Neck Body Alignment

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scamp
Posts: 223
Joined: Sat Mar 26, 2022 8:19 pm

Neck Body Alignment

Post by scamp »

Beginner question of the day!

I am at the point where the body of the guitar is closed up and I am about ready to rout the edges for the binding.
I did a quick assessment of the neck/body alignment and there are a few issues and I don't know if they should be corrected now or after I rout the edges for the binding.

The guitar has a bolt on neck. If you bolt on the neck ( just the neck without fret board ) the plain of the neck is about .05 inches below the surface of the top.
IMG_2030.JPEG
Also, if you remove the bolt on neck screws and slide the neck up to be flush with the top and put the fret board on, the fret board at the sound hole is about 0.035 inches above the top surface at the sound hole ( I have heard this referred to in Bill Cory's book as the ski jump effect).
IMG_2032.JPEG
Additionally, if you also use a flat edge with the neck flush with the top, and measure the displacement at the bridge location, it is about a bit over 1/8 inch. Looks like about 0.3 or so over 1/8 inch.

So, it looks like I would need to sand down the top of the guitar a bit between the sound hole and the top ( maybe by about 0.03 inches at the very top ramping down to 0 at the top of the hole) and also elongate the bolt on neck holes in the neck block by 0.02 inches or so.

Does this make sense??

Also, does it make sense to try and do this before I rout the bindings?

If I do it after I rout the bindings, the bindings at the neck end of the guitar on the top will be a bit narrower. If I do it now ( before I rout the bindings ) I am concerned that when I rout the perfling ( which is 0.06 inches tall) it will go through the top ( since the top is now 0.1 inches and if I remove 0.3 inches and the perfling routing is about 0.06 inches I am getting close ).

So, do I try and correct this now or after routing.

Any opinions???
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tippie53
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Re: Neck Body Alignment

Post by tippie53 »

You need to set the neck you do have to adjust the neck angle. A slight drop off is desirable say about .035 in.
if you need to elongate the bolt hole that is ok to set the fret plane level.
It won't take much. You can level the fretboard plane then level sand the area of the extension.

there is a more geometry going on than you may realize. after a few guitars you will understand this .

You do not want a toe up fretboard as this can give buzzing issues.
With a straight edge on the neck , the point where the saddle should be you want to be between 1/16 to 1/8 in off the top.
If you set the fretboard on the neck , and set the bridge at the point of the saddle location without frets you want to be just touching or off the top of the bridge . With frets on the neck I like to see 3/8 in off the top. It is easier to adjust the bridge by sanding off the bottom if need be.

you are close and you should have a good outcome for sure.
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
scamp
Posts: 223
Joined: Sat Mar 26, 2022 8:19 pm

Re: Neck Body Alignment

Post by scamp »

OK...

So....

1 Don't do anything to adjust the neck body alignment or sand the neck/body interface until the binding is compete.

2 Once the binding has been completed ( including scraping and sanding etc.) elongate the bolt on neck holes to get the neck ( without fret board ) level with the top of the guitar at the neck body interface.

3 A straight edge extending the plain of the neck should be between 1/16 to 1/8 inch above the guitar body at the bridge location. With the fret board ( without frets installed ) it should be just touching the top of the bridge and with the frets included it should be about 3/8 inch ( 0.375 inches ) off the face of the guitar at the bridge location. If not, then some adjustment is necessary.

Please let me know if this is correct.

OK. One area of confusion I still need help with. I put together what I have to take a look how close things are now to correct ( don't worry... I won't do any adjustments until I complete the binding etc.) and it is very close to ideal with the neck flush with the top. That said, the fret board extension over the body ( beyond the 14th fret ) develops a slight gap between the fret board and the body as it approaches the hole that gets up to about 0.025 to 0.035 inches by the time it's at the end of the fret board. You mention a "slight drop off" of about 0.035 inches. Is this what your talking about?

