The two most common problems when cutting and routing acrylic welding of the material and poor edge finish. In this article, I will focus on routing. The top reasons for chip welding and poor finish are: 1) inappropriate tool selection 2) improper chip load 3) small tool diameter size 4) direction of the cut Plastic is extremely sensitive to heat. Routing at a high feed and spindle speed will cook things up. Chip load, which is the shape and thickness of the chip formed, is a function of feed rate, spindle speed, and the number of cutting edges on the router bit. The chip itself is the way heat is transferred away from the tool and the part. Generally speaking the larger the chip, the better the heat removal from the work area. However, heat removal runs into the problem of good edge finish. So, like many things in life, there are no fast and set rules, only guidelines. The guideline applicable here can be expressed as the formula Chip Load = Feed Rate / (RPM x The Number of Cutting Edges). Looking at the formula, you can see there are several ways to adjust chip load. But merely raising feed rate for example to achieve maximum chip thickness is not always the best approach. This is especially true in the case of small parts where feed rate is limited. In such cases, higher spindle speed will maximize chip load. Welding can also occur because of small tool diameter and the direction of cut. Small diameter tools have limited chip clearance capability which can cause welding. I briefly discussed tooling geometry in a previous article and even though the tooling geometry (see below) is correct, the end result can be lousy because the other parameters in the formula above are not correct. For example, using a down cut spiral in a blind slot will cause the chips to be recut over and over until they weld. Cut direction may also cause problems. In most cases, conventional cutting rather than climb cutting is recommended.