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Distance Off The Top At The Saddle
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=50747		 Page 1 of 2
Author:  Jules [ Mon Jun 18, 2018 7:24 pm ]
Post subject:  Distance Off The Top At The Saddle
When placing a straight edge on a neck w/o the fretboard, what is the measurement from the bottom of the straight edge to the top of the soundboard at the saddle - or end of the scale?

The O'Brien video says 3.5mm but I'm wondering what the thickness of the saddles he uses are. Is 3.5mm pretty standard?
Author:  John Arnold [ Mon Jun 18, 2018 7:47 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
I use 3mm. That works out to a string height at the bridge of 1/2". The bridge thickness I use is 0.360", which leaves a maximum saddle height of 0.140". Fingerboard thickness is 0.225".
Author:  Bri [ Mon Jun 18, 2018 8:27 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
John, is that .225 at the centre of a 16” radius? Same for the saddle, .140 at the centre, assuming a radius on the saddle?
I don’t think I have seen mentioned a minimum saddle height.
Thanks
B
Author:  Jules [ Mon Jun 18, 2018 9:01 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
John Arnold wrote:
I use 3mm. That works out to a string height at the bridge of 1/2". The bridge thickness I use is 0.360", which leaves a maximum saddle height of 0.140". Fingerboard thickness is 0.225".

Thank you, John.
Author:  Freeman [ Mon Jun 18, 2018 9:13 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
The way I do it is to clamp the actual radiused fretboard to the neck, stack a couple of business cards at the first and last fret (unless its been fretted), put the bridge that I'm going to use in place and put a straightedge on the top of the fretboard. The end of the straightedge should just sit on the top of the bridge or be a hair above it.

That works for any fretboard thickness, any bridge height and any top configuration. I use it on "flat top" acoustics and archtops and slab electrics and everything in between. However I also do the final neck set after the fretboard is fretted and on the neck and the bridge is glued to the top.
Author:  DennisK [ Mon Jun 18, 2018 9:14 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
Yes, that should be good.

My magic number is fret plane projection 2-2.5mm below target string height. That takes all the neck angle/fingerboard thickness/bridge height out of the equation. All other measurements can be calculated relative to that. Subtract fretboard thickness+fret height to get bare neck projection. With typical values, 3.5mm should be about right.
Author:  Freeman [ Mon Jun 18, 2018 9:30 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
Interesting to mix metric and english measurements here. 3mm is 0.118 plus a nominal fretboard of 0.025 in the center plus 50 thousand for the frets is right at 0.375, which is the nominal height of many bridges. Add 0.125 of saddle for the high E, maybe a bit more for the low and you'll end up with action in the 70 to 90 thousands range.

Working with the actual neck, fretboard and bridge means that you don't have to calculate anything
Author:  Terence Kennedy [ Mon Jun 18, 2018 10:56 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
The big hooker is how much your neck moves under string tension and how much settling in you expect in the first six months to one year.

A double tenon bolt on may move and settle much differently than a glued dovetail and extension.

With certain neck attachment systems you may need a bigger gap to allow for the settling. Only seeing your guitars back after an interval will really give the answer.

If a straightedge just clears the bridge with no string tension on a new guitar there could be problems down the line. I think it is really important to make an effort to look at as many of your guitars as you can after they have been out in the real world a while. The owner may not have noticed a rising action or a rising extension but you will and it will impact your upper bout geometry, bracing, and neck angle on future builds.

It did for me and if you fix it the owner will be astounded at how much easier it plays.
Author:  Woodie G [ Tue Jun 19, 2018 6:21 am ]
Post subject:  Re: Distance Off The Top At The Saddle
For your 000, we would use the following calculation to determine height without fretboard:

Bare Neck Plane Height at Saddle Location = Desired string height - string height above fret plane - fret height - fretboard thickness + body distortion (top rise) + (2 x relief)

h_subs_om = 0.500" - 0.173" - 0.045" - 0.250" + 0.050" + 0.008" = 0.90" = ~2.3 mm

For a dreadnought with a 0.240" board thickness and 0.037" frets, and a bit more total body distortion factored in, the measurement would be very close to the 3mm suggested above.

h_subs_dread = 0.500" - 0.173" - 0.037" - 0.240" + 0.060" + 0.008" = 0.118" = ~3.0 mm

For a smaller body, we usually see less distortion, so the 'top rise' number varies from about 0.060" for a new dreadnaught to 0.030" for a new Size 5. On existing instruments, some portion of the body distortion remains after strings are removed, so a measurement of relief and clearance over the bridge under string tension and one without is useful to get a sense of how flexible things are.

