Glueing on the Neck Block

[Darryl Young]

I just glued the neck block to the rims on my 00 build at lunch today while I was home. I am using a bolt-on neck so you try to get the neck block in position so the bolt holes will align when the top of the neck (where the fretboard will be glued) is even with the top of the soundboard. This isn't the easiest thing to guesstimate. That the 1.5deg angle isn't yet sanded into the rim above the soundhole complicates things more. So the thickness of your top and the neck angle to figure into the equation.

I can see the benefit to cutting the mortise in the neck block after body assembly......and that is what would do if I were making my own neck.

So I'm curious how the good folks here determine how to position the neck block when gluing it to the rim......at least for bolt-on necks when you would like the existing holes to align when the neck is in the correct position.

[johnnparchem]

The holes for the bolts in the neck blocks should be more like slots, to give a little bit of slop to set the neck in the right place. I set both blocks just proud of the rims on the top to deal with the fact that I radius the rims to 28'

[Kevin Sjostrand]

Darryl,
Alot of the answers to your questions depends on whether the block is already sized, that is, the correct height.
If you have a block with the mortise cut and bolt holes drilled, and a neck with a tenon and the holes/inserts already positioned, but the height in not already set, then you can install the neck in the block. Where the neck heel contacts the heel block at the top, you need to make a mark, and then come down the thickness of your top and make a mark. This will be where you want to cut off the block (for the top), and you would glue this flush with the sides at the neck end, top side. Do remember to leave about 3/32" to allow for the radius you will want for your neck set. This way with the top in place you will have a flat plain where the top of the neck blank fits against the body for your fretboard to lay flat onto the top.
Hope this makes sense.

Kevin

[Darryl Young]

After the rim is assembled to the neck/tail blocks.......do you guys then sand the 1.5deg slope above the soundhole? I've not done the math but this will lower the top of the neck block some but not sure if it's enough to cause the bolt holes to be out of alignment.

Kevin, I did very similar to what you described. My bolt holes aren't slotted. I think I will be close but wouldn't be surprised if I have to elongate the bolt holes a little bit after sanding the slope in the upper bout.

Thanks for sharing how you guys approach this!

[Kevin Sjostrand]

Darryl,
I always cut the blocks to height and put the radius on them before I glue them in. I have the sides very close in size, but are a little bit proud of the blocks, and I plane and sand them down to the block....I do both ends this way. I will glue the blocks as flush as possible with the "top" side of the sides, so very little to do there.
You will want to elongate those holes some anyway to be sure your neck drops far enough down to allow the fretboard to sit nicely on the top.

Kevin

[Dan Bombliss]

I have an equation that would be helpful for you I believe. It's the equation to determine you're "Neck Extension Height". Which is, in essence, you're neck angle.

Things you need to know to determine the desired neck extension height:

Bridge height
Fingerboard thickness plus fret height
Expected settle in

There is some information on expected settle-in which is a guestimation of how much your top will move once it's under the amount of weight of the string pull. Different body styles, bracing patterns, string gauge all effect what the educated guess of the number is.

For example:

Settle in example,
25.4" scale lenght
Light gauge strings (.012"-.052")
25' Radius top
OM to Dreadnaught size body= Expected settle in, 1/16"

Some things that change the expected settle in, and by how much:

24.5" to 25" scale length -1/64"
Medium gauge strings (.013"-.056") +1/64
20' radius top -1/64"
15' radius top (Larson bros bracing) -1/32"
Small size (14.5" lower bout of smaller) -1/64"
Large size (17" Jumbo) +1/64"

So there's some number examples for figuring what you'd might be looking at for settle in. Settle in is a nice thing to account for, but you might not want to go about it blindly. Before I knew this information, on my first neck reset (On my own dovetail guitar), I tried to account for settle in and added more than I should have for height. Now my guitar's neck angle is too high and I needed to make a saddle that was extremely tall, much taller than it should be for that bridge. Sure, an easy fix if I were to either reset the neck again, or put a taller bridge on it and reroute for saddle, then saddle would be regular sized.

That's a little example of my first learning experience with settle in. Also, I'd like to add that the reason that that guitar needed a neck reset is because it was the first one I had built, and I hadn't accounted for settle in. So my issue was that the action was always way too high, and my saddle was a very short one. In the winter the guitar was fine, and summer it was unplayable. Now it's vise versa! ;)

Anyhow, account for settle in or not, it's your choice, but above is the information to help account for it in a more accurate fashion.

So now to the formula:

So to determine your desired neck extension height (NEH, add your bridge height (BH) and settle in (SI) and then subtract the fretboard Thickness (FT)
NEH = (BH + SI) - FT

An example of the OM with a 3/8" bridge and 9/32" fretboard (1/4" fingerboard plus 1/32 for frets, don't forget the fret height!)
3/8"(BH) + 1/16" (SI) = 7/16" ; 7/16" - 9/32 (FT) = 5/32" (NEH)

-Dan

[Dan Bombliss]

Ok, now Darryl, the part that I thought might help you there is the actually neck extension height. You mentioned something about sanding the soundhole, which my understanding of that was sanding a ramp into the top before the soundhole, to begin you're neck angle for you're fingerboard.

If that's what you had meant, here's how you do that:

If we take the example I posted in that formula, the NEH is 5/32". That's what you're neck angle would be with out a bridge or fingerboard included... Meaning if you set you're neck on the guitar, and it was flush with you're top at the neck to body joint, then you're straight edge on the neck should measure 5/32" at you're bridge location.

So, what I do to get that ramp in my top, which makes for no dips in you're fingerboard on the body, is you make you're self a 5/32" shim... Whether it's 1 piece, or a stack of pieces that is 5/32", it doesn't matter.

Now tape those shims down at you're bridge location, and get a very flat block of wood that is long enough to reach and then some. Put sand paper at the end of the block, and have the other end riding the top of you're shims. That will sand you're top into the degree ramp specific to you're guitar. I don't like the general thought of 1.5 degrees or what ever, seeing as how settle in varies, along with variations of fingerboard height and bridge height.

If you use that formula, and sand the ramp into you're body as so, you're bound to have a very accurate neck set, and very smooth fingerboard all the way down, with no dips at the body.

-Dan