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Materials
Tools Used Machinists Square, Dowling Jig, Drill Press, Band Saw, ¾ Hole Saw, 5/8 Forstner Bit, Electric Drill, ¼" Drill Bit, 1/8 " Drill Bit, 19/32 drill bit, Disc Sander, Sharpie Marker, Pencil, ½ " Wrench, Chop Saw, Fly Cutter. Procedure: First I cut two 10" X 13 1/2 X 3/4 MDF blanks from some 12" strips I had ripped out of a 4' X 8' sheet at Home Depot. I used the Chop saw to ensure all the blanks were good square cuts. I then marked the exact centerline on one end of each piece with the machinist square set at 3/8" and marked 3 evenly spaced locations on each one that would be inside the cut line for the final jig. Next I drilled six holes at the marked locations using a doweling jig and a 1/4" bit. this ensures all the holes are centered and perpendicular.
When using MDF in the past I have found that small screws don't hold very well in the end grain and strip out very easily. For that reason I will be using some rubber 1" X 1/4 #6 Expansion plugs. These are rubber tubes with a # 6 brass threaded insert at the end and a collar at the other. When you insert these into a 1/4 in hole and put a #6 machine screw in them they expand as you tighten to fill the hole and make a nice tight fit. After you drill the 1/4 " holes with the doweling jig you must inlet the them about 3/32" to allow for the rubber collar. I used a 1/2" forstner bit in the drill press to accomplish this.
I next cut some 1/8 X 3/4 X 10" aluminum strips and drilled and countersunk them to accept #6 Flat head Machine Screws at the locations previously drilled and installed them on the ends of the blanks with the Rubber expansion plugs and six #6 1 1/4 flat head machine screws.
The reason for this procedure is to allow for the different cap strip thicknesses at the Spar end of the rib. By removing or adding 1/8 in strips you can cut each rib with the router to the exact length needed for each location on the spar. you must do this operation to the blanks first so that you will already have the 1/8" strips installed when you align and trace the rib outline onto the blank for cutting. I then placed the master template on the nose rib blank and aligned it to the main spar line and drilled and pinned the nose alignment hole with an alignment pin, (make sure the aluminum strips were perfectly aligned with the main spar line and allow .035 for the spar web.) Note I completed the above procedures for both the nose and center rib blanks at the same time the only difference was that the center rib gets a 1/16 strip on the rear spar end instead of a 1/8".
The next step was to trace around the master template with a sharpie marker and a plastic disk I had from an oil seal installation tool . You can use any method or tool you want as long as you get a nice 9/16 in flange around the master template.
I then pinned the blanks together using the alignment holes and 1/4" alignment pins and cut them out on the band saw. I first cut to the line with the band saw and then removed the line on the disk sander. the completed blanks were then separated and the back side of one was inlet for the "T" nuts that will be used to secure the two halves together at the three alignment holes. I used a 3/4 hole saw with the drill bit turned around to mark and inlet the desired depth. Then a 5/8" forstner bit was used to remove the material in the center. Next a 19/32 drill was used to ream the bolt holes 1/2" deep to allow for the T-Nuts. The "T" Nuts were then tapped in with a hammer and 1/4-20 X 1/12 bolts and washers installed and tightened to set the T nuts.
I then separated the two halves and used the Master template to set the Fly Cutter diameter to the proper size for the first lightening hole. I then installed the fly cutter into the drill press and set it to its slowest speed. ( Caution: The fly cutter is very dangerous and can only be used in a drill press and then only if all pieces are properly clamped.) Take your time with this and don't force the drill press. let the fly cutter do the work. Repeat the process for the other hole saving the plugs to be used when centering the jigs for flanging later on. Reassemble the two halves and you have a completed Nose Rib Routing Jig. Completed 03/19/2005. Time to complete 3 hours.
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