Off Center Neck

[Ian Kipgen]

I am settling in a neck into a tapered dovetail body mortise and discovered that the neck alignment is off center when projected to the tail end of the body by 3/16". I have never had this experience before and am clueless as to how to correct it. What I call the face of the neck's dovetail cut (the surface that pulls in tight against the outside surface of the body) on the treble side is tight where as that on the base side stands proud almost 1/16".

I have no idea how I managed to create this situation but I'd certainly appreciate some advice on how to manage it. Many many thanks!

Ian

[Charlie Schultz]

Hi Ian and welcome! I don't have any help for you but someone should be along soon to comment.

[Mark Swanson]

You'll need to trim by hand with a chisel. Take off the areas that are now "in the way" from allowing the neck to sit the way it is supposed to! that can be a bit of a trick, you'll have to carefully look at it and think about where to remove the wood. Without me seeing it, I think you'll need to remove wood to make it sit flush with the body all the way around while at the same time bringing it in line with the center line. All that while maintaining the proper neck angle of course!
Now, are we havin' fun yet?

[Ron Daves]

Newbie, here. At least when it comes to building guitars. Intuition tells me that you can trim this butt-join 'til you get what you want. If you over trim, glue on a sliver where it is needed. If that doesn't work, start over. You'll eventually get it right.

[Dave Stewart]

Yep, fitting a neck properly is a challenge, as you are trying to get "roll, pitch & yaw" of the neck to all crash together just as it drops to the right height & become tight!
Hope this isn't too basic, but if the heel is the final width, undercut a bit from an edge allowance (1/8" +) toward the tenon, so only the outer perimeter of the heel becomes the contact area. You may find fit has improved. From there on, "flossing" can correct pretty much anything, (eg flossing one side only ....and maybe the opposite side dovetail "cheek"... corrects "yaw" 'till neck c'line is pointing down the center). And the undercut speeds flossing a lot. (Search around...lots of good info/tutorials on flossing out there.)
Other than than, use chaulk / graphite to identify interference points & just work away. Glue veneer on the cheeks of the dovetail if you need to, although this shifts the whole thing left or right rather than correcting yaw. Don't forget to double check that the dovetail isn't bottoming in the mortise as you floss away wood from the heel. Lots going on....very satisfying when done!

[Mark Swanson]

Dave, you should explain what you mean by "flossing", I think you are talking about using a strip of sandpaper placed in the neck joint and then pulled out, to sand and fit the neck to the body.

[Dave Stewart]

That's it Mark. Strips of sandpaper (I use 1" wide strips) are pinched and held between the body and the heel. Pulling the sandpaper straight out (away from the top) sands the heel (make sure backing is to body) such that it conforms perfectly to the body for a gapless seam. It also adjusts things....3 pulls one side/1 pull the other ROTATES the neck as well as settling it (what I meant by "yaw" above). Neck angle , or pitch, can be affected some by just flossing the bottom or top half of the contact area (ie 'till it's correct, then floss the whole length). Roll is harder. If the top surface of the fingerboard is not the same distance from the binding on both sides, adjustments to the dovetail cheeks is required 'till neck "rolls" back to proper position.

[Ian Kipgen]

Thank you guys for all the help and I understand almost 70% of it It gives me a lot, and I mean a BUNCH, think about here before I start whacking away with my chisels. Sure makes me wish I'd done it right the first time!

[Ian Kipgen]

Now that I've thought about it a little Dave I'm afraid I don't understand how I can 'floss' those faces as I settle the neck down into the mortise since they are pulled tight against the side. I'm confused.

[Patrick Hanna]

Ian, don't give up. Believe me, I wrestled with this problem on my own archtop. Keep working on the areas where the dovetail wants to seat in its socket and also where the two sides of the heel meet the body. It's complicated for sure, because you are working on depth of the neck into the mortise, alignment of the neck with regard to the body, and angle of the neck with regard to the string line to the proposed bridge. It's HUGELY daunting! But...if I did it, you can, too! I'd work first on where the heel sides meet the body. Then I'd work on the tenon shoulders. If I removed too much wood here (and I did on my own) I'd glue veneer strips on one side or the other (or both) to adjust. Then I'd slowly file or sand a little off on one side or the other until the neck was centered. I'd personally save the neck angle / string angle for the final adjustment. If you go slowly and patiently, you will be fine in a day or two. You really will.

[Nelson Palen]

Ian,

I am settling in a neck into a tapered dovetail body mortise and discovered that the neck alignment is off center when projected to the tail end of the body by 3/16". I have never had this experience before and am clueless as to how to correct it. What I call the face of the neck's dovetail cut (the surface that pulls in tight against the outside surface of the body) on the treble side is tight where as that on the base side stands proud almost 1/16".