We use a shop-made tool that measures this height at the saddle location with a digital dial gauge referenced to a selected plane defined by the two legs (at 1st and 12th fret location)...very handy for repair work as well. A photo of the gauge is shown in this thread:

http://luthiersforum.com/forum/viewtopic.php?f=10101&t=48344&hilit=neck+set
Author:  Brad Goodman [ Tue Jun 19, 2018 8:12 am ]
Post subject:  Re: Distance Off The Top At The Saddle
Terence Kennedy wrote:
The big hooker is how much your neck moves under string tension and how much settling in you expect in the first six months to one year.

A double tenon bolt on may move and settle much differently than a glued dovetail and extension.

With certain neck attachment systems you may need a bigger gap to allow for the settling. Only seeing your guitars back after an interval will really give the answer.

If a straightedge just clears the bridge with no string tension on a new guitar there could be problems down the line. I think it is really important to make an effort to look at as many of your guitars as you can after they have been out in the real world a while. The owner may not have noticed a rising action or a rising extension but you will and it will impact your upper bout geometry, bracing, and neck angle on future builds.

It did for me and if you fix it the owner will be astounded at how much easier it plays.


This is sage advice....

The other wild card that I would like to add to this is to factor in how much the top rises up (bellies) under string tension.

(I also make the Stella style 12 strings with the tailpiece-so on these you have to think in reverse, since the top is being pushed down.....)

Depending on how heavy/light you build the bracing, top thickness and species will play a role in this.

My experience (with the way I build) over 100 instruments has been that I need to have the straight edge higher than the bridge for all this to work out.

I also like a little more saddle height for better break angle than was mentioned in a previous post.
Author:  Jules [ Tue Jun 19, 2018 9:11 am ]
Post subject:  Re: Distance Off The Top At The Saddle
Thank you for all the information. Now I'll try to put that to work.

As things stand right now, the numbers are:
Distance off the top at the end of the scale w/o FB - .07"
Distance off the top at the end of the scale w/ FB - .31"
FB thickness - .24"
Bridge thickness - .377"

Materials on hand:
Two fret wires - .048" at the crown, the other is .053"
SM rosewood bridge with .09 wide slot
Micarta saddle .145" wide x .468 high
Micarta nut .273" w x .439" h

The neck is a bolt-on using barrel nuts and KD bolts. This is my first acoustic. I have no idea how things will change once under string tension.

Based on the numbers, I'll have to work on the neck set to raise the height at the saddle. But I have some questions.

1) Once you get close, is it better to keep working on the neck set or sand down the back of the bridge?
2) Does it matter how thick the saddle material is? Right now I can either widen the slot on the bridge or thin the saddle.
3) How much of a fudge factor is there at the bridge?
4) How much does the saddle typically rise above the bridge at the center?

Sorry to ask for all this information but I don't have an acoustic here to measure from nor do I know anyone who has one.
Author:  mountain whimsy [ Tue Jun 19, 2018 9:35 am ]
Post subject:  Re: Distance Off The Top At The Saddle
Great info here. Especially the top rise. My first OM used the low end of O'brien's 3 to 4 mm number. I braced it pretty lightly. Now, 6 years down the line I've dropped my saddle about as far as possible to compensate for the belly rise. I wish I had added a little more room to work with. 3.5 to 4 mm would have been better for that instrument. I've been using 3.5 mm pretty consistently now with good results.
Author:  Freeman [ Tue Jun 19, 2018 10:21 am ]
Post subject:  Re: Distance Off The Top At The Saddle
Since I have stopped making dovetails unless it is absolutely necessary (archtops) and as long as I don't glue the f/b extension down at first I can completely assemble the guitar, string it up, play it for a few months and then reset the angle if necessary. It usually isn't.

