cncparts - CNC tutorial | Lesson 6: CNC Operation

Upon successful completion of this lesson, you will be able to:

List the steps to set up and operate a CNC
Identify the location and purpose of the operating controls on the Haas CNC Mill
Start and home a CNC
Load tools into tool
Set Tool Length
Set Fixture
Load a CNC program into the machine
Safely run a new CNC
Adjust offsets to account for tool wear and
Shut down a CNC machine correctly.

6.1 Overview of CNC Setup and Operation

CNC machine setup and operation follows the process shown in Figure 1:

Figure 1: CNC Process

Pre-Start

Before starting the machine, check to ensure oil and coolant levels are full. Check the machine maintenance manual if you are unsure about how to service it. Ensure the work area is clear of any loose tools or equipment. If the machine requires an air supply, ensure the compressor is on and pressure meets the machine requirements.

Start/Home

Turn power on the machine and control. The main breaker is located at the back of the machine. The machine power button is located in the upper−left corner on the control face.

Load Tools

Load tools into the tool carousel in the order listed in the CNC program tool list.

Set Tool Length Offsets

For each tool used, jog the machine to find and then set the TLO.

Set Fixture Offset XY

Once the vise or other fixture is properly installed and aligned on the machine, set the fixture offset to locate the part XY datum.

Set Fixture Offset Z

Use a dial indicator and 1−2−3 block to find and set the fixture offset Z.

Load CNC Program

Download the CNC program from your computer to the machine control using RS−232 communications, USB flash memory, or floppy disk.

Run Program

Run the program, using extra caution until the program is proven to be error−free.

Adjust Offsets as Required

Check the part features and adjust the CDC or TLO registers as needed to ensure the part is within design specifications.

Shut Down

Remove tools from the spindle, clean the work area, and properly shut down the machine. Be sure to clean the work area and leave the machine and tools in the location and condition you found them.

Warning

Never operate a CNC machine or any shop equipment unless you have been properly trained on its use. Observe extreme caution at all times. Follow all safety rules.

6.2 Machine and Tool Offsets

Fixture Offset XY

Figure 2 shows a plan view of how the Fixture Offset XY works. The CNC operator finds the fixture offset values by jogging (moving) the machine from the machine at its home position the CNC program datum. This can be any point on the part, stock, or fixture, as long as it can be found by mechanical means such as an edge finder or part probe.

جهت خرید قطعات سی ان سی و اطلاع از قیمت های لوازم cnc اینجا کلیک کنید.

The incremental X and Y distances moved between points is recorded and entered into a Fixture Offset Register on the CNC control. Think of the Offset registers like a table in a spreadsheet. The CNC control references these values in the table each time a motion is commanded, adding or subtracting them from coordinates in the CNC program. In other words, Fixture XY offsets convert Machine Coordinates into WCS coordinates.

Most machine controls support at least six fixture offsets, labeled G54 thru G59. Multiple registers are needed because most parts use a different fixture offset for each side of the part machined.

Figure 3: Fixture Offset Plan View

The Fixture Offset Z−coordinate is not used to shift the Machine Z. Use of the Fixture Offset Z is covered in the next topic.

Fixture Offset Z

The purpose of the Fixture Offset Z is to record the incremental distance from a tool setting position to the part datum. The tool set position can be a tool probe or, as shown in Figure 10, the top of a precision 1−2−3 block set on the machine table. The approach shown in Figure 10 involves using a dial indicator and this process is detailed in Lesson 6 (CNC Operation: Set Fixture Offset Z).

The CNC control adds the Fixture Offset Z and Tool Length Offset for the active tool together to calculate the distance from the tip of each tool at Home to the Z−datum on the part.

Figure 10: Fixture Offset Z

Tool Length Offset (TLO)

Every tool loaded into the machine is a different length. In fact, if a tool is replaced due to wear or breaking, the length of its replacement will likely change because it is almost impossible to set a new tool in the holder in exactly the same place as the old one. The CNC machine needs some way of knowing how far each tool extends from the spindle to the tip. This is accomplished using a Tool Length Offset (TLO).

The TLO is found by jogging the spindle with tool from the machine home Z−position to the tool setting point on the machine. This can be the top of a tool probe, or as shown in Figure 11, the top of a 1−2−3 block resting on the machine table. The distance travelled from home to the top of the block is recorded, and the value entered into the TLO register for that tool (called an H−register, because it is preceded by the letter H in the CNC program).

If a tool wears or breaks, it can be replaced, the H−register reset to the new tool by touching off again on the 1−2−3 block, and the program continued with no other changes.

Figure 11: Tool Length Offset

Haas Control

The Haas control is shown in Figures 2 and 3. Familiarize yourself with the location of buttons and controls. Detailed instructions on the following pages show how to operate the control.

Figure 2: Haas CNC Mill Control

Figure 3: Haas CNC Control Buttons