02/16/14 22:54 Filed in: All
The original mixer (partially disassembled) looks fairly primitive next to the nicely CNC machined parts of the new one. I was never a huge fan of the single bolt in the center holding the "wings" together.
Start by drilling the hole for the safety wire on the fore/aft arm. On the collective slider I did them "free-hand". On this piece and with the mill and a couple of holding blocks this is achieved in very short order and with less hand wringing. Center punch the start location. Use a center drill to provide a "divot" so the real drill doesn't wander and away we go.
To precisely align the mixer with the control stick I made a little jig. Those two aluminum plates were machined in a stack, so they exactly match. The holes were drilled and the top edge machined to form a precise reference edge/plane. Both plates are exactly the same dimensionally. Then I made a little spacer on the lathe the exact same width as the cyclic bolt tube. Bolt 'em together and place a bar across the reference edges. My digital level was then used to get the angle between the reference and the bottom of the mixer block to exactly 0.0degrees.
Of course right when I was feeling smug and competent, BAM. The drill bit snapped off on the first hole. Crap! About half an inch into the hole. Of course you can't drill into a drill bit, so instead of boogering things up I stopped and stared at it for a while.
First I tried digging the broken bit out with a pick and needle nose pliers - no joy. Then I milled the hole slightly and the broken end of the drill bit. At least at that point I could remove the mixer block.
I tried using the "old" rearmost vertical hole first and matching the hole (you can see the hole on the left) Though very, very close, the hole on the other side of the tube was slightly oblong (by about 10 mils). I went ahead and drilled the horizontal cross bolt.
Why the bit snapped I don't know. It was only eating into aluminum at that point. It was well oiled, and I was backing it out regularly to clear chips. I was attempting to use a #30 bit as the pilot and that is probably a little wimpy for a hole this deep. Here you can see the remains of the broken bit with about 0.5" missing (in the mixer block).
Even though it probably would have been OK, I carefully measured and determined that there was room for a third hole in between the others. You can see the middle drill bit here showing that hole. Pretty busy. The forward most cross hole is perfect, nice and snug. The rearmost one is the one I tried to match - sloppy on the far side. The middle is my auxiliary hole - also nice and snug. OK. Good. Crisis averted.
The mixer block removed from the cyclic control tube showing the three holes. Since it is solid aluminum I have no concerns over strength. The broken bit will ride along with me forever stuck in the aborted hole.
The rest of the mixer assembly is a non-event, just assembly with a little sanding to make everything slide together smoothly. Off to paint.