To answer your questions

1) I tape the bridge in place while I'm doing the preliminary set. Once it curves to fit the top I don't lower it any more. Once it is glued on I can't lower it any more. I've been brought up to think that a certain amount of bridge is desirable so I don't go below that.
2) Typically saddles are either 3/32 or 1/8 wide. It is advantageous to use standard thickness saddles just from availability. A wider saddle allows you more material for compensation, however most people are able to adequately compensate a 3/32 saddle. If you have already routed the slot is its difficult to accurately increase the size and the saddle should fit snugly
3) How much fudge factor.......? Most acoustic players are not as anal about intonation as electric players, as a setup guy I'm probably more anal than they are. Remember that a whole series of Martin guitars had their saddle slots in the wrong place and many people didn't seem to notice. I heard that audiologists say the average person can't detect 5 cents of difference.......
4) How much does the saddle rise above the bridge? A good rule of thumb for proper neck angle is IF you have acceptable action AND you have at least 1/8 inch of saddle sticking out of the slot THEN you neck angle is OK. Many people feel that if you 1/16 or less you are badly in need of a neck reset. I find that if the straightedge is just sitting on top of the bridge I can get the action I like (0.060 to 0.090) with 1/8 or slightly more, that seems to give me good future adjustability.
Author:  Jules [ Tue Jun 19, 2018 12:18 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
Thank you for answering my questions, Freeman. Much appreciated.

I was just working on putting a little more angle in the neck when I decided to check what angle I should shoot for. I found a thin piece of wood .134" (3.44mm) that would put me in the ballpark. When I went to measure the angle I noticed the radius in the top, from the neck to the soundhole, put the straight edge .23" from the top at the bridge. At that height, the angle measured about 1.5 degrees. Stew Mac says the angle should be 1.5 degrees but that puts the height at the bridge at .23". idunno
Author:  Freeman [ Tue Jun 19, 2018 3:00 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
Julie, you are probably getting really tired of hear "how I do it" and how I do is probably very different from a lot of other folks. But this is how...

I build the body with whatever dome it ends up with. I have a 20 foot radius dish, I shape the braces and build in that. With all the things that happen in shop I'm happy when the box is closed to have a nice dome.

When I start building the neck I know that the angle should be one or one and a half degrees (can you really measure a half a degree and cut to it?). I know that on a Lester or archtop its 3-1/2 or 4 degrees. I cut the heel at that angle when I'm making the tenon (or dovetail on the few that I still do that way). I make or buy a bridge - my standard there is 3/8 thick and I shape the back of the bridge to fit the top. I make or buy a fretboard, radius it the way I want it.

Then I put it all together and look at the geometry. I don't measure anything, I just look at it. I look at the way the f/b sits on the top and I look at the end of the 24 inch straightedge relative to the bridge. A measurement doesn't mean diddly poop - the geometry does. I haven't done a lot of these but I have learned that every time I have the straightedge on top of the bridge the guitar comes out just fine. I'll work on the heel cheeks with chisels and implements of distruction unlit the straightedge is where I want it, then floss the heel to make it fit as perfect as I can. I'll futz and worry and fiddle with the area under the f/b until I have the minimum drop off, but I also know that a little is OK.

Then I'll fret the board, glue it on the neck, check the angle again and floss if I need to, shoot some paint at it and check the angle again.... Put it together but I don't glue the f/b down, glue the bridge on (I do it after the neck is finally positioned to minimize the intonation shift. Make a nut and saddle and pins and things, put strings on and check that angle again. Eventually I'll take it apart, maybe make a minor floss but its usually not necessary and lightly glue the f/b extension down. My oldest guitar is 12 now, its neck angle is perfect as are all the others that followed.

