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Action and string height at bridge. (again)
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=54555		 Page 1 of 1
Author:  Dave Higham [ Fri Nov 19, 2021 11:39 am ]
Post subject:  Action and string height at bridge. (again)
I have looked at various threads and found various opinions, but, in general, this is what I’ve found.
I’ve read that a good figure for the bridge thickness is 3/8” (9.5mm) and that one should put a straight edge on the neck, touching the frets, and the straight edge should clear the bridge by about 0.031” (0.8mm). For good action this should give a saddle height of about 0.125” (3.2mm).
But recommended action (clearance between strings and 12th fret) is around 0.080” (2mm) for the top ‘e’ string and 0.100” (2.5mm) for the bottom E. This gives a saddle height of:-
(2 x 0.080) + 0.031 = 0.191” (4.85mm) for the top ‘e’ and
(2 x 0.100) + 0.031 = 0.231” (5.87mm) for the bottom E.
That’s a lot more than 0.125”. It also means that the height of the strings over the soundboard is between 14.37mm and 15.35mm which is apparently more than people aim for.
Any opinions?
Author:  Jim Watts [ Fri Nov 19, 2021 12:06 pm ]
Post subject:  Re: Action and string height at bridge. (again)
Dave,
your saddle won't be that tall. The guitar tries to fold in half under tension. Your assumption is that nothing moves.
Author:  Dave Higham [ Fri Nov 19, 2021 12:27 pm ]
Post subject:  Re: Action and string height at bridge. (again)
Jim Watts wrote:
Dave,
your saddle won't be that tall. The guitar tries to fold in half under tension. Your assumption is that nothing moves.


Yes Jim, that's true of course.
So that means that you only find out what height the saddle needs to be when you've strung it up.
Which would be a nuisance, except that I didn't metion that it's not really a problem for me as I'm making an adjustable neck so I can tilt it to suit.
I suppose what I'd really like to know is what's considered to be an ideal height for the strings above the soundboard at the bridge, which can't be fixed of course, because the fingerboard is radiused so the saddle has to be too.
Author:  johnparchem [ Fri Nov 19, 2021 12:30 pm ]
Post subject:  Re: Action and string height at bridge. (again)
Just like James says the guitar bends, I always assume 1 mm at the saddle with calculating. If I took your 14.37mm and 15.35mm number I would project 13.37 mm and 14.35 mm. My target for a steel string is 14 mm, so I would be happy.
Author:  Barry Daniels [ Fri Nov 19, 2021 3:03 pm ]
Post subject:  Re: Action and string height at bridge. (again)
I think you action measurements are too high. I like about .050" on high e and .070" on low E.
Author:  Clay S. [ Fri Nov 19, 2021 9:52 pm ]
Post subject:  Re: Action and string height at bridge. (again)
On the smaller bodied guitars I build I like the string height above the top to be 7/16ths, with a bridge thickness of 5/16ths. For larger bodied guitars I prefer to have the strings an 1/2 inch above the soundboard at the bridge. A 16th inch higher or lower I can deal with, but not much more than that starting out.
Author:  Woodie G [ Sat Nov 20, 2021 6:50 am ]
Post subject:  Re: Action and string height at bridge. (again)
0.500" string height at bridge with 0.150" saddle height/0.350" bridge thickness on most acoustics, although for 0 and smaller, we found something closer to 0.525" drove the top with more authority. On vintage resets, we reduced this height over top where there were concerns over the ability of the bridge/saddle to handle the saddle height which would generate the desired geometry.

Body deformation and that (hopefully!) 0.004"-0.005" or so of relief will cause a 1/32"-1/16" reduction in string height over the top...about half to 3/4 of that within a short period of time after string-up and the rest over the next 3-6 months. On new guitars, if we saw .515" - .520" after adjusting to 0.100"/0.070" (E2/E4), we could be certain of things settling to 1/2" by the first 'well guitar' checkup.

For resets, different rules apply because there will be permanent body deformation which will not be shrugged off by the instrument with destringing, and in the case of the excessive neck relief commonly seen in guitars built without neck reinforcement or square neck reinforcement bars (later 1960's Martins to 1984/85 start of one-way Gotoh adjustable truss rod use), that needs to be taken into account.

