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How to Start: Cutting Data

General Principles
Cutting speed Vc and feed per tooth fz, the first key parameters in milling, depend on
different factors.
Before everything else, a carbide grade. The harder grade has higher wear resistance and enables
higher cutting speed. The tougher grade with its better impact strength is intended for the
lesser speed, but allows greater feed per tooth.
Machinability of engineering materials is different, and even the same material can be substantially
different by its machinability (for example, milling a tool steel in different conditions: annealed,
pre-hardened and hardened). Therefore, a specific force needed for removal of a unit of a chip
section, and load acting on an insert differ too. It is evident; the machinability factor should be
taken into consideration.
Insert geometry is also important. A sharp cutting edge, which is brittle and can not stand up
against a serious load, sets the upper limit to the feed. The T-land, a negative land protecting
the cutting edge, conversely, binds the feed below because too small a feed causes in this case,
considerably increased cutting force.
Another factor - the milling tool body. A durable design of the body and a reliable method of
Milling Tools
securing the insert ensure machining under high cutting data.
Further, the application. What is the aim of tool use? In rough milling, when a relatively large
volume of material is removed, the feed is high and the cutting speed is moderate. At the same
time, finish milling operations performing with small allowances demands maximal speeds and
small to medium feeds for high machining accuracy and good surface finish. Different limitations
such as large overhang (in milling deep cavities, for example), improper clamping, workpiece with
a thin wall and others lead to decreasing the speed, the feed or even both.
Lastly, the machine tool and toolholding. Poor machine conditions and not rigid toolholders create
an additional barrier for increased cutting data.

The mentioned arguments are very general; and no doubt everyone who is involved in metal cutting
is familiar with them. They are a good illustration of complex dependence or the cutting data on
different attributes. How to go from the generalities to the particulars and specify the
starting cutting data?
We can take into account the application factor and the machine tool conditions by introducing
operation estimation: light, medium and heavy. Then we can prepare the tables with the
recommended cutting speed and feed for every milling line and thus provide the user with the
cutting data. It is a correct approach; and the cutting data recommendations in full application
guides, tool advice software and specific guidelines use it in full.

In the U.S.A., instead of the term “feed per tooth” (“fpt”), “chip load” is often used; “advance per
revolution” means “feed per revolution” (“fpr” or “feed”) and “advance per minute” or “feed rate”
– “feed speed” (“feed per minute”, “fpm”, or “table feed”).

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