Creating a 3D Pentagram: Find Equation for Sheetmetal

[lookingdown]

Im looking to find some type of equation that i can plug numbers into for making a number of different sized 2-D pentagrams out of sheetmetal?

 

[DaveC426913]

What is a 3D pentagram? The only pentagram I know of is 2D.

Here are some http://en.wikipedia.org/wiki/Pentagram#Three-dimensional_figures"...

 

[lookingdown]

What is a 3D pentagram? The only pentagram I know of is 2D.

Here are some http://en.wikipedia.org/wiki/Pentagram#Three-dimensional_figures"...

my mistake.. I am running into the problem that if i change the size, all my angles change.

 

[DaveC426913]

my mistake.. I am running into the problem that if i change the size, all my angles change.

I think you're going to need to elaborate.

 

[lookingdown]

I think you're going to need to elaborate.

i am making 2 dimensional pentagrams.. i am running into the problem that if I make one to a certain size I can't just enlarge the pieces to make one bigger.. ??

 

[lookingdown]

see I am basically cutting out diamond shapes and breaking them in a metal break to put an angle on the diamonds running the length of them,, but where they all connect at they have to be a certain angle and I am not sure how to upsize or downsize measurements to make this work out

 

[DaveC426913]

Can you supply a diagram or a photo?

These diamonds, are you basically making 5 of them and joining them into a star pattern? The central angle would be 360/5 = 72 degrees. It is not the same as the angle at the outer point, which will be different if you want them to be true pentagrams, as opposed to simple stars.

See attached samples of different five-sided shapes.

I suspect you are trying to construct #1. But if you use true diamond shapes (opposite angles are equal), you will end up with #2.

 

[lookingdown]

they are not flat they are raised in the middle.. see I am putting a bend right down the middle of the center of the diamond so it sticks up in the middle..

 

[DaveC426913]

they are not flat they are raised in the middle.. see I am putting a bend right down the middle of the center of the diamond so it sticks up in the middle..

Ah. But otherwise, does it look like #1 in my diagram?

How much is it suppsoed to bend up?

 

[lookingdown]

yes it does look like that diagram it doesn't matterjust nothing with too much of a pitch

 

[DaveC426913]

yes it does look like that diagram it doesn't matterjust nothing with too much of a pitch

Is the centre raised with the points set back? Or are the centre and points in the same plane? i.e. if you lie it flat on the table, will the centre touch the table?


[ EDIT: Nevermind, the centre and points can't all touch ]

If you want to simply do a rough trial, then try this:


Take one of the diamonds I diagrammed.
On paper, scale it up to the size you want.
Add about 5% to its width (i.e. if your diamond is 10" from side-to-side, make it about 10.5")

This should get you a diamond whose inner angle is a now little more than 72 degrees. You will need to crimp it down the middle to make it 72 degrees, at which point 5 of them will complete a circle.

 

[lookingdown]

center raised out