igniting swarf

[Plum Creek]

I need a hardened 2.06" pin for a project.
The closest thing I have at hand is a through hardened 3" wrist pin from my excavator.
The band saw wouldn't touch it even after making a 1/2 " deep starting cut with an edge cutting disc. It throws very short medium yellow sparks with tiny burst. Oddly enough its quite malleable on the shoulder end.
The surface is irregular so I Try a .010 skim cut with a TCMT 32 at 320 rpm. Way to slow, leaves a decent finish for the speed, but chips are quite hot. Second pass same, doc at 440 rpm (which worked well on HT 4140) chips ignite and burn. Stopped applying cutting fluid and it became worse. The fire was yellow not white like I would expect with magnesium or titanium. The cutter looked undamaged to the naked eye.
Whats going on here?

 

[willthedancer]

Iron does burn if it's finely divided enough. Take a lighter to a piece of steel wool if you don't believe me.

You will likely find that this is not hard through.

A Kennametal K090 insert may ease your efforts, but the swarf will burn with it too.

 

[Wreck™Wreck]

Are the chips burning or just glowing at the point of cut? Hard turning creates a good deal of sparks and glowing red chips when done properly with ceramic tooling. Gives excellent finishes and holds size very well in my experience, very hot however. NO COOLANT

A hard turning insert will also dislike non hardened steels so be careful if you go through the case, do not ask how I know this.

 

[Plum Creek]

Ok, thanks guys.
Now that you mention it I remember seeing steel wool type fire starters in survival packs a few decades ago.
Yes they were burning! It was a was a bit unnerving seeing flaming clumps flying out of the cut like that. I was glad the chip tray was empty but concerned about all the oily residue.
The lathe wasn't making the low freq moaning like it does when the cutting loads are high. It seemed well.. normal.
I will take a look at the K090 and the ceramics. So what happens when the ceramics get through the case, do they dig in?

 

[Wreck™Wreck]

Ok, thanks guys.

I will take a look at the K090 and the ceramics. So what happens when the ceramics get through the case, do they dig in?

They seem to just fracture at the cutting point, there are several theories about hard turning none of which are considered conclusive.
Interesting reading here:
https://dspace.lib.cranfield.ac.uk/bitstream/1826/131/3/Chapter 1 to 4.pdf

 

[willthedancer]

They seem to just fracture at the cutting point, there are several theories about hard turning none of which are considered conclusive.
Interesting reading here:
https://dspace.lib.cranfield.ac.uk/bitstream/1826/131/3/Chapter 1 to 4.pdf

Its all about surface footage and chip load. soft material requires much higher surface speeds, so the transition past the case hardened area is problematic, as you find yourself going too slow

 

[Plum Creek]

That was an interesting read. I'm not sure I got much out of it on the first pass but it did answer some questions.
I looked at the ceramic inserts and think I need to do more research, but plan to add a couple to my next order.
I got the pin turned using the Tcmt. It's toast, but never chipped.
Turning got easier at about .025 depth, but produced sparks all the way to the final cut. The shear zones were problematic . The interrupted cut through the worn areas were problematic.
I still have some work to do on the saddle and cross slide. Waaay Too much slop.
All in all I learned a lot, Thanks