Speeds and Feeds
Spindle speeds given
in RPM
• Revolutions Per Minute
RPM Formula:
Applies to lathe,
mills, drilling, etc.
Cutting Speed
• normally given in tables
• based on Surface Feet Per
Minute (SFPM)
• tool to work piece
relationship
• # of feet per minute that
pass
• formula converts to inches
per minute
Cutting speed tables
in text
CS D = ?
• Drill Press = Dia of twist
drill
• Lathe (Drilling) = Dia of
twist drill
• Lathe (Turning) = Dia of work
piece
• Vertical Mill = Dia of cutter
• Horizontal Mill = Dia of
cutter
Cutting speed
constants influenced
by:
• tool material
• work material
• rigidity of setup
• use of cutting fluids
Use lower cutting
speeds
• for machining hard or tough
materials
• if vibration or chatter
Feed
• the machine movement that
causes the tool to cut along
the surface of the work
• usually measured in
thousandths of an inch
• expressed in different ways
on different machines
Drilling Feed Rates
• feed expressed in inches per
revolution (IPR)
• drill advances into the work
a given amount for each
revolution
• no formula - simply look up
in table
Sensitive drill press
• no power feed
• operator senses or feels the
correct amount of feed
Drilling feed
variables
• drill diameter
• drill material
• work material
Lathe Feed Rates (Two)
1.) Turning
• expressed in IPR
• single point cutting tool
advanced along the work a
given amount for each
revolution
• no formula - look up in table
2.) Facing Feed Rates
• expressed in IPR
• no formula - look up in table
• problem of uniform finish on
large diameter work piece
• CNC lathes equipped with
Constant Surface Speed
Turning & Facing
variables
• tool material
• work material
• surface finish required
• depth of cut - roughing cuts
should be as much as possible
without undo stress
Milling
• Vertical and Horizontal
Milling
• expressed in Inches Per
Minute (IPM)
Milling Feed Formula:
Feed (IPM) = RPM x #
teeth x IPT
• IPT = inches per tooth taken
from table
• Vertical Milling IPT usually
between .001” and .010”
General rule for depth
of cut in steel for
end mills
• standard end mill depth is
approx. 1/2 diameter of the
tool
• roughing end mill depth is
approximately 1-1/2 times the
diameter of the tool
Calculating drill
point angle distance
• .3 x Diameter of the drill
• example: 1/2” drill
• .5 x .3 = .150” drill point
angle distance