Plywood ski jig
I really like Harry's ski jig's but thought that most woodworkers wouldn't want to fool with getting the steel rods made. I came up with the idea of using a plywood "H" frame to support the router and it worked out ok. Here are the basic steps to building your own.
Start by getting the furniture hanger bolts, washers and knobs.(8 of each required) If you are building a ski jig for a trim router then 1/2" plywood and 1/4" hardware is fine. The jig shown is 3/4" Baltic birch plywood and needs either 5/16" or 3/8" hardware. Your hardware determines the size of the slots and the bit required to make them.
Next you will need the plastic to mount the router on. This jig has Lexan but Plexiglas would work just fine. The plastic should be 3/8" thick x the width of your routers sub base plate x the width plus 1-1/2" for the length. IE.. 6 x 7-1/2". Mark the center of the plastic by running lines from corner to corner. If you want to use guide bushings drill the hole and countersunk area to fit them or just cut out a 2" hole if the jig will only be used for planing and sign making. Using the sub base plate from your router as a template mark, dril and countersink the holes to attach your router.
The long rails of the H frame are 1-1/2" x 24". I chose this length so the jig would handle boards up to 10" wide without needing to adjust the router on the rails. The short rails are 1-1/8" by the short dimension of your plastic. IE.. 1-1/8" x 6". Attach the short rails to your plastic plate by drilling, and countersinking holes for #8 x 3/4" flat head screws. I centered one hole and added another 2-1/2" from each end so they would not run into the furniture hanger bolts when installed. These 6 screws had no problem supporting the PC 690 series plunge router. Using a router bit to match your hardware adjust your fence so it is 3/4" from the center of your bit and cut the slots in the long rails leaving 2-1/2" on each end. A spiral up cut bit works best for this. Clamp your long rails and the short rails mounted on the plastic(with the plastic on the bottom) to a bench and drill the holes for your furniture hanger bolts. Use two nuts jambed on the hanger bolts to install them. Fasten the long rails to the short rails with the washers and knobs This is best done with the pieces sitting on a flat surface; this compensates for any slop in the alignment. With the H frame assembled you can measure the spacing required for the slots in the end plates. Add at least 1" on each end, IE.. 7-1/2" slot spacing plus 2" = 9-1/2" length. I added more so I could make saw handle grips as shown in the photo; I thought this would give even more control.
I started on the end plates by making a template out of 1/4" Masonite. I cut the angle and used tin can geometry for the corners. By this I mean I grabbed a can of wood putty and used the base as a guide to mark the curved corners. I drilled two 1-1/2" holes for the handle and made straight cuts with a jig saw to connect them and then to shape the corners. A touch of light sanding and the template was done. I adjusted the fence on the router table so it was 1-1/2" from the center of the bit. I made the slot in one end of the end plates. Next I adjusted the fence and made the other slot cut. I attached the template with some double stick tape and routed the outside of the end plate to shape. I drilled a starter hole in the handle and routed out the opening. After both end plates were cut I changed to a 1/4" round over bit and rounded over all the edges. Assemble the end plates with the washers and knobs and it is time for alignment.
Install the router to the plastic plate. Set the jig on a table and support the H frame with pieces that are a uniform size on each end of the long rails. I used steel 1,2,3 blocks because I had them but you could make a set out of hardwood... 1" x 2" x 3". Since I was working with a piece of 2 x 4" for a planing test cut I used the 2" height adjustment. Tighten the knobs, install your bit and make some sawdust.
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