Official Luthiers Forum!

I am not sure who all I am in agreement with here, but I think Todd stated it best - the two drawings are in fact identical as far as the top, fingerboard plane, and bridge are concerned. All you have to do is rotate the bottom drawing up a bit so that the top to sides glue line is horizontal in both drawings - the tops are then identical in their layout. Assuming a straight line is drawn between the two blocks, the centre or highest point of the top is exactly halfway between, unless you sanded it weird !!! Changing scales or fret joint moves stuff a little but not enough to worry about, at least not when I build.

the discussion way back on the MIMF had lots of folks is a tizzy .. because mainly until someone establishes a frame of reference, someone can say almost anything, and in a certain context, its true. One guy said the peak of a domed top can be at the tail block .. well sure it can .. all you have to do is drop the headstock to the floor and then see, the tail is the highest point !!! But take the same guitar and point it to the sky and the neck block is the highest point .. am I not right ????

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

If I was standing on the highest point of something like a big spherical pitcher's mound, and it was build on level ground, then I'd be in the center. If it was on a slope the downhill edge of the mound would be farther from me than the uphill.

I'm going to assume that the dome of the top is close enough to a true sphere so as not to matter. To maintain that dome you have to dress off the edge of the rim to match. If you take the saqme amount of wood off the neck and tail blocks, then the high point of the dome will be in the center of the length of the guitar: you've built a mound on a level field. If you remove more wood from the tail block than the neck block (assuming the top edge was 'flat' to bgin with), you've tilted the dome down toward the tail, building on a slope, and the high point will be moved toward the uphill side, nearer the neck.

Note the situation with the backs of most guitars. The back is domed, too, but most guitars taper toward the neck. What's the highest point? Often it's near the tailblock, and the back and side come close to making a right anlge at that point. Not so on the other end, where the combination of the taper and dome make the back slope upward from the side as the guitar is held top down on the bench.

I like to move the high point of the dome up a bit, so that the bridge is sitting on the backside of the slope relative to the neck. Seems more stable to me.

I must disagree somewhat Alan - if the top rim prior to putting the top on is level, then the peak of the dome is halfway between the outer edges of the blocks - agreed. Now if, as you state, you sand the tail block more than the neck block, you have a downward slope between the blocks - thats true, but simply bring the new plane you have established back to level, put on the top, and the peak is exactly the same as the other one, in the centre. What you have done though, is changed the angle of the sides to the level plane from 90 degrees to some other angle, which in this case is now greater than 90 - its all relative.

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

Tony you are correct. I was setting here going something is wrong in my drawing then I realised the tops arc cord is not at zero in the X axis it was a copy rotate error. Simple geometry and I missed it.

Brain fart

If the guitar was rotated so that the top cord was true zero angle

Bad miss for an engineer

What is worse is I build this error into my sanding fixture for this guitar .088" dropMichaelP39071.7512731481

Micheal I am laughing to myself as I post .. I was looking at your first drawing going, wait a second something is wrong here, thats not possible, and was trying to see how and why you got the two numbers you did between the blocks for the peak - then I saw it - the arc in dwg 1 is not truly level, it is stepped .. and then you reposted !!!

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

[QUOTE=TonyKarol] I must disagree somewhat Alan - if the top rim prior to putting the top on is level, then the peak of the dome is halfway between the outer edges of the blocks - agreed. Now if, as you state, you sand the tail block more than the neck block, you have a downward slope between the blocks - thats true, but simply bring the new plane you have established back to level, put on the top, and the peak is exactly the same as the other one, in the centre. What you have done though, is changed the angle of the sides to the level plane from 90 degrees to some other angle, which in this case is now greater than 90 - its all relative.

[/QUOTE]

That's what I was trying to say.

Now, take a look at Charles Fox's Ergo guitars for an example of an elevated fretboard design that does shift the "peak" of the top, in relation to the plane of the fretboard, way back toward the tail block -- maybe even off the butt end of the guitar entirely. In Al's terms, the pitcher's mound is on sloped ground (again, in relation to the plane of the strings); there's a "negative" neck angle. On these guitars, the sides are perpendicular to the back (not really perpendicular, because the back is domed, too, but you know what I mean) rather than to the top.

