Threads Per Inch Covert to Feed Rate

What are Machining Speeds and Feeds

One of the basic tasks a machinists must learn to perform is calculation of speeds and feeds required for milling, drilling and turning.

It starts from knowing your workpiece materiel and tooling you are going to use in order to cut it.
The combination of these two factors determines your initial Cutting Speed and Chip Load that you can put into the speed and feed formulas to calculate the cutting tool RPM and feed rate.

Cutting Speed is the speed at which the tip of the tool travels through material. It is commonly expressed in Surface Feet per Minute (SFM) or Surface Meters per Minute (SMM).

Chip Load is the advancement of each tooth per revolution of the tool.

In other words Chip Load is the thickness of the material that each tooth removes per each revolution.

So how do you find the Cutting Speed and Chip Load for your tool?

Tool manufacturers often post Cutting Speeds and Feeds for their tools for various materials and cutting conditions.

Most experienced machinists simply remember cutting speeds and chip loads for materials they machine most often.

Here are commonly recommended cutting speeds and chip loads for carbide tools for a couple of materials:

• Aluminum: 300SFM, 0.7% of the diameter (for example fz = 0.5"dia x 0.007 = 0.0035in/tooth)
• Annealed Tool steel: 150SFM, 0.4% of the diameter (for example fz = 0.5" x 0.004 = 0.002in/tooth)

When you have manufacturers data simply find your tool in the catalogue and cross-reference the cutting speed and chip load against the tool diameter:

Since cutting speeds can be in either Imperial (SFM) or Metric (SMM or m/min) units, you have to use two formulas to calculate the RPM.

Imperial Speed and Feed Calculation

Code

RPM=	12 x SFM	= Please enter Speed and Diameter
	3.14 x in

Feed Rate = RPM x x in = Please enter RPM, number of teeth and chip load (in/min)

Metric Speed and Feed Calculation

Code

RPM=	1000 x m/min	= Please enter Speed and Diameter
	3.14 x mm

Feed Rate = RPM x x mm = Please enter RPM, number of teeth and chip load (mm/min)

Want something better?

Try our desktop  HSMAdvisor Speed and Feed Calc or Mobile/Online FSWizard

More about formulas needed to calculate turning, drilling, and of coursemilling speeds and feeds

Here are a few basic formulas with term explanations to get you going:

Calculating Spindle Speed (RPM) Using Imperial Cutting Speed:

Code

RPM=	12 x SFM
	3.14 x Diameter

Simplified imperial formula:

Calculating Spindle Speed (RPM) using Metric Cutting Speed:

Code

RPM=	1000 x SMM
	3.14 x Diameter

Simplified metric formula:

Calculating Feed Rate :

Feed_Rate=RPM x N(teeth) x CL(chip load)

Definitions

• RPM= Revolutions Per Minute, Spindle Speed , Number of revolutions of spindle per minute
• SFM = Imperial. Surface Feet Per minute, Cutting speed , Speed at which tip of tool travels through material
• SMM= Metric. Surface Meters Per minute, Cutting speed , Speed at which tip of tool travels through material
• Feed_Rate= Inches Per Minute or Millimeters Per Minute, Feed Rate , Distance in inches or millimeters the tool the will travel through workpiece per minute.
• N = Number of teeth on the cutter
• CL= Chip Load per tooth, This is the advancement of the cutter per revolution per each cutting edge. Otherwise generally explained as the thickness of material each tooth takes per each revolution

Examples:

Calculate Speeds and Feeds for 1/2" (0.5 in) 2 flute end mill in Mild Steel at cutting speed = 100(ft/min), Chip Load=0.001(inch per tooth)

Calculating Spindle Speed (RPM):

Code

RPM=	12 x SFM
	3.14 x Diameter

=

RPM=	12 x 100(ft/min)	=764(revs/min-1)
	3.14 x 0.5(in)

For turning applications, we do not need this formula since Spindle Speed is usually given in Constant Surface Speed (CSS), which uses SFM value directly. But if you still want to use the RPM formula, then the diameter value is the actual diameter of the workpiece.

Calculating Feed Rate in Inches Per Minute (IPM)

The formula is used for milling and drilling applications. Please note that some tool manufacturers provide their recommended feed rate as feed per revolution. In such cases do not multiply by the number of teeth.

Code

Feed Rate = RPM x N x CL

Feed Rate = 800(RPM) x 2(teeth) x  0.001("chip load) =1.600 (in/min)

Easily Calculating Speeds and Feeds on your smartphone or computer

Our own free Speed and Feed Calculator can help you calculate cutting parameters for many different material groups.

Tags: Spindle Speed Feed Rate

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Source: https://zero-divide.net/?article_id=4209_general-speeds-and-feeds-formulas

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