So now that only vinyl record enthusiasts and the semi-elderly understand what "...not to sound like a broken record..." refers to, I'll just repeat myself until others become physically ill: it's worth investing the time in going beyond Rule of Thumb saddle height and understanding the arithmetic. Getting action at the 12th and bridge thickness/saddle height right with related ability to measure in any configuration between bare neck/bare top to assembled/fretted is worth the time. I've published the relevant diagram with neck/fretboard/fret top, and string plane and body distortion relationship often enough that it can be found here in numerous action/setup/neck setting threads. Understand that diagram and you'll understand the arithmetic.
Author:  Dave Higham [ Sat Nov 20, 2021 8:03 am ]
Post subject:  Re: Action and string height at bridge. (again)
Thanks again for your input John, Barry, Clay and Woodie.
I've never seen your diagram Woodie, but I have had periods of absence from this forum in the last 16 years. I do generally understand what you're getting at as I've spent my life measuring and calculating. I've drawn up all the instruments I've made in CAD because that was my job, but that hasn't stopped me from making mistakes when taking a tool to a piece of wood.
But hey! Are you accusing me of being semi-elderly because I know what a broken record sounds like? I'll have you know I'll only be 80 next birthday. Yeah, OK, I'm a fully paid-up grumpy elderly fart. ;)
Author:  Barry Daniels [ Sat Nov 20, 2021 10:23 am ]
Post subject:  Re: Action and string height at bridge. (again)
I have Woodie's chart hanging right over my workbench as reference.
Author:  DennisK [ Sat Nov 20, 2021 4:10 pm ]
Post subject:  Re: Action and string height at bridge. (again)
Barry Daniels wrote:
I have Woodie's chart hanging right over my workbench as reference.

Is this the one? http://www.luthiersforum.com/forum/viewtopic.php?p=712194#p712194
Author:  Woodie G [ Sun Nov 21, 2021 5:34 am ]
Post subject:  Re: Action and string height at bridge. (again)
Yes... intended to make the adds and subtracts a bit easier to account for on a neck setting job.

The other tool we had in the shop which complemented that sketch was a Harbor Freight digital dial gauge mounted on a piece of aluminum sheet stock using the StewMac mount. A shop-made mount would work as well for the dial gauge, and would not be difficult to fabricate from scrap brass, aluminum, phenolic, or an engineered plastic like Delrin capable of holding threaded fasteners such as the set screws used to attach mount to body of tool.

With one edge of the tool body relieved so that the points of contact occur at 1st and 12th fret locations, the dial gauge gives a third point of contact to measure distance from top (or top of bridge, top of saddle) to any of the reference planes. When zeroed reference a flat surface, the dial gauge gives a direct reading of distance at the measuring point above or below the reference plane.

Let me see if I have a photo of that tool - will post if so.

Edited:

Attachment:
Neckset_Tools_01.jpg


Attachment:
Neckset_Tools-02.jpg


The long and short scale tool body is shown installed, with the additional tool body we used for Size 5 and octave mandolin work. The vertically oriented shot shows what I believe is an earlier version of the tool (the yellow, grad'ed rule) - I never used this, as it required more coordination that I possessed to juggle tool, 6" ruler, and the instrument. The dial gauge version was zeroed prior to every use session and provided an unambiguous reading of the difference between reference plane and the measured point (negative measurement are below the reference plane and positive above). We had a jointer outfeed table that was handy for calibrating the dial gauge prior to use, but a straight edge of sufficient length would work as well.

I do not recall that we ever produced measured drawings of the tool body design, but not difficult to lay out if distance from 1st to 12th fret for the scale length is known, and distance from 12th to the center of the saddle slot (1/2 scale length plus saddle compensation on centerline or desired point of measurement).

Finally, I am sure that someone, somewhere makes this tool and sells it... just too handy not to have demand such that it is available for purchase.
Author:  Mike OMelia [ Tue Nov 23, 2021 10:57 am ]
Post subject:  Re: Action and string height at bridge. (again)
My absolute go-to for setup: http://thbecker.net/guitar_playing/guit ... ge_01.html

For neck resets: https://hazeguitars.com/blog/neck-reset ... we-measure
Author:  Mike OMelia [ Tue Nov 23, 2021 11:03 am ]
Post subject:  Re: Action and string height at bridge. (again)
Barry Daniels wrote:
I think you action measurements are too high. I like about .050" on high e and .070" on low E.



That is impressive. I never can get that low. What playing style? (strum/finger). And what string gage? Me, 0.07 high e, 0.1 low e
Author:  Barry Daniels [ Tue Nov 23, 2021 11:12 am ]
Post subject:  Re: Action and string height at bridge. (again)
The majority of the guitars I work on are for finger pickers using light gauge strings. A low action depends upon the frets being well leveled with a bit of fall away. Also, my Teeter string tension compensation jig usually helps to get a lower, buzz free action. Some people that have me work on their guitars have to adjust to playing a guitar with a low action.
Author:  SteveSmith [ Tue Nov 23, 2021 11:26 am ]
Post subject:  Re: Action and string height at bridge. (again)
I do about what Barry does fingerpickers with light gauge strings. I use very little relief on the hi E but only after I have leveled the frets. For strummers with medium gauge and very good pick control, again after I level the frets, also very little relief and about .063 hi E and .085 lo E. I'll note that I put in a bit of additional relief on the bass side when I do the fret level.
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