Self center mortising jig with 75" diameter guide slot, adjustment from 1" to 2.5". slots long with stops.
OK! No guess work here, thinking and designed behind jig is making it real accurate.
1)One thing to remmeber about (Aluminum 6061 bar) 2 pcs I made exact same length and same width (0 to 1" tenth Mike was used, and 12" calipers). Tell you in a moment. I swept the center in both directions with a Indicator on a vertical mill, for center tap hole. When tapping the 2 end tap holes, moved 1/2 distance to the edge width from center, drilled and rotated aluminum pcs around to get exact center distance from center, do both pcs same setup time. (that's why both pcs are same all aspect) This makes the jig more accurate off the center line off your work Pcs each end.
2) The 2 wooden pcs that attach to Aluminum bars, holes are done the same way(length, width, and height)same on both pcs. (trick of trade being a machinist for a long time, that worked well for me is drilling under size, than step to hole size you want, this makes the hole more straight and more accurate in diameter and location.
3)The 3/4 slot on the router base, was done on a router table with a under size router bit. I made the slot to accuate diameter of.751 for the reason the part was rotated from side edge to side edge width to make the slot accurate fom center line for a .749 bushing guild. A stop was setup at the time I made router base working off center for length (1/2 distance) of slot. In the future this may change to longer height for angle slot.The accuracy of the jig is up to you! When I checked out the wood parts, they had .002
thickness difference from each other, error, the jig keep it to a minimum of .003 total from center. This can be done on a drill press if the head is (Trame) indicated in to the table, plus a thickness gauge, shims and table jig.
Now, I came up with a attachment, mount on a worktable with vacuum hose.
This router jig has (2)1/4" shoulder bolts, and (2).250" oil lite bushings with flanges, on each hole on main router base, and they are centered, and added short wood support to each side arm keeps it very stable when routing 3/4" malt. The 1/2" wide aluminum bar, has (2)#10-24 tap hole in the center of the bar, and (2)5/16 tape hole on each end to the center hole. Clamp your pcs in place to center and set your stops, and plunge to depth per path. This was drawn up on a (2)cad design program (Inventor and Solidworks). You can even predrill the slot in the pcs with a drill center jig if you what to, before using router jig if you prefer. Then clean it up with the router jig.
I Been machinist over 40 years, Around machines all my life, you need respect for that machine you are running(ALWAYS). Other words keep your head focus on what you are doing (ALWAYS). This lawyers s _ _t is going to cost the woodworker like you and me more money in the long run. Stupid Dumb_ _ s lawyer. The main point is responsibility for running the saw. The Guy need to trade all is tools in Dumba_s.
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