More notes on Planning a CNC program and setup

Planning a CNC Program
When writing a CNC program planning all the steps ahead of time is very important. The machine that is used and the operations done on that machine is the first step in the process.

Consider things like the size of the part to be machined, required horsepower, number of tools needed and the availability of the machine.


The Part and the Tools

The blueprint or drawing of the part is the basis for writing a NC program; dimensions from the drawing are converted directly into a program. A plan has to be developed for each operation on the part that allows for the sequence of tools to be used and the operation each tool will perform.

The use of extra tooling, using the same tool more the once, or having the tools programmed in the wrong order are things to be avoided. Fixtures and holding devices should be planned for early in the process; pay close attention to clamp locations in order to program around them.

Writing the Program
Planning out each operation on the part allow the machinist to prepare the sequence of tools and the operation each tool will perform before actually writing out the program.
In a nutshell a program is simply a series of commands written in the order they are to be executed. The controller interprets, and then acts on these commands one at a time without stopping.
With the operations defined, the tools selected, and the feeds and speeds calculated the last step is to write the program. This can be done on paper or with the aid of a computer; a part set-up sheet is developed with a tool list. Now the machine can be set-up and the parts machined.
Tool Length Offsets on the Mill
What is an Offset?
With a program written for multiple tools it is crucial that there a method accounting for the difference in tool length of each tool used is relayed to the controller. If these differences are not taken into account crashes will happen.
G43
The introduction of the G-code G43 (tool length offset code) is the solution to tool length compensation. G43 “talks “to the CNC controller to look in a special place within its memory for the length of the tools being used. During the setup of the program, the setup person or operator would have “touched off” each tool used in the program, input the value traveled from the tool change position to the Z-zero plane of the part. When M6 tool change is encountered the controller will make all the additions or subtractions necessary that the programmed value of Z0.0 will be adjusted for the tip of each tool to rest perfectly on the Z-zero part plane.