Thursday, September 11, 2008

Corner Mullion Leg Calculator - "L" Corner Mullion

Regarding defining a precise inside mullion width at corners of curtain walls: Craig Thomas with Leo A. Daly shared this concept with me. It goes something like this: (Craig writes)

I did some experimenting and found I could make the “L Corner Mullion” work to my satisfaction (your expectations may be different) for angled curtain walls. (Craig wants to define the inside edge exactly) This is what I found.

If you know the angle between the two curtain walls (A), the desired width of the mullion along the face (in my case 2 ½”) and ½ the frame depth (y), you can calculate how long to make each leg on the mullion (X”)(see image below – from Type Properties of “L Corner Mullion”). Here’s the formula:

X” = 2 ½” + (y * tan(90-(A/2)))

At first it may look like a lot of work, but with the calculator on your PC you can easily do the math. Then save the mullion based on the angle. In my example, I had a 7” deep mullion at 150°, with 2 ½” exposed in the corner.

I named it “L Corner Mullion – 150 degrees”.

Steve says, "You can enter this formula in the Leg 1 and Leg 2 field directly too! and make sure you use inches!!"

This is the result in the project:

Thanks for sharing Craig!!

I thought I'd "pile on" and add something to this concept. I built an annotation symbol that consists of parameters to enter the data required for the formula and does the calculation for you. Place the symbol next to your corner. Enter values, get the result. Then you can edit the mullion, create a new type and enter the values.
If you'd like to play with this you can download the file here!


Erik said...

You guys and you math! I love it.

Steve said...

It's not "my" math...its Craig's math! I have trouble with grocery store math.

ventrell.williams said...


Would you happen to have this file availble in the 08 format (for the rest of us that can't keep up with the industry). In particular, I am interested in to exactly how the legs of the corner mullion angle? Is the interior frame depth locked in and the extrusion locked to an angled reference line to control anterior face of the mullion length ("x").


Steve said...

There isn't anything in 2009 that wouldn't work in 2008. All this post is doing is using trig to figure out what Leg 1 and Leg 2 need to be so that the inner edge of the stock "L" shaped curtain wall mullion family is a specific size. In the example we wanted it to be 2.5" wide.

I don't have 2008 installed on my computer anymore so I'd have to rebuild the annotation family after installing the software. I don't have any immediate plans to do either, sorry. If I find some time to do it I will.

That said, if you sketch two curtain walls at an angle to each other and place the "L" Corner Mullion family at the corner you can follow the directions and enter the formula right in the properties of the mullion for Leg 1 and then copy the result into Leg 2.