I am confused as to whether I need to sand the top down enough so there is no gap between the fret board and the guitar top all the way to the sound hole, with no downward bow of the fret board into the top, or if it's OK to have a slight gap develop and in the end you just bend the fret board down slightly and glue to to the top and this is what you call ... " a slight drop off" of about 0.035 inches. If this is correct, then it's clear that you need to glue on the neck even if you have a bolt on.... Correct??

A bit long winded question but I wanted to be clear on my confusion.

Thanks
tippie53
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Re: Neck Body Alignment

Post by tippie53 »

look up the neck setting videos I have on your tube that explains the process. You can pre set the neck without the binding being done and the process is pretty detailed . A lot more info there than what we can type
the only difference is that you would work the dovetail.
so here is the link
https://www.youtube.com/watch?v=nF57G5Ih-qY
https://www.youtube.com/watch?v=FNcbA1P95KE
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
scamp
Posts: 223
Joined: Sat Mar 26, 2022 8:19 pm

Re: Neck Body Alignment

Post by scamp »

tippie53 wrote: Mon May 02, 2022 6:29 am look up the neck setting videos I have on your tube that explains the process. You can pre set the neck without the binding being done and the process is pretty detailed . A lot more info there than what we can type
the only difference is that you would work the dovetail.
so here is the link
https://www.youtube.com/watch?v=nF57G5Ih-qY
https://www.youtube.com/watch?v=FNcbA1P95KE
Thanks John

Videos helpful

If I am following your guidance from the videos, it appears you need to sand the neck and top body of the guitar so the fret board is flat against the guitar top all the way to the end of the fret board near the sound hole without any bow in the fret board. Said another way, the surface of the neck (without the fret board) and the surface of the guitar top under the fret board are an absolutely continuous flat surface. Correct?
tippie53
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Re: Neck Body Alignment

Post by tippie53 »

yup this process is called setting the neck
I do this in 2 stages pre set without the fretboard then
there I will create that plane for the fretboard to come onto the guitar and set up the final geometry then once I am finished I will retrue everything and set the inital set up with the frets on and I can then tweak the bridge for the final set up.
You can figure the top to rise about 1/16 and that takes a few days so that is when you do the final set up , once the top settles,
in the perfect world you should be about 1/2 in string height in front of the bridge
your action height should ba 2/32 on the high e and 3/32 on the low
your neck relief should be about .004 to .006 when you fret 1 and 13 , this relief measurement would then be at the 6th fret
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
scamp
Posts: 223
Joined: Sat Mar 26, 2022 8:19 pm

Re: Neck Body Alignment

Post by scamp »

Followed the excellent guidance/advice and here are the results.

Elongated the bolt on neck holes to get the neck flush.
Tweeked the shoulder of the neck mortise and tenon to center the neck with the body ( needed to move the projected center line from the top of the neck to the tail over about 1/4 inch )
Sanded down the neck and top so the fret board was flat out to the sound hole.
IMG_2033.JPEG
And miraculously....

The distance from the projected neck plain ( without fret board ) at the bridge to the top was 3/32 inch ( .094)
IMG_2035.JPEG
The distance from the projected neck plain with the fret board was 22/64 inch ( 0.343 )
IMG_2037.JPEG
The distance from the projected neck plain with the fret board to the bridge was just shy of the top of the bridge.
IMG_2038.JPEG
And the distance from the projected neck plain with the fret board and shims to simulate the frets was just a hair over the top of the bridge ( about 1/32 over for a total distance from the plain projection to the top of about 0.39 inches ).
IMG_2039.JPEG
All good for now I think. Thanks for the help and let me know if I did anything wrong.

Scamp
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tippie53
Posts: 7011
Joined: Fri Mar 03, 2006 7:09 pm
Location: Hegins, Pa
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Re: Neck Body Alignment

Post by tippie53 »

looks perfect
John Hall
Blues Creek Guitars Inc
Authorized CF Martin Repair Center
president of Association of Stringed Instrument Artisans
http://www.bluescreekguitars.com
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