I have no idea how I managed to create this situation but I'd certainly appreciate some advice on how to manage it. Many many thanks!

Ian

Ian, I'm curious about the "base side stands proud almost 1/16". I take this to mean that you're seeing a 1/16" gap between the neck and the body? If so, that indicates perhaps a bottoming issue that Dave alludes to above. You may want to investigate what is causing the gap.
Also, I'm curious where you're at with the neck extension. Has it been mated with the top of the body? That would normally be done after the dovetail is dialed in and can influence the "roll" to some extent.

[Ian Kipgen]

I have been executing the advise given and have managed to chisel the heal "flats" that meet the body so that there are no gaps on either side and the neck is now square to the body. I had to router the mortise 3/64 deeper to keep from bottoming out and therefore had to add shims and start the settling process over again. I was 1/4" from touching the top with the neck extension when I started all this and am now "blue-printing" the neck extension down to the top.

My nerves are shot! I was so nervous that I could have threaded a sewing machine running wide open! But, thanks to the support from you folks, it appears that I have persevered and the archtop saved. Thank you guys so very much.

Ian

[Mark Swanson]

Good work! Remember, easy does it!

[Dave Stewart]

Congats Ian......knew you'd get there. Now just keep things in balance as the neck lowers into position.

[Steve Senseney]

I am glad this worked for you.

Did you figure out what occurred that you had problems? I wonder if your neck block got slightly off of square during your build, or something else got out of kilter.

(I don't pretend that this has not been a problem for me!!)

[Michael Lewis]

Now you have been through the process it only gets easier. Some things that might help in the future are "gun sights" at each end of the fingerboard. For this I use masking tape and make a small mark on the center line of each and a center line on a card taped either to the butt end of the guitar or at the bridge that sticks up high enough you can sight it with the neck. The "sight" at the body end of the fingerboard should have a flap to stick up 1/8" or so so you can see it when sighting along the neck. A small ruler helps measure the height of the bottom edge of the fingerboard to the top of the guitar, keep this measurement even as you lower the neck into the mortise, this shows the roll is correct and the gun sights tell you if yaw is correct and you need a straight edge on the fingerboard to project to the bridge area to get the pitch. Whatever bridge height you are going to use you want to shoot for about 3/16" below that to allow for the action of the strings.

As Dave Stewart mentioned, slightly under cut the inside of the heel leaving about 1/8" of contact area all round the edge. This undercut needs only to be a few thousandths deep but a little deeper is OK.

I use strips of transfer paper from a sewing shop to test the fit of the tenon to the mortise. This stuff has sort of chalky stuff on one side and it transfers easily, much better than carbon paper. It comes in white, blue, red, green,and I don't know what all else. It comes in a roll like waxed paper or aluminum foil, and you have to cut your own strips. Make them only wide enough to fit in the mortise, which will be slightly wider than the faces of the tenon. Only allow the "chalk" to contact the surfaces you want to trim., otherwise you end up with "color" getting all over everything and you won't know where to trim.

[Nelson Palen]

Dave and Michael,
I understand the utility of the undercut mentioned but my concern is that some glue surface will be lost if the undercut if too deep.
Maybe you're talking just a couple thousandths undercut so that glue strength isn't affected significantly?
Nelson

[Mark Swanson]

You don't need to put glue in the undercut at all, in fact you shouldn't. You only need to glue the dovetail and if you ever have to steam off the neck you'll be glad you didn't get glue outside of the dovetail.

[Nelson Palen]

Mark, I could possibly see gluing only the dovetail if the body and neck were going to be finished seperately and then assembled.
Probably would also need to allow a little bit of "room" for finish thickness when flossing if assembling after finishing.
I've never had to floss an archtop neck as the body and neck dovetailing fixtures assure alignment between the neck and body.
I also use a fixture on the edge sander that "kisses" the neck mounting surface on the body to also ensure alignment.
I then finish with the neck attached and would be afraid of stress cracking the lacquer between the neck heel and body due to string load over time if the "flat" surfaces were not glued.
Another issue would be getting moisture in the joint when wet sanding causing the wood (and finish) to swell. That could be prevented, however, with careful sanding with something other than water for lubricant.
I may be overlooking something here and I suppose everyone does things a little differently.

[Dave Stewart]

Very interesting Nelson....as you say, everyone has his own way. I almost responded last night, but thought "no, it's me ....something I don't understand about why Nelson asked his question". I typically bolt-on after finishing (I may floss the heel a bit before buffing, if the finishing has changed anything), so no glue and the undercut is a non-issue.