SFM Calculatorturning

When using a conventional tapping cycle, optimum performance is insured by slightly underfeeding the tap, normally by 2% – 10%. This forces the tension stroke of the tapping head to be used and eliminates any effect of the machine tool. The Z axis feed distance must be reduced by this same percentage. The axial float in the Tapping System takes up the difference between the required thread depth and the programmed depth. If a 10% underfeed was selected, the calculations would be as follows:

SFM to RPMlathe

Can the surface speed formula be used for materials of any shape? The surface speed formula provided is specifically designed for cylindrical components. For non-cylindrical shapes, different formulas or considerations may be necessary to accurately calculate surface speed, as the shape affects how the material moves past the cutting tool.

How does the diameter of the stock affect the surface speed? The diameter of the stock directly influences the surface speed. A larger diameter means the material’s surface moves faster at the same spindle RPM compared to a smaller diameter. This is because the circumference of the stock, which determines the distance covered per rotation, increases with diameter.

Experience has shown that a tap will cut the best quality threads when allowed to act as its own lead screw, feeding precisely on pitch to exactly the required depth of thread. The machine must be prevented from forcing the tap to do anything else or the thread quality will suffer or the tap may break. The tension stroke in the Tapping head provides the freedom required to cut the best quality threads with the least risk of breakage. Tapping Systems can be used on any suitable machine tool which has a reversing spindle. Effective choices of spindle speeds and feeds for particular tapping requirements can be made by the following sample calculations:

Feet per minuteto RPM Calculator

A surface speed, often referred to as SFM, is a term used in machining to describe the tangential velocity of a rotating piece of stock in a spindle.

RPM toinches per minuteCalculator

Tapping a 3/4 thread 1” Deep in mild steel: RPM = (12 x SFM)or(3.82 X SFM)/D where D is the tap diameter. RPM = (3.82 x .50)/.75 – 255 RPM Tap Feed Rate = Pitch x RPM = .100 x 255 = 255 = 25.5 inches/minute. Feed in and out at the same feed rate.

This unit is used in converting the spindle rotation into the velocity of this stock which is used for determining certain feed rates etc. for machining the material.

In this scenario, the surface speed will be in the same distance or length units as the stock diameter. For example, if the stock diameter is measured in feet the surface speed will be feet/minute.

When using a synchronous tapping cycle, the drive system inertia may create the undesirable effect of tap elongation, or thread distortion. The best answer to this problem is the use of tension only tapping heads.

SFM toIPM

SFM calculator

If the tapping cycle is controlled by a “canned” program which calculates its own feed rates from an input of pitch and speed. The desired underfeed can be obtained by deliberately entering a reduced value of pitch or an increased value of threads per inch as follows

Actual TPI = 10 (pitch = 1/10 = .100″) Input TPI = 11 (pitch = 1/11 = .091″) Program Feed Rate = .091 x 255 = 23.2″/minute Program Feed Depth = .91 x 1.000 = .910″

What is the significance of measuring surface speed in machining? Measuring surface speed is crucial in machining because it helps in determining the optimal feed rates and cutting speeds for machining operations. This ensures efficient material removal, prolongs tool life, and prevents damage to the workpiece.

The following formula is used to calculate the surface speed of a rotating cylindrical component. The surface speed is often measured in surface feet per minute denoting it SFM.

SFM to RPMDrillingcalculator

Program Feed Rate = .90 x on pitch feed rate = .90 x 25.5 = 22.95″/minute. Spindle Z-Axis Travel = .90 x required depth = .90 x 1.000 = .900″. Axial Float used = 1.000 – .900 = .100″ Do not allow the Axial Float used to equal the tension stroke length (.35).

If the CNC machine has a slow spindle reversal, the program must compensate for any drive system inertia by including a dwell not long enough for the spindle to come to a full stop when the tap has reached full thread depth. If the spindle has not stopped when the program calls for it to feed out, the tap could break or be pulled out of the adapter, or the threads could be ruined. These problems can be rectified using a program similar to the following:

Enter the stock diameter and rotations per minute (RPM) into the calculator to determine the surface speed. The calculator will display the result in feet/min, feet/second, and in/min, and m/s.