The JET JWJ-8HH is the largest and most sophisticated jointer made by JET. It is nearly identical to the JWJ-8CS, but upgraded with a helical cutterhead.
The Helical Cutterhead is a major upgrade, because the JWJ-8CS only has standard blades, whereas on the 6-inch standard model at least you have quick-set straight blades.
Spiral cutters are quieter and give better jointing results, especially on complicated grains. They are also easier to set up, last longer because of the 4 sharp sides and are cheaper to replace if one of them breaks.
It is more powerful than JET’s 6-inch jointers (2 HP vs 1 HP), and has more jointing capacity (8 inches), making it a very useful upgrade over the smaller models. Still, 8 inches is on the small side when face-jointing boards.
The jointer uses a classic wedge-bed dovetail system over which the tables slide up and down. The chrome handwheels make it a lot smoother to move the tables than on many comparable machines. It also has a special rabbeting ledge.
The JET JWJ-8HH also has long cast-iron tables and a solid, rigid fence. The fence has three positive stops at -45, 90 and 45 degrees.