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Old Streetfighter Motorcycle Forum Post 08-19-2019, 04:43 PM   #4
RTharalson
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Default Re: Rectangular steel tubing bend procedure part one

That is the most difficult part of the entire project, and the aspect that took the longest to get right. With the advent of ever better CNC LASER cutters it is possible to make a consistent cut all the way to the apex of the two lines with a total cut width less than 0.001 inch. Of course when I figured out this procedure LASERs of any sort were the stuff of science fiction, at least for the average Joe, and it took lots of experiments and failed parts to get it right.

Essentially, when the patterns are applied to the stock center punch the ends of the patterns circled in red in the illustration, then when the patterns are removed drill at the center punched location with the smallest drill you can obtain, my preference is a #60. It's easy to break especially when drilling steel so spin it fast and feed it slow, frequently backing it out to clear chips. This gives a good target to end the cut. Continue to drill progressively smaller holes (Green in the illustration) until you can't guarantee that they will stay inside the pattern. To cut out that area I use a Dremel with a #545 diamond wheel, the thinnest they have at 0.023 inch, and tough as hell. Using the lower boundary as a guide cut until the wheel gets to the drilling. Once that is done on both sides use the cutoff wheel to continue the cuts all the way across the bottom of the pattern. The same wheel can be used to cut just under the radii, then brought to the scribed line of the radii first with a fine carbide burr and when that gets too big: needle files. The initial straight cut will leave a 0.023 inch gap (if you have a steady hand) about 3/4 inch long (horizontal Red line on the illustration) that you can't do anything about, but this will have minimal effect on the bend, and will be filled when welded.

When I get a CNC LASER cutter it will take almost a minute to cut. Hey, I can dream, can't I?

Finishing writing the actual bend procedure. Some small details that can snatch success from the toothy maw of failure. Will post it probably tomorrow.

Rob
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