What's new
What's new

Do you use G90 and G94 on a lathe with G-code System A?

sinha

Titanium
Joined
Sep 25, 2010
Location
india
Nobody seems to be talking about these cycles (G90 and G94), though these are very convenient for turning / taper turning and facing / taper facing, respectively. People tend to use G71 / G72 for simple cases as well.
Nothing wrong in it.
What I am wondering is, should these cycles be a part of a CNC training course?
Why teach something which a person would never use!
 
I sometimes work part time on weekends at a company when they need someone and the main lathe guy there loves the G94 facing cycle.
I have never seen anyone use G90 though.
 
The reason why I asked this question is this:
Most of my books are too detailed, hence may not be very suitable for absolute beginners. I am, therefore, in the process of writing another book for those who know nothing about CNC programming. This will cover only lathe programming.
I have just started, and it will take several months.
Based on the response to my query, I am thinking to exclude the description of G90 and G94.
 
Honestly, I never used those cycles because like you said, even for a simple profile I just use G71/G72.

Something I didn’t find in books was how to calculate tool radius compensation for a profile feature and manually applying it; most of what I learned in that regard was either by researching this forum and reading old threads, asking questions at this forum (thanks angelw) or self-learning using a CAD software.

Cheers
 
I sometimes work part time on weekends at a company when they need someone and the main lathe guy there loves the G94 facing cycle.
I have never seen anyone use G90 though.
I use G94 regularly as well.

If I was taking a CNC class, I would like the instructor to cover as much as possible. Gives the student more cutting options to consider. I had a half-semester CNC course before starting my own shop. Learned the rest with the books that came with the machines.

Bill
 
OK. Some useful comments. Thank you.

If the requirement is to just reduce the diameter of a workpiece by, say, 2 mm, it makes no sense to use G71. Most people would do it with a combination of G00/G01, in one or two passes. four (or at least three) lines of codes would be needed for each pass. On the other hand, all the moves corresponding to every pass can be combined in a single G90 cycle. Since G90 is a modal code, all subsequent passes would need just the next X value to be commanded. For example, if X30 is to be made X28 up to Z-50, with 0.5 DOC, we can write
G00 X30 Z2;
G90 X29 Z-50 F_;
X28; (G90, Z-50 and F_ are implied)
And, it is done!
There can be a similar example for G94 for facing.

G90 and G94 can also be used for taper turning and taper facing, respectively, by including an R word (as is done with G92 for taper threads). This requires some understanding, and it might be simpler to use G71/G72.

I have, therefore, decided to only partially explain G90/G94, i.e., without any R word.
Leaving it out completely does not seem desirable.
 
In G code System "A" - G90, G92, and G94 are sometimes called "box cycles."
They work well and are very handy when you want to have maximum control over the D.O.C.
 








 
Back
Top