There was a big techie article in AL a while back about calculating neck angle on an acoustic guitar. I'm an engineer, I took one look at it and said "the only reason someone would write an article like that was to put it in a magazine, there was nothing there that would help me set a neck"

If I was in a production situation, making lots of little bodies and lots of little necks and trying to get each one the same then these measurements would be very useful. Fo me its one guitar at a time, understand the geometry and work until I get there.

Image

Image

Image

fwiw - that is a ladder braced 12 string. As Brad says, you have the opposite problem, the vertical string vector wants to push the top down. But the geometry works the same. And it works the same on a carved top Les Paul or a flat top Tele or a jazz archtop.
Author:  Haans [ Tue Jun 19, 2018 5:07 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
The way Freeman shows it in the first photograph is the way I've always aimed for it in the past.
Author:  Woodie G [ Tue Jun 19, 2018 6:00 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
The value to using a neck angle methodology based on actual measurements of components and desired final values for string height, etc. is that the general formula is good for both new work or repairs, or for any of the planes of interest, including bare neck, fretboard, fret top plane, and string plane...as well as developing an understanding of neck geometry. One tool can do the work of several go/no-go gauges, and handles both new instruments and repair work such as resets.

For the OP's OM with 0.048 crown frets and a 0.240" fretboard, target numbers are:

Bare neck:

h_subs_om_bare = 0.500" - 0.173" - 0.048" - 0.240" + 0.050" + 0.008" = 0.097" = ~2.5 mm

With fretboard in place (leave out the fretboard term):

h_subs_om_fretboard = 0.500" - 0.173" - 0.048" + 0.050" + 0.008" = 0.337" = ~8.6 mm

With frets in place (leave out fret and fretboard terms):

h_subs_om_frets = 0.500" - 0.173" + 0.050" + 0.008" = 0.385" = ~9.8 mm

No matter the configuration, a measurement with a shimmed straightedge (to clear body and to avoid problems with slightly convex necks) or - better yet - with a purpose built tool as shown earlier gets a usable number without too much messing about. One formula...multiple planes. The real value here is UNDERSTANDING what the elements are in the neck setting task, versus rote memorization...rules of thumb are great, but understanding why they are rules seems worth doing.

Plugging in the OP's current numbers shows that the neck plane is about 0.027" low at the saddle location (0.097" - 0.070" = 0.027"). This suggests that the heel needs to be flossed to bring the neck plane up to the desired value. An OM heel is about 3.25" deep from underside of fretboard to heel cap, and the distance from body edge to the saddle is about 11.5", so using the ratio of 3.25"/11.5" as a multiplier (hint: similar triangles), the material which needs to be removed from the heel to bring the neck into alignment is 0.283 x 0.027" = ~0.008", or about 1/128"...an easy job for P150 and some package tape on the back to make things slippery.

The other issue is fretboard extension fit...I assume that the measurements taken were with the fretboard in full contact with the top, and if the extension is dead level, a bit of fall-away would not be out of place. 0.020" of fall-away is not uncommon, and another 0.007" would save 0.025" in saddle height at the bridge, so a fair trade for what is seen on many an older Martin. If the extension shows a gap at the edge of the body at current neck angle, the adjustment will definitely help close that gap, while a gap at the end of the board with the current neck set means even more fall-away will be introduced with correction, so a wedge and or some adjustments to the extension area of the top might be needed.

On bridge height, we mill all bridges or new work to 0.0360 before radiusing of the bottom, resulting in 0.350" at the D with radius milling and a 0.150" saddle after the guitar finishes settling. We usually see 1/3 to 1/2 of the total top rise immediately at string-up, and the remainder coming in over the first few weeks. Don't be surprised if string height comes in higher at string-up than the 0.500" target...it does settle in if the geometry is correct and the estimate of total body distortion is close.
Author:  Woodie G [ Tue Jun 19, 2018 6:20 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
The reason why Mr. Keller's straightedge-on-bridge top works for a bare board is that his bridge is likely close to his fretboard plane height at saddle...as long as the bridge thickness is not too far off the calculated value, string height comes out fine.

