Brian's Morning Newsletter October 30th 2009
Good Morning
A brisk five degrees this morning.
I spent the day yesterday for the most part sanding on our newly CNC router cut blades while watching old Alfred Hitchcock black & white movies. Luckily the sanding was more than enough for entertainment value for me. The first set of blades were sanded with an orbital sander at 80 grit, and I took a sanding block to them using 100 grit sandpaper. That was a lot of work, and makes me think we should have let the CNC router do a finer cut after the first cut left deep grooves in the wood.
Somehow we're out of fresh linseed oil, our preferred wood finishing agent. Usually we have at least a gallon on hand, but I looked in all the regular places and could only find a one quart coffee can with a small paint brush stuck through the lid and maybe a pint of gelled oil in the bottom. I added two parts mineral spirits to the oil jelly and it came back to life with just a little stirring. Having spread out newspaper on the kitchen table I began, doubtlessly ahead of reason, to oil the first set of blades.
Ahead of reason? Interesting statement. Well it is early and I couldn't think of a way to describe the intricacies of hand tuning a CNC router cut airfoil shape. I know it is flat on one side and bowed on the other. This shape creates lift due to the fact that air travels a longer distance moving over the curve than the flat side. Everyone knows how a wing works, right? So yeah, I was focusing on the general smoothness of the surface with the first set.
The second set was a different story. For the next set of blades I needed the shop warm so I could use the belt sander which was already clamped in the big vise to fix the sloped transition between the airfoil shape and the root of the blades, where the router had cut four deep steps in the wood. It had begun to snow by 2:00PM when I went out to the shop wearing house loafers. Getting a fire started was easy with the touch of forethought I had stockpiled kindling and firewood next to the woodstove and now that I finished the stovepipe, roof interface the area around the stove was dry, as was the wood.
Although our camera seems to pick up the smallest detail when there is a blemish, and blur the image when we want to see the full color and texture, like when the turkeys walked by the window yesterday morning, and then again on the opposite side of the house later on in the day, what are ya gonna do? Blame it all on the camera, just like I do, right? Anyway, you may notice the small crescent shaped marks in the trailing (knife) edge. I tried like crazy to sand those away, but there they are, still. Those marks are the result of the router bit passing over the wood cutting a 1/2 inch wide path as it carved the curved edge. Next time we will program the router to make a second sweep from a different direction to smooth the wood so we don't need to spend the time to sand, sand, sand.
Above are the hub disks which hold the blades in position until they are mounted on the turbine which has steel disks to sandwich the whole affair and big heavy nuts and bolts to compress everything so it stays together in the wind. I posted yesterdays newsletter on the Other Power forum and received a fair amount of praise while one "Expert" said "If you start increasing blade sizes on a given design you must increase the alternator offset. Just playing with the tail will probably end up in a situation where it just won't furl. You will convince yourself that it does and one day the big wind will come and you will cook the thing. I think the standard 10ft machine is about at the limit of offset and any larger blades will need more. If your extra blade power breaks you through stall it will pull straight into the wind and you will see real power that the windings can't handle." Flux
Now Flux is very knowledgeable, so I responded, " Thanks Flux. Seeing this alternator put out too much, hmmm, don't know if I care, this is all an experiment, for sure. Please tell me which offset you are talking about, the tail bracket? The hub assembly?" Of course we want criticism, as long as possible solutions are provided. Last night I was showing off my work with the wood finishing to Kevin and Nell, and hopefully this story has come back around to the beginning, because I need to get ready for work, plus you need me to make my point pretty soon too. I mean we all got places to be, right?
There is all too often a bit of doubt in doing new projects. Remember when I said the cabinet shop owner was a bit of a perfectionist? At the time we told him that we were trying to shape the blades and he thought we should be finishing the surface. He kept saying, "keep the sander moving, etc." I remember from talking to Kevin on numerous occasions that the bottom of the blade could stand to have a negative cut, meaning it curves up slightly in the direction of the other side. We never really saw that shape come from the CNC router, so I thought Kevin abandoned the notion of two curves. For some reason the router actually cut the flat side with a slight bow in the wrong direction, so as I ran the flat side over the belt sander I was trying to get it back to flat.
Last night Kevin suggested (a little too late) that I could accent the negative cut if I wanted to make the finished blade come out closer to the prototype. "Next set, these are done," I said.
Alrighty then, it is Friday. I don't know exactly what all I need to accomplish this week end, but I'm pretty sure it is great.
See ya Monday
Brian Rodgers
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