Machinability Guidelines and Comparisons

An often asked question is how to compare machinability of different alloys. The answer is available here on our website. The key column is relative machinability, listing speed as a percentage of B1112.  B1112 is a free-machining steel and the industry standard alloy for machinability comparison.  It is the one of the easiest grades of steel to machine, and the machinability for all other alloys is based on the machining speed for this alloy. 

How does one use the chart?  Let’s assume that you have a good history of machining 304L.  Now you are quoting a job using RA330, but have no experience with this alloy and have to estimate costs.  In such a case, the relative machinability of 304L is 44 while RA330 is 24.  This means that RA330 has to run at a rate of 24/44 or 55% of 304L.  With this information, you can estimate how much more time will be needed to machine each part and build this cost into your quote to your customer.

There are some assumptions to all these calculations, namely that these operations are single point turning operations and machining is done with high strength tool steel.  The reality in today’s world is that more and more machine shops are using carbide tools, and the tool manufacturers are developing tools specifically tailored to classes of alloys.  So it may be possible to use new tools to run at even faster speeds.  HOWEVER, the guidelines are still based on relative machinability.  This means that we do not have to differentiate based on the type of tool.  However, you should check with your tool supplier to determine whether they have a tool for a specific alloy that will enable you to machine even faster.  The tool supplier should be able to provide machining parameters for such specialized tools, so you can maximize his productivity.