Really, this article should be used in conjunction with the article on a Bolt On Acoustic Guitar Neck article, as you need to make these sort of adjustments before you finally set the neck bolts. Also you haven’t already, read the article Mortise and Tenon Neck Joint for addition information and clarifications.
Fitting the neck onto the acoustic guitar body in no small order. This can be a very time-intensive project and one that you should not get frustrated with if things do not go perfectly.
This is probably one of the most important and precise projects you will have in making your guitar. Why do you say? The reason for this is we are dealing with tiny fractions of a mm to make adjustments either right or left or up or down in the neck angle.
The best advice that I can give you is to go slow and make all of your cuts precise. Check dimensions, double and triple check them. Please follow the instruction to the letter in the article Mortise and Tenon Neck Joint. If you do you will not go too far astray.
Tools and Materials Required:
36″ Steel Straightedge: This has to be a straight edge that is absolutely precise. If all else fails and you can’t find one, use a good quality 48″ aluminum level.
Stationary Belt Sander:
10″ Table Saw
Fine-Toothed Japanese Pull Saws:
Woodworkers Marking Knife
8″ 4-Way File
For a Bolt-On Neck:
Make sure that the tenon of the neck fits into the mortice without undue force. A bit of friction would be perfect. We don’t want a sloppy joint here. Also note that the bolt-on option gives you additional strength and stability when test fitting the neck to the body vs. a dovetail joint. This will ultimately provide a much better neck fit once the neck is glued on. You will find that with a proper bolt connection, there is little need if any for clamping the neck and only the force of the the bolt(s) can be used.
GLS Tip #1: If you have a space between the guitar heel and the body and you can’t seem to get rid of it, try back-sanding the surface of the heel that meets the body at a very slight angle toward the tenon joint. I usually clamp the neck in a woodworking vice with vertically so I have excellent access to this surface.
If you want to take away material by hand, do it with a 8″ 4-Way File8″ 4-way file. Tilt the file toward the tenon slightly so you take off material mostly near the tenon. Be careful as you usually do not need to take off too much material. Also – you need to take off exactly the same amount on both sides of the tenon.
Check Neck Angle:
For guitars with flat tops and no perceivable arch (which is what all of my plans show), the neck angle to the top should be “0” zero, flat or no angle.
Clamp the neck to the head block and carefully check the angle by holding a straight edge on the center of the neck, all the way to the guitar bridge. You should not see any crack of light on either the neck or the body. If you do, the neck angle needs to be adjust very slightly.
If the angle is too high you need to take material off the neck mostly from the bottom of the heel to to the top of the heel. This has to be completed on both sides of the tenon, with exactly the same amount of material coming off or you will throw the sideways angle of the neck off center.
Again, check the neck both horizontally and vertically and keep sanding until your alignments are absolutely perfect!