angle of the neck at the heel

[buckhorn]

having several dozen mandolins under my belt, i have grown comfortable with the Siminoff design and used his plans fathfully...i try to hold the neck angle at the heel at between 5 degrees and 7...this has been a challenge at times to maintain a consistent height at the bridge...a few times i have had to adjust the bridge up or down to the extreme...now, what i really hope for is to be reasonably consistant with the height of the strings at the bridge....the neck angle as well as the height of the arch of the top plate must be kept the same to keep the height the same....NOW,i have built several necks for another builder that requested the heel angle to be between 2 degrees ... but this also changed the length between the fretboard and the bottom of the heel... if not, the height at the bridge would be way too low...MY question is...what do the majority of you builders preferr ; a higher angle with a shorter heel length or a longer heel length and a lesser angle....the longer heel length makes the fretboard higher at the top plate to clear ....would this help with being consistant ?....would it change the tone or sound ?...i would appreciate any imput as to which way to go...........thanks, keith

[sunburst]

I went through a similar process, trying for consistent bridge heights while it seemed like the same math led to different results each time. I settled on a fairly low overstand (the height of the neck above the top) and a relatively low bridge. That gives me a similar string breakover angle at the bridge as if I used a tall bridge and a high overstand. As for sound, I don't hear any difference between my taller bridges and lower bridges outside of normal variation.
One of the reasons I like the overstand lower is weight. If the heel of the neck (heavy maple) is shorter, it is lighter. When I'm cutting out a neck blank, I cut the heel at about a 6 degree angle, and when I set the neck in the body it almost always changes slightly one way or the other. I gave up trying for any mathematical consistency all the way through the process of making and installing the neck for a consistent bridge height. I like to vary the height of my top arch for different pieces of wood and for tweeks to the sound, so trying to establish a consistent neck angle is difficult if not impossible for me. I use a gauge to check the projected height of the fingerboard surface of the neck at the bridge position of the top as I'm setting the neck. That gives me a fairly consistent bridge height, but for whatever reason, that measurement has varied from about 3/8" to 1/2" over time. I changed fingerboard thickness, so that explains part of it, but the rest of the variability in that height remains a mystery to me. I generally like for my bridges to be between 3/4" and 7/8" high measured at the center of the bridge.

[Dick Hutchings]

I like to vary the height of my top arch for different pieces of wood

John, you have mentioned this in at least one other thread I've read. I don't understand how or when you make that call. It seems it would be too late to make much of a change after most of the carving is done so I'm guessing you can tell or just know at the wedge stage. Is that correct?

Sorry for the hijack kterry, but I've been wondering about this for a while.

[Dick Hutchings]

having several dozen mandolins under my belt, i have grown comfortable with the Siminoff design and used his plans fathfully...i try to hold the neck angle at the heel at between 5 degrees and 7...this has been a challenge at times to maintain a consistent height at the bridge...a few times i have had to adjust the bridge up or down to the extreme...now, what i really hope for is to be reasonably consistant with the height of the strings at the bridge....the neck angle as well as the height of the arch of the top plate must be kept the same to keep the height the same....NOW,i have built several necks for another builder that requested the heel angle to be between 2 degrees ... but this also changed the length between the fretboard and the bottom of the heel... if not, the height at the bridge would be way too low...MY question is...what do the majority of you builders preferr ; a higher angle with a shorter heel length or a longer heel length and a lesser angle....the longer heel length makes the fretboard higher at the top plate to clear ....would this help with being consistant ?....would it change the tone or sound ?...i would appreciate any imput as to which way to go...........thanks, keith

I have a friend who uses the Siminoff joint and he has the same problem. Part of it lies in the fact that the alignment can't be checked while it's in the gluing fixture. Seems to me the fixture should take care of what ever height you want by making the bridge in it that height and not worry at all about the angle. It is what it is. When I make a dovetail joint I start with a certain angle but quickly abandon it to get the height I want which is more important.

[sunburst]

...It seems it would be too late to make much of a change after most of the carving is done so I'm guessing you can tell or just know at the wedge stage. Is that correct?

Partly, I've got a bunch of wood from the same sources so I have a good idea what I'm working with. Basically, stiffer top, lower arch, looser top higher arch. When I have the top rough-carved I can start to flex the piece and if it is stiffer than I expected I can decide to carve more off of the top and still have plenty of wood to graduate to my chosen thicknesses. In other words, when the center is still 7mm or 8mm thick I can still remove wood from either side but it is thin enough to flex and judge the stiffness. I generally only vary the height within 2mm, I've never gone under 14mm and I never go over 16mm. Most of the red spruce that I have likes to be closer to 14mm or 15mm. Also, if a customer wants bright trebles or deeper chop chords I feel like I have a little more control over that by varying the arch height along with wood selection, so I may start out planning for a higher or lower arch.

