“Angle, center, elevation”…how to close this gap in the neck?

[Peter Katsaros Katsaros Guitars]

Here is an SOP I wrote when working at a big name shop. I hope this helps out, read thoroughly and go in this order. Your gap could be a few things.

Here is a brief description of how to manipulate the dovetail while fitting a neck.

The pitch measurement is taken with a straight edge in the center of a straight fingerboard, projecting this plane to the top center of the bridge. The neck relief must be adjusted before taking this measurement.

The dovetail must not be loose during this measurement or you will get an inaccurate reading.

PITCH

If this pitch is low, we take full pulls(meaning the entire length of the contact area) of sandpaper under the heel to bring up the pitch. Assuming the string alignment is where we want it, we’ll take equal pulls with sandpaper on both sides of the heel. Taking material off the back of the heel will gradually loosen the dovetail in the back.

If the pitch is too high then we need to carefully chisel the heel forward. This can be risky, and must be done correctly, shaving off very little at a time and then checking. Chisel from the back of the heel forward towards the fingerboard.

Once we are where we want to be, we take short pulls (not the entire length of the contact area) with sandpaper to improve the appearance of the mating surfaces. It is not advisable to bring the pitch forward by pulling sandpaper.

It is also important to note that this will gradually loosen the dovetail in the front.

When the neck is pitched too high and the bridge has been located, the relation between the 12th fret and the saddle slot will be affected by bringing the pitch down. This negatively affects the intonation. This is very important in the overall outcome of the guitar.

String alignment

If the adjustment is a small amount, thinning the contact area of the heel on the side that we want to affect and pulling sandpaper should do the trick. Larger amounts need to be chiseled and then sanded.

Twist

When the dovetail has a twist in it, it cannot be considered fit. If the fingerboard is proud on, for example the bass side and flush on the treble side, the dovetail needs to be rotated.

If the fit is already loose, we need to add a shim before removing material. If the fit is tight across the entire dovetail before starting, then we remove equal amounts on both sides. If the fit is tight in the front, then we determine which side to take material off according to which direction we want to go. Same thing if it is tight in the back.

It is imperative that the side of the dovetail that we are working on is straight when we are done. Check your work use a straight edge (6” ruler).

Elevation

It is important to address the twist Before addressing the elevation. If the dovetail is too tight and the fingerboard extension will not seat at the top, and there is no twist. Then we can carefully take off a small, even amount from one of the sides of the dovetail. If doing so is going to negatively affect our string alignment, then we need to carefully take off even amounts from both sides of the dovetail.

Our desired final elevation is achieved when we can easily clamp the fingerboard extension to the top with a moderate amount of clamping pressure.

Once we have done so, the heel is tested lightly by trying to open the joint. If there is no movement, the neck is ready to glue in. It is important to simulate the string tension when doing this. The neck is glued in only when the pitch is correct and the dovetail is properly fit.

Generally speaking, bridges with a through slot or pyramid bridges are pitch 1/64 below the top of the bridge, never above.

[Randy Zwitch Zwitch Guitars]

This is helpful, but I’m not sure what my next step is. As far as I can tell, the neck is exactly where I want it from the pitch, string alignment and elevation. But I also have the .035” gap.

So not sure where I should target to close that gap without making everything else that is correct not be worse

[Ian Davlin The Looth Group]

This might be easier to look at online. Have you been on the loothalong ?

[Randy Zwitch Zwitch Guitars]

I wasn’t familiar with the loothalong, thanks! I *think* I have figured it out, first checking for mystery bumps/undercutting further and using sidewise flossing (we need better names for this!) on the purple tape side and base of the neck.

If I don’t get it in an hour or so, then I’ll jump into the loothalong. Thanks Ian and Pete for putting some ideas out there for me to think about 🙂

[Peter Katsaros Katsaros Guitars]

I’m with Ian on this one, getting more eyes and being able to walk through it with video would help a lot. If you can’t do the loothalong and want to video chat DM me and we can schedule a video call.

[Ian Davlin The Looth Group]

One thing to check when getting mystery gaps is that there is a gap between the face of the mortise side and the tenon side. Since you cant see inside the joint when the neck is in, you can check it by chalking one side.