13. Programming With Variables

RS274NGC makes provision for the inclusion of variables in the numeric part of program words. Variables can be named with any number up to 5399. You can access the value of a variable in a gcode program by placing a hash (#) sign before the number/name of the variable that you want to reference. Often in the EMC literature the terms variables and parameters are used to refer to the same thing.

For those who learned part programming on older machine tool controls, the inclusion of variables makes for some strange looking program blocks. But variables can be very useful programming tools. This unit develops the concepts of variables as a gcode programming tool and applies them to five common milling tasks.

Before we begin, you need to understand that the NGC development defined a lot of variables and how they should be used in machine control. But the EMC and its interpreter only takes advantage of a few of these variables and those only for its built in coordinate system. You can see which ones, all in the 5000 + range if you view the emc.var or generic.var files shipped with EMC. A typical variable file is listed below. We will add and use several variables that do not have predefined functions in the EMC.

Format is:
<variable> <value>
<variable> runs from 1 to 5399 inclusive, <value> is a number.
Units for <value> are INCHES, the default units for RS-274-NGC.

Lines not of that form, or blank lines, are considered comments. Don't enter a line beginning with two numbers unless you mean it.
You can put whatever you want in here as user variables, but some are reserved. See the RS-274-NGC manual for the reserved variables.
This file is loaded into the interpreter at the beginning, and dumped from the controller at the end.
Only variables you put explicitly in here will be dumped out from the interpreter.

Axes offsets for G92
5211 0.000000
5212 0.000000
5213 0.000000

Coordinate system for G54 - the default used at start
5221 0.000000
5222 0.000000
5223 0.000000

Coordinate system for G55
5241 0.000000
5242 0.000000
5243 0.000000

Coordinate system for G56
5261 0.000000
5262 0.000000
5263 0.000000

Coordinate system for G57
5281 0.000000
5282 0.000000
5283 0.000000

Coordinate system for G58
5301 0.000000
5302 0.000000
5303 0.000000

Coordinate system for G59
5321 0.000000
5322 0.000000
5323 0.000000

Coordinate system for G59.1
5341 0.000000
5342 0.000000
5343 0.000000

Coordinate system for G59.2
5361 0.000000
5362 0.000000
5363 0.000000

Coordinate system for G59.3
5381 0.000000
5382 0.000000
5383 0.000000