5 G-Code Tips to Increase CNC Efficiency
Efficiently programmed ATCs and internalized M codes are two ways to increase the efficiency of the CNC.
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Recently, these columns have focused on factors that contribute to the productivity of G-code programs, such as consistency, compatibility, ease of use, and security. Improved programs in these areas generally result in better machining efficiency. Simply put, by making programs more consistent and compatible, easier to use, and safer to run, machines — and the people who run them — can naturally be more productive.
When it comes to efficiency, however, one has to be careful. When you do something that improves efficiency, machining can become more difficult and, in turn, more dangerous. By increasing the skill of the people operating the machine, this can be an acceptable outcome. Having greater skill will allow CNC users to safely perform more complicated tasks.
That said, I’ll focus here on G-code programming techniques that improve efficiency and don’t, for the most part, sacrifice usability or security. There are, of course, countless improvements one can make to processing, fixture, and cutting tools that will help reduce program execution time. But here we focus on free techniques, requiring only to restructure a program to run faster.
As with all of my productivity columns, my intention is to inspire readers to consider their own CNC environment and seek ways to optimize it. Use my suggestions to get started.
The shortest distance
Where possible (and safe), ensure that as many axes move together during non-cutting commands. This includes approach, retraction and movement as tools move from one machined surface to another. However, when approaching during machining center programs, if operators are accustomed to seeing X/Y axis movements first and then Z axis movement, they may be nervous to the idea of having all the axes move together within 0.1 inch (2.5 mm) of the work surface. . If so, first bring the tool 1.0 inch (25.0 mm) above the work surface in the Z axis, then accelerate the rest of the way in the Z axis .
Be sure to include M-codes with motion commands whenever possible. This includes turning the spindle on and off and turning the coolant on and off. This way, the M-code activation time will be internal to the time it takes to perform the move (or vice versa). This is especially important with machines that only allow one M code per command. For these machines, it is not possible to start or stop the coolant and the spindle at the same time, unless the machine builder provides additional M codes for this purpose.
Efficiently program automatic tool changers
While this may be common knowledge, here are some reminders:
- Include an M19 in the tool movement to the tool change position. This will align the tool change arm keyway with the tool holder keyway during movement.
- For dual arm tool changers, always have the next tool ready (specify the T code for the next tool) soon after performing a tool change.
- For short machining cycles, make sure the tools are loaded consecutively into the tool changer magazine.
Pay attention to the constant surface speed
With turning centers, an inefficiently programmed constant surface speed is indicated by the slowing down and acceleration of the spindle during tool changes. This increases program execution time because the spindle typically takes longer to slow down and accelerate than it does to complete the retract/approach motion. It also causes excessive wear on the spindle drive system and wastes electricity.
To fix this for consecutive tools that use constant surface speed:
- Temporarily select rpm mode and specify the rpm for the next tool approach position during tool retraction to the turret index position. This will save you time because the spindle won’t have to slow down.
- Index the turret and give the command to move to the approach position of the new tool.
- Select constant surface speed mode again. The spindle speed will not change since the spindle is already running at the correct rpm.
Look for noticeable breaks
Analyze running programs and eliminate the reasons why the machine stops. If there is a pause during a tool change, it is because the magazine is still rotating to the next tool. Place the tools in consecutive order in the magazine. If the tool has changed but there is a delay before the tool begins its first move, then the machine is changing spindle range. Understand the cut-off point for spindle range change and run tools that require the same range consecutively when possible.
If there is a long pause between drilling pitches during screw-pitch drilling cycles, reduce the parameter value. For the G73 cycle, 0.005 inch is appropriate, while 0.04 inch is appropriate for the G83 cycle. A parameter controls the amount of backup between peaks and most machine tool builders set them very conservatively.