Practical explanations of machining formulas, cutting parameters, tooling and everyday shop calculations.
Learn the relationship behind the result
A calculator is easier to trust when the formula is visible and the meaning of each input is clear. These guides explain the common relationships behind the tools on The True Machinists. They are written for someone who wants a working understanding, not just a definition.
CNC Milling Basics
A practical overview of tools, workholding and cutting parameters. CNC Milling Basics CNC milling is a combination of geometry, motion and process control. The cutter, workpiece, workholding, toolpath and machine
Read Guide →CNC Turning Basics
Key relationships between diameter, surface speed, feed and depth of cut. CNC Turning Basics Turning uses diameter, surface speed, RPM, feed per revolution and depth of cut to describe the
Read Guide →Cutting Tool Basics
A practical reference for end mills, drills, turning tools and tool geometry. Cutting Tool Basics Cutting tools are not interchangeable simply because their diameter is the same. Tool material, flute
Read Guide →Drilling Feed & Speed Basics
The core inputs used when drilling holes. Drilling Feed & Speed Basics Drilling uses a smaller set of basic inputs than many milling operations, but the hole geometry adds process
Read Guide →How Tap Drill Size Is Calculated
Understand the basic metric tap drill relationship. How Tap Drill Size Is Calculated Tap drill size starts with the thread size and pitch. A simple metric relationship can provide a
Read Guide →How to Calculate Chip Load
The feed, RPM and flute relationship used in milling. How to Calculate Chip Load Chip load is the feed associated with each cutting tooth. It becomes useful when you need
Read Guide →How to Calculate CNC Feed Rate
Calculate milling feed rate from RPM, flute count and chip load. How to Calculate CNC Feed Rate For milling, feed rate is commonly calculated from spindle RPM, flute count and
Read Guide →Material Removal Rate (MRR)
Understand width, depth and feed in a basic MRR calculation. Material Removal Rate (MRR) Material removal rate is a useful way to compare roughing conditions because it connects the volume
Read Guide →SFM vs RPM
Understand the difference between cutting speed and spindle speed. SFM vs RPM SFM and RPM are related but they are not the same thing. SFM describes surface speed at the
Read Guide →What Are CNC Feeds & Speeds?
Understand spindle speed, feed rate, cutting speed and chip load.
Read Guide →Use a guide with the calculator
When a guide references a calculation, use the linked calculator to test the relationship with your own values. When a calculator raises a material or tooling question, move to the corresponding reference page. The site is built so these resources support each other.
Understand the calculation before using the result
A calculator becomes more useful when the relationship behind it is clear. The True Machinists guides explain the common machining formulas in direct language and connect them to the calculator that performs the arithmetic. The aim is practical understanding. You should be able to see what is known, what needs to be found and why the result changes when an input changes.
Feeds and speeds
Start with Feeds & Speeds to see how cutting speed, tool diameter, RPM, flute count and chip load are connected. Then use Chip Load, Feed Rate, Spindle Speed or SFM when the job gives you a more specific input.
Milling and turning
Milling and turning use related calculations but the process context is different. Milling commonly uses flute count and chip load. Turning often uses feed per revolution and the changing diameter of the workpiece. The Surface Finish, Tool Engagement and Turning Speed tools give the next level of detail when the basic relationship is not enough.
Drilling and threading
Drilling adds the practical problem of chip evacuation and hole depth. Threading adds the requirement to match thread standard, pitch, fit and tooling. Use the Drill Feed & Speed Calculator for the basic relationship and the Tap Drill Size Calculator for a basic metric starting calculation.
How to use a guide with a calculator
- Read the formula and identify the known input.
- Open the linked calculator and enter the same values.
- Check that the units match the formula.
- Compare the output with the expected order of magnitude.
- Verify the final number against the actual tooling, material and machine information.
Keep practical context with the math
The guides are not written as universal production instructions. Cutting conditions depend on the actual cutter, material grade, engagement, machine rigidity, workholding, coolant and tool condition. A calculation can still be correct when the production setting changes. The formula gives the relationship. The setup gives the acceptable range.
Guides that support the calculator library
The guides are designed around the formulas and process questions that appear most often in the calculator library. They explain the terms in plain technical language, show how the variables relate and point back to the tool that performs the arithmetic.
Start with the known value
A reliable workflow is to write down the known value, keep its unit visible, identify the variable that needs to be found and then select the smallest useful calculation. This makes the result easier to check and helps avoid using a more complicated formula than the job requires.
Use guides for context, not as a replacement for tooling data
The actual cutting condition depends on the tool, material, engagement, machine, workholding and process. Read the guide to understand the relationship, then verify a production setting against the current tool maker and machine information.