I was tapping a hole yesterday with my uncle into a piece of soft steel. (A tap cuts threads on the inside of a hole, to accept a machine screw or bolt.) The tap was NOT magnetic! As I finished boring through the soft steel, I noticed that the steel shavings (or chips) were magnetized. I didn’t take a picture of it but one can see the steel shavings in the image below.
I could clearly see that steel shavings were standing perpendicular to the tap itself, not attached by any other means. My question is how does hole tapping (friction) align the domains of the chips?
I could conceivably imagine that the soft steel is being heated up that loosens the “weakly bound domains” of the soft steel and that maybe, just maybe, they are aligned by the earth’s magnetic field. However, I would guess that the earth’s magnetic field is too weak over such a short time period. None of this makes any sense to me and therefore, I am asking for help on my question.
Best Answer
I'm not sure what kind of steel you are using, but with stainless steel, many varieties are slightly magnetic. As I recall, when we were building a spectrometer that was very sensitive to magnetic fields, we were careful to use only "austentic stainless steel", which is not magnetic. I think that we paid extra for this feature.
So, I agree with the comment from @lionelbrits, the steel could have already been lightly magnetized but you could only observe it when you cut a very small piece.