I needed to make an adapter plate to mount the read head of my new DRO. I rummaged through a scrap bucket and found a piece of Mystery Metal I could easily machine to the size I needed: 3/16" x 1" x 3 1/4".
Put it in the vise, start machining. Going along fine and Wham! Totally whacked the end mill. Say 10 bucks woth of end mill destroyed.
Switch to carbide insert cutter to finish the job. No problem.
Drill two mounting holes no problem. Start to use center-cutting end mill to counterbore the holes for button-head capscrews. Start the plunge cut, Wham! Trashed that end mill. Another 10 bucks worth of tooling destroyed. I begin to see a pattern here.
Switch to lathe. Mount piece on faceplate, bore counterbores with weeny carbide boring bar. No problem.
Mount plate on milling machine, Transfer punch locations of holes to mount DRO read head. Remove, drill and tap the holes, no problem.
So...I used a "free" piece of steel, but in the process I managed to trash about 20 bucks worth of end mills, not to mention all the extra time and aggravation. It would have been a lot more to the point to buy a piece of Starrett ground stock, of known qualities, and saved myself a lot of grief (and some money).
As for the "mystery metal" problem. There was a discussion about a similar problem a while ago. Somebody else had machining difficulties. At the time I suggested that the problem was an inclusion in the metal. Others suggested the problem was work hardening. Based on my latest disaster, I'm now leaning more toward the work-hardening theory.
Try to make a living, not a killing. -- Utah Phillips
Don't believe everything you know. -- Bumper sticker
Everybody is ignorant, only on different subjects. -- Will Rogers
Law of Logical Argument - Anything is possible if you don't know what you are talking about.