[Lefty Luthier]

I prefer the dovetail joint over the Siminoff for a variety of reasons including those stated above plus the fact that the dowel pins prevent the neck from being easily removed in the future. I cut the dovetail angle at 5 1/2 degrees and use a fixture to set the bridge height to 7/8 inch after attaching the top to the rim but before attaching the back. Seems to give pretty consistent results. I start with a arched fretboard center thickness of 0.28 and make minor adjustments to the bridge height by removing thickness.

[buckhorn]

It's been my understanding that the higher the bridge is above the top plate, the more pressure is placed on that top plate...and also, you get a louder sound to go along with it....I have had a couple of mandolins that I've either had to shave the bottom of the bridge to get low enough or make an entirely new bottom to get it high enough...it would be sweet if you could count on a consistant bridge height right out of the box....but ,how I jest.........so what John is telling me is the only thing that's consistant is the non-consistancy..(is that a word)....i guess we are all working for that same sound time after time from a build that is the same time after time...still, what is everyones' thought -overstand or under with hight..........thanks , keith

[sunburst]

It's been my understanding that the higher the bridge is above the top plate, the more pressure is placed on that top plate...and also, you get a louder sound to go along with it...

I've decided there isn't much to that, and in fact I don't think it's true at all. More string break-over angle does put more downward pressure on the top, but depending on other things (like arch height and overstand height), different bridge heights can result in the same break-over angle on different mandolins. Also, the downward force of the strings is a static force, whereas string vibration is a dynamic force and is mostly independent of static forces. I think too much downward static force on the bridge damps the top too much and it's better to have less of it, within reason of coarse, the bridge needs to stay put, after all.

[kkmm]

According to the law of physics, there should be more downward pressure on the top if the saddle is higher, althought the increase is pretty small as the saddle can only be higher by a few mm.

[sunburst]

According to the law of physics, there should be more downward pressure on the top if the saddle is higher...

How can a higher bridge saddle apply more downward pressure unless the string break-over angle is more acute?

[Joshua Vest]

Let me, if you dont mind, put in a different "way to look at it". After studying mandolins, and many years of repairing them and building and consulting with builders and consumers and players of all levels, I find a common similarity- over analyzing. Yes the mandolin is one of the most complex acoustic intsruments out there and getting the "math" right can be mind boggling but there are certain aspects of it that really dont have to be. Most try to over think this drastically. One thing that can really help is to lessen the matter of thinking in "degrees" as a measurement (thats for engineers, we are luthiers and builders). I have set and reset literally hundreds of necks on all variations of instruments, archtop and flat top, and on both the same thing holds true just requires a different measurement number. Lets use a more common and simpler measurement- the inch, and the fractions of. For starters every neck reset, which is really no different from the first neck set, by most of us is done by hand. Even the big "production" mandolins are at some point hand fit (most guitars too) The joint may start from jigs, fixtures or CNC machines but the final is by hand. For the moment lets not focus on the height of the carve on the top, the amount of rise under the fingerboard extensions, the "actual" angle the neck comes into the body at, fingerboard thickness, and string break angle- or amount. When in the final stages of fit, one of the best things you can do is get out a straight edge and a 6" ruler. Clamp the neck in at the edges leaving a clear path down the center of the fingerboard. Place the straight edge down the center from the nut area out over the body past the point where the bridge should place. At the point where the center of the bridge should be (by scale measurement) place the 6" ruler to measure the distance between the top and the straight edge, what would be considered a "perfect" angle would measure 3/4 of an inch. Some of us will use 13/16 just for a little extra room and a real solid break angle behind the bridge. (this commonly adds a little extra "pop" to the instrument). If your low or high to that measurement, carve you heal the appropriate direction to achieve it. I can tell you from experience 7/8 is typically to high and 5/8 is typically to low, there are problems that can come from both. This WILL work no matter the height of your top carve, fingerboard thickness, extension risers ect. All those items are a completely different consideration to the outcome of the instrument and can be adressed if need be. Just to note. these measurements should be made after the fingerboard is on the neck, or atleast clamped on with the center line being left open for a straight edge to run. Seriously try this, youll be suprised on the outcome and it will give you a consistent bridge height as long as the bridges are consistent. Obviously you need to make sure the neck is in straight and without side to side tilt (bass to treble being level). If curios a few people that live by this and spent/ spend their careers using this method, Jackie Miller (Gibson) David Harvey (Gibson) Joshua Vest (Gibson, Big joes Guitar Works) and Charlie Derrington. Simplify it, no need to over complicate.

