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DRILLING.TXT
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1989-08-22
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Starting the drill is often a greater problem in drilling stainless steel
than in carbon or alloy steel, mainly because stainless steel is more easily
work hardened. When a spot is severely work hardened, it will cause the drill
to wander or overheat thus dulling the drill in a few revolutions.
When conventional center punches are used, they must be tapped lightly
(especially when the higher-nickel grades of stainless are being drilled to
avoid creating hard spots. Triple punches are preferred because they are less
likely to cause work hardening in the center. The use of drill templates is
another means of avoiding work hardening. When starting or re-entering the
hole, the drill should be at full speed with positive feed. Dwell periods
should not be permitted.
When numerically controlled equipment is available, center drilling is
often used for locating and starting holes. The two examples that follow
describe operations in which certain drilling and the use of numerically
controlled machines eliminated the need for drill jigs. In some applications,
the use of spiral point drills has eliminated the need for jigs or center
drilling when numerical control is used on the machine.
==============================================================================
Nominal Speeds and Feeds for Drilling Stainless Steels
with High Speed Steel Drills
Type of Condi- Brinell Speed Feed (ipr) for nominal diam.(in.) of:
steel(a) tion(b) hardness sfm .125 .250 .500 .750 1.000 1.500 2.000
FM Fer Ann 135 to 185 140 .003 .005 .010 .014 .018 .020 .025
FM Mar Ann 135 to 185 140 .003 .005 .010 .014 .018 .020 .025
Ann or CD 185 to 240 130 .003 .005 .010 .014 .018 .020 .025
Q & T 275 to 325 65 .002 .004 .006 .008 .010 .014 .018
Q & T 375 to 425 40 .001 .002 .004 .006 .008 .009 .010
FM Aus Ann 135 to 185 100 .003 .005 .010 .014 .018 .020 .025
CD 225 to 275 90 .003 .005 .010 .014 .018 .020 .025
Ferritic Ann 135 to 185 60 .002 .003 .006 .008 .010 .014 .018
Mar(410) Ann 135 to 185 70 .003 .004 .006 .008 .010 .014 .018
Ann 175 to 225 60 .002 .003 .006 .008 .011 .014 .018
Q & T 275 to 325 50 .002 .003 .005 .008 .011 .013 .016
Q & T 375 to 425 40 .001 .002 .004 .006 .008 .009 .010
Mar(431) Ann 225 to 275 50 .002 .003 .005 .008 .011 .013 .016
Q & T 275 to 325 45 .002 .003 .005 .008 .011 .013 .016
Q & T 375 to 425 40 .001 .002 .004 .006 .008 .009 .010
Mar(440) Ann 225 to 275 40 .002 .003 .005 .009 .010 .012 .013
Q & T 275 to 325 35 .001 .002 .003 .005 .006 .008 .009
Q & T 375 to 425 25 .001 .002 .003 .004 .005 .006 .007
Q & T Rc 48 to 52 20 .0005 .001 .002 .002 .003 .003 .004
Aus(304) Ann 135 to 185 50 .002 .003 .005 .009 .010 .013 .016
CD 225 to 275 45 .002 .003 .005 .008 .011 .013 .016
Aus(316) Ann 135 to 185 45 .002 .003 .005 .008 .011 .013 .016
Abbreviations used:
FM = Free Machining Fer = Ferritic Mar = Martensitic Aus = Austenitic
Ann = Annealed CD = Cold drawn Q and T = Quenched and tempered
Hard = Hardened N and T = Normalized and tempered.