# Thread: OT: How to layout for a Cone?

1. Senior Member
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## OT: How to layout for a Cone?

I would like to make a cyclone for my dust collector, but I'm unsure of how to do the layout so I don't have a weird shape at each end.

Can someone help?

Thanks, Dennis

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A cone is just a circle with a pie slice cut out.

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So if I draw two circles, one inside the other, cut a pie slice out of the piece, then when I join the edges to make the cone, the defined circles (top and bottom) will be parallel?

4. dp
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http://www.sheetmetalguy.com/cones.htm

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I have made a lot of frustums so I might be able to help a little.
I have a large trammel with a pencil insert.
I lay everything out on carboard first.
And then make a model out of cardboard.

The tip of the cone is where you start your arcs-where the point goes.
The large arc is the curcumfrence of the large end of your cone.
measure down to the height of your cone and make the other arc.
The small arc is the opening at the small end of the cone.
I use a dividers to check the length of my arcs.
Once you are satisfied with your carboard model, lay the carboard on your piece of metal and cut out around it.
You can then either roll it or make tiny incremental bends with a bending brake.

Circumfrence is Pi X Dia.

6. gary350 Guest
I make cones all the time it is not hard. I really need some photos it would make it easier to explain.

You need to make a scale drawing on paper. Start by drawing a straight line call one end A and the other end B.

Take a look at cone calculator.

http://www.cleavebooks.co.uk/scol/calcone.htm

also

http://www.anvilfire.com/21centbs/math/cones1.htm

Put your compas needle at A then draw a line at B. The distance between A and B is the length of the side of the cone from the point to the large diameter or top end of the cone.

Put your compass needle at A again this time draw a line some where between A & B this line is the lenght of the side from point A to the small diameter of the cone.

Use cone calculator to find the diameters of each end of the cone. Start with the large diameter. Once you find the diameter lets say it is 24" you need to mark off the radius line you drew at B in 1" marks like a yard stick. Draw a mark very inch in that radius until you get the full circumfrences. Diameter x pie = circumfrences so 24 x 3.14 = 75.36 inches. Draw a line from the 75.36" spot to point A. This gives you the other side of the cone.

Now you can cut the drawing out and bend it and it will make a cone. If your using thin sheet metal they you do not need to take into consideration the metal thickness.
Last edited by gary350; 11-14-2010 at 06:17 PM.

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If anyone can tell me how to pst an excel file I'll share on that I have used many times to make cones up to 3/8" thick x 12' major OD to small ones out of sheet metal. It is for standard cones, offset ones are more tricky.

Or send PM w/email and I'll send copy.

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Originally Posted by dlsinak
So if I draw two circles, one inside the other, cut a pie slice out of the piece, then when I join the edges to make the cone, the defined circles (top and bottom) will be parallel?
Yep, that will do it. And the length of the top and bottom arcs (segments of the two circles included in the "pie slice" you took) will be the circumfrences of the top and bottom circles of the cone. The trick is getting the correct sizes for the circles to get the diameters or circumfrences you want --- with the desired distance between them of course. It looks like dp's referenced web page does the math.

Or you can do it yourself.

d = diameter of small end
D = diameter of large end
a = axial distance between ends

x = half angle of cone

x = arctan ((D-d)/2a)

r = radius to layout smaller arc

r = d / 2 sin(x)

R = radius to layout larger arc

R = rD/d

B = angle of the arcs on layout in degrees (angle between straight sides on layout)

B = d*180 / r*3.141
B = 57.296 * d/r

That's all you need to lay it out. Draw two straight sides with angle B between them. Then draw two arcs between them with radii r and R. Done.

Oh, don't forget to add some extra for overlap unless you plan on a butt joint.
Last edited by Paul Alciatore; 11-14-2010 at 06:06 PM.

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Awesome, Thanks for the replies!

Dennis

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