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
Metric Speed and Feed Calculation
Want something better?
More about formulas needed to calculate turning, drilling, and of course milling speeds and feeds
Here are a few basic formulas with term explanations to get you going:
Calculating Spindle Speed (RPM) Using Imperial Cutting Speed:
||12 x SFM
|3.14 x Diameter
Simplified imperial formula:
Calculating Spindle Speed (RPM) using Metric Cutting Speed:
||1000 x SMM
|3.14 x Diameter
Simplified metric formula:
Calculating Feed Rate :
Feed_Rate=RPM x N(teeth) x CL(chip load)