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I like that tool a lot -- nice design

Here's the similar tool at the Martin factory -- I think she is selecting bridge thickness can't recall, note that we are only talking a few .000 variation so they do get the initial angle pretty darn close. Yes that's a capo holding the neck at the sound hole.

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Ken Cierp

http://www.kennethmichaelguitars.com/

She looks happy as a clam!!!

I see two hold-heat pots behind this nice lady. Since it's unlikely that Martin heats it's white glue.... they must use the pots for HHG and the series Martins with HHG? Ken did they mention anything about HHG use?

Regarding the tool this is what it's like working with David Collins. I never know from one day to the next when he will dream up something very useful for me to use and benefit from. It's like Christmas here year around never knowing when he will create something that makes my life easier!!

At this very moment I am using rare earth magnets attached to a teflon device that makes loose brace gluing simple enough that even a Hesh can do it... And of course the bearing surfaces are teflon so nothing sticks to them, imagine that!

It's like sharing a shop with Bill Nye the Science guy...

The HHG usage is based on series -- at least it was

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Ken Cierp

http://www.kennethmichaelguitars.com/

Another gadget useful for minor adjustments in the upper bout contour in some situations.

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

Here's Martins new simple dovetail replacement for the MT joint -- CNC machine, fit -- Bam -- done! Hesh have you seen any of these yet?

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Ken Cierp

http://www.kennethmichaelguitars.com/

Terrance I've seen that before -- what keeps it located at the bridge? Is there an adjustment to control material removal or angle?

I've always done that upper bout tweaking with a sanding block

http://kennethmichaelguitars.com/NECKSET.html

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Ken Cierp

http://www.kennethmichaelguitars.com/

It's a Charles Fox jig I learned at his course back in 2003. You just hold the pivot block at the bridge location and the 1/4" plexiglass sanding board mimics the fretboard. It's for minor tweaks only. It presupposes that you have already sanded the geometry into the rimset in the upper bout.

You can set the pivot height at whatever you want depending on the upper bout geometry you are shooting at. A typical value would be your average bridge height. I have used it mainly for fine tuning and flattening the area under the fretboard. I have been messing around with a 60' radius on the UTB (with a 30' overall top radius) and it helps level any slight dome that results from that. With the neck attachment system I've been using I like just a little drop off in the upper bout so I can use this gadget to help with that.

If you have your neck set perfect and you want the upper bout to be perfectly co planar with the neck then I think the sanding block would probably be better.

I have Trevor's books and really like his total bolt on neck with a fully supported fretboard extension which demands a perfectly coplanar upper bout. I have been using the Bourgeois design which does not integrate the fretboard tenon into he actual neck so the end of the fretboard can rise if settling of the upper bout occurs.

Trevor if you are listening, as compared to your guitars with a glued extension, do you ever have issues with head block rotation a few years out requiring a neck set tweak in your double tenon bolt ons?

Thanks

Terry

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

Short answer, no. Never. As you'll know from the books, the head block and its top plate assembly is pretty robustly engineered (Section 9.3, Build book), with the top plate of the head block butting the UTB. The next place any "folding" may happen is going to be across the sound hole. But if you look at the engineering around that (particularly on the falcate braced tops where I'm not following some traditional pattern) the sound hole braces are well sized and socket into the UTB and then overlayed with CF. "Ain't nothin' goin' nowhere".

On more traditional designs, it's still important for long term stability to fill the gap between the head block and the UTB with something solid and use decently sized bracing around the sound hole (see the pics p12-8, Build).

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Paul,
Nice guitars on your website.
Although your math might be correct. I doesn't take into account what is important to make things right.

I will try to get some time to post an exact answer.

Queston:
Do you use an extended block under your fingerboard like in a photo on your site?
What radius is your top bracing pressed into?
What radius do you sand your ribs, if any?
What is your desired bridge thickness.
What is your fingerboard thickness.
Ken

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Ken

This is kind of a Gibson thing. But I think it is a good way to prevent problems with neck angle and sinking fingerboard down the road.
G company used a flat rim that is sanded just a little at the end of the body. This mates with a 1.4 degree neck angle. The fingerboard sits on the top which is domed as a result of the bracing. This puts the top above the rim line by just a tiny amount. Some of the old G guitars are notorious for sinking above the soundhole because the bracing is very light..

In my diagram you can see the OO guitar drawn with a flat top and 28 foot radius top on the right and on the left is the same guitar with a 28 ft radius on the sides in addition to the 28 foot top.

My drawing is as if the bracing under the fingerboard is meant to be flat. No arch (dome). You will accomplish this by sinding your neck block flat and having flat braces in this area at least as far as the diagram shows.

If you raise your tail up on a block by 0.47 inch and sand to rim for the amount in the drawing, your rim will have the complimentary angle of the flat neck projection. After sanding, match your angle, body end, top surface and that will be the exact angle you should angle your neck. 180 minus 88.5 = 91.5

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Ken

Ken,

Thanks for the compliment.

