# Calculating 45 Degree Elbow Radius For AutoCAD Plant 3D

This week I’ve been working on creating some Fusibond catalog content. One of the items I’m creating is a 45 degree Flanged elbow.

What I’m given in the cutsheet is the B and C dimensions:

However, in the spec editor, I only have the option to enter the radius.

The question of the day was how to do I calculate the radius from the B length. One easy solution is to draw the arcs and lines in AutoCAD and then take a radius measurement. I wanted to use a formula so I can set up a spreadsheet to calculate it for me.

I had some help from Ken Fauver, the spec/catalog guru from Autodesk. He gave me the formula that I was searching for.

R = B x SIN((90 – A /2)*PI /180)/SIN(( A /2)*PI/180)

where R is the radius, B is the takeout length (per image above), and A is the angle of the elbow.

I’ve posted a spreadsheet that utilizes this formula here:

https://docs.google.com/spreadsheet/ccc?key=0AuwoFe9y_YbsdEY5SkMyem43Z21lem1VNzNHTUtDVHc

One key note is that O31/O32 indicate whether the radius measures to the back of the flange or to the face of flange.

Feel free to make a copy or download the spreadsheet so you can automate some of the calculations.