Hey ALL…found out something crazy today. Here is the scenario: yesterday my students are running linear programs through a paper maze with a marker. I have them program through one way in Absolute and then the opposite way in incremental. Basically the same program start, simply insert a G91 in the first movement block. WELL, the program finishes and the next student gets on the machine. sets their work offsets and goes to MDI to check the location of the G54/G55. Types G00 G54 X0Y0 …cycle start… no movement. LONG story short and several hours of head scratching I figure out that by not changing the G91 back to a G90 puts the machine into incremental mode and it is NOT just isolated to the program. It stays there. I VERY RARELY program this way and had never experienced that scenario. Am I the only dummy who didn’t realize this simple fact LOL???
Sometimes you need to step back and look it over. My habit is G00 G90 G54 X Y enter cycle start. I always have multiple Work Offsets set up from left to right on each vise. Just makes things faster for me.
great habit apparently!
its good to run into things like this especially in the classroom that shows these kids that even the simplest things can hang you up. So if you can’t figure it out go to the simplest form and start again.
Its a good lesson on Modal and how that works -
In the 80’s we all hand programmed and got into habits - Like each tool we start with G00 G90 G54 - if you did a reset and run at T4 you may still be in G91 and your machine default may be G91
I teach G90 in my safety block, but neglected to switch back from the G91 in the code and YEP the Modal got me!
That is why we call them modal codes. the machine stays in that MODE. Until told other wise. that is why a good program format accounts for all modal states that machine could be in or its behavior could be unpredictable.
The old way of going to Machine home was G91 G28 Z0 ( some post processors still spit that out)
so you Had to do G90 on next tool. - If you do G53 Z0 you are still in G90 - But I would still make a habit of forcing the G90 G00 G54 at each tool change. even back in the day of hand programming G code we looked for ways to not type so much but some code you need no matter what.