There are lots of reasons why you might want to put slotted holes into a piece of metal. If something needs to slide or be adjusted, it's a great way to secure pieces together.

I made this at TechShop where I used the vertical mill to make the holes.

Step 1: What You'll Need

For this Instructable, you'll need the following:

Parallel bars
An end mill
Coolant and cutting oil
Your work piece. I'm using 2" steel angle iron.
Sacrificial paint brush to remove metal flakes
Sacrificial square tubing. Since I'm using 2" angle iron, I'm using a 2" square tube

Step 2: Setting Up Your Piece & Machine

Securing your work is really the trick to this entire thing. The milling is easy. I found this to be the easiest way to clamp your angle iron and get it ready for milling.

Please see my notes inside the image for details.

Put your endmill in the machine and set your speed. I'm using a 5/16" endmill, so I used the following calculation:

172 / 0.3125 = 535 RPM

Once your material is secure and the endmill is installed, you can optionally position the endmill where you need it and set your zeros.

Step 3: Mill the Hole

Now it's time to turn on the machine and start milling.

Apply some coolant or cutting oil to your material. Begin by plunging into the material. When you do this, peck at it by only going a short ways in, then backing off. For my material and endmill size (1/8" steel and 5/16" cutter), I decided to make my slot in 3 passes. So I only went 1/3rd the way through the material.

When you get to your desired depth, use the quill lock to hold it in place. Now, move your X or Y axis (depending on which way you're making your slot) very slowly. Continue to apply coolant and use your paint brush to remove chips and see what you're doing.

Repeat until you are all the way through the material.