When I started on the neck reset, the very first thing I did was to take a measurement on the difference the neck plane was beneath the top of the bridge.
Armed with that measurement (it was .203 inches), I can then calculate the amount of material I need to remove from the bottom of the neck heel in order to tilt it back so that it's aligned, or "set," properly.
The picture above is my sheet of calculations. This is from Dan Erlewine's repair book. It's a common formula.
I need to remove about .071 of an inch from the bottom of the heel. We'll be taking a pie-shaped slice off - wider at the bottom and tapering to zero at the top where the neck meets the body.
The 'crumbs' on the page are small rosewood chips from drilling the steamer access holes. I plan to glue them onto the top of the fills at the end.
This picture hopefully shows what's being removed - a pie-shaped slice that's wider at the bottom of the heel, tapering to zero at the top. Visualize the material being removed and you will also picture how this will make the neck tilt backward a small amount, and correct the neck set.
I now have some nice German-made Two Cherries chisels from Diefenbacher Tools. I honed them super sharp and they easily take the mahogany off the heel. I'm still on the lookout for some Swedish chisels - they are harder to come by over here.
The stick is just a paint stirrer with strips of sandpaper attached to either side with low-tack (removable) spray adhesive. I sanded the stick down so it's more flexible (to follow curves better). One side has 120 grit paper, and the other has 320.
Houston, we have success!
Then I hold the neck tightly in place, and pull the paper out. The heel will take the contour of the body for a nice looking joint.