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Old 08-15-2019, 09:30 PM
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Default Bump bending

I have to make two cones that are 18" at the top and 8" at the bottom 35" inches tall. Making them out of 12 gauge.
I have got the steel cut and the bend lines scribed. I will bend 2.25" apart on the top and 1" apart at the bottom.

I have 24 inches of die that is 1.5 wide, so I may have to bend the line, slide over and bend again.
I've done this before but it was not exact and I overbent and had to straighten, and that sort of crap.
I think I should be working from each side and do the last bent in the middle.
I would like to know how to calculate the angle for each bend, so it comes out sort of round.

So any tips and experience would be appreciated.
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Old 08-15-2019, 09:39 PM
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I am not much help on the angle question, but I also would start from each end and meet the middle.
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Old 08-15-2019, 09:42 PM
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Quote:
Originally Posted by Ironman View Post
I have to make two cones that are 18" at the top and 8" at the bottom 35" inches tall. Making them out of 12 gauge.
I have got the steel cut and the bend lines scribed. I will bend 2.25" apart on the top and 1" apart at the bottom.

I have 24 inches of die that is 1.5 wide, so I may have to bend the line, slide over and bend again.
I've done this before but it was not exact and I overbent and had to straighten, and that sort of crap.
I think I should be working from each side and do the last bent in the middle.
I would like to know how to calculate the angle for each bend, so it comes out sort of round.

So any tips and experience would be appreciated.
8" x 3.14159/ # of bends should give you how many inches between bends on the 8" end. Likewise for the large end.

360 degrees/ # of bends should give you how many degrees per bend.

You might be able to lay out a series of short kerfs or notches in the Plasmacam software spaced out to mark the ends of the bends
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Old 08-15-2019, 09:55 PM
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Quote:
Originally Posted by camdigger View Post
8" x 3.14159/ # of bends should give you how many inches between bends on the 8" end. Likewise for the large end.

360 degrees/ # of bends should give you how many degrees per bend.
In this case the number of bends are determined by the width of my die.
But I am glad to see you came to the same conclusion about the angle. I overthought it and talked myself into something else, instead of that.
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Old 08-15-2019, 09:59 PM
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You got it right to do the center last. I would make a template of the large dia and and start at each side and work toward the center
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Old 08-15-2019, 10:01 PM
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Quote:
Originally Posted by camdigger View Post
8" x 3.14159/ # of bends should give you how many inches between bends on the 8" end. Likewise for the large end.

360 degrees/ # of bends should give you how many degrees per bend.
In this case the number of bends are determined by the width of my die.
But I am glad to see you came to the same conclusion about the angle. I overthought it and talked myself into something else, instead of that.
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Old 08-15-2019, 10:09 PM
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If you make a bend every inch on the perimeter of an 8 inch circle, that will be about 25 bends. 360º/25~14.4º. Strike 25 (maybe 24) rays out from the 8" circle onto the 18" circle, divided into 25 (maybe 24) pieces. That perimeter is about 57", so the marks should be 57"/25~2.8". You will have a 25-sided cone. Not too shabby, I guess. Sort of round.

If your die isn't tapered (pretty likely) the bends on the 18" circle will be more noticeable, though.
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Old 08-15-2019, 11:20 PM
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Gerry, you don't have a slip roller?
I use my slip roller to make cones after I cut the pattern out.
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Old 08-15-2019, 11:30 PM
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No, I'm not a Platypus, so there are some tools I don't have.
Also this is a few thou off 1/8" thick.
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Old 08-16-2019, 12:55 AM
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Quote:
Originally Posted by Steeveedee View Post
If you make a bend every inch on the perimeter of an 8 inch circle, that will be about 25 bends. 360º/25~14.4º. Strike 25 (maybe 24) rays out from the 8" circle onto the 18" circle, divided into 25 (maybe 24) pieces. That perimeter is about 57", so the marks should be 57"/25~2.8". You will have a 25-sided cone. Not too shabby, I guess. Sort of round.

If your die isn't tapered (pretty likely) the bends on the 18" circle will be more noticeable, though.
Another train of thought...

1.5" die = .75 between bends on the small end

8*pi = 25.132
25.132/.75 = 33.5 bends

So call it 32 bends
360/32 = 11.25 degrees/bend

.75 * tan 11.25 = .1492 depth of bend (punch)

A template for both ends and one for the middle since your punch/die combo is not full length. For air bending, start with a depth of .135-.140 and then see how the template matches in the first four bends, adjust from there.Might want to cut a strip 1-1/2" wide and experiment.

What kind of press are you working with? 10/20/30 ton HF hydraulic press or a press brake with air bending dies?

On edit,...
18 * pi = 56.5487
56.5487/32 = 1.7671

For quickie calculating, I'm assuming 8" and 18" are the neutral axis. If your shooting for an outside of 8" and 18", the neutral axis is the OD minus one plate thickness. For an ID, add one plate thickness for the neutral axis.

And, yes, start from the ends and work toward the middle.
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Last edited by arizonian; 08-16-2019 at 01:06 AM.
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