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Hi guys, I'm having a complete 'horror-show' with my current build and need some advice.

It's an all Koa cutaway. I've made the neck, made and bound the body, cut the channels ready for the abalone purfling etc etc.

Today I routed the body for the mortise and tenon join. I put the neck in and 'HORROR' - the neck angle is way out!!! I don't get it. I put spreaders in when gluing the top and back etc. I can only assume that something happened and the top and back didn't join to the sides at right angles.

The neck is set at a 1 degree angle which is what I normally use. BUT, In order for the neck to join this body correctly I'm going to have to change it to a 2.5 degree angle .

Do you think that this will be acceptable?? I can't believe it. I've been working on this for months. The thought of chucking the body is really depressing. The body itself looks amazing and apart from the hours and hours of work, it's not exactly 'cheap' wood.

Shall I carry on with the 2.5 degree angle. Will this effect the structural integrity of the guitar? dang, dang, dang

Thanks for your help

Mat

Mat, it's not the exact number of degrees in the angle that are important. It's the way the plane of the neck/fretboard lines up with the bridge that counts. If it has to be 2.5, then that's what it is. I never measure what the actual angle is on my acoustics or electrics. I just get it so I have the proper alignment at the bridge location.

I think you will be just fine!

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Mike

"The Dude abides. I don't know about you but I take comfort in that. It's good knowin' he's out there. The Dude. Takin' 'er easy for all us sinners. Shoosh." The Stranger

That's a relief -
Thanks Mike

What Mike said!!!! Here is a sketch showing what is important on an acoustic. keep in mind if the geometry of top radius, bridge location and thickness, design neck back angle and square-ness of the rim at the mortise is all perfect my 1.5 degree back angle will render this situation. But seldom is everything perfect.. If one or more is off a half degree change, more or less may be needed to achieve proper fretted FB plane to bridge relationship. but at the end of the day I still want the fret plane to be somewhere between .06-.13 above the bridge at the saddle slot.

Thanks Michael, I appreciate it.
The 2.5 degree angle will give me roughly what you are saying but i'll obviously have to fine tune it as the build gets further down the line.
It was a real shock to me earlier today and I thought that i'd ruined the build.
Panic over!!

Let me ask a couple questions. How tall is your bridge? What scale is the fretboard? What body is the guitar (Dread, SJ, OM,?) what top radius are you using and from the butt of the body how far is it to the apex of the dome? I can lay this out in cad real quick and see pretty much what induced the the extra degree needed. This might help you on a future build.

Michael -

1) I haven't made a bridge yet but is typically 8mm high
2) The fretboard is 25.4
3) The body shape is my own (see pic)
4) The top radius is 28'
5) From the butt to the centre of the x-brace is 10'' (is this what you mean by the apex of the dome?)

However, I think the problem is that somehow in the joining of the body, the headblock did not come out perpendicular to the sides.

Thanks
Mat

Ok then all I need to lay this out is the overall length of the body. One question is if you do not have a bridge height made yet how did you know it was going to take 2.5 degrees? I am guessing you used 8mm to determine this or this 2.5 degrees was what it took to make the fretboard meet the top flush. Anyway if I have the body length I can lay this out for you in just a few min.


So you are saying the angle the neck is fitting to the rim is 2.5 not that the angle needed for proper bridge to FB plane is 2.5. In either case using the edge joint at the top as a given datum plane with the info I can find where the problem would have to lie with some degree of certainty all I need is body lenght

Length of body is 19 and 13/16''
I calculate the angle by running a straight edge from the bridge position to the headblock. I place the straight edge on a piece of wood so it is raised 2mm at the bridge position.
I then take the angle at the head by following the line of the straight edge using an adjustable angle measurer.
- (I haven't explained that very well have I).
It's based on the technique in the 'Kinkead' book

Thinking like this will only cause you to worry and may just get you in trouble.

This is one reason why I never put anything but a right angle between the top face of the neck/head block and the sides of the block. I clamp the neck block down to my flat granite slab than glue the sides to the block all in the mold. This way I'm sure I have the block glued in correctly. But having said this, I still machine my angle into the neck block and rims after the rims are fully assembled with lining installed.

If you have any radius on the top and back, they should NEVER come out perpendicular or at a right angle to the sides. There should be an angle greater than 90* on both the top and the back when looking at the sides. If the top where flat (thus creating a right angle between the top and side) where the fretboard is glued down you'd have to add a shim under the fretboard inorder to set the neck angle properly. It's easier to build that angle into the construction of the rims and thus the top when it is glued on versus making a shim for under the neck.



This is also a good reason for the Woolson/Fox neck jig. If one has the ability to lay everything out in cad (which I do like Michael) it's much easier to see how the design of the neck set works with the height of the bridge etc... But if not, than the Woolson/Fox neck jig is really an asset in getting the neck 95% there with only a bit of fine tunning to go.

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Thanks Rod
Where can i get info on the Woolson/Fox neck jig you mention?
Mat

I don't know what has happened to the library of plans, but somewhere here at the OLF is a number of plans for jigs and guitars and Michael P has drawn most if not all of them.

The Wooson/Fox neck jig is one of these plans and is very good (I made mine off of them). So you might want to PM Lance or Brock and ask about them. I gave my set away already otherwise I'd have just given them to you. Maybe start a new post seeing if anyone has a set of the plans they will give you if they are not in stock with Lance or Brock at the moment.

Here's some results on the search for woolson neck jig

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"There's really no wrong way, as long as the results are what's desired." Charles Fox

"We have to constantly remind ourselves what we're doing....No Luthier is putting a man on the moon!" Harry Fleishman

"Generosity is always different in the eye of the person who didn't receive anything, but who wanted some." Waddy Thomson

OK. with the info you gave me assuming the rim is square 1.5 degrees should have been perfect for 19.8125 body 25.4 scale 28' top radiusand .31 bridge height. And using Kenkead method the angle would have been 1.11 degrees. this info tells me either the location of measurement for the bridge is wrong or the rim in out of square to the top seam. Tha tis the only way tht a straight line from the edge of the neck block to a 2mm high at bridge position forms a 2.5 Degree angle.

Thank you Michael - that's pretty cool.

The answer is that my rim is not square to the top seam. That is what I was trying (and failing) to explain.
I am really annoyed that this has happened. I have set the 2.5 angle and the neck fits ok. However - I don't know if I should continue the build with the rim being so off?
Will it matter?

Finish the build!!!!! Just adjust the heal angle of the neck so that the fretted fretboard plane is .06-.12" proud of bridge height at the centerline of the guitar and saddle slot and all will be fine.

Will do
- thanks