For the OP, with her thicker bridge, using this rule of thumb would push her final string height at saddle closer to 0.540", which would be welcome on a Size 2 or Size 5, but a little higher than we like seeing for long term service with medium strings on a larger body.
Author:  Bri [ Tue Jun 19, 2018 9:00 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
Woody, can I assume that all these measurements are taken on the centreline? If I am understanding this correctly, measurements taken on the outer edges of a bare neck would be greater than stated, due to the induced dome of the top, highest point is the centre. Measurements taken with an attached FB and bridge need to take into account the radius(16”) which I determine at .050” difference in thickness center to edge. If my saddle has a height of ~.150” above bridge centreline, would that then be .100” above at E pins?
Author:  Freeman [ Tue Jun 19, 2018 9:20 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
Woodie G wrote:
The reason why Mr. Keller's straightedge-on-bridge top works for a bare board is that his bridge is likely close to his fretboard plane height at saddle...as long as the bridge thickness is not too far off the calculated value, string height comes out fine.
.


Woodie, since you like doing it with the numbers, here is my thinking. First, I assume the neck is fretted and flat, extend the fret plane to the bridge area. If the saddle were at that plane the strings would be on the frets. Now I add a bit of relief, lets say 5 thou at the 5th fret. With most boards that will be a couple of thou at the 12th. Lets put a nut in there - I like 14 to 18 thou of clearance at the first fret. Now the strings are off the board - lets just say they are 0.018 at 1, they will be half that at 12 plus the little bit of relief, I get 10 or 11 thousands. Actually they will be a bit higher because once I tension the strings I start pulling the head up and back as well as creating relief.

With the saddle at the fret plane that is the absolute bottom lowest you could ever make the saddle, in other words its bottom limit. If I start raising the saddle it will start adding to the contribution from the nut and relief - when I have, say, 0.125 of saddle the action at the 12th fret will have gone up by half that, 0.0625 plus the 0.010 already there, for a nice 0.0725.

I have collected factory setup specifications from as many brands as I can find, recommendations from luthiers and tech who I admire. No matter what units you use most of these people are in the 60 or 70 or 80 thousands range for action at the 12th fret, maybe 5/64 or 3/32 or 2 or 2.5mm - in other words I'm right in there. (I personally play with 0.060 to 0.090 inches of 12th fret action on most of my guitars - acoustic, electric, 12 string. Resos are a bit higher)

The significant part of this is that the thickness of the fretboard and bridge, the angle of the neck relative to the body and the overstand, the amount of curve or arche to the body don't matter. As long as I base my absolute lowest possible action as the fret plane hitting the top of the bridge it works. Bingo

Archtop, floating bridge about 7/8 tall

Image

ES335, the ToM is sitting on little pieces of wood that emulate the posts

Image

A Lester, again the ToM is sitting on little blocks while I set the neck

Image

Flat assed tele - you get the action with the overstand. These are easy, if the angle is wrong just throw a pick in the neck pocket and try again

Image

Tricone resonator

Image

Six string acoustic

Image
Author:  Terence Kennedy [ Tue Jun 19, 2018 10:30 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
Good stuff here. A couple of thoughts, with a bolt on you can attach the neck after fretting, tape the bridge in place, and support the headstock and add around 6 lbs of weight to each upper bout shoulder. (10-12 lbs total)

I have found this will roughly approximate the tension of light-med light strings. It won’t show top belly but that is more minor. If your straightedge still clears the bridge you should be good. If not tweak the neck angle.

I have found that if you use a bolt on with a glued extension the neck moves slightly less after gluing the extension as it acts as an additional brace so you have to think about that. I think if you have around a 1/32 gap with the straightedge under tension with the extension unglued you would be pretty safe.

Another thing I try to remember to do when fretting is to fret to around 10 and then support the. headstock and weight the body to look at the extension drop off under simulated string tension. If it is not enough I can sand some in before finishing fretting.

