According to the 1964 owners manual (linked to in the first post of this thread), you can use either a 9” or 10” blade. The larger blade will give more depth of cut, of course. On most small RAS’s, torque to cut with the larger blade may be marginal. But with the Sawsmith, you can reduce the speed, which will boost the cutting torque proportionally. I’d go with a 10” thin-kerf blade, as 9” blades are scarce these days.
On page 12 of the same manual, under the Arbors section, it says that you need a 1-1/4” arbor to use Shopsmith blades, but that “some accessories” can be mounted directly on the 5/8” spindle shaft, using the supplied nut and washer. If you have those (the nut is probably left-hand threaded), I’d bet that you can use a standard 5/8” bore saw blade.
However, you don’t want to use just any blade on a RAS. Using the wrong blade is a major reason that they developed a reputation for being unreasonably dangerous. A typical tablesaw blade has an aggressive positive tooth hook, which on a RAS can contribute to the blade “climbing” the workpiece and running out toward the operator. (This problem is excarbated by poor structural rigidity on some saws — I’m not sure how the Sawsmith compares on that front.) Chop-saw blades typically don’t have enough hook, and perform very poorly for ripping on a RAS.
On the DeWalt radial arm saw forum, the top-rated RAS blade is the Forrest Woodworker I TCG (Mr. Sawdust) blade. This universal blade gives excellent results on every cut you can do on a RAS. You can order directly from Forrest, but they have new sales personnel who will probably try to sell you their standard Woodworker I ATB blade instead. It’s easier to order from Slivers Mill.
https://www.sliversmill.com/category_1_Woodworker_I.html
The next-best, and considerably less expensive, blade is the the Freud LU83R, available from Amazon.
Conventional wisdom says that RAS blades should have a negative hook angle. But testing done in cooperation with Forrest determined that a small positive hook is ideal.
