cuting arch top dove tail

[Greg Martin]

Need a little clarification please. Im ready to cut my dovetail, the neck angle will be 4.5. do I cut the end of the neck blank at 90 and insert it into my angle jig to cut the dovetail at the 4.5 degrees . Or do I cut the end of the neck blank at 4.5 degrees and then insert it in the jig to cut the dovetail??

[Chris Richards]

The usual approach would be to cut the neck blank with a 4.5 degree tilt (or close to it) the sawn surface at the end of the neck, which will end up being the back of the dovetail, this surface is not meant to press firmly to the back of the dovetail socket...there is a "designed" gap (to allow the neck to be removed in the future with steam).

If you're routing the dovetail, the router cutter will accurately (providing the jig is good) form the face of the dovetail that fits to the body sides and (obviously) the dovetail flares.... Ideally the finished joint should only be glued on the dovetail sides and a blob of glue on the underside of the neck extension.. NO glue on the front face of the body.

Hope that helps
Chris

[Chris Richards]

Although it's nice to get a snug fitting joint straight from the jig by the time the neck extension is fitted and the guitar sides are trued-up...retaining a tight joint is pretty difficult and I don't thing there's any "shame" in having to shim the dovetail joint... This also allows you a bit of "wiggle room" if the neck doesn't quite line up.

[Greg Martin]

Thanks, I was unaware that glue would not be put on all surfaces, Ill have to ponder that one. I guess it depends on how well I fit the joint in the first place. I never like the idea of shims.
now if Ive screwed up, then its a necessity the goal is to make this one better than the last. Funny We all know where every flaw is on our work even if the end user never knows, that really bugs me, every time I see that guitar i go oh yea I screwed this or that, probably you as well.

[Patrick Hanna]

Hi, Greg,
I think Chris has given very good advice. In my view, you should leave a gap at the very back of your joint, where the neck heel meets the recess in the neck block. First, this part of the joint adds nothing to its strength. The joint strength is derived from snugging the neck up to the body sides and, of course, the dovetail itself. Second, you need a place for excess glue to squeeze out of your joint as you press the neck home. The gap at the back provides this place for squeeze out. Third, at some point in the future, you might need a place to insert a steam needle, to separate the joint for a neck re-set. You will do this by removing the fret over the position of this gap, drilling a tiny hole for your needle, and inserting the needle into the gap.
I know it's a bit of a "head-scratcher" to ponder all this, but it really works out that way.
Patrick

[Chris Richards]

I agree Greg.... Every guitar I have built has flaws, each subsequent one seems to get better but I don't know whether that's because I'm building them better or I'm making a better job of hiding the flaws! A bit of both I guess. What has helped me is learning ways to avoid making errors...Say by making jigs or doing a certain task in a different way, I've recently started pressing frets in before I profile the back of the neck, it makes the job so much easier.

Going back to gluing the neck dovetail....I had quite a long discussion about where the glue should go as I couldn't see why the whole area of the joint shouldn't be glued... Because of the nature of an archtop guitar it is likely to move over time and at some point the neck will most probably need re setting and a good dovetail joint should be mechanically strong enough without glue, thus you only really need the glue to hold it in place rather than additional strength..... I've got a picture book of an archtop build on my website www.3rguitars.co.uk click on the archtop build menu, some stuff might help you...

[Greg Martin]

great discussion. so I guess I shouldn't use epoxt huh?? no no just kidding, its the old boat builder in me that said that.Id never do that .
I didn't think about squeeze out, and resetting in the future great point.
I have 2 3/4" dovetail bits 9 degree and I think 14 degree , since the tightening of the joint really happens toward the tighter width at the bottom, does the degree of the dovetail come into play?

[Michael Lewis]

" does the degree of the dovetail come into play?" Yes. A narrower degree makes a stronger joint. Actually, a straight mortise and tenon that is well fitted is plenty strong for a neck joint, but the flair of the dovetail allows more opportunity to make a close fit, and actually pulls itself together when clamped into place. The inexpensive Chicago factories (Harmony, Kay, etc.) used a very wide splay of the dovetail, and these can break off due to the short grain while still glued to the walls of the mortise, there by locking the loose neck into the body until it can be steamed apart. So, a shallow angle for the dovetail is fine, 14 degrees or less.

[Chris Richards]

A bit of a "curved ball" here..... I've only built one archtop, most of it based on the Benedetto book, I cut the neck dovetail with jigs and a router but it still required fettling by hand... I just wanted to add here that for me it was the most satisfying part of the build, until I'd done this part it wasn't a guitar, just components that I was making but once I slipped the neck on the body it became a guitar and I felt that I was on the home run so to speak... I took a GREAT deal of care getting the joint perfect so that both the surface mating with the body sides was absolutely flat, the neck extension sat on the body perfect and the neck lined up PERFECTLY with the centre line of the body. It took me a whole day scraping and sanding minute adjustments but in the end I got it spot on, I was like a kid in a sweet shop! One of the most satisfying things I've done in any guitar build.....

So take your time to get it right... start by block sanding the guitar sides around the neck joint area and get them absolutely flat then cut the dovetail....Good luck.

[Greg Martin]

Thanks chris for the comments, I agree there is that one point for a builder where it all becomes clear. Ive always dug shaping the neck ,but with the arch top the dove tail has been the spot where Ill make or break. Its funny that the comment about the dovetail bit being stronger with a less angle is the better !. When I wrote the post I was think the same, but it seemed many were using a 14 degree bit so I assumed it was correct and went against my own experience.

[Michael Lewis]

The strength of the joint will come from the quality of fit. The point I was trying to make is to avoid anything like a 45 degree cutter because the flared 'wings' of the dovetail can easily break.

Benedetto design uses a very narrow taper from top to bottom, and I think it should splay more toward the top. The wider top to bottom splay of the tenon releases much easier if removing the neck is a consideration. The Benedetto design is almost parallel bottom to top, which is much more difficult to remove.

[Greg Martin]

hi I found a 7-8 degree freud 3/4" by 7/8" bit with 1/2 shank,I think its a 22-114 ,so Ill pattern up for that,thanks again.

[Michael Lewis]

Make up a test neck joint to try it out. A couple pieces of framing lumber will do well enough.

I usually cut the mortise 3/4" deep and the tenon 5/8", so that leaves the 1/8" gap at the back.