Solo, I understand about the hole size. I do have a concern about threading the blades. With the plastic being very thing is there enough material to actaully make more then 1 revolution with the tap? I did it but then thought again and put a nut on it. Now I didnt think about going the plastic bolt and nut but still. I just drilled a smaller hole and screwed the bolt in. I really dont know how well it would hold. Besides, doing that, how do you keep it loose enough to rotate, unless you dont tighten, then I think your asking for more problems without the nut. It could be just me though. Growing up on a farm I tend to over build things.
[/quote]
Right now I'm running on the edge of - actually in the middle of - bad engineering principles. I tighten the screw , then back off a quarter turn and flex the blade until it's loose. The blind nut won't spin because I left just a little of the barb on the underside when I cut 90% of the barb off. And the screw is in a bind because of the centrifugal pull from the blade - it binds the screw I guess. Anyhow, it doesn't fall apart in the air.
Threading the blade is iffy at best. A #4-40 screw has a thread pitch of .025 and the blade is .056 thick. That's a couple of threads. Full torque of the screw requires 3 threads or a thickness equal to the screw diameter. For a #4-40 that's about .112 thick. But this isn't about maximum torque. I only need enough torque to keep the screw in shear, but two threads in plastic is still iffy. If the screw was a large head, I'd go with it. Plastic #4-40 screws have the advantage of being easier to hang on to. So if I use #4-40, put an aluminum tubular sleeve over the screw that is a few thousandths longer than the combined thickness of the grip + blade, I can tighten a plastic nut onto the sleeve and be in pretty good shape. A little CA on the grip / screw / aluminum sleeve will reduce the number of loose parts, so a blade change requires only that I remove the nut and replace the blade. As long as the screw / sleeve is rigid, the blade will swing easily.
Just thinkin' out loud - one farm kid to another.