Anyone ever have this happen?

[drf256]

Odd issue with a Mahle 034 Super jug.

A first for me. All was going well until my final band cut. I came back into cylinder was like I always do by around .002 and heard a ripping noise. I was already at .037 out of the band and was going for the final .003 cut which I like to do with autofeed.

The plating ripped away from the jug. It’s probably fine to use, as it still sits above the top ring, but this jug is going across the pond and I don’t want any issues.

I’ve done hundreds of jugs the same way at this point, and this is a first. I found another jug in my stash and did it the same way without an issue. I’m trying to figure out if it was a manufacturing defect in the jug, or just one of those things.

Here is the problem child.

 

[drf256]

And here is the second jug which was fine

 

[Squareground3691]

Possible air gap between plating ,

 

[srcarr52]

With 0.037" already out you should have been well away from the plating at that time. Maybe you had a plating chip tumbling around that finally stabbed in?

 

[Ketchup]

That happened to me on a used 346 jug. I thought it was something like Shaun is saying. Mine was a little more uneven. Some little bits of plating stayed behind on the wall. I was cutting with a mandrel and felt something weird. Scrap now

 

[legdelimber]

Look at your surface finish in the squish band guys. Might be a telltale there.
That plating blunts the tooling at first touch, it's pretty slight, but....
But look at the finish in the squish band. See that roughness and how the tool marks are rough from the chip bunching up in front of the tool.
The tool has just enough edge or point dulled that the aluminum blend is pushing in front of the tool point.
You guys that have turned hot rolled steel on a lathe know what happens when the chip sticks to the tooling or wads up around it. All that rough, scared part surface from the chips/cuttings dragging the workpiece.
If the chip (remember the old timers calling it a "Bug") piles up, I could see it trapping enough material to drag the sidewall while you're still close.

Do a bit looking in the cuttings and see how large of plating flakes you might find coming off of the combustion chamber ceiling that could get trapped and drag the side wall or cause the tool to skip over them and do something unwanted.

Admittedly a bit of a bother, but, just stopping and refreshing the tool bit or swapping insert after breaking under the plating or mill scale or rust will do wonders for that rough roof in the chamber.
I picked up this habit back when was still I was still running engine lathes.
Made ya appreciate a turret lathe for doing those rough passes, then indexing the sharp tool in for the last pass, once the crust was cut away.
And That stray plating or dingleberries of it, are all over many of the cylinders I've seen shown online.

If your base gasket cut is scruffy? same deal with refreshing the cutter!
Remember, aluminum likes a sharp tool or it tears and leaves that scratchy finish.

 

[drf256]

That happened to me on a used 346 jug. I thought it was something like Shaun is saying. Mine was a little more uneven. Some little bits of plating stayed behind on the wall. I was cutting with a mandrel and felt something weird. Scrap now

It is uneven. The area one missing plating is only around 1” of the perimeter. The rest is fine. Pics to follow.