Mystery metal - what is it?

[tkitta]

So I am trying to make my own rotary table for my mini-mill - a fun project. Its a small table as the mill is small - just 4 inches.

I got from the scrap yard a block of steel that was around 4 inches in diameter and maybe 4 inches long. The block looked like something used to be rolling on it - maybe part of a roller in a chassis of a large machine such as excavator - there were many similar looking parts around. So for few dollars I got my steel.

The lathe didn't have much of a problem turning the steel through I did get a carbide disposable bit dull. After turning it and getting it to shape I had to slice it in half as obviously I didn't need a 3 inch high rotary table surface. The band saw is 5 by 4 with stock blade - I got it to cut the steel but for some reason it cut at an angle with blade angling to the inside - even after making the blade very tight.

Back on a lathe I fixed the off-cut and time to mill.

And here is where issues started...

I was planning to cut 4 short rows 1/2 inch wide and then use a T-cutter for a slot. So I placed my 1/2 inch rough end-mill from HSS and just set it for 10/1000 of an inch 1/4 of a mm. Well, this is strange, instead of cutting the steel the bit "polished it"!

So I assumed the bit is just dull and got a 3/8 inch brand new HSS. It cut great for about 120/1000 maybe 3mm and then high end pitch sound made me realize its dull already - after cutting about 1 inch long row by 120/1000.

So I took out my beaten up carbide 3/8 which has only one tooth left - I broke the others off as I was playing around with it. It cut great for about 6/10 of an inch - then I switched to the other row and it got dull.

Well, I know my piece is not a high carbon one b/c the band saw cut it off... but it is clearly not so soft stuff...

So what am I dealing with?

 

[rmack898]

Since the material can be cut on the lathe and the band saw it doesn't seem to be a material issue.

Is the mill turning the right direction? After switching back and forth from using the back gear, I sometimes turn the mill in the wrong direction.

 

[dracozny]

The Round D2 Tool steel I have does exactly what you describe. it's actually easier to drill it and profile it, but parting it seems impossible. It actually has decimated saw blades and grinding wheels.

 

[JimDawson]

It sounds like you are work hardening the metal. Slow spindle speed with a reasonably high feed rate might fix the problem. You might also try taking a bigger bite if your mill will take it. It sounds like a 41xx series steel, or maybe 8620, something like that.

When cutting work hardening material, you can't baby the cut. You have to get a bit aggressive with it.

 

[Ebel440]

if your only going .o1 deep per pass your most likely work hardening it you need to cut deeper. What rpm were you using that may also be burning up the end mill