Using GOTO and IF-THEN-ELSE G-code Commands

[rgsparber]

If you deal with CNC machines, cutter movement must come to mind. Yet G-Code can also do math and logic. This article introduces a few of these commands and then explains a program that drills an array of holes.

If you are interested, please see

https://rick.sparber.org/GcodeLogic.pdf


Your comments are welcome. All of us are smarter than any one of us.


Thanks,

Rick

[rgsparber]

I see more than 400 people have at least started to read this article. It is my first attempt at explaining G-code and I'm not sure if my assumptions about the reader's background are correct. Please let me know if you felt it was too simple, just right, or too complicated.

Thanks,

Rick

[Paul Jones]

Thank you for the detail on the GOTO and IF-THEN-ELSE G-code Commands.

[tonyfoale]

I see more than 400 people have at least started to read this article. It is my first attempt at explaining G-code and I'm not sure if my assumptions about the reader's background are correct. Please let me know if you felt it was too simple, just right, or too complicated.
Rick

Rick,

Your post has a limited readership, almost by definition so it would not be wise to limit it further by aiming it only at those with a higher starting knowledge. I think that you got the level about right. I assume that only those who have manually written G-code would be interested and so there should be no need to assume a lower starting level than that. For completeness you could add explanations of subroutines as well.

If I had to criticise, I would say that you might retain reader interest longer if you gave some very brief examples near the beginning of the document rather than starting off with the meat. As it is, you start off with "here is some great stuff that you might not know about", I imagine some readers thinking "so what?" and going elsewhere. If initially you showed some examples that would be long winded without these techniques and then offered them as a solution I think that more readers would stay the course.

My comments should be taken as from someone who has written engineering application software since 1960 and who regularly hand codes G-code. For me there was nothing new in your post so maybe i do not have the best perspective to comment on the level for your expected/intended readership. Take my comments with that in mind.

[rgsparber]

Rick,

Your post has a limited readership, almost by definition so it would not be wise to limit it further by aiming it only at those with a higher starting knowledge. I think that you got the level about right. I assume that only those who have manually written G-code would be interested and so there should be no need to assume a lower starting level than that. For completeness you could add explanations of subroutines as well.

If I had to criticise, I would say that you might retain reader interest longer if you gave some very brief examples near the beginning of the document rather than starting off with the meat. As it is, you start off with "here is some great stuff that you might not know about", I imagine some readers thinking "so what?" and going elsewhere. If initially you showed some examples that would be long winded without these techniques and then offered them as a solution I think that more readers would stay the course.

My comments should be taken as from someone who has written engineering application software since 1960 and who regularly hand codes G-code. For me there was nothing new in your post so maybe i do not have the best perspective to comment on the level for your expected/intended readership. Take my comments with that in mind.

Great suggestion. How does this look (see page 2): https://rick.sparber.org/GcodeLogic.pdf

I have also rewritten the explaination of the code example. As the author, I am unable to see what does not work for the readers so PLEASE give me your comments.

Thanks,

Rick

[tonyfoale]

Great suggestion. How does this look (see page 2): https://rick.sparber.org/GcodeLogic.pdf

I have also rewritten the explaination of the code example. As the author, I am unable to see what does not work for the readers so PLEASE give me your comments.
Rick

As an author of two technical books as well as a contributing author to other books and 100s of magazine articles I am only too well aware of the difficulties of determining how the average reader interprets one's work. This applies much more to technical works because it is hard to strike the right balance between those with the minimum starting knowledge and those with much more. It is easy to lose one extreme or the other if the balance is wrong. I do not read fiction ( never get past the first page when I have tried ) but I guess that these considerations do not apply to that genre.

I think that your page 2 additions are much more likely to suck the reader in. Great choice of variations on the same theme, very clever. You state that conditionals and navigation statements will be discussed but then you start talking about variables without initial explanation. I would suggest an early mention that variables are useful in conjunction with the conditionals and navigation statements.

[rgsparber]

As an author of two technical books as well as a contributing author to other books and 100s of magazine articles I am only too well aware of the difficulties of determining how the average reader interprets one's work. This applies much more to technical works because it is hard to strike the right balance between those with the minimum starting knowledge and those with much more. It is easy to lose one extreme or the other if the balance is wrong. I do not read fiction ( never get past the first page when I have tried ) but I guess that these considerations do not apply to that genre.

I think that your page 2 additions are much more likely to suck the reader in. Great choice of variations on the same theme, very clever. You state that conditionals and navigation statements will be discussed but then you start talking about variables without initial explanation. I would suggest an early mention that variables are useful in conjunction with the conditionals and navigation statements.

Thanks Tony, changes now implemented. https://rick.sparber.org/GcodeLogic.pdf

Rick

[marksbug]

I used to program& run cnc mills back in the mid 90's ( hurco mills) a lot of aerospace stuff, DOD mill spec stuff& prototype stuff. the boss said I did not want to try to learn G code for the other machines....I did some checking and reading and...he was right. I liked the simple programing the hurco's have. I dont understand why everything isant simple to program...why still G code stuff.....I sure would love to convert one of my mills to cnc but not if I gotta do the g code. these days I dont think my brain could stand the abuse.

[tonyfoale]

I dont understand why everything isant simple to program...why still G code stuff.....I sure would love to convert one of my mills to cnc but not if I gotta do the g code. these days I dont think my brain could stand the abuse.

You have to have some means of transferring instructions to a machine and it is hard to imagine anything simpler than G-code. The stuff that Rick showed could be considered advanced and be a bit intimidating to non-programmers but you do not need to write code using those advanced features. Mostly you can just use the simple commands which reduce down to only two sets of commands. One, to go from where you are to where you want to be in a straight line, and two, to do the same on a circular path. e.g.

G1 X20 moves in a straight line 20 units (usually inches or mm) in the X direction.
G1 X15 Y10 Z5 moves the tool or work piece (depending on the machine type) in a coordinated fashion to the position (15, 10, 5)

If the tool centre is at (0, 20) then either of the following will cut a path to (20, 0) on a clockwise circular arc
G2 X20 Y0 I0 J0 (I and J are the absolute coordinates of the centre) or G2 X20 Y0 R20 (with R being the arc radius)

I find it hard to imagine how you could transfer instructions much simpler than that. In any case many machinists do not manually write the G-code. CAM software takes a CAD drawing and spews out the G-code for you. I don't use CAD and so I either write the code manually or write my own software to generate the G-code for specific purposes. You can also do a lot of machining using wizards ( pre-written G-code often called "conversational").

[DIYer]

Thanks Rick! We've added your Gcode Methodology to our Machining category, as well as to your builder page: Rick's Homemade Tools. Your receipt:

Gcode Methodology by Rick Sparber

tags: electronics