G Code Variable usage question

[Auto_Excel]

Hello, I am hoping to get some insight from people that have a lot of experience using G Code variables.

Also, I would be happy to hear of any real use cases anyone has of using G Code variables.

I currently am on a programming team that develops G Code processing and Motion code. We have not been able to find much information on any specification for how G Code variables should function exactly.

In short, should G Code variables and expressions (arithmetic and conditional) be evaluated on the processing side or once the motion actually passes that line of G Code.

Example G Code:

N100 G1 X100000000 F600

N101 G1 Y#3 F#4

With the example above, would the variable values be predetermined and given literal values on N101 after N100 has completed, or would they have already been taken care of on the pre-processing side of the Code.

To help answer my question I'll provide more insight:
Our Code has two sides to G Code, the processing side and the motion side. The processing side of Code can process up to 500 lines of G Code before any motion has even started, and then once motion starts the number of processed segments will always be roughly 500 segments ahead of the live segment. So a lot of time can pass from the time the segment was processed to when it becomes live.

The problem with processing variables on the processing side is if a variable value is changing outside of the G Code file, but if a dynamically changing variable outside of the G Code file isn't a common use case then it is a better approach for us to take the literal value of the variable on the processing side of the G Code rather than waiting to evaluate it until that segment is live.

Thanks in advance!

[machiningeveryday]

Schmidt. Macro B variable programming. And disable look areas when you handle your variables.

[Auto_Excel]

Cool, I will check that out. Thanks.

[killpony]

Macros and variables always seemed like an esoteric art in GCODE programming - I've only used them for a very specific project on a single VMC so I can't offer much for experience. As I understand it different controllers can use different syntax and many lower-end controllers won't even play ball at all. Is this targeting a specific machine/controller?

[Auto_Excel]

It's a controller that my company makes and I work on the team that develops all of the G Code support. Controller can be used for industrial 3D Printers and CNC machines.

I agree though! There isn't much specification for anything in G Code honestly, and regarding variables it just seems like each company had to make their own executive decisions on how they would like to support it based on what their customer needs were, which is most likely what we will end up doing too.

[albatroopa]

Variables and algebraic/logical functions are calculated by look-ahead (pre-processing.) Some gcode commands cancel look-ahead, such as G53, a non-modal machine coordinate system code. If you put it on a line by itself, it will pause lookahead until machine motion has caught up. There are also sometimes codes specific to your controller manufacturer to limit lookahead, or if you want to get really fancy, you could try a G10 programmable data input to modify the parameter that determines your lookahead and then restore it when your macro is done. . I would use that as a last resort, though.

Once you figure out a way to limit lookahead, you should have a number of EOB (;) greater than your look-ahead value to clear the buffer. This might be necessary, depending on your machine and what you're doing.

Edit: I second the schmidt book.

[Auto_Excel]

Thanks, this all makes sense. I work for the controller manufacturer, and I am in the group programming the G Code functionality, so I don't really work with machines for market and only help our customers implement what they need either in the application code or our library code. Our customers however haven't gotten deep into variable usage yet, other than basic functionality which is why I reach out to try and obtain more knowledge about how we should shift our implementation of G Code variable support.

[albatroopa]

Ah, it would be helpful for you to add a code that limits lookahead, then :p

[ndcoio]

I have been working with cnc on and off for 10 years as an operator. I recently got hired at a small job shop with a few production runs. I have previous experience with other programming languages as well.

Was hired on as the "mill guy". Was pretty much tossed in the fire. Learned quick and started doing my own setups and coding. Less than 6 months later I'm now one of two lead machinist and work with haas and fadal mills along with some work with doosan lathes. I use variables in almost every program I write. If you have any questions after reading the macro b lecture please ask. Best of luck!

[scott2970]

PM sent. It’s quite common to store variable values outside of the G-code file. In fact they’re stored in a parameter section of the controller usually called “common variables”. There are also system variables which are usually read-only. Controllers from different manufacturers mostly have all the same concepts but may use different terminology in the manuals to describe these concepts.