CNC router as a template engine.

The CNC router is a fantastic tool to create arbitrary shapes with great precision. Before I owned a CNC router, I would make templates by hand. Any sophisticated shape with a lot of curves took a fair amount of careful work to get right. And often it was "good enough" and not "perfect". So, I tended to only make templates when there wasn't much in the way of alternative approaches. With CNC and a good CAD program, you can make just about any shape you want, perfectly. The only limitations are size and imagination. And even size can be overcome with some imagination. I find myself make templates on my CNC machine a lot more often.

Let's take a look at a project I made that uses CNC for multiple templates. It is a Shaker inspired step stool. My dad made one in the 1970s and I've had it ever since. The handle makes it really convenient to move where ever you need it. We used it all the time and often I had to wander all over the house to find it. So I decided to make another. After a little CAD work I realized that there were a couple of flaws in my Dad's design and made a few changes to make it easier to create. The main change was to use a mortise and tenon base rather than cleats to hold it together. I also wanted to update the legs to give it a more modern look. You can see the results to the right.

As shown in the shop drawing below, the stool is constructed of 4 different parts that each have multiple curves in them. Cutting identical parts by hand is possible though it would take a fair amount of sanding to get them exactly as drawn. Worse, making sure that the legs, handle and "rails" were symetrical and identical would be tedious. The upright handle is especially tricky to make symmetrical by hand. I know, I've tried. And my Dad's version isn't spot on either. He was an outstanding woodworker so it's clearly a real challenge. However, cutting these as templates, trimming most of the waste and then using a router with a trim bit to clean up the edges resulted in perfect parts. I also cut the mortises with the templates. The one in the stool top is through while the ones in legs are blind. I used a 1/4" spiral to make those and cleaned up the corners with a chisel.

Usually I cut my templates out of 1/4" MDF, clad on one side with a white vinyl. Double sided tape sticks really well to the vinyl. Routing with it against the spoil board results in a much cleaner cut requiring less trimming. I have also used 1/4" plywood but MDF tends to cut better and requires a lot less cleanup.

One problem I often run into are parts that are bigger than my CNC machine can handle. I cut them in sections and then align when taping them to the work piece. Creating an alignment key makes it nearly foolproof. The step stool handle is a perfect example. It is 22" long.

The stool went together fairly quickly and now we have 4! Because the templates are reusable, I was able to make 3 in short order. There are a couple in the planning stages for Christmas gifts and I'm sure there will be requests from family members.

I'm sure a lot of people are saying, just cut the parts on your CNC machine directly. In many cases, the work piece may be too big. On one project, I cut handle holes into fairly large pieces - much too large for my machine (even for the much larger one I am considering purchasing). Decorative edging is another example. In addition to the size issue and even with a fast and rigid CNC machine, it is a lot faster to use templates. And, it is much worse on a hobby level machine. The templates for the stool took about 40 minutes to cut out. Multiply that by 3 for the thicker 3/4" wood, then 50% more because there are 2 legs and rails. I'd estimate it would take 4 1/2 hours of machine time to make all the parts. It took me about 1 hour to trim and rout the various parts using templates.