How do I calculate CNC feed rate?

CNC feed rate is calculated using the formula: Feed Rate = Spindle Speed (RPM) × Number of Flutes × Chip Load. The chip load varies by material - for example, softwood typically uses 0.011 inches per tooth, while aluminum uses 0.003 inches per tooth.

What is a safe plunge rate for CNC?

A safe plunge rate is typically 35% of your feed rate. This slower speed when plunging into material helps prevent tool breakage and ensures clean entry cuts.

What stepover should I use for CNC roughing vs finishing?

For roughing passes, use a stepover of about 50% of your bit diameter for efficient material removal. For finishing passes, use about 15% stepover for smoother surface finish.

What is the difference between upcut and downcut bits?

Upcut bits pull chips upward, clearing material efficiently but may cause tear-out on the top surface. Downcut bits push chips down, leaving a cleaner top edge but requiring shallower passes. Compression bits combine both - upcut on the bottom and downcut on top - ideal for plywood and laminates.

Free CNC Feeds and Speeds Calculator

Tool & Material

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Material

Bit Type

Number of Flutes

Bit Diameter

Up-Cut Length

V-Bit Angle (degrees)

Taper Angle (degrees)

Cutting Parameters

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Spindle Speed (RPM)

Material Depth

Number of Passes

Cut Type

Using Coolant?

Calculated Results

Tool Risk Level Safe

Safe Caution Danger

Settings are within safe limits.

Feed Rate (click to edit)

Plunge Rate

Surface Speed (SFM)

Pass Depth

Number of Passes

Stepover

Chip Load

Material Removal Rate

Suggested RPM

Compare Roughing vs Finishing

Roughing

Feed Rate--

Stepover--

Pass Depth--

MRR--

Finishing