I love using crosscut sleds but I find them fussy to make and maintain. I have always made mine with MDF bases, hardwood fences, and I’ve tried a number of different types of guide bars. My most-used sled recently developed a curious rise in the middle that I couldn’t fix. I don’t know why or how the hump happened, but I couldn’t get a vertically square cut without tipping the blade. Not being able to flatten the base was as frustrating as it was perplexing.
I decided NOT to rebuild my sled using unreliable and often irregular sheet goods. Needing something dead flat and easily worked with the tools I have, I decided to try plastic.
Acrylic sheet plastic, A/K/A Plexiglass, should stay utterly stable and flat forever. It is easy to cut and drill without special tools. But that isn’t what makes this worthy of notice. What makes this worth making is that by using a transparent material you can make and adjust this sled from above the table. That takes a whole lot of the fuss out of making and maintaining this sled. The photos below say more.
In this view from above you can see I’ve used guide bars with spread washers so they can be mounted and adjusted without removing the sled from the saw. I used my rip fence and clamps to hold everything steady while drilling the mounting holes. I used washers in the miter slots under the guide bars to raise the bars up against the bottom of the acrylic sheet. I drilled and tapped 4 holes in each bar to accept 10-24 X 5/8” machine screws for mounting. The holes were made by first drilling the countersinks in the plastic. A 13/64 bit centered in the bottom of the countersink opened the hole for the bolt through the plastic and marked the hole for the tap. Without moving anything the bolt hole in the aluminum was then drilled with a 5/32” bit, the correct size to tap the aluminum for a 10/24 bolt. The bit self-centered in the divot made in the aluminum by the 13/64 bit. By following this drilling sequence, the bars mated to the plastic perfectly straight and without having to move either the bars or the sled until it was time to tap the holes.
This close-up shows one mounting screw and one adjustable washer in close proximity. A ¼” hole was drilled directly over each spread washer so that the guide bars can be adjusted to the miter slots from above the table. Maintaining a perfect slop-free fit will be a snap with this arrangement.
As if Karma demanded that I prove my point about the value of above-the-table adjustments, I dropped this sled a short time ago while trying to stow it in its cubby. I knew immediately that all calibrations were lost. The impact closed the kerf, pinching the saw blade. I was able to remove the fence, readjust the base to the blade, and reinstall the fence fairly easily. Squaring the fence is the same pain as always from below, but those final adjustments to reestablish slop-free and smooth operation are child’s play from above.
I hope you’ll try this on your next sled and let me know how it goes!