On repairs where a neck reset is needed, especially dovetails, I try to remember to measure where the straightedge hits the bridge under string tension and unstrung and record the difference. That gives a rough idea of how much movement to expect when resetting the neck. I think I learned that trick here. Maybe from John H or Woody.
Author:  Woodie G [ Wed Jun 20, 2018 6:49 am ]
Post subject:  Re: Distance Off The Top At The Saddle
Bri wrote:
Woody, can I assume that all these measurements are taken on the centreline? If I am understanding this correctly, measurements taken on the outer edges of a bare neck would be greater than stated, due to the induced dome of the top, highest point is the centre. Measurements taken with an attached FB and bridge need to take into account the radius(16”) which I determine at .050” difference in thickness center to edge. If my saddle has a height of ~.150” above bridge centreline, would that then be .100” above at E pins?


Using the centerline is convenient - especially for new instruments - but it does introduce some error, as the highest point on a flattop saddle is usually offset from the centerline towards the bass side - usually just outside the D string - and there is already a height differential due to the higher action set on E2 versus E4. Practically speaking, this has the effect of translating the high point of the saddle towards the bass side and rotating it a bit towards the treble side, so the OBSERVED drop in height between the highest point on the saddle - near the D string - is something like 0.030" at E2 and closer to 0.070" at E2. All this is easy to measure on a Taylor-style bridge, as the thickness is uniform and the top unradiused, while for a Martin bridge, the radiused, offset top makes this a more interesting chore.

The total error in using the centerline versus the D string line is about 0.008" for radii near 17", so we generally don't worry too much about it, although it could be included as a term in the formula. While I've been here, I have not seen a neck reset or action on a new instrument that varied from the desired target string height by more than 1/64", so the approach seems to work well.

Guilty, Mr. Keller - I do like math where it begins to explain the why of things! To better understand things like why the edge height of a radiused fretboard varies with width despite a uniform thickness at the centerline - a problem related to this discussion - it is worth playing with some of the calculators on the Liutaio Mottola Lutherie Information Website.

http://www.liutaiomottola.com/formulae/sag.htm
Author:  Freeman [ Wed Jun 20, 2018 10:27 am ]
Post subject:  Re: Distance Off The Top At The Saddle
Actually Woodie, I was going to point you and Julie to this calculator on Mottola's page.

http://www.liutaiomottola.com/formulae/bridgeHeight.htm

Also his article in the fall 2012 issue of AL, issue 111 (its probably in one of the later Red Books, I don't have the whole set). One of the terms in his equations deals with the effects of the string plane relative to a curved ("cambered") fretboard.

edit to add, I was surprised that his calculations predict a negative neck angle for classical guitars - I've only built one and as I recall the neck came out flat. But the numbers don't lie.....
Author:  Jules [ Wed Jun 20, 2018 10:58 am ]
Post subject:  Re: Distance Off The Top At The Saddle
I appreciate all the help here. My problem is I don't know what many of the abbreviations stand for and there are some terms I don't know. So even though math has always been my strong suit, I'm struggling with how to insert what into the formulae.

I'm thinking I should set the neck at 1.5 degrees and see how that goes.

There was an article in AL where a guy created a jig that would slide over the end of the guitar to accept strings. He could then slide a saddled bridge under it to find the correct bridge location. That might help me understand the relationship to all the factors in place. I learn much better watching and experimenting than reading.
Author:  Woodie G [ Wed Jun 20, 2018 2:46 pm ]
Post subject:  Re: Distance Off The Top At The Saddle
Honestly, this is an easy one.

- Put the neck in place, put a yard stick on the neck, and measure the distance above the top at the saddle location
- Somewhere around 0.090"-0.100" ought to be just fine...closer to 0.100" is better if you don't wan tto thin the bridge down to closer to 0.350"
- Its as easy to put the wrong angle on the neck as the right one, but 1.5 degrees is a good start
- Flossing the neck to correct angle and centerline alignment (well covered in the archives)
- Once fitted, clamp the fretboard in place and assess the fit of the extension...either right on or up to a gap of 0.030" at the body end of the board (fall-away) means a good fit is likely.
- Finish the neck and body
- Do final flossing to perfect the fit and assemble (finish can get on the mating surfaces of the cheeks or underside of fretboard)
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