Segmenting help

[Peter Luch]

I need to make a ring that will use 8 pieces.

The finished inside diameter needs to be 3"
The outside needs to be 3-1/4" to 3-3/8"

So how do I find the angles and sizes?

This is a one time thing so buying software would not be worth it.

Thanks for any help!

Aloha, Pete

[David Christopher]

this should help

[Tom Veatch]

Assuming you're talking about a regular octagon and that the diameter is the distance from side to side across the flats. The distance across the corners will be longer.

All miter angles = 22.5°
Thickness of each segment = 1/8" (O.D. = 3 1/4") or 3/16" (O.D. = 3 3/8")
Length of each segment along outside edge (point to point) = 1.346" (O.D. = 3 1/4") or 1.398" (O.D. = 3 3/8").

For other diameters, Thickness of each segment is 1/2 the difference in diameters, and the length of each piece along the outside edge is 0.4143 * O.D.

Or, for the general case of any regular polyhedron:

N is the number of sides (i.e., 4 for a square, 6 for a hexagon, 8 for an octogon, etc.)
D is the width of the polyhedron across the flats

Miter angle = A = 180/N (i.e.., 180/4 = 45° for a square, 180/6 = 30° for a hexagon, etc.)
Length of a side along the outer edge = D * tan(A)

[Peter Luch]

Thanks guys!

I'll go over it all in the morning when I'm clear headed

Aloha, Pete

[Jim Kountz]

Here ya go.

[Peter Luch]

WOW!

That's the ticket Jim!
The least my little brain has to figure on angles the better it is for the project

Thanks so much!!!!

Aloha, Pete

[Jim Kountz]

Glad to help!!

[John Fricke]

Hey Jim,

If you don't mind me asking, what software did you use for that printout?

[Ralph Barhorst]

The length of the side with a 3" inside diameter


inside length = diameter / 2.61313 = 3/2.61313 = 1.29155"

Outside length will depend on the thickness of the material.

[Tom Veatch]

If the OD is the distance across the flats (circle tangent to the outer sides) and the ID is the distance across the inside corners (circle passing through the inner corners), for any segmented ring with 3 or more segments, the dimensions are given by:

Number of Segments = N
Miter Angle (A) = 180/N
Width of each segment (W) = [OD - ID*Cos(A)]
Length of each segment (L) = OD*Tan(A)

Ring Dimensions.jpg

Example:
ID= 3
OD= 3 3/8
N = 8
A = 180/8 = 22.5°
W = [3 3/8 - 3 * Cos(22.5)]/2 = 0.302
L = 3 3/8 * Tan(22.5) = 1.398

[Jim Kountz]

Hey Jim,

If you don't mind me asking, what software did you use for that printout?

John, sorry I didnt respond sooner, I just saw this.
I use Woodturner Pro. I got it as a suite of software and it came with 3d Design Pro and Lamination Pro. The 3d pro does a great job of letting you trace shapes for segmenting, as well as design from scratch. The Lamination Pro lets you produce banding and other multi laminated units for all kinds of different things.
The entire suite was $99 and a bargain if you ask me. You can download it and begin using it right away with basically little to no learning curve. If you can point and click you can use this software. Thats why I like it!!
You can check it out here---->
http://www.woodturnerpro.com/