CNC Program Quiz What’s Wrong?

I got a desperate call from a customer asking me what was wrong with the CNC program below as he kept getting alarms.

The machine is a Horizontal Mazak running an (G Code) CNC program. It’s a thread milling CNC program.

I found quite a few errors in the code quite quickly and congratulating myself confidently told him to run the program.

This guy has been my best friend since I was 17 and I couldn’t resist a bit of sarcasm (we call it piss taking here in England).

You have to be careful when you have a go at Garry. Ever since our days together as apprentices at Rolls Royce (circa 1971) whenever I took the piss out of him he would get me back 10 fold.

(It’s no coincidence that Rolls Royce went bust in 1971)

I remember my first time at arc welding nervously trying to master the technique. Garry thought it might be amusing to smash a large mallet into the underside of the metal clad welding both.

I have always been the type of person who jumps and alarms quite easily.

Panic struck I threw the complete welding torch into the air and spontaneously evacuated my bowels. It sparked and flashed around the cabinet, which I had long since vacated, for a good minute before the instructor intervened.

I was the subject of ridicule and derision for the next few days by the whole of the Rolls Royce training school (about 200 teenagers).

For the younger generation, it was in those strange halcyon days when the UK invested in manufacturing. Oh and we had Black Sabbath, Led Zeppelin, Deep Purple and the fuckin Osmonds.

The CNC Program

Anyway enough of that. So yea I thought the program was OK but it alarmed out again.

A sarcastic laugh ensued and comments about “how the Mighty Fall”.

Needless to say I hadn’t found the real error in the code.

I have to call it a school boy error, mind you when I was at school I couldn’t even write my fuckin’ name, let alone error check a complex CNC Program.

I must have demonstrated this a hundred times on a whiteboard. My students took it all in but obviously I didn’t….. So what’s the error?

N30 T16 T72 M06 (5/8″ THREADMILL)
M911
B0
M51
M08

G90 G0 G54 X0 Y35. S3000 M3
G0 Z2.0
G91
G01 Z-20. F1000.
Z0.605
G41 Y-10.548 F263.
G03 X0 Y22.003 Z.907 I0 J11.002
G03 X0 Y0 Z1.814 I0 J-11.455
G03 X0 Y-22.003 Z.907 I0 J-11.002
G40 X0 Y10.548
G90 Z2.
G0 Z50.

Some hints If You Haven’t Got It Yet

When you are in cutter compensation the machine is reading ahead so the alarm my well be a few lines in front of where you are.

There are errors which are more a matter of discipline but won’t cause alarms.

When I check word documents I always put my finger on each word as I read the document.

I find that when you read it your brain is making the same mistake as when you wrote it.

Biggest clue read this on Modal Information.

Thanks

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