Sizing Down Sheet Goods with a Shop-Made Saw Guide
A common, compact, portable circular saw with a coarse, wide saw blade is great for framing and other site work, but it can be tamed for finer things. By merely swapping the blade and increasing the base dimensions, you’ll experience controllable precision like never before and will be able to crosscut sheet goods to size with ease and accuracy.
Begin by replacing the 8-1/4″, 24-tooth general purpose blade with a 7-1/4″ 40-tooth, thin-kerf “Finishing Blade”. This will be fine for cutting stock up to 2v thick. The tighter radius and greater tooth count produces a smooth kerf with virtually no tear-out, and the thin kerf greatly reduces resistance so cutting takes less effort.
All the Parts
The sled base consists of two parts which fit almost perfectly against either side of the blade, two smaller parts that fix the first two parts together, and a longer piece on the side of the sled that helps register the saw in place.
Accurate Hole Locations
Salusbury snipped the head off a bolt, ground the tip down to an even point, then threaded the bolt tip through the hole in the saw's base to leave an imprint on the plywood base.
Playing Card Shims
Playing cards are placed between the blade and the base when gluing the base parts together. They provide a small gap to allow the blade to run without heating up or losing power.
Glued and Clamped in Place
The sled components are now glued and clamped around the saw's base plate.
Drilling the clearance slot in the base for the blade guard is done with a sharp Forstner bit.
The Completed Sled
Though it's not fancy, the completed sled is a precision-made assembly that will make smooth, straight and quick cuts in sheet goods.
Build a base
To make the friendly accessory sled (more like a toboggan), begin by measuring from the side of the blade tips to easily memorable widths just beyond the overall widths of the saw. In my case, this was 8″ on the left (motor) side, and 2″ on the right. For control, make the length of the sled a few inches longer than the stock base; my stock base is 12-5/8″ long, so for convenience I made my sled length 16″, but a bit longer would be fine. Cut left and right panels for the sled base from 3/8″ Baltic birch plywood at the table saw. Using a 1/2″ piece would also be fine.
Now invert the circular saw (unplugged of course), and with the blade fully lowered, the blade guard temporarily retracted (I used an elastic band), and a couple of playing card “shims” on either side of the blade, front and back, clamp the panels for the sled base centrally on the saws base plate and snug to the blade sides. Trace the base’s outline onto the sled panels for later reference. Also mark out the margins of the blade guard so you can drill clearance for it after final assembly.
Secure it in place
Locate convenient spots near each corner of the base plate to drill clearance holes for bolts to secure the sled panels to the base plate. I used 1″ flat head machine screws with nyloc nuts and flat washers through 3/16″ holes. To accurately transfer the hole locations onto the sled panels, upright the saw onto the sled panels within the lines just traced, tap a spare bolt, clipped and ground to a point on one end, deftly through each hole. Once this tapered bolt is threaded through the hole in the base of the saw, it will leave an imprint on the plywood base, marking the exact location of the required hole. Drill the four holes through the sled panels, then countersink the holes in the underside of the plywood base to allow the heads to sit under the bottom surface of the base.
Back at the table saw, from 3/8″ Baltic birch plywood, cut panels for left, right, front and rear supports. These should be sized to bracket the saw’s base plate for easy registration and reinforcement and trimming to final size after assembly.
With the countersunk bolts securing the sled panels to the saw’s base plate, add the three support panels, snuggly framing the base plate. Make the front and rear supports 1/4″ shy of the ends of the sled panels and chamfered to improve sighting of the saws kerf in use. Glue, 5/8″ pins and clamps will bring the parts all together.
Fully cured, unclamp the assembly, remove the saw and bolts and clean up any glue squeeze-out. Now trim all margins to the exact dimensions left and right of the blade, as discussed earlier. You will also have to ensure the edge of the sled is perfectly parallel to the saw’s blade. After defining the location of the blade guard, at the drill press, drill a series of closely overlapping holes using a Forstner bit for clearance and full operation of the guard. Be sure to not remove the area immediately beside the leading edge of the blade, as that material will press down on the workpiece during the cut and reduce tearout.
Sand and finish
Sand overall, ease all edges, dust, and apply three coats of urethane for a hard, slick finish. Once cured (72 hrs.) re-bolt the sled to your saw’s base, a scribble of paraffin wax on the sled bottom and left edge and you’re ready to enjoy some smooth fine cutting.
As a bonus, you can use straightedges of whatever thicknesses are convenient, as your reference edges are beyond the margins of the saw body, while the sled gives you lengthy reference surfaces before and after the cut.
Now it’s time to reduce heavy, cumbersome and often expensive sheet goods into manageable panels to be cut exactly into parts on a cabinet saw. I provide lift for the sheet being cut by supporting it above my workbench with 3/4″-thick strips of plywood. This helps protect against blowout and provides much-needed support to the panels after they’re cut.
First, the sheet is placed on a firm, fully supportive flat surface, be it a floor, bench or saw horses with lumber cross members. On top of that, support strips of 3/4″ plywood are laid in line with the cut, two narrower strips to support the outer ends of cut panels and a 4″ to 6″ strip to be laid directly under the full length of the cut, supporting the cut ends/edges of the panels plus the fibres on either side of the cut, eliminating blowout.
The straight cut is guided by a quality drywall square clamped in place on both ends, eliminating movement.
In use, the full-sized sheet is placed on the bench or floor, and then the support strips are positioned as required. The drywall square blade (fence) is clamped in place to the left of the cutline to exactly the width between the left of the blade kerf and the left edge of the sled. The saw blade is set so it clears the thickness of the sheet by a mere 1/8″. With the sled guided deftly along the fence, a clean, precise cut is safely crafted. A chore no more and for a fraction of the cost of a dedicated track saw.