Steve Jacobs wrote: > Can you say a bit more here Mark. Any time spent getting this right > will save gobs of time shaping and sanding the spars later (empennage as > well as the wing spars), particularly with the AS sections. I am not > convinced that what I am visualizing is right, i.e. - cutting a few > inches; shutting down; changing blade angle; starting the saw; cutting a > few more inches etc. You mention "required no sanding", so obviously no > steps??
Steve, below is a message I sent to KRnet about 5 years ago that answers your question, as well as several that you didn't ask. I just figured I'd throw the whole thing out there just in case it'd help somebody else too. Yes it was cut continously, without switching off the saw. You'll need a wife that's not squeamish about flying sawdust, or some other form of human helper. My wife and I PERSONALLY built our house (no contractors other than slab and drywall), so she was up to the job... List-Post: krnet@list.krnet.org Date: Jan 25, 2000 6:11 AM From: Mark Langford <langf...@hiwaay.net> Subject: Re: Wing spar sanding > I would like some advice on the sanding of the spars to fit the contour of > the airfoil, what is the best way to get this contour ? > By sanding, hand plaining ,machine plaining ,.....? I used a table saw to do the tapering, and changed the angle of the blade as I tapered. I marked the spar every foot or so, divided the total number of degrees of change by number of feet, figured out how many degrees of blade tilt corresponded to one turn of the wheel, and told my wife "every time one of these marks goes by the edge of the table, I want this wheel to have gone around a half a turn", or whatever it was. The result was a spar that I didn't have to touch with a sander or planer. Just went on to foam and glass. There are a bunch of pictures of this process at http://home.hiwaay.net/~langford/kspars.html . The whole process of tapering (the height) and tapering (the airfoil) took maybe 2 minutes while I ran the spar thru the saw. I did spend about 15 minutes dividing number of degrees per turn by number of feet, and making sure that I knew what was going to get cut, but you can't beat this method for speed or accuracy of the final cuts. Having said this, you better be pretty sure of your work, and take into consideration where the top of the blade is going as the angle changes. Perhaps slicing up a 2x8 would be good practive to see if you've got the methodology down right. Maybe a planer or sander would be safer in this regard, but it's just as easy to take out a nick with a sander or planer, I guess. Note that there are several places on my web site where there are a zillion spring clamps. Most of the time these are holding the spar cap to an aluminum angle to keep them straight, not squeezing all the glue out of the joint. In some places there are Jorgensen clamps shown holding spar caps together while "scabbing", but they are lightly tightened, just enough to make sure there's contact, and to squeeze out the enormous amount of T-88 that I applied to each side to "soak" into the wood a few minutes before joining the two pieces. Having said this, I HAVE presoaked two pieces of wood, clamped the crap out of them, let them cure, and broke them days later, and the joint failed elsewhere. When the epoxy is 10 times stronger than the wood it doesn't take much epoxy to get the job done, especially when there is no possiblitiy of voids. I'm not saying you should over clamp T-88 joints (I know you're not supposed to), but I wouldn't throw away my spars if I'd already built them that way. Why do I say that? Well it just so happens that I have an extra set of spars that I built, and didn't think that I had put enough epoxy between the "scabbed" spar caps, because I didn't have any "squeeze-out" in several places. After my new ones were built (they were lighter anyway because of a little design change) I started wondering how strong the old ones were, and tested them to failure. The glue joint isn't where the caps separated... ---------------------------------------------------------------Mark Langford, Huntsville, ALN56ML at hiwaay.netsee KR2S project N56ML at http://home.hiwaay.net/~langford
