In case someone is looking for a simple neck joint to replace a more complicated mortise and tenon or dovetail joint, etc., I thought I'd show a few details of my bolted butt joint. Since, I didn't take pictures with this tread in mind I don't have the views that I'd like to have, but some random pictures I happened to find capture enough detail to give you a good idea of my approach.
Big picture: The neck's heel sits right on the head of the body and the fretboard tongue is glued to the top. Allen head bolts with Bellville washers, from inside the body, go through the body's head block and screw inside threaded inserts in the neck's heel. They are easily tightened with an allen wrench from inisde the body. (With the Belleville washers, I've not seen this bolts work loose.)
This is the top of a raw head block before cutting to final size, shape and drilling. Note the 3 laminations which make up the final thickness. Hard quarter sawn maple is sandwiched between 2 pieces of mahogany with non-aligned grain. The thicker piece of mahogany will be glued to the head of the body's rim after the block's face is radiused to fit the curvature of the rim.
This is the same block as shown above, but turned to show it's side. Note the non-aligning mahogany grain.
Here the head block has been shaped, drilled and glued to the body's rim. There is a small hole for the truss rod at the top, and two larger holes for 1/4-20 threaded allen bolts. The bolts are counter sunk into the head block so that the Belleville washers will bear against the hard maple in the block instead of the softer mahogany. This allows the washers to deform and lock the bolts tight. Unlike the Martin and Gibson head blocks of solid mahogany which break (fail) in two pieces along grain lines after years of service, I don't think that these blocks will break.
This view shows the rough neck. A channel was routed completely through the heel from top to bottom. Then a large piece of hard maple was pressed and glued into the heel with it's side grain showing all around (it's end grain is at the bottom & top of the heel.) This allowed the maple to be glued to mahogany side grain on 2 sides of the maple block. It also gives hard maple side grain instead of fragile mahogany end grain for the threaded inserts to cut securely into. (I don't understand why people put inserts into the end grain of mahogany or other woods in guitar building. It is understandable as to why a joint depending on end grain fails.) A typical threaded insert for wood is very course and dull, and tends to crush the wood as it enters the pilot hole. These inserts were made to cut into metal and therefore cut their threads/groves into the maple. It would take a very big force to pull these two inserts out.
Note that the maple and part of the mahogany has been relieved about 1/8" from the heel's face leaving about 1/4" of mahogany on each side of the heel to kiss the face of the body's rim. This is so it is easy to get the neck flush on the body and to easily adjust the neck's angle in any direction. Without this relief, much more material would have to be removed to adjust the neck's angle and get a tight fit to the body. Since the body curves here, this difficult task is eliminated.
Here are the 3 parts times two. Note the dome/bell shape of the lock washers which will flatten under force and push back aginst the bolts. They are superior to standard type lock washers. Monte Montgomery, an excellent player, does neck bends on a regular basis. He has an Alverez Yari guitar with, I believe, a dove tail joint. Over the years, his neck has come off the guitar twice while doing a neck bend. I don't see that as being the case with this butt joint.
This is a full scale drawing of the side profile of the neck, and a full scale cutout of the neck's section. The bottom of the heel ends up being about 1.125" deep (out from the rim) due to the pointed design. This is the same as a Taylor guitar and close to Martin's. If this is rounded it will suck back closer to the rim. This shape can be made a little smaller, but mine is a fairly traditional shape and size. In other words, I don't see that my butt joint design has caused an increase in size compared to many leading factory makers making millions of guitars.
Here's a view of a completed neck joint.
Here's a neck that is about to have finish applied.
My name is cut/routed into the peghead veneer and then filled with white epoxy. The interesting thing is, of EVERYTHING I have done in guitar building this gave me the most difficulty to accomplish. (I've never built a kit guitar. My first one was scratch built from mahogany that I re-sawed.)
Back strap epoxy filled and waiting for sanding.
This is a side view of a Taylor neck. I'm not trying to duplicate Taylor, but given how well accepted their shape and size neck heel is, I though it would be a decent reference point.