CNC

CNC is an abbreviation that stands for computer numerical control. CNC machines come in a variety of shapes and sizes, and they are frequently used as the first stage in the process of fabricating a component or part by removing material. As soon as a part has been developed in CAD software, CAM (computer-aided manufacturing) software is used to generate toolpaths, which are instructions for a CNC machine on how to move the part during manufacture.

How much does CNC machining?

Typically, one of the largest costs associated with CNC machining is the CNC machine itself. Entry level machines start around $5,000 with high end machines reaching upwards of $500,000. The cost depends on factors like size, power, spindle speed, multi-axis capabilities, and accuracy. Once you have a machine, you will need to purchase cutting tools to machine parts. To generate the instructions required for CNC machining, it’s common to subscribe to a computer aided manufacturing (CAM) software as well. So, while there’s no one size fits all answer, CNC machining requires some up-front investment to get started.

What is the difference between CNC machining and milling?

Milling is one style of CNC machining. CNC machining is any process where a part is manufactured by a machine that is controlled by a computer. In milling, a cutting tool spins at high speeds and advances into or across the work piece to remove material. Other types of CNC machining include turning, routing, plasma cutting, and water jetting. Turning and milling can be combined into a single machine, as can additive and subtractive operations, creating even more complex styles of CNC machining.

How is CNC machining different from 3d printing?

3D printing, or additive manufacturing, is the process of depositing layers of material to build up the desired geometry. Generally speaking, CNC machining is used to refer to subtractive processes, where material is removed from the work piece, resulting in the desired geometry. While 3D printing processes can create more complex geometry like internal latticing, parts must also be supported during the printing process to prevent failure. CNC machining generally produces more accurate parts and can be significantly faster, especially when manufacturing single parts.

How does CNC machining work?

CNC stands for Computer Numerical Control, which means that a computer controls what the machine does, including but not limited to the spindle speed, feed rate, position. In order to program the computer, often called a control, a person can use computer aided manufacturing (CAM) software. CAM software generates a series of instructions called toolpaths and then generally uses a post processor to translate that toolpath data into code the machine can read. Then a person would transfer that code onto the machine and run it to produce their final part.

What is the workflow to go from CAD TO CNC?

Once your CAD model is imported into CAM, the software starts preparing the model for machining. Machining is the controlled process of transforming raw material into a defined shape through actions like cutting, drilling, or boring.

The general workflow to go from CAD model to machined CNC part is:

  1. Begin with CAD model.
  2. Establish Job parameters including CNC coordinate system and stock shape/size.
  3. Select CNC process.
  4. Select cutting tool and machining parameters.
  5. Select driving CAD geometry.
  6. Verify toolpath.
  7. Post Process.
  8. Transfer G-code program to CNC machine.
  9. Set up and operate CNC machine to make part.
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G-code is a programming language constructed from a series of precise commands intended to carry out exact functions. The machine’s controller will convert the G-code commands into tailored motion instructions for axis, spindle, and coolant actions. Below are a few examples of G-code instructions: 

  1. G21: Sets the measurement base to metric, mm
  2. G0 X34: The tool moves +34 mm along the X-axis from the previous position at the maximum traversing speed. 
  3. G1 X34 F150: The tool moves +34 mm along the X-axis at a specified speed (150 mm/s). 

The code also commands such aspects as: geometric positions in which the cutter is to be placed, the required spindle speeds and tool changes, and the speed and route to be used on the approach to the part. Many G commands are modal, meaning that the computer will consider them binding until they’re superseded by another modal command of the same type. 

What is the Function of G-Code?

G-code is intended to tell machines what to do or how to move. It codifies a 3D reasoning process, guiding cutters, print heads, etc. through a path that positions them for the intended task and executes the command. Along the way, G-code specifies spindle speeds and coolant flows and controls any necessary tool changes. The language allows CNC programmers (or other computer-based machiners) to write cut-and-move sequences that create detailed procedures that their machines can follow without supervision.

Where is G-Code Being Used?

G-codes are most often used in the programming of complex computer-aided manufacturing machines such as: CNC 3-axis mills, CNC 4- or 5-axis machining centers, CNC lathes, CNC jig borers and drills, and electrical discharge machining or other wire-cutting machining centers. It is also very common in 3D printing operations of all types.

