How to calculate lathe speeds and feeds?

Discussion in 'QUESTIONS & ANSWERS (Get Help Fast Here!)' started by Nels, Apr 20, 2011.

  1. Nels

    Nels Founder Staff Member Administrator

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    Hey Guys,

    In Darrell Holland's video on Lathes, he gives a formula for calculating speeds and feeds. I believe it is:

    SFPM X 4 divided by diameter = RPM

    SFPM is surface speed per minute in feet this is the speed your cutter is cutting at, whether it is a milling cutter or a lathe bit contacting the revolving work, or a shaper bit, or planer, or a grinding wheel. Feed rates are termed in inches per minute.

    Others have said that with High Speed Steel they use 50 sfpm to start with, and then work up, especially with mystery material. This way it is easy to figure also, 200rpm for 1.00 dia. so 2"=100rpm 1/2=400rpm 1/8=1600rpm. Staring at this low surface speed saves drill bits, I have seen people burn up big bits, this formula is easy to figure in your head and avoids problems.

    As to feed rates, he mentions that it depends on size and power of the lathe and how good a finish you need.

    How do YOU calculate speeds and feeds on a typical home shop lathe?

    Thanks,


    Nelson
     
  2. martik777

    martik777 Active Members Active Member

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    Top speed on my SB9A is only 650rpm so I guess I'll be a little slow for small diameters
     

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