Tech Talk
What is a “Chip Breaker”?
When machining steel at high speeds with tools of the usual shapes, a continuous chip is normally produced. This continuous chip is not only hazardous to the operator, but also difficult to handle. One of the means of controlling the chip is the ground-in chip breaker, which, essentially, is a step ground into the tool’s top surface so as to curl or break off the chip. Both depth and width of the breaker vary with the depth of cut, feed, type of metal being machined and cutting speed.
Three types of ground-in chip breakers, sometimes referred to as the “angular”, “parallel” and “groove” types, are recommend by the carbide tool manufacturers.
The ease at which the chip can be broken depends upon the chip cross section or area, the nose radius and the physical characteristics of the material being cut. A thin, springy chip is hard to break but can be coiled, whereas a thicker chip with some stiffness can usually be broken.
Whether a chip can be stressed to the point of breakage, for a given feed, depth of cut and type of steel, will depend upon the depth and width of the breaker. It is also possible to stress the chip to the breaking point, when using a tool with a given depth and width of chip breaker, by varying the speed or feed in order to obtain a chip of sufficiently stiff cross section.
The angular type of ground-in breaker is satisfactory for the majority of jobs and is the easiest to grind. The chip is deflected back against the uncut portion of the work where it is broken without any damage to the tool. By varying the depth and width of the step, this style of the breaker can be adapted to practically any set of conditions. An angle of 8 degrees to 15 degrees will be found generally satisfactory. On cuts 1/32” or less, the angular type of breaker is usually more effective when a nose radius of 1/32” or less is used.
For light, fast finishing cuts, not exceeding 1/32”, an angular type chip breaker ground at 45 will give good results. This style of breaker forces the light chip either into a spiral coil or a small ball that can be easily handled. Usually the width of the step does not exceed 1/16”.
The parallel type of chip breaker is also widely used, particularly where the cuts extend to the shoulder or where it is desired to force the chip against the work and cause it to break. The groove type of chip breaker resembles a high-speed steel tool that has been allowed to wear its own chip breaker. This type has been successfully applied where the depth of cut varies and cutter speeds are relatively low. The land between the cutting edge and groove is parallel to the top face and should be one to one and one-half times the feed. A 2 negative rake on this land will strengthen the cutting edge. The width of the groove should be three to four times the feed to be used and the depth, not over .010”.
