Determining Material to Calculate SFM

[kirker912]

I'm having a problem getting the correct feeds and speeds because I do not know the properties of the material being machined.

What tests or other methods do you use when when determining properties of a piece of metal to be machined? The only one I keep hearing is to see if a file cuts it which basically divides steel up into two categories, hard and soft, and a third category for aluminum. I would like to be a little more exact because 'soft' still leave a large range of feeds and speeds to cut at.

This problem stems from me making home items from scrap material. In production or in college I always known the properties of the material and can lookup the speed and feed. A special note to anyone in college...enjoy all the tools at your disposal because chances are later in life you won't have a rockwell hardness tester, microscope, acid etch, tempering ovens....

If someone has links to a thread about this elsewhere please post them. I've been searching and have come up empty handed.

[Cruiser]

The problem here stems from your term of "scrap" matr'l. If it is drops from saw work it would be normalized. If it is from machine parts & shafts then it could be heat treated or cased. Then, are you using carbide ? or hss ?
I wouldn't worry too much about saw drops when using carbide, just stay moderate in speed and chip load.
If using something that is heat treated or cased then, also using carbide, I'd keep chip load low and speed low and keep an eye on the chips coming off and an ear tuned in. The chips coming off too hot and blue is an idication of something pretty resistant to cutting and so would slow down some more.
If the chips coming off the cutter are taking a second or two to turn blue then you are about right.
Another way of testing steels is to use the grinder test and watch the spark pattern or fan array. Soft steel will have less of a spark out than something of high carbon and hardness. This testing method is an old school method and there used to be charts showing examples and maybe a mention in machinery handbooks of old.
It is also possible to get a rough idea by using a sharp punch and a light hammer, but you need something to compare it too or you will still be wondering what ya got.

[kirker912]

My scrap varies widely. Some of it I buy, some I save from other projects, some of it friends run across and save for me.

I did find a short description of the 'grinder test' here:
Spark testing - Wikipedia, the free encyclopedia

I've often wondered about the punch idea. I was thinking of having a few different auto center punches with different springs in them. Like a very rough rockwell tester.

On the lathe I use HSS for most things and carbide inserts for anything important. On the mill I do all aluminum with 2 flute HSS, and steel with the cheaper TiN coated end mills(I'm looking for some new endmills as soon as my QCT holders are finished).