Calculating the Sag (saggitta) on a radius dish

[jiefu]

We can all build the jig to use the router to cut the dish, but calculating the sag (how far down the router goes in the middle of the dish) is harder as is how to draw the curve for those of us without 'expensivecad' or some other complex software. So attached is a table to stick on your wall for 26"disks (better than 24"- sandpaper lasts longer) and a description of how to use a long compass (2 sticks of wood) to draw the curves for your router jig. Easy now....

[Nick]

& the table is where?

Hi jiefu, welcome to the forum.Hope you brought a sense of humour with you cos we're a strange bunch (well, some of us are). Your table hasn't come though (or the link, however you posted it) so you might want to have another crack.

[hilo_kawika]

Here's a more general solution until jiefu gets it together...

http://www.ukuleles.com/Technology/calcarc.html

aloha,

Dave Hurd
http://www.ukuleles.com

[Nick]

Thanks Dave :serg :serg

[chris paulick]

Is this what you are after?
http://www.liutaiomottola.com/formulae/sag.htm