# Segmented Ring Calculation



## Bob_Garrett (Apr 9, 2012)

My shop PC finally died taking with it my Woodturner Pro software. I could load Windows on my Mac but, aside for the extra cost, it just offends my sensibilities. 

What I really liked about the Woodturner Pro application was the segment calculator. By entering the number of segments, the outer ring diameter, and inner ring diameter it would tell me the miter angle, board width, and segment edge length. I'm sure this is something that could be done easily in a spreadsheet, but thought it would be worth asking whether anyone in the community has done this already.

Any help will be greatly appreciated.


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## Maurice (Sep 24, 2004)

You can still get Woodturner Pro as a download from
woodturnerpro.com as a demo for 30 days or buy it for $50.


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## BernieW (Sep 12, 2006)

I have Woodturners Pro and my computer went belly up about 8 months ago. I had purchased it about 5 to 6 months before. I contacted them and downloaded it to my new computer. You might contact them.


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## Dmeadows (Jun 28, 2011)

Hi Bernie. I think the problem is that they do not have a Mac version!


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## BernieW (Sep 12, 2006)

Guess I didn't catch that. I am guessing he bought a Mac to replace his old computer. I assumed he bought another windows machine.


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## harrysin (Jan 15, 2007)

I don't know if this works with a MAC or even if it does what you want but it's free and used by a friend of mine for making segmented coffee mugs.

Segmented Turnings


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## Bob_Garrett (Apr 9, 2012)

Guys - thanks so much for replying to my request. 

Harry - that's exactly what I had in mind, and since it is a web page it works fine on my Mac.

I must admit though that since posting earlier this week the nerd in me challenged my manhood to solve the problem. How hard could it be, after all? This is high school trigonometry, and even after . . . ummm, a long time since high school . . . I should be able to solve this. And with a little help from a very slick trig web site, I did.

Attached is an Excel spreadsheet for anyone who wants to use it. It is by no means a replacement for Woodturner Pro which provides a wealth of capability. But if you're like me, too cheap to spend $120 for Windows 7 to run on a Mac, but still want the basic segment calculator, this may be a reasonable alternative.

Enter the number of segments, the desired inside and outside diameters of the ring into the appropriate spreadsheet cells and it will give you the miter angle, segment length, and board width. It also gives an estimate as to the length of board needed for all segments to be cut - for grain-matched and alternating-grain segments.

You can use a calculator with trig functions to do the math, but it takes a lot of button pushing. Here are the formulas:

Miter angle = 360 / (number_of_segments * 2)
Segment length = outside_diameter / tan(90 - miter_angle)
Board width = (outside_diameter - (inside_diameter * cos(miter_angle))) / 2

*Caveat emptor* - I've made some basic test with the spreadsheet and it appears to generate the right values. If you use it, try it first on an inexpensive piece of wood. I'll try it in earnest this weekend.

Thanks again to all!


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## BernieW (Sep 12, 2006)

Thanks Bob. Quick and simple.


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