would be however high my frets are which sometimes differs. 1.2mm sounds about right or reasonable, and some people like to have even a bit more backset to accommodate the top pulling up under string tension.

So IMO I think you’re good but let’s hear what some other folks have to say…

Nice clean work!

What's the height of the bridge?

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

The bridge is 11/32 inches/8.7 mm high.

I ignore the bridge height and go by how high I want the strings above the surface of the soundboard (since that's what determines torque on the bridge). Fret plane projection 2-2.5mm below the target string height. That accounts for about 0.8mm (1/32") pull-up under tension.

So your current projection of 9.9mm should give around 12mm string height, with a little over 1/8" saddle stick-up. Personally I'd aim another half millimeter higher, but it's fine as-is.

You need to know how much your neck attachment system moves under tension and settles after 8-12 months. If quite a bit you’ll need more initial clearance over the bridge.

You can duplicate string tension to some degree by supporting the headstock and adding about 12 lbs of weight to the upper bout. I like the straightedge to clear the bridge by a 32nd or so under tension on my guitars.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Hi,

Same topic, different guitar. The guitar is finished, I'm ready to glue the bridge. However, the clearance over the saddle slot is 2 mm and the bridge is 9.5 mm, which I think is too high. I really hope I don't have to do a neck reset so I'm considering making a thicker bridge. Any thoughts?

Support the headstock and add 12lbs of weight to the upper bout and see where the straightedge falls.
It’ll actually come up a little more with string tension as the top bulges.

Conversely if you have a similar guitar completed you can measure the gap with and without string tension to get an idea of how much movement to expect.

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It's not what you don't know that hurts you, it's what you do know that's wrong.

Without going to the workshop and loading up the guitar here's my take on that.
Forget messing with the bridge height, string height at the bridge is what counts (torque).
9.5 + 2 = 11.7 mm FB plane projection at the bridge.
If you add average action as say 1.8 @12th fret, gives an increase of 3.6 mm at the bridge, add say, 0.3 mm for effect of relief and ~0.7 mm for soundboard pull-up, gives a total of 16.3 mm string height at the bridge. or 0.64 inches.
I aim for, a fingerpicker, 13 mm, less for bluegrass/strummer.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

@Colin North So you think I should do a neck reset?

If my calculations are correct, and double check them, that increases the torque at the bridge by ~25%, bridge rotation by a similar amount, and (I'm told) will choke off the response of the guitar. (never actually tried it, but don't want to)
(edit) I think the relief will actually lower the saddle height for then same action ( )
Even that would make the saddle height 15.7 mm, making it 2.7 mm higher (20%) than I would like to see it at a maximum depending on what style of playing it's intended for.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

I find it easiest to do this check earlier, when setting the neck angle, before gluing the fret board to the neck.
Basically for a 6 mm fret board thickness, I look for the plane of the top of the neck to be (about) 1/8" or 3 - 3.5 mm above the soundboard (use a 3-3.5 mm drill bit under the straight edge)
FB + fret height = 7 mm, so the top of fret lane projects 10 - 10.5 mm above sound board, add 3.6 (2 x average action) gives a string height above soundboard 13.6 to 14.1 mm above soundboard, this allows for "top pull-up" and a smidgen back down for relief.
Makes life a lot simpler

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

So 11.5mm over the surface of the soundboard? That should be 13.5-14mm string height by my numbers. At most 10% over the standard 1/2". I'd say string 'er up and adjust later if the bridge rotation is over 2°.


I think your pull-up compensation is in the wrong direction. When the bridge comes up, you have to shave the saddle down to get the action back where you want.

All this talk about bridge height. Bridges vary in thickness. Saddle slots' depth vary. Both depend on the person who made the bridge. I've found it makes more sense for me to choose the height of the strings over the fingerboard first and work backwards from there, having taken my best SWAG.

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Peter Havriluk

It's not a minus in front of the pull-up compensation, its "~" (approximately).
AS I edited in my later post, the relief adjustment was wrong, it should have been a minus.

_________________
The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

Of course me too and that's what I did. And I don't understand where things went wrong. I did the finishing and didn't touch it for 6 weeks. I keep the workshop around 45% humidity but I wonder if the top or the neck could have moved during this time.