Square bearings steady saw guard

Littlestown, PA —Saying that the new Angle Boss saw from Vista Machines, Inc. is a "cut above" other radial arm saws is somewhat of a misnomer. Unlike most radial arm saws that cut from above, this new saw cuts from below. The Angle Boss does, however, provide users a safer way for making accurate cuts compared to other saws, thanks to the inclusion of square bearings from Rexnord Corp. (Downers Grove, IL).

A saw cutting from beneath is unusual, but not a totally new idea. With other saws that cut from below, the guard is mechanically tied to the upstroke of the saw carriage. In the Angle Boss the guard must be down and clamped before the blade raises, thereby minimizing risk to the operator.

In the prototype, a dual shaft arrangement guided and stabilized the guard that rode up and down on two round shafts. The two-point arrangement caused binding or "window locking" as the guard rose and fell. Such binding limited the table's rotation and reduced its mitering capability.

Unlike the prototype, the final design uses two Duralon bearings from Rexnord operating on a single 1-1/2-inch square guide shaft. Square bearings, one positioned on top and the other at the bottom of the guard support shaft, provide stability against rotation. "Vista's use of a single square shaft and a square bearing accommodates the vertical travel of the guard, which eliminates the possibility of window locking," says Bernie Harris, the engineering manager at Rexnord.

"If we use linear ball bearings, it is impossible to completely seal. Eventually the loss of lubricant causes galling on the shaft," says Toby Dennis, one of Vista's founders. Galling restricts the saw's mitering capability. Lack of a seal also allows sawdust and other contaminants into the bearing, which causes premature wear and, eventually, bearing failure.

The patented process used for making square Duralon®bearings begins with a square arbor for tooling. Teflon®and Dacron®fibers are tubular woven into fabric and heat shrunk around the arbor. Continuous strands of fiberglass roving are wound in a helical pattern over the fabric and impregnated with epoxy resin. The matrix is cured at evaluated temperatures to form the bearing structure. The resulting bearing has fabric bonded to the fiberglass and epoxy resin shell. "The composite bearing is self-lubricating, self-contained, and has compressive strength as high as 80,000 psi," says Harris.