Shaker Hanging Shelf - Dado Jig

Given the poor quality of the dado set I have for my saw, I will be using a router to cut the dadoes that support the shelves. The router is safer, in any case, and will cut cleanly and accurately with the proper jig. I will be using a 1/2" outside diameter guide collar in the router with a 5/16" straight bit to make the cuts.

Jig Layout

I decided to use 1/2" MDF here again, as I did with the other jig for this project. The photo at right shows my layout. After marking the desired placement of the dadoes, I drilled a 1/2" hole at the end of each one to aid in setting up the router to cut the three slots. The remaining layout lines are for the placement of the 1/4" masonite strips that will position the work piece under the jig and for the placement of the horizontal batten that will be used to hang the shelf unit.

Setting the Guide

I used a clamp-on straightedge to guide the router, which was equipped with a 1/2" straight bit. I positioned the guide by dropping the router bit into the hole I had previously drilled in the MDF and moving the straightedge until it contacted the router base. After double checking the position of the guide with a try square, I locked it into position.

I made the cut in three passes of gradually increasing depth. The guide is positioned to the left of the router because routers move to the left as you push them away from you. Thus, I started the cut on the edge of the MDF nearest to me and continued cutting until I reached the hole I had drilled at the far end of the cut. Highland Woodworking has an excellent article on this subject at:
http://www.highlandwoodworking.com/routersgoleft.aspx.

The two jigs I made for the Hanging Shelf project represent my only experience so far with MDF. The material is quite dense, stable, and consistent, making it suitable for jigs, but it is unpleasant to work with. The high resin content means that it scorches easily when machined and smells bad when it does scorch. Working MDF with the router produces large volumes of fine dust and is probably harder on bits than is real wood. Still, it seems the most convenient and inexpensive material I can think of for this application.

Underside of Jig, w/Slots

The last photo shows the jig with the masonite strips ready for glue up. The guide slots came out clean, crisp, and square. I am anxious to try both jigs out on some actual wood! I haven't yet made up my mind about how I will make the notches in the side pieces for the hanging batten. I may add that feature to this jig or perhaps nibble them out with the table saw.

To be continued...