This router guide, when used with a top-bearing-guided pattern-maker's bit turns your router into a jointer as well as a precise trimmer. An embedded aluminum bar makes this jig more accurate and durable than others like it.
To make it, cut a piece of one-half inch birch plywood about 4-inches wide, that is, about half the diameter of the router's base plus one inch and make it 4 feet long. Rip a piece of one-eighth inch thick hardboard one-eighth inch wider than the plywood used for the guide's base. Now cut a 4 foot long piece of one inch wide, one-eighth inch thick aluminum bar available at home centers or online from Granger.com Clamp the bar about one-sixteenth inch proud of the plywood's edge and then rip a pierce of one-eighth inch piece of hardboard to fill the space behind the aluminum. Glue this filler to the plywood. Now assemble the guide with three-quarter inch screws. Finally, with the router bit's bearing on the aluminum, make one full pass to establish the reference edge on the exposed hardboard. Your guide is complete.
To use, just clamp the guide to the workpiece with the lower edge aligned with your layout marks. Set the router depth so the bit's bearing in on the aluminum edge and trim away. Be sure the guide is clamped securely at two points at all times. Also, don't let the router tip.
Note: This sounds like a terrific jig and certainly could be used to make the router joint the long edge of boards. Because of the length of some boards you may want a second jig at a longer length.
Yesterday I stopped at Home Depot to buy one-eighth inch thick hardboard and a one-inch-wide bar strip of one-eighth inch thick aluminum. Cost $4.38 for a 24 by 48 piece of hardboard and $8.75 for the aluminum, or a subtotal of $13.13 plus 7% sales tax for a total of $14.05.
I ripped a 4-inch wide strip of the 4-foot-long hardboard, then reset the tablesaw rip fence slightly in and ripped a second piece just slightly narrower than 4 inches. Then I took the strip of aluminum and set its long edge against the fence as a spacer and ripped a third piece that became slightly narrower than 3 inches wide.
I then prepared to glue up the sandwich of layers. I used my work bench at the work surface so I could position the long edges along the edge of the workbench for easy clamping. First I laid down the exactly 4-inch wide piece with the smooth side down and the rough side facing up. I positioned the aluminum strip along one edge so that the hardboard just slightly extended proud of the aluminum, about one-sixteenth inch. Then I applied a heavy wavy bead of yellow glue to the exposed rough surface of the hardboard and spread the yellow glue with a hard rubber roller. It was very difficult spreading the glue since the rough side seemed to soak up most of the glue and I added more glue to be sure there was enough. I laid the three inch wide piece of hardboard, smooth side down, onto the glue.
Next I picked up the aluminum strip and applied medium blobs of CA glue to the exposed rough surface of the hardboard, sprayed a fine mist of water on the strip of aluminum to activate the CA glue and repositioned the aluminum onto the gluey surface. I checked to make sure that the bottom piece of hardboard was slightly proud of the aluminum along its full length.
Next step was to apply yellow glue to the top of the hardboard, followed by CA glue to the aluminum. I sprayed a light mist of water to very slightly moisten the rough surface of the hardboard area that would fit on top of the aluminum, and applied the top layer of hardboard, smooth surface up. I made sure that the hardboard did not extend all the way to the edge of the aluminum.
I laid cauls on top of the assembly so that I could spread the clamping pressure and then used all of my clamps spaced about 4 inches apart. before tightening the clamps I once again made sure the the bottom layer was slightly proud of the aluminum and the aluminum was slightly proud of the top layer. After tightening the clamps, I used a rag to wipe away some of the CA glue that had squeezed out. Then I let the glue dry overnight to give it a chance to cure.
When I unclamped everything a few minutes ago the assembly was plenty rigid and could easily be used without bending the aluminum guide strip.
I then assembled my small trim router with a top-bearing pattern bit to flush trim the hardboard that peeked out under the aluminum guide strip. Even with using eighth inch thick layers I still had to pull out the router bit about a quarter-inch so that the guide bearing would ride on the aluminum edge. I set it up, carefully checked to make sure that the bearing was on the aluminum edge and got ready to flush trim the jig.
And here is where I scared the pants off of myself and want to give all of you a warning heads up.
It's absolutely critical to keep the router flat on the surface and not to tip it. With the small base of the trim router I did tip it slightly over and the router bit grabbed the aluminum edge, skittered a bit, whereupon my reaction was to let go and the router went to the floor. Fortunately it is rather light weight, landed on its side onto a cushioned mat and I was able to turn off the power by the switch on the power strip. But I was shook.
So a number of lessons learned. First is that a larger base seems better because there will be more of the base riding on the jig--but even so a lager base probably means more weight and therefore a greater tendency to tip. Second, if I were to continue to use the jig, I would build some sort of attachment that would be level and parallel with the jig and provide a running surface for the other side of the router's base. This would prevent tipping. Third: I'm bothered by gluing to the rough side of the hardboard but I don't have any experience with it so it may not be a problem after all.
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