Brown & Sharpe Machining - Discussing Screw Machine Parts and Engineering.

Brown & Sharpe
Screw Machine Formulas
by Kathi Stringer

The formulas provided here are a requirement for accurate cam layout. I've used these formulas many times to enhance rapid cycle time.

Formulas with an "*" are intended for pickup cams.

Glossary

S.F.M. =
Surface Feet Per Minute
T.P.I. =
Threads Per Inch
S.S. =
Spindle Speed. Spindle Speeds have ranges. Example: High S.S. (turning) and Low S.S. (threading).
Revs =
Revolutions
R.P.M. =
Revolutions Per Minute
Total Revs =
Total Revolutions for the runtime (job) including indexes and etc.
Hunds =
Hundreds. A full cam cycle has 100 hundreds. Each tool lobe, indexes, feedouts, clear and etc. has corresponding hundreds.

Formulas that PRODUCE

Contents

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To find Spindle Speed
SFM / .262 / Stock Dia = Spindle Speed

To find S.F.M.
Stock Dia * .262 * R.P.M. = S.F.M.

To find Hundreds for a Tool
Total Job Revs / Tool Revs = Hundreds [for Tool Lobe]

To find Revs for Thread
T.P.I. * Distance = Revs

To find Revs for Tap Out
T.P.I. * Distance + 3 Revs = Revs for Tap Out

To find Thread Pitch
T.P.I / 1.000 = Pitch

* To find total Revs for Pickup Cam
Hundreds on Single Lobe on Cam	= Total Revs Needed for Job
Revs on Single Lobe Required

To find Rise for Pickup Cam with Thread
Rise	*	T.P.I.	*	6000	= Seconds
.9		Hunds		Low S.S.