I wrecked two 1/2" two flute center cutting end mills in a row. I"m trying to figure out what happened.
A friend gave me a couple of cast iron clamps from his tractor wheels to mill 1/2" keyways in.
I had intended to "drill" down with the end mill and produce a series of overlapping holes, and then side mill the slot - cheapo me - I can sharpen the ends of end mills, but not the sides, so I try to put my wear on the ends.
I moved the table up until the end mill was just touching, then started to pull down on the quill handle. I was putting a fair amount of pressure on to get it to cut and it just grabbed and fractured. The first time I could blame it on the vise and work piece not being clamped tight enough. The second time the cast iron work piece moved less in the vise when it grabbed than before, but it still moved when the end mill grabbed. After this I did the slot in the conventional way, side milling out the metal. I didn't feel any hard spots when I came in from the sides.
What happened? Doesn't cast iron like to be drilled with an end mill? It seemed to work ok when I was feeding the table up to get into bright metal, but when I pulled down on the quill handle, it broke apart. Did I put too much pressure on with the quill lever? Thoughts?