Pattern Guides On The Table Saw: Fast In The Straightaways
I’ve never seen it done before or demonstrated on any woodworking shows, and this would be the last thing that I would come up with on my own. But, thanks to Don Snyder, a fellow St. Louis Woodworkers Guild member, I can now add using a pattern to cut pieces on the table saw to my playbook. It sounds simple, and it is, once you understand what is happening.
Don’s program was provocatively titled, “How to cut polygonal shapes.” I initially thought that there was going to be a lot of talk about angles – and there was. The information was “informative”, but seemed like something I could figure out on my own if I needed to. I could figure out the angles necessary for a 32-sided shape; but I was looking for a trick, something that I hadn’t seen before, and Don delivered.
The reason for using a pattern on the table saw is to produce exact copies of shapes with multiple sides quickly, accurately and repeatedly. This is necessary for making more than one simple project or a lot of pieces for a complex project. Don got in deep, even showing how to use this method to make three-dimensional shapes like polyhedrons.
The first step it to make a pattern, a perfect pattern, of the shape that you would like to repeat. For this method, especially on the table saw, all the sides of the shape need to be straight lines. The table saw is not good at curves. The pattern is cut from 1/4″ thick material, which is easily worked and provides enough structure to run along a guide. MDF is fine for short runs. Plywood is more durable and a better pick for longevity. Solid wood is not a good pick because it is not dimensionally stable. Remember, accuracy is very important.
The next step is to secure the pattern to the wood that will be your final piece (or, of course, a test piece). This can be done with nails, double-stick tape, spray adhesive, etc. as long as the pattern can later be removed and not damage your final piece. You want the pattern to stick firmly to the piece you are cutting. If not, the lumber could twist on the sawblade and cause a violent kickback (this is something you want to avoid).
All that is left to do is to make your auxiliary fence for the pattern to follow. This fence will attach to your regular fence and extend over the blade so that the outside edge of the fence is above and in line with the outside edge of the table saw blade. Set the blade to just clear the thickness of your final material and set the auxiliary fence about 1/16″ above the blade. The auxiliary fence should extend well beyond the front of the blade so that the pattern can engage the fence before the final material is cut (this is also for safety, as well as accuracy). The same is true on the back of the fence to allow for a safe finish on the cut.
To cut a piece like a pentagon, first make a perfect pattern then attach it to a board. Put the pattern against the auxiliary fence well before the blade and push it through. Rotate the pattern to the next side and make a similar cut. Do this for all five sides and you have a pentagon exactly the same as the pattern. Watch closely for cut off pieces accumulating under the fence and remove as necessary. Don said he turns off the saw and removes the cutoffs after every cut to avoid them binding in the enclosed space and kicking back.
This setup ends up working like a router with a bushing that follows the pattern, with a couple of major differences. The router can follow curves, as well as straight cuts, while the table saw method will only work on straight cuts. However, the table saw can be set to cut at an angle, which is essential for joining three-dimensional shapes like a polyhedron. The table saw method also allows the pattern to be followed with only one step, while the router method usually requires a rough cut beyond the pattern (done with a saw) before the finish cut with the router. Both methods have their advantages, but the table saw wins on the straight cuts, which was Don’s focus. As a matter of fact, Don started his presentation showing several pictures of woodworking with organic shapes and all of them were crossed out with big X’s. Don doesn’t like curves.