[SML] question for router wizards

[Jon Lagerquist]

The string length for an ellipse is:

2*(half the major axis + focus)

The focus is the distance from the center to the nail.

The focus for an ellipse is a version of the Pythagorean formula:

Square root (half major^2 - half minor^2)

So for an ellipse with a size of 10 x 8 the focus is:

Sqrt(5^ - 4^2) = Sqrt(25 - 16) = Sqrt(9) = 3

And the string is

2*(5+3) = 16



On 12/17/2016 9:17 PM, Bill Nelson via Stagecraft wrote:
>> If I'm recalling my woodworking class from 40 or so years ago, you can
>> easily draw an ellipse on the wood by putting a nail at each focus, then
>> using a loop of string to constrain your pencil, just draw the thing.  I
>> don't have a formula to calculate the length of the string, as the class
>> was back in 7th grade woodshop, and we were making plaques for something.
> 
> It would be two times the length of the major axis.
> 
> The width of the minor axis is determined by the spacing between the two focii.
> 
> Bill
> 
> 
> 
> 
> 
> ____________________________________________________________
> For list information see <http://stagecraft.theprices.net/>
> Stagecraft mailing list
> Stagecraft at theatrical.net
> http://theatrical.net/mailman/listinfo/stagecraft_theatrical.net
> 

-- 
Jon Lagerquist
--