Backer Board

Dan Neubecker with Dave Tutelman -- March 19, 2005

If you have not already, cut the two rectangular backer board pieces from the hardwood plywood stock. Depending on your tools, you might consider cutting these about 1/8” wider, then ripping them down to the final 8” after they are rough screwed and glued together. This will help ensure that the edges on the top and bottom of the backer board will be perfectly flush.

Clamp the backer board halves together. I suggest you temporarily clamp from the top and bottom and front to back to try to ensure that the two pieces align properly. Once aligned, install the eight screws from the back of the backer board. (Four of the screws are shown in the photo.) These screws will act as an alignment for the pieces whenever you need them together, until they are finally glued together to become the Backer Board subassembly.

Make the cutouts

I recommend starting with the backer board pieces already screwed, but not glued together. This will ensure that the cutouts will line up from one piece to the next when finally glued together. It is especially important that the tops of the cutouts line up so that the cam clamps operate properly.

Mark the locations of the edges of the cutouts. The cutouts are essentially rectangular, but look better (and may even be easier to make) if they are radiused. If you elect to radius the cutouts, also mark the center of each circular cutout. Make these marks on the front of the backer board. I elected to make inside rounded edges for the cutouts and did so with w 2-1/8” forstner bit.

Now, setup your drill press with a scrap piece of plywood under the backer board and with the proper setting so that the forstner bit can cut all the way through the 1-1/2” backer board. Align and clamp the backer board to the plywood and drill press table so each successive hole lines up with you guidelines and marks and bore each hole all the way through the material for each of the eight holes. By clamping the backer board to a scrap piece of plywood, you can cut all the way through the material while minimizing splintering and chipping around the backside of the holes.

Clamp and cut the straight sections of the cutouts between the holes. To get the best line and minimize splintering, use an orbital saber saw with a blade with the teeth that angle down. Also clamp a straight edge, guide piece along the backer board to help keep the saber saw cut straight.

Finish the holes with by smoothing the edges of the cutouts. One way to do this is with a router and straight bit, also guided by a straight edge. Going a little over halfway through the piece. Then, either use the router and guide on both sides of the backer board, or extend the router shaft (if your router can extend that far) in order to get both sides even. Another way to finish the cutouts is with a drum sander.

Finally, chamfer or round the edges of the cutouts with a router and bit and sand as needed, in order to protect the hands from sharp edges or splinters.

Final steps

Glue the two backer board pieces together using woodworkers glue. Spread a thin coat over both surfaces and use the screws you already installed to help align the pieces together. In addition to the screws, I recommend liberal use of clamps to press the wood together. Periodically wipe off any excess glue along the outside edges and around the cutout areas. Most wood glues dry for further work in an hour or two, depending on the temperature of your work area. After the proper drying period, you can proceed with further work.

If you decided to make these 1/8” wider, now is the time to rip them down to the final size. Set up your saw with a blade depth a little over 1-1/2” and rip about 1/16” from each edge. Rounding or chamfering the corners is optional, but if you plan to do, now would be a good time. But do not round or chamfer the top edges; they must be left full-width and square-edged for a variety of reasons.

Drill the 5/16” hole for the pivot bolt assembly. This must be done with a drill press and the backer board should be clamped in place as described above to ensure a perpendicular hole and less splintering. Be careful to locate this hole as closely to plan specs as possible.

Drill the 5/16” vertical holes from the top of the backer board through to the cutouts. It is critical that these holes be drilled no farther than 11/16” from the front of the backer board, measured at the top edge of the backer board. This will ensure proper spacing and sliding of the t-slot during NF4 operation. (The position of the exit hole in the cutout is less critical.) Again, I recommend that you drill these holes with the backer board clamped in place so that the holes are parallel to the sides of the backer board and perpendicular to the top.

Finally, rough and finish sand the backer board as needed.

The photos below show the backer board finished and assembled.

Last modified 8/21/2005 by Dave Tutelman