Radius dish depth

[gilles]

I'm hoping someone with a few radius dishes can help me out...

How deep is the center point on a 15' and a 28 (or 30)' radius dish?

I have access to a drawing bow and it would make life easier when I build the router sled to carve out the dish with these numbers.

[John Parchem]

What you really want is the sagitta of an arc. This website is from a member of the forum. He has a tool to calculate what you want. https://www.liutaiomottola.com/formulae/sag.htm

It is easy to use the tool, enter the radius and half of the dish diameter and it will give the depth. For example, a 2' diameter 28' radius dish would have a .216" depth.

Also with this information instead of the bow, you may consider a long compass or shipwright's compass https://jsevy.com/luthierie/compass/Long_compass.html

http://www.anzlf.com/viewtopic.php?t=6168. It is an easy tool to make and a little more accurate than a bow.

[John Parchem]

updated post with more info

What you really want is the sagitta of an arc. This website is from a member of the forum. He has a tool to calculate what you want. https://www.liutaiomottola.com/formulae/sag.htm

It is easy to use the tool, enter the radius and half of the dish diameter and it will give the depth. For example, a 2' diameter 28' radius dish would have a .216" depth.

Also with this information instead of the bow, you may consider a long compass or shipwright's compass https://jsevy.com/luthierie/compass/Long_compass.html

http://www.anzlf.com/viewtopic.php?t=6168. It is an easy tool to make and a little more accurate than a bow.

[Kenny Wiebusch]

My dishes are 23" across. My 15' dish is 10mm deep. My 28' dish is 5mm. Take into consideration the accuracy of my old eyes and the tiny lines on my scale!

[gilles]

My dishes are 23" across. My 15' dish is 10mm deep. My 28' dish is 5mm. Take into consideration the accuracy of my old eyes and the tiny lines on my scale!

Thanks! This is the info I was looking for!
(not a mathematician)

[John Parchem]

The depth depends on the size of the dish. I was not holding back, your original post did not list the diameter of the radius dish you wanted to make.

[gilles]

The depth depends on the size of the dish. I was not holding back, your original post did not list the diameter of the radius dish you wanted to make.

Understood.
24 inch MDF, so the 23" measurements work.
Thanks for your input, John.