[ghyman]

Out of the blue, in the middle of a run, the machine started cutting oversize.
By oversize, I mean the bore, which had been running ±.001 all day, suddenly started cutting .075-.080" oversize.
The OD, which had been holding ±.005" all day, suddenly started cutting .060" oversize. (Technically more than that, as the turn was only .060" inside the bar diameter.)
Cutoff tool suddenly started leaving a .085" tip on the end of the bar.

I pulled a drill out of the turret that has always had a ~.005" offset, and used a coax indicator in a collet in the chuck to sweep the drill holder.
I reset machine Zero to the holder, and the machine zero changed by exactly .0397"

It has been a few decades since the old Cincinnati Milacron 15-U that I used to run, but I recall a few times seeing every offset in the machine suddenly being "off" by exactly .100"
In those days, the phenomenon was called "skipping a grid", and was usually attributed to dirt or power surges.

This machine is about the same vintage (early to mid 80's); is this something I should be on the lookout for?

[underthetire]

X Axis drive belt
Broken sheer pin in the pulley coupling
Turret not clamping correctly.
I HIGHLY doubt its electronic.

[ghyman]

X Axis drive belt
Broken sheer pin in the pulley coupling
Turret not clamping correctly.
I HIGHLY doubt its electronic.

Thx, underthetire.
I will check those.
The "off exactly 1mm" just seemed a little too exact.

But I appreciate the input and will look into them.

[Algirdas]

check X Z alignment of the turret. Don't worry if there is no sign of turret hit

[broby]

check X Z alignment of the turret. Don't worry if there is no sign of turret hit

Al, you do not read these posts very well do you?

In the original post the person stated that they had indicated the bore of teh drill holder already!

Obviously, if they had found that the turret was out of position, then the answer would be self evident!
Thus the reason they are asking for ideas as to what may be happening.

[Algirdas]

they had indicated the bore of teh drill holder already
a turret Z and X alignment is quite different issue for your information

[littlerob]

a turret Z and X alignment is quite different issue for your information

Really, how are they different Algirdas? Would it be because THEY ARE DIFFERENT AXES? Again we are back to these worthless posts that don't benefit anyone, anything.

[Algirdas]

Let's start from the very beginning. Easy to understand.
used a coax indicator in a collet in the chuck to sweep the drill holder. I reset machine Zero to the holder, and the machine zero changed by exactly .0397"
Mr. underthetire suggested to check ... and I added the check of turret alignment. In my opinion, the hit of turret can cause this. Post your suggestions, please, if any.

[broby]

Let's start from the very beginning. Easy to understand.
used a coax indicator in a collet in the chuck to sweep the drill holder. I reset machine Zero to the holder, and the machine zero changed by exactly .0397"
Mr. underthetire suggested to check ... and I added the check of turret alignment. In my opinion, the hit of turret can cause this. Post your suggestions, please, if any.

Easy to explain eh?
First thing first... ghyman stated that the machine had been running without fault all day... then sizes went pair shaped!
I would be extremely surprised had he NOT checked for the obvious fault of a crashed machine by checking the alignment of the X & Z axis alignment of the turret.
Since no mention of a crash is made, I can safely assume that none took place.
As he states it seems very unusual and the suggestions given along the lines of "Underthertire" seem to me to be very good.
Your ability to give out crap advice is just wasting time and effort and you gain no respect every time you grab the keyboard.
If you can not understand the written english word why not just shut up?
You can and do offer some good advice on the odd occasion, but for goodness sake keep clear of the nonsense the rest of the time for goodness sake!

[underthetire]

Al, sometimes your posts are really out there. Could be a translation thing, could just be nonsense, I don't know or care. I personally think maybe your first post should have said," I would double check turret alignments, to rule out the possibility of a crash". That would have been smart, to the point, and helpful. That's about all I'll say on this, I am taking a swiss stance on this from now on

[broby]

hear hear!
I concur!

[Algirdas]

is it technical discussion about lathe turret fault or it is surgery of my person?
First it was not clear why X and Z alignment must be checked.
Now you see somehow that X and Z alignment was checked for sure.
You play a kindergarten, I play role of resentful?