All Replies on Calculating ring segment lengths

Jack … I played with this myself in Excel … never getting the right result.

Then I stumbled onto Woodturner Pro ( http://woodturnerpro.com/ ) and haven’t looked back. It was a little pricey, but when you consider the advantages it has, it was worth it (to me).

-- Gerry -- "I don't plan to ever really grow up ... I'm just going to learn how to act in public!"

Jack … I played with this myself in Excel … never getting the right result.

Then I stumbled onto Woodturner Pro ( http://woodturnerpro.com/ ) and haven t looked back. It was a little pricey, but when you consider the advantages it has, it was worth it (to me).

- TheDane

Don’t get me wrong, and I agree Woodturner Pro is fine, I was just wrestling with the math method rather than brute force method. My DeltaCad and SS program produce very fine results that I believe has been shown with the pics uploaded here. Again, I was asking for a way to incorporate a different formula using

IAW trig math.

-- "PLUMBER'S BUTT! Get over it, everybody has one"

Your formula looks right, except I don’t think you need the sum(), and spreadsheets usually use “[asterisk]” for multiplication, but I’m not sure what syntax your spreadsheet uses.In Excel it’d be 2[asterisk]rad[asterisk]sin(angle/2). Functions in Excel use parentheses for their arguments.

In mathspeak it would be c = 2r·sin(θ/2), or “two times the radius times the sine of half the angle.”

Note: Apparently this forum uses asterisks for bold text and bulleted lists. They don’t say what you’re supposed to use for asterisks; that’s why I’m using “[asterisk].”

-- Unix programmers never die; they just > /dev/null

Just in case you haven’t seen this, I’m not sure it will help—
http://www.woodturnersresource.com/extras/projects/segmentcalc/index.html

-- Lew- Time traveler. Purveyor of the Universe's finest custom rolling pins.

I have a sheet made up for the woodworking club it goes to segment rings bigger than I ever intend to make.

Jack Lewis,

I am not exactly sure what ideas you are looking for but since you are looking for formulas on the web I assume it is a set of equations. If in fact you are seeking math equations to determine the inside and outside length of the segments and the formula for determining board feet after applying an allowance for scrape, here is what I came up with. However, since I am like you with my math being pretty rusty, independently deriving or empirically verifying might be a good idea…

I assume you are able to program these formulas in Works. It has been a long time since I used Works, but from what I recall it is similar to Excel.

When I got into segmented turning I started to find all the equations and build my own spreadsheet, until I found Segmented Project Planner. For $37 it did all the calcs and gave renderings of the project, and is easy to change or update the project. It was just too easy to pass up. Along the lines of “make or buy” discussions about tools, jigs, etc., this was a definite “buy” for me vs make.