[Stanley Cox]

My thanks to all that have responded to this thread. Any pics of the "gauge" or
"fixture" you use to set the bridge height? I know MacRostie shows one in his
video. A lot of good info in this thread.

Stanley

[fscotte]

Simply moving the bridge back or forward an 1/8" or so will yield different break angles, so you can get an idea how the sound may change without screwing with string height. Towards the tailpiece, more break angle, more down pressure. Away from the tailpiece, less break angle, less down pressure.

My opinion is that ideal break angle will vary with every instrument.

[sunburst]

Any pics of the "gauge" or
"fixture" you use to set the bridge height?

No, because I make it again each time. It is simply a 6" rule taped to an 18" straight edge/rule at the 13 7/8" mark, extending down 1/2", more or less, depending upon the bridge height I want.

Well, OK, I'll set it up and snap a pic. Back in a minute...

[sunburst]

Here's the "gauge", a 6" rule taped (with masking tape) to the 18" straight edge, and here it is in place on this mandolin as I used it to set the neck.
(Well, OK, back in 11 minutes...)

[Stanley Cox]

John, Thanks for taking the time for the pics. Are you saying that the bridge
height might change from instrument to instrument?

Stanley

[fscotte]

To maintain consistent break angle, then the bridge height will always be different heights. There's too many variable involved for it to be consistently the same height - arch height, neck angle, neck depth, distance of bridge to tailpiece... to name a few.

[sunburst]

Are you saying that the bridge
height might change from instrument to instrument?

In the picture the "gauge" is set for a little under 1/2" for this mandolin. When I started doing the neck set this way, about 3/8" gave me a good bridge height, but my bridges started to be lower on subsequent mandolins, so I started going up on the "gauge" measurement, first to 7/16", then gradually up to 1/2"just to maintain the same bridge height. At one point, I started using thinner fingerboards, so that would account for a little less than .050" of the change, but I don't know what caused the rest of it. Now, I generally have pretty consistent bridge heights doing it this way, but a few years ago I had one mandolin with an inexplicably taller bridge than usual, though I set the neck this same way.
So, yes, I'm saying that the bridge height could change from instrument to instrument... but it might not. I don't know what caused mine to change, so I don't know if yours will, and if they do, I don't know why.

[HoGo]

To maintain consistent break angle, then the bridge height will always be different heights. There's too many variable involved for it to be consistently the same height - arch height, neck angle, neck depth, distance of bridge to tailpiece... to name a few.

I'd say you can easily have consistent bridge height BECAUSE you have so many variables. Actually you need to control only three of them. Arch height, heel height above rim (riser height -just hair under 1/2" for "correct looks") and neck projection at the bridge position (just like John, I use 12mm box of pencil leads as gauge).
The projection plus f/b thickness (I use approx. 5mm+) plus fret height (~1.5mm) plus 1/8" for typical action will give you bridge height (~7/8") regardless of the other two variables. I don't measure angle, I know the angle on my Drawings is typical 5.5degree and If I use higher arching than on plans, I'd add almost the same amount to the riser if i really want to get consistent break angle over bridge, but the differences are probably rather minimal unless you really change the angle drastically (I wouldn't claim anything without making identical mandolins with just that angle changed) compared to other aspects of building. Thre's quite large margin for acceptable error in the neck set.
I once got higher bridge than usually and it was because I used too much clamp pressure to hold neck in place during gluing and the angle changed a bit. I didn't notice anything really different in the sound of that mandolin versus others.

[buckhorn]

thanks John for the pic of the gauge....i have one very simular to yours but my way of building is much different than most...i cut a straight dovetail joint into the rim before the top and back plates are glued up....i then lay the gauge across the neck starting at the nut and hope that other end rests on the tailblock at the proper offset height....then i lay a straight edge from the headblock to the tailblock and measure the height from the bottom of the straight edge to the bottom of the gauge at the center of the body ...hopefully that measurement would equil the original thickness of the top (about 5/8in) plus the height of the bridge (about 5/8in) and another 1/4in for fretboard thickness plus string height.....all of that should be the about the height at the break angle at the strings....my problem is there are just too many variables...and by the time i get this far along there is just no changing a wrong measurement , short of resetting the neck....if the angles are off then the bridge is high or low to the extreme....maybe i should change my build sequence and glue the top plate on first and go from there...holding the right neck angle has become even more important...........keith