The TM-1 Tenonmaker is a very useful tool that is precision machined from anodized aluminum. It simplifies the process of making an accurately sized tenon to fit an existing mortise. It works with any cutter that leaves a clean, repeatable kerf, such as table saws, router tables, or the Jointmaker Pro. For mortise and tenon joints, typically most woodworkers will make the mortise first, either by hand, or using a router, mortising machine etc. They will then cut the tenon to fit, either by trial and error, or by cutting it oversize and then using shoulder planes, router planes or other method to adjust the fit.
The TM-1 removes all of this uncertainty in creating a well fitting joint. To use it, a sliding arm on the TM-1 is adjusted to the exact width of the cutter kerf and then locked in place. Then another sliding arm is adjusted to the width of the mortise. The fit of the joint can be changed by adjusting the pressure you use on the gauge arm when setting the mortise width. After these adjustments, the TM-1 is used as a spacer against a fixed stop or fence to cut one of the tenon cheeks. It is then flipped to create an offset to cut the other cheek on the tenon, either by moving the stock or a tenon jig. It works on tenon widths up to 51mm (2”). After cutting the tenon shoulders, the tenon will fit the mortise precisely.
To see how this works in more detail, there are several very good videos on youtube showing how it works.