Question about angles in open vs closed segments

Crazynewfie

Crazynewfie

PRO Member
I was curious about the different angles using segment pro for open vs closed projects. Here is an example of what I mean. For a 48 closed segment project the angle would be 3.75 degrees for each side. 3.75 x 2 x48 = 360 degrees. When I change the setting to open for the same project the angle changes to 2.75 degrees. Just wondering why? I understand the SEL will be a smaller number for open segments because of the gap needed but why must the angle change?
 
The formula used for open segment accounts for the gap. Not sure why for the formula. Maybe because the wood gods determined it to be so?

Closed Segments: 360 / segments / 2
Example for 12 segments: 360 / 12 / 2 = 15 degrees

Open Segments: (360 - (segments * gap)) / segments / 2
Example for 12 segments with 8 degree gaps: 360 - (12 * 8) / 12 / 2 = 264 / 12 / 2 = 11 degrees
 
If you just changed the SEL and not the miter angle then the miters would not point to the center of the ring. The miters must point to the center for any alignment jig to work.
 
Simple 12 segment open ring. Shows that the reduction in angle has the segment pointing to the center as MSelser stated.


1739767775959.png
 
No horse is so dead that it can't be beaten.

Instead of looking at the segments in the sketch above, look at the gaps. By reducing the cut angles on the segments, the gaps remain proportional to the segment width as the OD is turned down. In the sketch, each segment is 22 degrees wide and each gap is 8 degrees wide, regardless of OD. If you make the segments 15 degrees wide and space them 1/4" apart, the segment to gap ratio will change with OD. I made one like that once, just to see how it looked, and my wife looked at it with a puzzled expression and said "That looks weird but I'm not sure why." It went in the fire pit like many of my experiments.
 
Thanks guys. I understand that the angle of the segment has to point to the center and it would be especially noticeable on projects with low segment prices like 12, 18, 24... I think if you made a project with 96 segments per ring you could get away with it because the gap would be small and the angle would be less noticeable.
 
When you make open segments, you can choose whatever gap you like and Segment PRO will correctly calculate the SEL.
Since I sell the SegEasy plates that Jerry Bennett makes exclusively for me (meaning that the hole in the center is sized to fit the Stomper), the gap is the default he has chosen for his plates. That means that if you pick any SE plate and set the number of segments accordingly, the gap will automatically be set to the correct gap for that plate. Refer Mike Fisher’s post for the calculations for determining the gap.

Feel free to overwrite it with your desired gap but you’ll have to use an indexing system to position segments for gluing, not a SE plate.
 
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