False economy....

[SGW]

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.

[3 Phase Lightbulb]

I haven't experienced using material myself with any kind of inclusions but I'm curious if you are using coolant or cutting fluid? It sounds like maybe you're running your tooling just above the right speed/feed(s)?

-Adrian

[imakechips]

It sounds to me like you had a problem with workhardening. A slightly dull cutting tool will ALWAYS exaggerate this condition, as will the lack(sometimes the presence) of coolant/cutting oil.

As an example, D2 tool steel will literally pop every tooth off a bandsaw blade if you use coolant, but if you run blade speed around 60-70 SFM and leave the coolant off it will cut all day.

[J Tiers]

Another point with mystery metal....

It seems to cause less trouble to start with slow RPM and slow feed, and increase if you can. The worst that usually causes is time loss, assuming you keep the cutter cutting, not just rubbing.

If you start fast, your first indication of trouble is often the sparks, or the heavy, steadily increasing pressure on feed required to cut.

[Paul Alciatore]

I had the same problem drilling a piece of known steel. Hit a hard spot. The drill broke. Tried a solid carbide drill. I still have the broken shank. Cut a new piece and moved on. I use that hunk of stock for backup on the drill press - always avoiding the area with the hard spot. It had a couple other holes in it.

Well, two drills are cheaper than two mills.

But "known alloys" are no guarantee.

Paul A.