I do not currently own a milling machine, so it is difficult to precisely drill equally spaced holes. I had a project in mind that would require four pieces of steel tubing to have holes that all align.
My inspiration for this came from my woodworking tools. There are several companies that produce jigs for making the Euro style adjustable shelving, but nothing that would work well for the smaller holes I wanted. I designed this using Fusion 360, then had a local machine shop make it for me.
I started with a piece of 1″ x 1″ aluminum bar stock cut down to 13″. Starting 1″ from one end, there is a 1/8″ diameter drill bushing press fit into holes drilled on 1″ centers. There are also four tapped holes through the side and one on each end. These allow me to add tabs so I can keep the edge aligned. If I want more space from the edge than the 1/2″ the jig allows, I put spacers between the jig and the tab.
There is a bevel cut into the bottom of the jig to allow the chips to clear during drilling. The threaded hole in the ends allows a tab to be screwed in to always start at the same relative location from the end of a work piece. The edges all have a slight chamfer on them to make the jig safer to handle.
Here is the jig in use. I needed the holes to be 3/4″ in from the edge, so I added a 1/4″ spacer. After drilling holes the length of the jig, I use a 1/8″ transfer punch through the jig into the last hole drilled so that I could make a continuous row of holes and maintain the spacing.
Overall I am quite pleased with this jig. Using just a hand drill, I was able to drill over 500 holes total over 8 pieces of tubing, and they all matched within the tolerance I needed. I paid about $15 for the aluminum bar from McMaster (part #9008K14), and $7.50 each for the drill bushings (part # 491A101). The machinist charged me about $50 or so to do the milling and pressing. I could have gotten by without the bushings and just used a hole drilled in the aluminum, but I wanted something that would last and remain accurate. It is a nice little addition to my shop.