SWMBO wanted me to build a shoe cabinet which required making dados and rabbets. I had made some with my router previously for the tool tote using makeshift straight-edges, but they weren't very clean so this time I wanted something more precise. Plywood comes in standard thicknesses except they don't really measure up to those thicknesses. 3/4" plywood is not exactly 3/4" and so your 3/4" router bit will make dado too big or too small. I decided that for this project, I will make a jig for making more precise dados.
After looking around the web, I went with the free plan available from WoodSmithShop.com. There are a lot of plans for adjustable dado jigs and they mostly follow the same concept just using different materials and techniques to reach the same result. In fact, right after I completed my dado jig, TheWoodWhisperer released a video how-to on how to make a very similar jig. Why didn't he release it two weeks earlier!?! ^_^. I watched the video and it is nice, but I actually think the method described by the WoodSmithShop is easier to construct and true-up.
In building this jig, I learned a lot about hardboard. One, hardboard have many different names which is confusing. Some places call them masonite, some call them duron, and some call them hardboard. Most big chain hardware stores only carry "peg boards" which are hardboard that is smooth on one side with holes and is often used to hang tools, etc. For hardboard that is smooth on both sides, it is called tempered or serviced tempered but sometimes they go by different name. To find these, you'll likely have to go to a lumberyard rather then a hardware store.
I had a hardtime finding the T-nut and knobs at the hardware store too and had to go to a woodworking shop instead so if you can't find one at your local store then try Woodcraft, Rockler or Amazon.
Making the jig is very easy and the plans are very detailed. I messed up the first one because I used the wrong side of my router base, but having made one already the second one took me only an afternoon. I cut the slots using plunge router and straight edge. It's not as clean as using an router table like what was shown in the TheWoodWhisper but I dont' have a router table, so...