Reader Charles Hoffman details his tip for routing perfectly parallel slots. With a Baltic birch plywood subbase and a hardwood guide, Charles finished his project in no time.
Routing Parallel Slots

I agreed to make a tally board for my bridge club, and my plan to use sliding dovetails for each player's name block seemed so simple. To lessen the strain on my router and prevent the dovetail slot from packing with dust, I decided to precut the slots with a straight bit, then rerout them with a dovetail bit. But how could I ensure dead-on spacing for all 20 slots?

To solve the dilemma, I fashioned a subbase for my router from 12 " birch plywood, with a 38 " x 516 " hardwood guide dadoed into place on the bottom (as shown in the drawing at right). The distance between the guide and a 516 " straight bit mounted in the router equals the intended spacing between the slots.

I routed the first slot with a 516 " straight bit in my table-mounted router, then used the same bit in my handheld router, with the subbase's guide in the first slot, to rout the second slot. The second slot guided the router for the third slot, and so on, until I had cut the number needed.

Next, I switched to my dovetail bit, and set the cutting depth so as to not widen the original 516 " slot. I used the second slot to dovetail the first slot, then rerouted the remaining slots into dovetails, using the adjacent slot as a guide.

The jig worked like a champ, saved me a lot of time over alternative methods, and the results were flawless. Before you try this, you'll need to make some test cuts to figure out the precise relationship between cutting depth, dovetail-bit angle, and straight-bit diameter to make sure the slots will work for your project.
—Charles Hoffman, Ellicott City, Md.