1) We do NOT use and extended Martin style neck block - we use something that can be seen in the attached photo

2) We use a 25' top radius - BUT - we use a perfectly flat UTB. We initially sand braces on this mold and press the top/braces into this mold when gluing . We sand the top rims on this same dish. We then sand the flat transition area in discussion.

3) Bridge thickness is .36" to .37" BEFORE we sand it to the dome of the top

4) Fingerboard thickness is .25"

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P A U L B U R N E R
Burner Guitars

Looks clean and nice.

Ok so can you see how the math works?

You can measure your depth of arch at the bridge from your dish. Only make sure to measure the depth between the neck edge to tail edge at the bridge distance.
Add your actual bridge height 0.3 something. This is your height that the fingerboard surface should project to.

More soon

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Ken

If you sand your rims and keep the sides perpendicular, there will result a difference in in the rib height neck to tail. You can measure this in your dome also.

Draw these points on paper full sized.
Tail point, neck point, bridge height point.
Connect tail and neck point with straight line.
make a point below the neck point 0.25 (fingerboard thickness) on the perpendicular line
from your measure of depth of arch at bridge point in the dish, add the bridge thickness.
Connect point of bridge (above) with the point on the body end that is down by 0.25 inch by straight line.
where the two lines cross is where you need to sand your rims and neck block flat.
Extend this line to the tail end of the body and measure up for your body to sit on a block this thickness for sanding.

Ha ha, clear as mud?

edit, you can also make a point on your rim line that you will chose to sand flat from there up to the body end. Then connect the point at the bridge to this point to get a steeper angle. Then take your body end angle and match it to your neck heel angle (with the complimentary angles).

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Ken

Don't measure the angle of the body, but match it with a angle gauge and that will give you your neck end complimentary angle. The result of these two angles is a straight line that projects to your bridge height.

Then you can think about your fret height, saddle height and string height and alter the above geometry if necessary. In addition, you can determine if there is any spring back that might result in lowering your bridge height.

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Ken

I think this is a prime example where using multiple references has caused confusion.

If you are doing this accurately you should be pretty close to where you want to be without having to sand the 1.3 degree tilted plane as per your original post (your flat transition area mentioned immediately above). Try using a 60' or so radius on the UTB and lowering the top of the head block to suit (remember it is still domed at the dish radius, and don't touch the rims) and you should be really close. (I use a slightly smaller radius but with the centre of the brace flattened where the fretboard glues). A straight edge resting longitudinally on the upper bout should have 0.1" (2.5mm) clearance at the saddle position. Try making a dummy top to this spec, tape it on the chassis and measure things up. If it hasn't got the 0.1" clearance at the bridge position, change the curvature on the UTB until it has. Don't touch the rims. If you're close, but not exactly on target, sand the top just above the sound hole to reduce the measurement or sand the top over the rims to increase it. The upper bout should always be maintained as a flat longitudinal plane so you can glue your fretboard down flat. Get this right and repeat on future builds and your problems with this should be over for ever.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

I like Trevor's suggestion. It uses your current method and his slightly arched UTB versus a flat will help for long term stability. Depending on how strong the flat one is.

You can see from the drawing I made of the rim with an arch at 28 ft (left above), that very little sanding is necessary to get the flat slope. 0.03 max over less than 2 inches.

I still think drawing your out full size will help you.

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Ken

The last few I've done have been with a 60' radius UTB on an otherwise 25' radius top. I use a long sanding block on top of a bridge-height spacer at the bridge location to flatten the top for the fret board. It has worked very well for me.

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Steve Smith
"Music is what feelings sound like"

What a great thread. During my last build I struggled through each of the issues discussed here. As frustrating as it was at times, I would not have learned as much without first making and then correcting my mistakes. I want to apply any wisdom gained to my next build.

I have Ken's Martin Style Size "2" template and will use my Mega Mold to apply the geometry discussed in this thread. I figured I would also build and use Robert O'Brien's mortise and tenon neck angle jig to zero everything in.

I have not been successful locating plans for this guitar, but will set out on my adventure without them. If anyone knows where I can get them or similar plans that would be great. I want to make sure I radius all of my bracing properly. This thread indicates the radius of the soundboard and the curvature of the upper transverse brace is a variable I need to keep in mind if I want to achieve an appropriate neck angle. Please let me know if you sense I am still confused and asking the wrong questions.

1. Is a 25' radius for the top and a 15' radius for the back still appropriate for such a small bodied parlor guitar? If not, what would you recommend?
2. What shape/radius should I use for the upper transverse brace so as to avoid the 14th/12th fret hump?

Thanks in advance for any help.

