Machining and CNC Technology Level 1 Programming.

Machining and CNC Technology

Level 1 Programming


Overview

“Since so few programs are written by hand today, why take the time to learn such a method?”

It’s a valid question with four very good answers.


Valid Skills for Trade Masters

The complete machinist needs to trouble shoot program codes to solve error messages.Then they edit out bugs or edit in improvements to make programs safer or more efficient. Third, during setups, commands are punched in at the controller, to make or modify tooling, and to move the machine by manual data input.All these key tasks require code reading-writing mastery.

Shop Talk – Programming

The final reason is advancement. Many machinists aspire to programming after running the machines for a time. Obviously a good command of commands is a must in that job!


Goals

Code Words and Program Conventions.> Name Six Word Prefix Letters

> Explain Groupings of Codes

> Begin a Vocabulary of Alphanumeric Words

> Compare Command Lines to Code Words

Outer Program Structure > Start Programs with Safety Modes

> Cancel Unwanted Modes

> End Programs with Safe Tool Movements


Goals Continued

Compensated, Linear Cutter Paths > Calculate Coordinates for the Tool Path

> Write a Manually Compensated Mill Program

Writing Arc Commands> Write Arc Commands using the Radius Method> Write IJK Arc Commands Center ID Method

Writing Compensated Programs > Use the G41/42 Compensation Codes in a Program> Write On-Ramps for the Cutting Tool.> Write Off-Ramp commands


Codes and Conventions

First, we'll examine a short code word vocabulary. Then we'll investigate data conventions, how to make entries the control can accept. Next we look at a set of command words to begin programs safely and how to end them too.Lastly, we'll learn program structure and how to join the code words together into complete command blocks.

Trade Tip on Memorizing

The main objective is not to memorize codes, although doing so will accelerate mastery. The goal is to learn the possibilities.


Terms Needed When you begin study, don’t bypass the terms.

Knowing their meaning will speed mastery,Alpha-Numeric CodeCommand (Command Line) Command Word (Word) Code GroupsPrepatory Codes (G Codes) M Code wordsModular Command


Codes to CommandsA command line in a program is a

complete set of instructions to be acted upon by the control.

It is composed of alphanumeric code words, coordinates and numbers.


Universal (Almost) Those code words come from a set that was

written before machines had micro-processors with RAM.

They could read code and act upon it but not use variables on the fly, such as offsets.

As such the 50 core G words and 50 M words survived from those early codes.

They cause simple motions such as feed rate linear or two axis circular motion.

They are standard codes everywhere.


But, the EIA originators that invented them could foresee their set would need space for expansion.

So they left 50 of the first 100 words blank in both the G and M categories.

Today, all of those words have been filled too. Some have become nearly universal CNC code, due to their use on Fanuc controls, an early leader in CNC.

But, today we have gone far beyond 100 words in both the Miscelaneous and the G codes.


Program StructurePrograms divide into three portions:Start, Body and End CommandsEven CAM generated programs need

beginning commands that set conditions or cancel unwanted conditions left over from the previous program.

And they require final codes to close certain modular modes and actions


Communication and File Names

Some controls require specific codes and labels at their beginning.

Others do not.To find out, simply read a program from

that machine or read the programming manual.


Generic Startup Commands

As a suggestion only, here’s a typical startup command set:

G80 G40 Cancel cycles & compensationG20/21 Inch or metric valuesG90 Absolute values (G91 incremental) G94/G95 Feed IPM or IPRFXXX Sets feed rate for first cutSXXXX First RPMG17/18/19 Sets active mill plane for

interpolation and comp

RPM and feed rates might also be placed later in the program, but must be entered on or before the line where they are used in a command. However, there is no harm in placing them in the header of the program also .

Your instructor will have a specific set of safety and startup codes required for your controller and situation

Your instructor will have a specific set of safety and startup codes required for your controller and situation


Retract DistancesThis is another area where your

instructor will set a policy as to how close to the work, new programmers can rapid their cutting tools!

A half inch is a good distance but may be too close especially for larger turning centers where crashes are spectacular.

A safe distance to rapid travel to and from


Compensating Programs

Break out your calculators for this unit!

Calculating compensated significant points can be a challenge.

It was in finding a better way to solve this kind of math that Mastercam software was born!


Coordinate shifts for uncompensated programs

To profile mill this shape, using a cutter path program, each significant point must be calculated as a distance off the geometry.


Points A and I are simple, their program coordinates A’ and I’ are the radius distance away from the geometry, at 90º

All remaining points require triangle solutions.


For ExampleTo find Point B’ based on Point B.


Unit 4 Writing Arc CommandsDon’t put your calculator away just yet!The next toolpath challenge is

calculating arc commands. Depending on the part shape, they can

be simple or require a bit of computation.


Arc ParametersWriting an arc

command is not unlike drawing an arc with a compass.

You must have five parameters


Three Command MethodsThere are three different ways to

program an arc. Each begins knowing by default, the

start point since it’s the current cutter position – it’s automatically known.

Then by identifying other key information, more parameters are automatically known as well.


For Example: If the center point is identified as a

coordinate, then the radius is automatically the distance from the start to the center.

Each of the three methods supplies a combination of key parameters such that the others are automatically known.


One command identifies the center of the arc, the end point, and the curvature.

Another identifies the radius distance, curvature and end point.

These two are the ones we’ll study in the text, the Radius Arc Command and the Center ID Command

A third method, not discussed in the text, is the polar method where the key parameters are the radius, degree of arc and which direction, clock-wise or CCW.


Writing Compensated Programs

OK – put your calculators away.After the last two units, you will have an

appreciation for letting the computer do the calculating using cutter comp commands!

For compensated programs, we use the part path geometry, not the calculated tool path.


Cutter Left or Right?The first item to define, after writing the

part path coordinates, is to which side of the geometry line is the cuter to go?

Think of it this way: if you are mowing along a fence, to which side of the fence are you? You (the tool) are either to the right or left of the fence (workpiece) looking in the direction you are walking.


Here’s what it looks like:

Fence

You and the MowerG41 G42


In addition to the compensation code G41 (cutter left) or G42 (Cutter right),

You’ll need to write a ramp-on path that brings the cutter to the work in such a way to begin compensating and not leave marks where it begins cutting.

You’ll also need to refer to the tool radius compensation memory for distance offset from the geometry.

Then with your program properly written, watch the magic happen as the cutter traces around the work shape!


Conclusion After working the problems of hand program

compilation, you can see what a time and math saver CAM software can be.

It does it all for you based on a part drawing! Still, you wouldn’t want to leave training

unable to write programs by hand. It’s not often the PC goes down these days,

but if it does, it’s the code literate machinist that saves the day!

Date post:	14-Dec-2015
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Machining and CNC Technology Level 1 Programming.

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