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Todd Rose
Ithaca, NY

https://www.dreamingrosesecobnb.com/todds-art-music

https://www.facebook.com/ToddRoseGuitars/

You have no Idea how dumb I felt yesterday. I am supposed to be a geometric whiz well this layout whizzed right by me for almost a year MichaelP39072.5107638889

Tony Carol wrote:
" but simply bring the new plane you have established back to level, put on the top, and the peak is exactly the same as the other one, in the centre. "

*sigh*

If your aunt had you-know-whats, she'd be your uncle.

Ok, so what's _your_ reference plane? I start out with the top edge of the sides straight before bending them. After bending, the top edge of the sides should sit flat on the bench top. Turn the guitar over, and that's what I call 'level'. Removing more wood from the tail block than the head block slopes the top down toward the tail, and moves the high point of the dome up toward the neck.

Yes, of course there's a problem with what reference you use: the only flat surface on the whole thing is the headstock. Maybe we should refer all of our measurements to that? ;)

Ah - But you havent put the guitar with the lowered tail block back down on the level bench (your initial reference plane) - you have changed it, so of course the peak is in a different spot. Think about where the fretboard planes of those guitars would be - are they the same plane - no they are not. The comparison is meaningless.

Using your reference - the level bench top between the blocks, every single guitar with a 28ft (or any other) radius, now matter how you sand the blocks, has a peak in the centre just like Michaels drawing. Its mathematically impossible to be anywhere else.

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

WAY BACK WHEN, most flattops were, indeed FLAT TOPS (without string tension load). When "doming" or arching the top braces started to evolve, there were several thoughts as to why.
First, the arched top braces put some pre-load (think drum skins) on the top and that induced different tap tones (pitches) to a braced top. Varied control of these factors produced new tonal characteristics, often resulting in a "signature" sound for a luthier. Next, there was the concept that the arched top had more give and take to help accommodate the movements caused by changes in humidity. We all know that a straight,
flat-across-the-top instrument has no where to shrink to when humidity drops. The arched top can settle back quite a bit before reaching the cracking point.
Then there is "top collapse", generally seen between the bridge and the soundhole. By arching the top, at or near the X brace intersection, you now have your bridge, under string tension, trying to rotate into a slight uphill slope. To get to a point of collapse, the bridge would have to induce enough force to first overcome the resistance in the arch (dome) and then to actually deform the top and brace structure into a negative aspect between the bridge and soundhole.

I build with a very slight arch, trying to incorporate both the characteristics of a "floppier" flat top along with a bit of the structural advantages mentioned above.

Since I have done all this using the cubic furlong per fortnight system of measurement, your mileage may vary.

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Hank Mauel

Michael, if you have the rim of the top level, (x=0)then a simple line drawn parallel to the rim and tangent to the arch of the top will give you the location of the apex.

To me, the whole question is moot because I don't make my top spherical. My rim is flat for the top.

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"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Well Mark (Tripp), as you can see, there is no consensus on where anything is ... except we all agree the strings usually go on top (not Fred Carlson !!!)

you will just have to build your guitar your way, and somehow figure it all out for yourself, cause I have given up on this one ...

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Tony Karol
www.karol-guitars.com
"let my passion .. fulfill yours"

    I am reading all the posts and to be honest , I use the center of the guitar. That is where the "peak" is for me.
   With the braces radiused to match the top rim radius ,for me 28 foot I do the radius to fall at the center of the top. THe fact is that the radius will in fact change constantly to the humidity conditions.
    The radius is there to allow movement through these changes so the tops to crack . As humidity levels drop the wood gives off moisture and the top radius actually lowers.
    The position of the peak is not as important as that you do have the radiusing. This has given me consistent results for building , so where you decide to make your "peak" the important thing is to choose a spot and keep it there.
    One benifit I feel I have from this is that the center is forward to the bridge , the center is where the most change occurs from humidity changes. My bridge is behind that so the amount of movement is less there in relation to the center and while I do see some changes in the top in relation to the humidity changes it isn't as much as where the center does.
   Hope you all have a great holiday.