Sliding-Table Saw That Switches Itself: A Hand Saw Under a Table on Balls, Turned On and Off by the Stroke (Tracy, 1941)

"The finger 25 is so disposed as to engage trigger 24 and close the switch when the table is advanced and just before the saw reaches the work under which the table slides, and to reengage the trigger and open the switch as the table retracts and approaches a fully retracted position."

Make an open-topped box of 18 mm plywood 900 mm long, 450 wide and 300 high, the end panels 2 standing 40 mm lower than the sides 1, glued and screwed. Bolt a steel channel section 5 along the inside top of each side, its open face inwards, as his channels on the beams 4.

Cut the table 6 from 18 mm plywood 600 x 400 mm with a saw slot 15 down its middle, and bolt a steel channel section 7 along each side edge, its open face outwards opposite the box's channel, reaching 100 mm past the table's front for the handle. Lay 10 mm steel balls 8 between each pair of opposed channels, three a side, spaced along, and slide the table in so it runs level with the box's top. Fit a hardwood handle 9 across the angles' front ends, and stops 10, 11 and 12 to limit the stroke to 450 mm.

Bolt the circular saw by its own base plate under the table, the blade up through the slot, the saw's depth set so the blade stands 10 mm above the thickest work. For angle cuts use the saw's own bevel adjustment, which does what his arcuate bracket 17 did. Tape or lock the saw's trigger on, so the new switch alone controls it.

Screw a lever microswitch rated for the saw's current inside one side panel, its lever 24 pointing up into the path of the table, with an outlet for the saw's plug and a supply cord through the panel, as his switch box 22 and socket; have it wired by an electrician. Bend a finger 25 of spring steel and screw it on a bracket 26 under the table, set so that, as the table goes forward, it flips the lever on 60 mm into the stroke, and as the table comes back it flips it off 40 mm before the end. Check it with the saw unplugged: you should hear the click each way.

Cut a half-round steel plate 27 to lie over the front of the box beside the saw, turn its straight edge up as a flange 28 and bolt a hardwood fence 29 to it, notched 30 for the blade. Pivot a link 31 on top of the plate and a link 32 under it at the centre of its arc; pivot a third link 33 on 31's end; take 32 and 33 back to a flange on the side of the box. Mark the plate in degrees and drill rows of holes along the arcs, and set the fence with a pin through link 31 into a hole, clamped by two wing-nut clamps 35, 36.

With the table fully back, hold a board against the fence with one hand and push the handle with the other. The saw starts by itself before the blade reaches the board, cuts through, and stops as you bring the table back.

**Mearl V. Tracy** of Sacramento, California, assignor of one-half to Marion M. Tracy, US 2,260,421, dated 28 October 1941, filed 18 April 1938. His one claim is the switch: a snap switch with a trigger moved one way or the other by "a resilient finger mounted on the table" that then passes and leaves the trigger, near but before each end of the stroke. He removed the hand saw's shoe and fixed its mounting block on an arcuately slotted bracket; modern saws differ, so we mount it by its base plate and use its own bevel adjustment. His box is sheet metal with the channels on bent beams; ours is plywood with steel channel sections. He gives no sizes; every size here is ours.