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A simple Formular for Segmented Angles

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Blog entry by Grumpy posted 12-14-2015 04:29 AM 966 reads 1 time favorited 8 comments Add to Favorites Watch

Here is what I came up with using my basic understanding of algebra.
The angles for segments are taken from the outside edge rather than from the centre for good reason but they are related to the angle from the centre of a circle.
Without boring you with the maths this what I came up with

X is the number of segments
assume the angle of the segment is Y

Y=90-(180/X)

eg. the angle for a 16 segment circle is as follows.
Y=90-(180/16) =90-11.25 =78.75 degrees

For 12 segments
Y=90-(180/12) =90-15 =75 degrees

If i’m wrong please let me know.

-- Grumpy - "Always look on the bright side of life"- Monty Python



8 comments so far

View Jim Jakosh's profile

Jim Jakosh

17191 posts in 2572 days


#1 posted 12-14-2015 11:50 AM

G’day,Tony.
Here is the way I figure them out:
There are 360 degrees in a circle so if you divide 360 by the number of segments, you’ll get the degree of each segment. Like for 16, it would be 360/16=22.5 degrees. For 12 it would be 360/12=30 and for 6 it would be 360/6 =60. That is the included angle of the segment.

Cheers, Jim

-- Jim Jakosh.....Practical Wood Products...........Learn something new every day!! Variety is the Spice of Life!!

View doubleDD's profile

doubleDD

5247 posts in 1510 days


#2 posted 12-14-2015 02:57 PM

There is more than one way to skin a cat. Thanks for posting.

-- Dave, Downers Grove, Il. -------- When you run out of ideas, start building your dreams.

View bbain32's profile

bbain32

21 posts in 642 days


#3 posted 12-14-2015 06:49 PM

Something certainly is not right here. The angles you are calculating do not make any sense to me. Are you calculating the angles for segments to make a circle or some other shape? Like Jim Jakosh pointed out above, to find out the angle you simply divide 360 by the number of segments to get the angle to make a circle.

View Karson's profile

Karson

35035 posts in 3867 days


#4 posted 12-14-2015 08:34 PM

Grumpy you used 180 in your formula are you figuring 16 segments in half a circle?

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Southern Delaware soon moving to Virginia karsonwm@gmail.com †

View Karson's profile

Karson

35035 posts in 3867 days


#5 posted 12-14-2015 08:37 PM

Grumpy you used 90 degrees in your formula so I’m assuming that you are using a cross cut sled to cut your segment. The crosscut would be 90 degrees to the blade. so 90 minus 22.5 would be 67.5 deg.

-- I've been blessed with a father who liked to tinker in wood, and a wife who lets me tinker in wood. Southern Delaware soon moving to Virginia karsonwm@gmail.com †

View Grumpy's profile

Grumpy

21571 posts in 3318 days


#6 posted 12-14-2015 11:21 PM

I don’t wan’t to open up a hornets nest here but I think some of you are thinking from the centre of the circle out not from the outside in which is important when using a tablesaw sled as Karson hints at.
Have a look at Sam Shakorie’s blog. Sam is an expert at segmenting.
I have just made the formula a bit easier to follow
http://lumberjocks.com/sydney/blog/25118
Also Jerry Bennett’s youtube tutorials like this one;
https://www.youtube.com/watch?v=6Yl-qDN1HtI

-- Grumpy - "Always look on the bright side of life"- Monty Python

View bbain32's profile

bbain32

21 posts in 642 days


#7 posted 12-15-2015 01:58 PM

I understand what you are talking about now, and your numbers do make sense, but you did not do a very good job explaining it.

A simple diagram would have helped a lot, or the explanation your calculations are for what angle to set your saw blade (or miter gauge/sled)at to make the cuts to get the proper angles for x number of segments. As well, it doesn’t matter if you are thinking from the inside or the outside of the circle when calculating the angles, as math does not lie.

View Grumpy's profile

Grumpy

21571 posts in 3318 days


#8 posted 12-15-2015 09:16 PM

bbain32, it’s fairly simple maths. This has nothing to do with tilting the blade. That’s a more complex issue.

-- Grumpy - "Always look on the bright side of life"- Monty Python

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