Actually that template was shadowed by Preston Thompson -- we digitized it and duplicated the brace layout. I believe it has a flat top or (52' maybe 40') certainly not 28. the back is likely 15'. He is currently making them using the KMG template. I'll contact him and check out his parameters. A couple of sound clips of one of his Size 2 is linked here:

http://acousticguitarconstructionforum. ... =24&t=1428

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Ken Cierp

http://www.kennethmichaelguitars.com/

Glad to see you are benefiting from this John. There is a lot of confusion and confusing information masquerading as tutoring on this part of guitar-making. While I am waiting for the plummer...

Edit, This site is not what I am writing about. Tutorials here are trustworthy and very helpful.

Here are a few goals for designing and building an acoustic guitar with a fingerboard that sits on the soundboard.
1. The fingerboard is flat and should remain flat forever. (with strings at pitch tension).
2. The straight fingerboard projects in a straight line to the bridge and the bridge is higher than the soundboard.
3. The fingerboard ordinarily sits on the soundboard from where it meets the body to its end. Therefor this portion of the top surface should be flat.
4. The end of the guitar body should be the reference for all operations and should be thought of as straight up and down (plumb).
5. The top edge of the body at the center line of the fingerboard is X Y Z zero (positive up, right).
6. Guitars with weak or flat braced tops become worthless or don't resonate much and should be avoided in design.
7. Since the fingerboard rises in Z height from X Y Z zero along Y, so must the soundboard underneath.
8. The soundboard can rise as a result of bracing glued to its under surface or rise as a result of the angle of the sides that it is glued to. Or a combination of the two.
9. The neck end mates the reference surface and angles back as determined from 1 through 8. The two angles should add up to 180 degrees when the strings are at pitch tension.
10. The neck angle is 180 minus the angle of the body (reference surface to top surface.)

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Ken

I think this is what Ken is describing:

http://www.kennethmichaelguitars.com/neckangle.html

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Ken Cierp

http://www.kennethmichaelguitars.com/

Kind of, but your kit instructions seem relate to a flat martin style rim. I am trying to set some rules that can be related to either that with a flat rim or a domed rim or a curved rim. Or for that matter any combination. Some confusion comes in when the tail is used as a reference to change the angle of the sanding of the rims.

What is important to understand is that the rim doesn't need to be sanded in some cases, just the neck block or top above it. That is depending on the angle created by the bracing or block itself. It seems there are a few choices.
1. rim is flat starting out and the angle of the rim plus the angle of the bracing under the fingerboard determine the neck angle.
2. the rim is either arched (under the fingerboard) in x-y or only in Y and the arching under the fingerboard is angled but flat.
3. the rim is arched under the fingerboard and the bracing is also arched.

I like your write by the way. Nice work.

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Ken

Thank you!

And yes the KMG kit instructions and parts supplied are designed to emulate the Martin factory.

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Ken Cierp

http://www.kennethmichaelguitars.com/

Ken M and Ken C

Thanks for all of the help here. I believe did not keep Ken M's point #8 in mind during my last build and it ended up creating a challenge later.

"The soundboard can rise as a result of bracing glued to its under surface or rise as a result of the angle of the sides that it is glued to. Or a combination of the two."

I may not have been careful enough when using the Mega Mold to create the side template for my last 00 guitar. The actual angle of the sides may have been higher than it needed to be. So when I combined that with the radius of my x braces it was to high for the angle I set the Mega Mold too when sanding the neck block and upper bout.

If I understand all of this correctly, I should be able to manage Ken M's point #7. "Since the fingerboard rises in Z height from X Y Z zero along Y, so must the soundboard underneath." However, I would love to have the parameters Ken C spoke of for Preston Thompson's Size 2 parlor. Those would help guide me in the right direction. I also like the width he chose for the fingerboard.

You are welcome,
If you make your decision based on what you want the guitar behave like then you will be ahead of the game.
Consider this: all the lower bracing will remain as on your plan. But alter the upper bout, just like the M company does these days by creating a little ramp on the sides. According to Greven, the G company did (have the angle on the rim) and these old guitars never or rarely needed a neck reset while the M company kept the rim flat and neck resets for the vintage ones kept the repair shops busy. In looking at the vintage M guitars though there IS an angle on the neck. It is set back and the fingerboard was flat when it was built. So therefor the angle under the fingerboard was from arched bracing inducing an angle on the top plate. This bracing is not strong enough to resist the pressure and they fold causing a high action and a neck reset is necessary. Looking at old G company acoustic guitars though, the angle is also present but is not solely a result of the bracing inducing it but a combination of the bracing, raising the soundboard under the fingerboard plus the drop-off of the rim under the fingerboard. The old L00 Gibsons did have a problem with the fingerboard sinking a little though. So the combination , although better than the bracing alone still is not strong enough to resist the problem over the long run.
Make your top strong under the fingerboard without adding too much weight. Make it slope at your desired angle and keep it simple by angling the rim to match. A simple way to do this is an extended neck block. To reduce weight you can make it U shaped like a classical or only extend the top to just about shy of the soundhole.

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Ken