# Cutting Parameters Explained This page explains general parameter behavior.\ Specific presets and parameter selection strategies are explained separately. ### Spindle Speed (RPM) **Spindle speed** is how fast the tool rotates.\ It is measured in **revolutions per minute (RPM)**. **Important:**\ RPM only tells you **how fast the tool spins**, not how fast it actually cuts the material. *** ### Surface Speed **Surface speed** is how fast the ***cutting edge*** moves past the material. This depends on: * spindle speed (RPM) * tool diameter A bigger tool at the same RPM moves faster at the edge than a smaller tool. *** ### Ramp Spindle Speed This is the spindle speed used **while entering the material on a ramp or helix**. **Why it exists:**\ Entering material is a sensitive moment. This parameter allows a different spindle speed to be used during entry, if needed. *** ### **Cutting Feedrate (mm/min)** Cutting feedrate describes how fast the tool moves sideways through the material. It is not an independent value. Cutting feedrate is determined by the combination of: * spindle speed (RPM) * number of flutes * feed per tooth In other words, feedrate is the result of how fast the tool rotates and how much material each cutting edge is intended to remove. If feedrate is too low relative to spindle speed and tool engagement: * the tool may rub instead of cutting * heat builds up If feedrate is too high for the chosen spindle speed and engagement: * cutting forces increase * the tool may bend or chatter *** ### **Feed per Tooth (fz)** Feed per tooth describes the **intended amount of material each cutting edge removes per rotation**.\ It is one of the most important concepts in CNC machining because it directly influences chip formation and cutting forces. Together with spindle speed and flute count, feed per tooth determines the resulting cutting feedrate.\ Changing any one of these values changes the others. *** ### Lead-in / Lead-out / Transition Feedrate These feedrates are used when: * entering a cut * exiting a cut * moving between cuts These movements use their own feedrate settings.\ If left unchanged, they may inherit the cutting feedrate. *** ### Ramp Feedrate This is the feedrate used **while ramping down into material**. Ramping means: * cutting sideways **and** * cutting downward at the same time Because the tool is doing more work, ramp feedrate is sometimes reduced. *** ### Ramp Angle Ramp angle defines **how steep the tool enters the material**. * Small angle → gentle entry, low stress * Large angle → aggressive entry, higher stress For small or less rigid machines, shallow ramp angles are safer. *** ### Plunge Feedrate **Plunge feedrate** is how fast the tool moves **straight down** into the material. Plunging is stressful because: * chips have nowhere to go * the cutting edge is less effective That’s why plunge feedrate is usually **much slower** than cutting feedrate. *** ### Plunge Feed per Revolution This is similar to feed per tooth, but applied to **vertical movement**. *** ### Stepdown **Stepdown** is how deep the tool cuts per pass in the Z direction. Small stepdowns: * safer * more passes * longer machining time Large stepdowns: * faster * higher load * more deflection risk *** ### Stepover **Stepover** is how much the tool moves sideways between passes. Small stepover: * smoother surface * lower cutting forces Large stepover: * faster material removal * higher tool load *** ### Coolant Coolant helps with: * heat removal * chip evacuation * tool life On many compact CNC machines, coolant is disabled or limited.\ In that case, **correct cutting parameters become even more important**. *** ### One Key Takeaway None of these values work alone. * RPM affects surface speed * Feedrate depends on feed per tooth and RPM * Stepdown and stepover control cutting forces {% hint style="warning" %} #### Being *too* conservative can also cause problems Many beginners start **far too slow**, assuming it is the safest approach.\ In practice, starting extremely slow often means the tool is **not cutting at all**. Very low feeds or very light engagement can lead to: * rubbing instead of cutting * excessive heat at the cutting edge * built-up edge in metals * sudden force spikes once the tool finally starts cutting Those force spikes can cause chatter, lost steps, or tool damage — even during cuts that *look* gentle. Cutting only becomes predictable once the tool is **actually removing chips**.\ Creeping up from near-zero values often never reaches that stable cutting range.\ \ The “play it ultra-safe” approach often fails because a tool that doesn’t cut will eventually bite suddenly — and that’s when problems start. {% endhint %} --- # Agent Instructions: Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. 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