I figured half a page of map printout is 5 1/2 x 4 1/4 inches, so I added 3/8 inch on all four sides and came up with 6 1/4 x 5 for the Lexan blank.
I had about a 16 x 20 sheet so I clamped a bar across the stock at the four inch mark and set to the usual v grooving with the back point of a sharp craft knife. No joy. So I deepened the score with three passes with the point of the knife. The bar was right at the edge of my 1/2 inch thick overhanging bench, so I leaned on it an it snapped cleanly. Then I did the same for two six inch piece from the four inch width.
I drilled and reamed four 1/4 inch holes for my 3/16 inch jig saw blade for a square tab on the back panel, but didn't saw or bend it.
I test drilled a scrap #25 and tapped 10-24 threads. Nice material, plenty of elongation, but clean yield to failure, good tight threads. You use coarse threads in plastic because the material is so much weaker than the fastener.
I marked everything out with a carpenter's square and Sharpie fine point, and used the automatic center punch in 14 places, five down each side, and four along the bottom, more to the outside than totally evenly spaced, as the division came out one off. I just marked off 1/2 inch increments and picked every other mark from the outside.
Then I laminated the parts together with double sided Scotch tape, taking care now to keep it clean, and faced the bench with paper. I drilled 14 places #25 through both parts, and should have held the edges together with pliers. I separated them and tapped 14 places.
I jigsawed the tab, bent it out by hand (one inch is about as much as I can handle with my thumb braced), and using the relieved corners to concentrate the stress, the tab bent out square and flat. Then I marked it and made a mistake, not thinking ahead, used the drill as a side mill to move the hole, and taper reamed for the strange 7mm bolts with 5mm button heads. Who ever heard of that?
I loosened the handlebar cap and added the map holder with its 14 screws in place, then I tightened the screw on the map holder and carefully tightened the other screw, as the seats were no longer quite square. I'd checked before to make sure this would work.
All it needs now is a cork block on the back, since it goes booing, but it can hold anything from a single page of quarter letter size to a whole travel booklet with the screws backed out. And you can adjust the screws with a dime!
What fun. Too bad there is no rec.crafts.plasticworking, as there is a rec.woodworking. Too bad they didn't put rw in the heirarchy as rcw. Oh well.
Very nice material, once fabricated it is indestructible. It doesn't crack when the drill bit goes through the way acrylic does either, and generates long tap chips as opposed to acrylic dust.
Next step, take it off and belt sand the sides flush with the screw head line.
All this for the new recumbent, a Lightning Cycle Dynamics Thunderbolt SWB model with 24-35-51 / 34-28-23-19-16-13-11 even double step gearing. 657% range, and AC and DC generators coming on line soon. Big ones.
The map holder is for the difficult navigation through Tyson's Corner Center streets, hills, and traffic, to Paradise on the other side of the Dulles Access Road, starting at Spring Hill Recreation Center. Paradise is the residential area called Knox Hill or something, and is multi million dollar homes. The community rec center is a lake. On the other side of Paradise, with its green lawns, tall trees, and rolling, winding roads, is Difficult Run Stream Valley Trail, leading to the little beach on the shores of the Potomac.
Why don't you join me some time? Bring a suit; one you like to take off.
Here's to Sun on Skin, Vitamin D, strong bones, and a good attitude!
Skin cancer be damned. (Until I get some.)
I made it as far as the lake last time and realized I didn't bring enough calories. Water, I had, but three snack bars just isn't enough. Next time I'm bringing jerkey, snack bars, and fruit.
I have osteoporosis and green leafy vegetables with yogurt dressing, sun on skin, and more weight in my backpack as I do my errands each week is part of my therapy. I also take Caltrate but that's just chalk. Just a little osteoporosis, around 50% of one standard deviation.
Fighting hard, I remain
Yours,
Doug Goncz ( ftp://users.aol.com/DGoncz/ )
Read about my physics project at NVCC:
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plus "bicycle", "fluorescent", "inverter", "flywheel", "ultracapacitor", etc. in the search box