MultiSpindle

Suggested Cutting Speeds with HSS Tools

Material	Brinell	Drills S.F.M.	Taps – S.F.M. Threads Per Inch
Material	Brinell	Drills S.F.M.	3-8	9-15	16-24	25 UP
Aluminum (die cast)	95-105	250	50	100	130	150
Aluminum	95-105	200	50	100	130	150
Bakelite	—	80	50	100	130	150
Brass	192-202	200	50	100	130	150
Bronze Common	166-183	200	40	80	100	150
Bronze Phos. 1/2 hard	187-202	175	25	40	50	80
Copper	80-85	70	40	80	100	150
Cast Iron – soft	126	140	30	60	90	130
Cast Iron – hard	300	45	10	20	30	40
Cast Iron, Malleable	112-126	85	20	30	40	50
Duralumin	90-104	200	50	100	130	150
Nickel	187-202	75	25	40	50	80
Rubber – hard	—	100	50	100	150	200
Steel – mild .20-.30C	170-202	115	40	55	70	90
Steel – .40-.50C	170-196	80	20	30	40	50
Steel, Stainless	460-520	20	8	10	15	20
Steel, Tool	241	50	15	15	20	20
Zinc	110-125	200	50	100	130	150

RPM =

3.82 x SFM
Dia.

SFM = .262 x D x RPM
1 ÷ Pitch = Tap Lead

% of Threads (cut Taps) = Threads per Inch x

( major dia. of tap – drill dia. )
.01299

Example for 1/4-20 tap, using # 7 drill.
.250 – .201 = .049 ÷ .01299 = 3.77 x 20 = 75% thread
Note: Use .0068 divisor for roll form Taps.

Tap Drill Size (cut Taps) = major Dia of tap –

( .01299 x % of full thread )
TPI

Example for 1/4-28 with 70% required Threads.
.01299 x 70 = .909 ÷ 28 = .032
.250 – .032 = .218 drill Size

Tap Drill Size (form Taps) = major Dia tap –

( .0068 x % full thread )
TPI

Example for 1/4-20 tap with 65% required Threads.
.0068 x 65 = .442 ÷ 20 = .022
.250 – .022 = .228 drill Size

Inch cycle time (seconds) =	( 90 x TPI x travel ) RPM
MM cycle time (seconds) =	( 2286 x travel ) MM (Pitch) x RPM

Example for 10-32 at 1140 RPM
90 x 32 x .625 ÷ 1140 = 1.6 seconds

Example for M10 x 1.25 at 860 RPM
2286 x .950 = 2171.7
1.25 x 860 = 1075
2171.7 ÷ 1075 = 2. seconds

Notes:
Formulas include 2:1 reverse found on all Procunier tappers. Travel Includes tap clearance above piece part and total depth into hole

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