17 Jan 2014 – Pattern Routing


Pattern bits or bearing-guided bits come in straight or spiraled flute designs. The different designs are meant to deal with different types of materials. Also the bearing configuration differs to assist with grain direction changes. First, are the straight bits. They usually have carbide flutes and some might have an angled flute, but they work best with straight grain lumber or plywood and MDF. They are inexpensive, but they wear out quickly. If you were only going to buy one pattern bit initially, I would recommend the spiral bit. It is ground from a single piece of carbide so it costs a little more, but it's worth it for hard woods. It produces a smooth surface with little or no tearout. I prefer the up-cut spiral because it helps keep the work piece next to the bit. The compression bit is one step better, but much more expensive. Now for the bearing location, The flush trim bit that has the bearing at the tip of the bit is safer, but I find a pattern bit with the bearing at the top is more functional for most cuts. There may be times when it is best to team up the different types of bits and bearing locations to create the perfect cut. In some cases with thick stock you may want to use both a pattern bit and a flush trim bit to complete the project. Also if there is a distinct grain change starting in one direction then switch directions at the grain change help avoid tear-out. Once you've tried out a few different bits you'll know exactly what works best for each project, but this guide and the Fine Woodworking article should provide a great starting place.