CNC Machine Design Concepts | Table Sawz
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CNC Machine Design Concepts - Knowing the basics will mean you get the best out of your CNC machine

CNC Machine Design Concepts

Knowing the basics of CNC machine design is essential to getting the most out of the capabilities. Learning how to operate the machine is one aspect, but if something goes wrong or you want to change a setting, you’ll need to be familiar with the working process and components.

Precision Motion Control

There are many kinds of CNC machines, but at their center is automated and precise motion control. Every CNC machine has two or more axes, which determine their direction and motion, and you can set the axes to automatically and accurately move in those direction (or travel). The most common axes are rotary (driving by a circular path) and linear (straight path).

Conventional machines are controlled by manually moving handwheels and cranks. CNC machine motions however, are operated by servo motors which are run by the CNC and a computer program. A CNC also lets you program the motion / feed rate, the axis movement and motion types, i.e. circular, linear and rapid.

Programs are used to execute CNC commands, informing the drive motor to turn a particular way and in a number of times. As the drive motor rotates, it moves the ball screw which in turn moves the linear axis. At the end of the ball screw is a feedback device which tells the control that the command has been executed.

The Components

You don’t need to memorize all the parts of a CNC machine to use it, but just as a car driver needs to know some parts to optimize performance, the same is true for running a CNC machine.

Your machine comes with an operator’s handbook, and that is your first step to understanding the most important components in your machine. If your system has a slant bed turning center, the most vital parts are the workholding device, tailstock, turret design, spindle, headstock, way system and bed.

Other information about the CNC machine design you need to learn are the following (specifications vary per machine, refer to the manual):

  • Maximum cutting feed rate​
  • Maximum traverse / rapid rate
  • The construction, i.e. the linear or dovetail, square, etc.
  • The number of tools the machine can handle
  • Maximum travel distance per axis
  • Axis drive motor and spindle power
  • You also have to learn the speed range of the spindle and the range’s cut off points

Axis Movements and Starting Points

You also have to learn how programmable the axes are. Usually linear axes are referred to by letters like X, Y, Z, V, U and W. Rotary axes are called A, B and C. Before you can use the device you have to be familiar with your system’s axis designations and motions.

If you want the axes to move, you have to specify the destination as well as the letter that correlates to that particular axis. A command of X 4.5 tells the machine to set the X axis 4.5 inches off the zero point.

Rotary axes also need a letter address along with a motion end point, which is set in degrees rather than millimeters or inches. A command of A30 means the A axis will be rotated at a 30 degree end point from the zero point.

Majority of CNC machines use one position on each axis as the reference or starting point. Your manual may refer to this as the grid zero position or the zero return position. No matter what the name is, the starting position is essential for a lot of CNC controls. In fact, CNC machines that use a starting point for the axis necessitate sending the machine to this point when powering up.

Command Notes

There are many types of commands in CNC machines, and they are comprised of a numerical value and letter. While there may be variations with newer models, the letter usually informs the control the word type. However you have to refer to your manual because brands change the addresses, names and their meanings.

The following are the most common letter address and word types used today.

  • M – Miscellaneous
  • T – Tools
  • D – Offset tool radius
  • H – Offset tool length
  • S – Spindle speed
  • F – Feed rate
  • R – radius
  • Z – Z axis
  • X – X axis
  • Y – Y axis
  • G – Preparatory function
  • N – Sequencing
  • O – Program number

The Control Panel

CNC machines have different control panels, but these are the most important in terms of function:

  • Power Buttons: CNC machines have two power buttons, one for starting up the system and the other to activate the tools.
  • Cursor Control Keys: a CNC control panel displays a prompt cursor to let you know an entry position’s location. It is usually an underlined or blinking character. By using control keys you’ll be able to set the cursor anywhere you want on the display screen.
  • Position Button: provides information about the position display.
  • Display Screen: this consists of control keys which let you choose what views are displayed.
  • Letter Keys: makes alphabetical entry possible. Some CNC systems have full keys (A to Z), while others are limited to the alpha keys used for programing. Number keys on the other hand, are used for numerical input.
  • Program Button: this button selector allows you to track which program is running in memory. You use these keys when checking automated programs or editing them.
  • Offset: this button is used to change the tool offsets. You also use this button to locate and make changes to memory offsets.
  • Input Key: You use the input key to enter data. You press this key when adjusting parameters and changing offsets.
  • Edit Keys: these keys are used for editing programs in memory, modification, verification and entry.
  • Reset Button: used to restore a program to its starting point. It can also be used to cancel the program or look ahead buffer cleanup.

Conclusion

CNC machines are powerful and when handled properly, increases productivity and reduces cost. For hobbyists and DIY enthusiasts, you get the opportunity to create everything from furniture to sculptures. Armed with a full understanding of how these machines work and their design, you’ll maximize their potential.

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