How Does G-Code Work?

G-code specifies a series of points and line-by-line instructions that are programmed into a CNC machine. It operates in an orthogonal (or occasionally polar) coordinate environment so that a programmer can write traversing movements, spindle speeds, cutting motions, and coolant commands. The commands are converted, within the machine controller, to control signals for parts such as motors and pumps. An instruction to, for example, move along a clockwise arc between two coordinates at a set speed must be converted to electrical signals that drive motors. A G-code, therefore, does not act as a direct machine control signal but instead provides instructions to a controller integrated into the machine. Much like machine code programming, high-level G-code commands are converted into a form of machine language for execution.

What Are the Types of G-Code?

There are several types of G-codes that are divided into functional groups or subclasses. Some commands are modal, meaning they are valid until superseded by another modal command. Others are non-modal, so they specify an action that happens only once. The basic categories are as follows:

  1. Rapid positioning: G00
  2. Interpolation types: G01, G02, G03, G06
  3. Selection of the reference plane for follow-on commands: G17, G18, G19
  4. Tool offset: G40, G41, G42, G43, G44
  5. Zero offsets: G53 – G59
  6. Uni-directional position: G60
  7. Exact stop mode: G61
  8. Description of the process: G80 – G89
  9. Dimensions: G90, G91
  10. Feed rates: G93, G94, G95
  11. Spindle rotation speed: G96, G97
  12. Wait time: G04
  13. Increment or decrement speed: G08, G09
  14. Thread (inner and outer) specifications: G63
  15. Set Work Coordinate Systems Shift Value: G92

What is the Best G-Code Editor?

The best G-Code editor depends on the user’s needs. There are two very different audiences for the language: regular programmers and light users. Regular CNC tool programmers — people who can essentially think in G-code — generally need a zero-frills text editor type of interface, a visualization tool, and a few bulk action shortcuts. Light users like beginners and home users, by contrast, may need more hand-holding. Below are listed some of the best G-code editors for users on both ends of the spectrum:

  1. NCPlot: NCPlot is a minimalist text editor environment that includes great tools for editing G-code. It also has a neat toolkit to generate G-code from text and has time-estimation tools.
  2. TextPad: TextPad is a low-cost but capable software with many of the tools needed for more expensive applications. It is basically a G-code-empowered version of Windows Notepad, but with some important differences including the ability to directly import and merge groups of G-code into a single file and the capability of coloring groups of code.
  3. G-Wizard Editor: G-Wizard Editor uses a very approachable method based on visual editing. This software, from CNCCookbook, is a collection of powerful tools and advisory information. The basic method is called “conversational G-code” and operates using high-level commands like “face mill the part,” automatically generating a block of G-code for this action. It also has an error-checking algorithm that guards against faults such as cutters crashing into the part during traverse stages.

How to Read G-code Commands

G-code is highly structured and easy to read at a high level. Even without knowing all the commands, a line of code can be understood in general terms. Each line of code is structured simply and consistently. For example:

G1 (move at specified speed) X60 Y30 Z80 (to these coordinates) F200 (at a  feed rate of 200 mm/s)

G0 (move as fast as possible) X0 Y0 Z0 (to the origin)

With a cheat sheet of G-codes and an understanding of the workspace’s coordinate system, the code becomes easy to read.

Is G-code used on All CNC Machines?

Yes, G-code is used on all CNC machines. It is a tool for translating design intent into cutter action.

What is the Difference Between G-Code and M-Code?

In the simplest terms, G-code and M-code are “off the shelf” and “tailor-made” commands, respectively, that drive machine functions. Generally, G-codes describe positions and M-codes direct the machine’s actions. Machining centers operate on 3, 4, or 5 axes and the motion is all driven by motors. Each machine has a spindle that holds the cutting tool. The computer must have an internal map of obstacles to be avoided when moving the cutter around the build space. It must also have controls with start and stop commands. The G-code is a nearly universal toolkit that can drive all these functions and more. 

No two manufacturers use the same coolant pump systems, Z and diameter offset tools, vibration/chatter compensation methods, condition monitoring methods, or automated texturing tools. Functionality that is unique to an individual machine manufacturer requires proprietary commands. Collectively, these commands are called M-code.

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