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Thread: Magnetized 4140
10-03-2010, 05:13 PM #1
I have noticed, to an annoying degree, that when machining 4140 pre-hard that it will become remagnetized. I demagnetize it, machine it more and viola! Back to being a magnet. Does anybody have any knowledge of why this happens and is there a procedure to stop the remagnetizing once and for all?
10-03-2010, 06:22 PM #2
Soft steels do NOT magnetize well as permanent magnets. Iron pretty much does not at all.
Hard steels do.
4140 PH is hardened, although it is not very hard.... Therefore it CAN magnetize, and it is no surprise if it does. You can magnetize some things weakly by pointing them North and whacking them with a hammer... machining a part lasts longer than a whack with a hammer.
10-03-2010, 06:52 PM #3
I have noticed straight tooth cutters tend to magnetize parts more than spiral tooth cutters. Form cutters such as gear cutters are especially bad. The teeth are just a series of little rotary hammers, each one imparting a small amount of magnetism.
10-04-2010, 08:25 AM #4
If you're using an insert cutter or a fly cutter it's worse.
Just make sure your mill table runs east to west, and you machine only when there isn't a full moon