This pertains to making shims for acoustic guitar dovetail fitment. You have already adjusted the neck shoulder areas for accurate alignment. The center line of the fret board aligns with the center of the proposed bridge location. And the plane of the fret tops aligns with your desired location at or above the top of the bridge. These two measuremets assure that the strings will align with the neck sides and that the saddle will have sufficient height standing proud of the bridge top.
So at this point the dovetail no longer fit the dovetail socket in the guitar upper bout. You may well have removed considerable wood from the neck butt end shoulders so as to achieve the foregoing alignment. Time for shims.
Accurately adjusted dovetai faces using shims is critical for neck stability under string tension. You want to creat two dovetail cheeks with align with the two socket cheeks resulting in a tight fit for the length of the dovetail mating or glue surfaces. You sure don’t want the neck coming loose from the guitar body.
The best possible shim wood is American Cherry. No other deciduous hardwood accepts glue better. For hundreds of years, Cherry was and still is the timber of choice for fine furnature. Proof of this is how nicely Cherry accepts stain. Only Holly soaks up stain better than Cherry, but Holly is too soft. We want a hard wood that will not compress while the neck is under string tenson. Not to mention that Cherry sands and chisels beautifully.
Small pieces of Cherry are available from Woodcraft.
The procedure for making dovetail shims has the following steps:
The diagram below shows shim stock cut to approximate length and width.\
On the diagram below note the diagonal fibers resulting from spliting the shim stock. The arrows show which way to glue the shim pieces to the dovetail cheeks. (A previous article explains why gluing shims to the dovetail cheeks is friendlier than gluing to the socket cheeks.) Using this method, your chisel cuts are much easier because the chisel will not dig into the shim but will shave very fine cuts as you work towards the best possible dovetail fitment.
The foregoing works nicely 90 percent of the time assumming you have chosed good quality shim stock. That part is up to your eye and good judgement.
©2021 D.R. Hanna