When the offsets are a bit off

[g-coder05]

SHABLAM!!!!

 

[Mud]

Oops. Looks like a brand new machine.

 

[Mhajicek]

You've got a nice, fine, grain structure there, it looks like the heat treat was spot on.

(Forged In Fire fan)

 

[Delw]

That sucks, that machine does look pretty clean if not new

 

[Spruewell]

Missed it by that much. do you think anyone heard that?

 

[Mhajicek]

About a decade and a half ago I was working at a job shop. I was programming late one evening in my cave (cramped little room), and felt an Earth shaking kaboom. My first thought was that a bomb had gone off. Turns out one of the night shift guys had crashed the brand new live tool lathe at full speed. It was not a small machine. IIRC is was six weeks and $30k to get it running again, and it was never the same.

 

[Herding Cats]

I don't know what it is with lathes. A 2 axis job should be stupid simple compared to mill work but the pucker factor is always so much higher with a lathe. Maybe its having a big turret so close to a big spinning chuck

 

[Mhajicek]

Imagine the pucker factor if on a mill the table were spinning instead of the cutter.

 

[Herding Cats]

Imagine the pucker factor if on a mill the table were spinning instead of the cutter.

Kinda like a lathe

 

[Mud]

I agree with the heavy chuck and part spinning being a lot of it. I also think some of it is because the rotating part is inline or close to inline with the operator's face. I have a CNC mill that has the spindle face right at my eye level and it stays there - the table rises instead of the head lowering. So even small drills and endmills are threatening when rotating at speed, flying chips ejected parts and broken tools weigh heavily on my mind and I wind up being way more careful than I am on a normal VMC.

 

[Delw]

lathes cause me more of a pucker factor than mills always.
I remember back in the late 80's running semi big cnc lathes with 100-150 IPM rapids LOL on 30" chucks/ 60" face plates using full circle jaws. I had one or 2 crashs in those days . as you couldnt read the program on the screen cause there was none, it was an old General Numeric type control on a seperate 5-6 foot tall metal box with the led type writing for the x and z moves along witha few buttons. one line at a time. Had to trust the programmer, or read through the 20+ pages of g code that was printer out.
happiest day in the shop when the 3 of them got converted to Fagor controls with real screens.
It was actually faster to pull the tool off the tool post then it was to try and stop the machine with the buttons.
talk about watching a slow train wreck.

They were old hes machines, the newer one we bought had a fanuc control on it , the 2 older ones were the old control

 

[g-coder05]

I think this is why I enjoy lathes so much, The rush you get when proving out a part is different than a mill. So many stupid things can go wrong before you get through 5 lines of code such as wrong G50SXXX! Guilty of that one on more than one occasion.

 

[CNC_Chip_Thin]

That's quite the crash there, it was probably heard in the next town over. Hopefully nothing but the chuck was damaged. Could have been a lot worse

 

[lobust]

The worst crashes are always lathes, so much more moving energy and inertia. With a bit of luck that chuck absorbed enough of that energy not to destroy the spindle, but I wouldn't count on it.

One of my guys broke an OD tool block in half by trying to run a 3" insert drill in G99 with a feedrate for G98... It was basically full rapid.

I crashed the turret of one of our big lathes into spinning chuck jaws because I forgot that machine resets the work offset when you hit reset. Luckily that lathe is built like a tank and other than a big dent in the turret and a bit of turret realignment there was no harm done.

I have heard tales of people ripping chucks off of machines them landing in the shop next door. I saw a big Doosan lathe in a dealer warehouse about a half a dozen years ago, brand new and shiny, bed casting split down the middle, headstock broken off at the base, and turret disk missing.

 

[g-coder05]

Some of my more expensive mistakes came from the A2100 control. The Cincinnati Hawk lathes use M6.1 for the tool change. It kind of works like Mazak just not as smart. You move z to the longest tool turn X the same way then set “tool change position”. If you you leave out the (.1) the turret rotates in place.

I got really good at brazing carbide boring bars...

 

[Mhajicek]

Back in 2000 - 01 when I was teaching Mastercam classes for Prototek one of our clients told me about an incident. They were turning aluminum castings (high RPM), and one came apart just as the operator turned away from the window to look at the control. The casting blew through the door window, flew right through where the operator's head had been a second before, and buried itself in the top cinder block of the far wall.

 

[lobust]

I got really good at brazing carbide boring bars...

I actually did an almost identical oops many years ago on an old gildemeister turning centre. It had a Grundig EPL control, actually a really nice control to use, but a bit odd. Quite advanced in many ways and weirdly limited in others.

One notable omission was the ability to call up a tool with a different offset. I forget what the part was that I was making, but I had a 12mm solid carbide boring bar, and I really needed two offsets on it.

I thought "there HAS to be a way, right?". I scoured the manual and found an m code that purportedly inhibited turret rotation when you called up a tool. Great! I left an empty pocket next to the bar, and set that up as my second offset, edited the code and the toolchange into the program, and hit start.

WAY too much faith in the manual. M code completely ignored, turret rotated in front of the chuck - spinning at about 3k - carbide boring bar rattled off the window and shattered it before landing in the conveyor.

Lesson learned about testing things first...

 

[g-coder05]

I got to the point were when the tool salesman came buy with those no name solid bars with 10 CCMT inserts for $100 I would snatch up about 5 and put in the file cabinet as It was inevitable on that control it was gonna happen again. the 2100 is one of my favorite controls but they just needed to get that M6.1 out. Oh, and "H' being a work offset call was a head scratcher on occasion.

 

[Oldwrench]

This is a sort of depressing subject but definitely lathes are more dangerous than mills. The local college teaches mill programming in the first semester and lathe programming in the second. Presumably it's because the concept of an X axis move doubling the diameter result is difficult to grasp until the students have mastered 3-axis coordinates—but I think it's because crashes are bigger and louder on a turning center.

 

[Mike1974]

Well to play devil's advocate here... Try telling the guy that lost the facing head in his mill that shot thru his entire building that lathes are always worse than mill crashes.

But I digress. It does seem that lathe crashes cause more damage in general. Usually if you rapid a mill tool into the part, worse case you lose the part and toolholder/tool. On a lathe crash it almost always means siginificant downtime to get 'er up and running again. I remember rapiding a long 1 1/2" or so drill into the sheet metal behind the chuck hard enough it took me all day to re-align the turret.