...improved production methods, Sept. 25th, 00
Some of the last small sheet metal parts left to make are the flap ribs. I already made some forming tools from particle board for the aileron ribs, but now that I'm almost perfect with the handling of the bending brake, why not use the brake instead of hammering? I gave it a try and the rib came out lovely.
Both flanges can be bent to 90deg. without problems at the brake. The big advantage is that the rib is flat afterwards like the Great Plains. If using a forming tool however I always had some problems. When hammering the flanges down they expand a bit which produces a slight 'banana shape' of the rib. What to do with all the bananas? Flute the flanges a bit? - according to Michel Colomban (the great French homebuilt guru) fluting straight flanges is a NoNo!? -also my thinking, probably the buckling resistance would be compromized. Maybe I'll redo the other control surface ribs using my new method.
...economic use of rare material
All this 1/8" thick small parts have been made from cutaway pieces of the extruded angles. I have not yet purchased any of the thick plates (will wait a while until the $$ goes down / the EURO goes up ;))
Isn't this a real piece of artwork? I could polish it all day long... maybe my real destination is a sculptor ...making naked ladies from 6061? ... if the ladies only could fly ...
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...L-Extrusions Sept. 20th, 00
The small (up to 600mm) channels are almost done. Next comes the angle stuff. These are most of the L-extruded angles necessary for the fuselage.
I cut them to size at a professional circular cutoff saw. I cut about 0.5mm oversize. This excess will be grinded off at the Scotchbrite wheel when polishing off the small sawmarks.The whole job took about 3 hours, where measuring took 80% of the time.
The real work begins now shaping the pieces according to the plans. I expect several weeks for this.
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...Intermediate Project Status Report to Sept. 14th, 00
total parts made: 250, hanging on walls and packed in 10 cardboard boxes. Yes boys, I think all the alum pieces of the Sonex could be stored in a medium sized closet. Besides - total scrap parts: about 20 (mostly small parts, one silly mistake made when cutting forward fuse sidewall). However I think this is still within limits.
A selection of my little gemstones. Bigger parts like fuse sidewalls, fuse botton are cut with about 5mm oversize and located beneath the big worktable. Some few larger parts are waiting for the sheet metal shop for bending. My bending brake is limited to max 2 ft. This is sufficient for making about 90% of all the 'L', 'U' and 'Z' channels.
Total working hours: 222.5 (so one part took average time of 1 hour - I think this is o.k. because I build from scratch - No fast build please. Never think you could make even the smallest part in much less than 1 hour. Take your time and enjoy building ;)))
total days elapsed since project start: 141
average working hours per day: 3.4
estimated remaining days till completion: 810 (estimated 1,500 total building hours)
thanks for the maker of the 'reality check' project tracking spreadsheet, it's marvellous and highly recommended.
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...more on bending sheet metal (Sept. 4th, 00)
Bending all these small angles from 0.025 and 0,032 sheet was easy. Mark the piece roughly, bend, then grind flanges to size, adjust angle.
Another story are these U- und Z-shaped channels. Always the the -outside- dimension is given for the U's. I started by transferring the nominal sizes from the plans to the sheet, then make a test-bend...
...then calculate the 'brake offset', then bend the real thing, then control and finally ...
... THROW PIECE IN SCRAP CONTAINER.
I assume that marking with fine liner and adusting at the brake knife is an too unprecise method of manufacturing. My aim is to maintain a tolerance of max. 0,3mm (< 1/64") for the channel widths. This is because I'll produce all the small parts first and start assembling later. Because Sonex doesn't give tolerances together with dimensions, I assume all measurements as 'critical' - just to avoid bad surprises that parts won't fit lateron
The enlighting hint I received from my fellow builder Kristen Thorrud (thanks Kristen). He suggested to make an adjustable stop block behind the brake. If this stop is properly adjusted, all the U's should come out of same dimension.
The distance between stop block (square) and moving blade is adjusted under consideration of 'brake specific offset' (+1.4mm in my case). This works great and deviation is less than 0.3mm.