Neck ange changes for dovetail set-up

[Francis M]

Hi I’m new to posting on this forum, I’ve been in the background for a while reading various topics as need arises.
I have a question regarding cutting dovetail neck joints and setting the cutting angle for the shoulder of the neck. I’m building my version of the O’Brien/LMI jig, I don’t have the room to store a full sized version where body and neck can be set-up at the same time, mine will be a one-sided affair, but retaining the adjustable angle neck support.
My question is when setting up the angle of the neck should the angle be ‘set’ before the dovetail socket is cut or after. For a square shouldered guitar it would make no difference but mine are slope or round shouldered guitars and cutting the dovetail socket first would change the angle very slightly due to material being removed on one side from the top of the curve (hope that makes sense).
From the O’Brien video I see that the angle is set to leave about 3/32” gap at the bridge position before the dovetail socket is cut – so I’m wondering if that 3/32” is compensation for the change in angle when socket material is removed?
Hope the attachment helps…
Many thanks.

[ken cierp]

Here's my article on neck set angle -- the key is the relationship between the angle on the neck heel cheeks and the slope off the soundboard where the fingerboard extension lays. The complimentary angle must make a straight line -- I suggest that you -- at this point -- forget about where the plane of the neck ends up over the top of the bridge location. As the article points out this is pure mathematics and you can plan exactly what needs to be done right from the start just like millions of factory guitars are regularly processed. So plan on having the neck tilt back at the common 88.5 degrees and go from there. There's a fixture being sold for about $150 I think on ebay that will greatly improve ones chances of getting the complimentary angle correct -- if I were a fan of dove tails (the joint from hell) I'd certainly make or buy the fixture. The bottom line in and my point is, don't plan for errors or adjustments plan and do it according to the math requirements.

http://www.kennethmichaelguitars.com/neckangle.html

[John Parchem]

I agree with Ken's comments. I use a tool very much like Robbie's but I now create necks with a fixed angle. I do not use the body to set that angle. Your illustration actually shows why there are issues with setting the angle using the body.

I have used a tool much like Robbie's in the way you describe. Then I set the neck angle using the body before cutting the neck tenon. I made the correction to get the neck angle correct based on what you show in the top picture when I fit the neck. If you have a classical or tapered style heal the neck cheeks will have to follow the curve of the rims as they narrow; the router will not cut that curve. As I have been doing cutaway guitars I switched to a squared neck heel I just clear the area between the cheeks and the mortise so the neck can sit flush.

The illustration you have shows one of the reasons I switched to a fixed neck angle. I work to keep the heel block square when building the rims and gluing on the top and the back, I am very careful to get the correct angle in the rims to be a complement to my desired neck angle and I make the neck with the designed angle. Using the body to set the angle just created another source of error. I always assume that I am going to need to correct the heel cheeks when fitting the guitar.

[Francis M]

Many thanks for the comments and the article link. I will measure mine and see what sort of angle I have. I use a 20' radius on my tops so the comments on the 1 - 1.5 degree from Martin guitars is very interesting and will be taken into account on future builds.

[ken cierp]

Actually its more than just a comment its a report of the facts -- we have sold a great deal of Martin necks and our own designs are based on reverse engineering. Also Martin bracing is contoured to 52' just enough to prevent the sound board from taking on a concave appearance.

[Francis M]

Ken, Sorry if my reply didn't seem to convey the gravity the contents of your reply and its enclosed link deserved. But as I have said I will be putting the contents of your article into practice in future builds. As to the current build - I will need to make some alterations to my original thoughts. The neck is at present in a roughed out state therefore I can apply the correct angle to the shoulder when that stage is reached.
Francis

[ken cierp]

I am a bit confused as to why you would put a radius on the neck/rim under the joint? We sell a varity of kits sloped, round, square shoulder etc. including J185's -- they all have neck blocks with a gentle contour on the edges, but the area under the neck heel is perfectly flat. And prior to neck fit the area is trued flat with a sanding block.