Today I tried doing a 1/8 inch depth pocket cut with my Zen Toolworks router. I’ve never tried this particular operation before, but with the new F8 leadscrew upgrades (my latest post on this), I expected it to go pretty quickly. Compared to the stock leadscrews, the F8 screws are incredibly fast as seen in my pocketing video below.
Although the lateral travel is incredibly fast, the 1/8 inch cutter, although good for many things, doesn’t seem to be the best choice for doing pocketing operations. With the improved screws, once can easily attain a lateral travel of 100 IPM (inches per minute). Unfortunately, when the router is cranked up to these speeds, the cutter just doesn’t have the proper rigidity to make good cuts and ends up skipping around and bending during travel.
After trying this operation several times, I eventually was able to cut the pocket at a speed of 30 IPM (inches per minute). For all of these cuts, I was only taking .015″ per pass which was probably conservative, but using this 1/8 inch cutter, doing a 2 inch circle 1/8 inch pocket took 19:24. Yes, Nearly 20 minutes. A long time.
Fortunately, I had a Dremel 115 bit with a 5/16 inch cutting head (I originally used this cutter to mill my router bed flat). This, like many Dremel bits, fits on the ER11 chuck for my ZTW spindle (see my article about your spindle choices). Since it’s much shorter and wider on much of the surface than the 1/8 inch bit that I was using, it was much more rigid. Also having a larger cutter diameter, the speed is much faster. Because of these improvements, I was able to run the feed rate at a full 100 IPM. Along with Gcode generated for this larger cutter diameter, this pocketing operation was reduced to a 2:25 cycle time!
Upon examination, the surface finish was better, and when measured with calipers, the accuracy of the pocket was closer to what it needed to be. With the Dremel cutter at 100 IPM, the resulting diameter was measured at a few points to within +.006 -.003. Using the 1/8 inch bit varied from -.010 to -.030 (more accurate and more precise, for you engineers). This makes sense, given the flexibility of the 1/8 inch cutter.
One takeaway from this is that if it seems like there is a better way to do something, especially in the CNC router arena, there’s a good chance there is. Even more important is that you should be reading JCOPRO constantly and subscribe via the RSS feed or Email updates!