knuckle radius

[Andydunkin]

I am having a little trouble calculating a knuckle radius for one of me parts. It is for a [highlight #FCE94F]2.1 Elliptical head with a 123.5 O.D[/highlight], I need to know the knuckle radius. I have crunched some number and came up with 21.3655 R by simply multiplying the O.D by 17.3 but it does not seem to be correct. Can someone please help me with this? It will be greatly appreciated!

 

[Duwe6]

Try asking this one in the Boiler & Pressure Vessel forum.