By:Scott Taylor, SigmaTEK Systems
A router can be a great option for cutting what would traditionally be considered “machine shop” parts. By cutting aluminum and hard plastics from sheets of material rather than bar stock you are able to cut large quantities of parts more efficiently by reducing setup times and tool changes that a machine shop would require.
One hurdle to overcome with cutting machine shop parts on a router is the need for tight tolerances. Router manufacturers will advise that a CNC router is only capable of holding +/- 0.005″, but by using roughing passes you cut the bulk of the material that needs to be removed, then follow up with a finishing pass that skims the sides of the part. The finishing tool is much less likely to flex, giving you the machine shop quality that you’re accustomed to.
This “roughing tool” can be easily created in your tool library so that you do not have to continually adjust your kerf. By creating a tool with a larger diameter than it actually is, the machine will offset that distance away from the edge of your part, allowing you to skim it with a finish pass to clean it up. For example, to create a 0.500″ roughing tool, make the diameter of the tool 0.520″. This will leave 0.010″ along the edge that can be cleaned up with a finish pass. Since it is such a light cut, you will get almost no tool flex and this will leave you with extremely clean edge quality and accurate tolerances.
Some of your traditional machine shop parts may be small, so you may think that it would not be a good fit for the router. However, by onion skinning the external perimeter, you can leave a small sliver of material that will hold the part in place and maintain proper vacuum on the table. With a 0.020″ onion skin on aluminum or plastics, you can easily cut that away with a sharp blade to break the parts free of the skeleton. Try out these tips for your particular applications and you’ll be surprised at what you’re able to accomplish with SigmaNEST and your CNC router.