Lay Out the Design + Mark the Hole Locations:
You can make this piece with either 3 or 4 shelves. I chose to do a 4 shelf layout, 4 feet long. Mark the desired locations for your shelves and place an X to mark the place where you will drill through the steel.
Drill Through the Steel:
Drilling steel is a little different than wood. Make sure you are using drill bits that are meant for steel and check your drill for the appropriate speed settings. Firmly clamp and secure your steel to a work surface when drilling. A lubricating oil should also be used. I didn't have any on-hand, so I used WD40, which was not ideal, but better than nothing. Drill a single hole that will align with the center of each 2x10 shelf on the front facing sides of the angle irons. Drill 2 holes on the other side for nails that will go into the end of the 2x10 and the sides of the baluster supports.
Trim the 2x10s:
It's critical that the 2x10 shelves are the same length. I used a benchtop chop saw to make nice accurate square cuts. You can do this with a hand held circular saw, but I would recommend using a speed square clamped on as a guide to ensure the cuts are square.
Sand the 2x10s:
Use an orbital sander to sand the 2x10s and supports with 220 grit sandpaper.
Screw the Supports onto the Shelves:
Use 2 1/2" screws to screw the supports to the underside of the shelves.
Round the Corners of the Shelves:
The inside corners of an angle iron are not perfectly square and have a bit of a radius. Sand the corner edges of the shelves so that they fit nicely into the angle irons.
Nail the Back Angle Irons to the Shelves:
Lay out the back angle irons on the floor and place the shelves in their appropriate locations. Starting from the bottom shelf, start nailing in one nail through the sides of the angle irons and into the ends of the shelves. Make sure the top shelf is flush with the top of the angle irons.
Nail on the Front Angle Irons:
Place the front angle irons on the shelves. Start with the bottom shelf, making sure it's properly aligned and then drive nails through the angle irons and into the wood. Next, align the top shelf and fasten it with nails. You may need to use a clamp or a second set of hands to wrestle the wood into to place. Nail the other 2 shelves and then stand the whole thing up.
Drive Nails Through the Remaining Holes + Rub a Coat of Danish Oil into the Wood to Finish
2x10s are affordable and look great, but can be a bit warped. This set of shelves is sturdy and functional but not perfectly square.