I'm kinda new at this and I am confused by the reference SFM. Is this the speed that the machine is going? I have a bridgeport the speed is just indicated by numbers....so am I talking SFM or RPM here. Just trying to understand here and figure out these speed feed tables.
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Sfm
- Thread starter Mike8623
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- Feb 8, 2014
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Surface Feet per Minute is a function of the spindle RPM and the tool diameter, or in the case of a lathe the work diameter. Cutting speeds for various materials are listed in SFM
SFM = Surface Per Minute
DIA = Tool Diameter (in inches)
RPM = (SFM * 3.82) / DIA
SFM = (RPM * DIA) / 3.82
SFM = Surface Per Minute
DIA = Tool Diameter (in inches)
RPM = (SFM * 3.82) / DIA
SFM = (RPM * DIA) / 3.82
So the numbers on the machine for speed are what are listed as the SFM on the cutting charts? So when you go to one of the charts and look the diam. of the cutter and then over to the SFM that is the number you are looking for on the mill for a cutting speed.
- Joined
- Feb 8, 2014
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No, the numbers on the machine are spindle RPM. You have to figure out the correct RPM for a given tool and the work material.
For instance, it the cutting speed is given at 100 SFM, and you are using a 1/2 inch diameter tool then your spindle speed would be
RPM = (100 * 3.82) / 0.500 = 764 RPM. If you have a step pulley machine you would want to go the the next lower RPM or 660 RPM.