Positive rake can pull In determining the most effective way to separate chips from your workpiece, several variables must be taken into consideration; however, probably the most important is selecting the right cutting tool geometry. After all, the collective angles formed by the dimensions of a cutting tool are what make a tool geometrically unique. When it comes to your metal cutting operations, you have three general milling cutter geometries from which to choose: double positive geometry, double negative geometry and positive/negative geometry. Each of these geometries serves its own unique purpose as well as features its own set of advantages and disadvantages. Let’s see how each one might apply to you. The positive axial rake lifts the chip and curls it away from the finished workpiece surface and toward the inside of the cutter body. The positive radial rake provides a sharper cutting edge and tends to pull the tool into the work (free cutting). Double positive cutters hold the inserts in a way that creates a positive rake angle both axially and radially, allowing for very free cutting and clean, quiet machining. It’s an arrangement that also minimizes work hardening of the surface, achieves excellent surface finish as well as generates very little cutting force. These geometries are good for machining non-ferrous materials, such as aluminum, copper and non-metallic materials, and even steels on smaller machines with limited power ratings. Care with the set-up is particularly important with these cutters as they are more fragile (leading to cutting edge chippage) and can lift the workpiece from the table. Overall Advantages Smooth cutting Good chip removal Good surface smoothness Overall Disadvantages Cutting edge strength Unfavorable entry contact Draws workpiece away from the machine table Double negative cutters have an orientation that uses a combination of negative axial and negative radial rake angles, which direct the cutting forces further back from the edge of the insert. This characteristic enables double negative cutters to show increased insert strength over the double positive and positive/negative cutters. However, while double negative cutters are very strong and rugged, their geometry can result in ineffective chip flow and potential issues with clogging. While double negative geometries are ideal for cast iron, it’s imperative you have a machine with sufficient power, as well as a rigid setup for the firm mounting of your cutting tool and workpiece. Also, keep in mind that modern technology has made it possible to add chip breakers to inserts, allowing today’s negative rake cutters to machine more freely than ever before. Because of this, double negative cutters can effectively machine all materials as long as you utilize the correct chip groove profile. Overall Advantages Cutting edge strength Productivity Pushes the workpiece towards the machine table Negative inserts double the number of cutting edges that can be used Overall Disadvantages Large cutting forces Chip obstruction Called in the industry shear-angle cutter. Often used in rough and finishing milling of tougher grade of aluminium and other non ferrous metals and for free machining of cast iron steel, steel, stainless and most high temp aloys which are milled difficulty using doubke negative Positive/negative cutters have an orientation that uses a combination of a positive axial rake angle and a negative radial rake angle. These cutters are the most popular because they offer some of the free cutting benefits of a double positive cutter and some of the strength of a double negative cutter. The positive axial rake lifts the chips, while the negative radial rake directs them outward. These actions, when paired with a high lead angle, help reduce or eliminate chip flow obstructions. Overall Advantages Good chip removal Favorable cutting forces Wide range of applications