Drilling the Main Landing Gear Pockets
Drilling the Main Landing Gear Pockets
by Roger Isackson
After reading the instructions for locating and drilling the holes for the bushing installation in the main landing gear pockets, it seemed to be straight forward and logical. However, when I started to actually drill the holes I realized it wasn't quite so simple.
The idea to drill successively larger holes in the pocket and the temporary bushings in the pivot bracket to adjust your hole location to the proper place is sound. But to actually drill the holes in line with each other is a little more difficult! I do not know of an angle drill physically small enough but with a 7/8" capacity which would fit in the pocket. Even then it would be hard to get perfect alignment. I have the quick kit and the 141 & 145.55 bulkheads are installed forward of the pocket so there isn't room to drill from inside the hull from the front. Aft of the pocket the hull curves in and causes interference. With the 141 & 145.55 bulkheads installed one must drill them both to get the shaft in anyway so it seemed logical to purchase some long drills. I located some 20" long drills in McMaster Carr, but the minimum set required by the construction manual ran approximately $160.00. Also, if one reams the holes for alignment a reamer with flutes to reach both sides of the pocket is necessary.
One note about straight chucking reamers or hand reamers is they cut on the nose of the tool. The flutes are only for a place for the chips to go. So to get a perfectly aligned hole either a piloted reamer or an expansion reamer with flutes long enough to reach both sides of the pocket should be used. Another $60.00 to a $100.00.
It was late, I was tired so I called it a night and slept on it. As often happens, when I woke a simple solution popped right into my head! I charged off to the local hardware store and purchased a 1/8" diameter by 12" long drill bit, a 1/4" diameter by 3' long steel rod, and a 7/8" diameter hole saw with a 1/4" diameter pilot hole extending all the way through. 14 Bucks!
I threaded the long drill into the holes in the pocket facing forward. I had to enlarge the aft hole slightly to do this. Then I "align bored" forward through bulkheads 141 & 145.55 by turning the bit with my fingers. I increased the hole size in the bulkheads to 1/4" then hole sawed them to 1 1/4" (I already had that saw). Then I followed the instructions in the manual. I was able to drill from inside the pockets up to 1/2" with my little angle drill. That was where I was at when I was satisfied with the hole positions.
I made two 1/2"od X 1/4"id bushings out of delrin stock and inserted in each side of the pocket. During a practice cut with the 7/8" hole saw in a piece of scrap I found it to cut oversize, so I chucked it up in a drill press and touched a grinder to the outside of the teeth. In removing just a little of the set, I now had a hole in which the bronze bushing would fit nicely. I ground a flat on the 1/4"rod 6 1/4" from the end for the set screw in the hole saw, and slipped the rod in through the front of the pocket. I locked the hole saw into position and cut the rear hole. Then I made another bushing 7/8"od X !/4"id and pressed it into the hole I had just cut. Now I put the "pilot rod" back into the bushed holes with the cutter facing forward, put my drill in reverse and cut the front hole. No chance of misalignment.
I keep an assorted stock of delrin in the shop and seem to always be finding a use for it. I have the luxury of owning a metal lathe, but accurate bushings can be made with a drill press with a little care. They can be made out of wood too, but the delerin comes accurately sized so it is really handy. Just another way to skin the cat!
Sincerely,
Roger Isackson
Hull # 132
