Let me know if I need to find another message board for this kind of question.  I've been playing around with cutting on a block of metal of unknown origin.  Even at very slow speeds, I'm ruining end mills.  I suspect that this steel is much harder than what I want to be playing with right now.
As I search the web, I find different kinds of steel; hot rolled, cold rolled, different machinability, etc.  Can someone give me a pointer as to what steel I should get to continue my experimentation?  thanks much

I meant to add that at very slow speeds and small bites, I'm getting burnt chips as well.  This is an RF-45 mill I just CNC'd with help from this board.

It's much better to test on known material.

Are you new to milling? Have you a speed and feed chart?

Have you tried the same tool and metal by hand?

Burnt chips is a sign of too much speed/not enough feed.

On an HSS cutter you want straw coloured chips, maybe a bit darker but not purple.

What size cutter are you testing on?

Agree with testing known material.  What would be a good steel to start with?  For instance, if I was going to build a train engine; one with say, 5" diameter wheels.  What would be the best material to mill the wheels out of?

I am new to milling.  I know relatively nothing about it, but am a good learner.  I CNC'd the mill and have learned the basics of getting it to make all its moves, etc, but now I need to get into learning how to actually mill with it.

I have not tried this piece of steel by hand, but probably won't because it's a rusty piece of scrap out of my pile from behind the garage and I don't know what it is or where it came from.  I'd rather work with a known quantity.

I've been using a 1/2" cutter.  Have ruined two of them now, so the local sharpening guy is getting some business.

I see feed and speed charts on the web; any favorites here?  I assume that before the chart is useful, I would have to know what steel I'm using.

Thanks for the feedback, rex

I'm a manual machinist, the only CNC I have is my plasma table so I won't be able to offer too much advice.

Yes, get a. Speed and feed chart but be careful as they tend to be biased for industry - maximum metal removal rates on big machines.

Googling speed and feed or milling speeds etc should bring up a wealth of info, it can all be calculated using metal type, cutter type and size plus chip loading per tooth etc, formulas are not too difficult once you get used to it.

SFM = 0.262 x D x RPM
RPM = (3.82 x SFM) / D
IPR = IPM / RPM or CHIP LOAD x F
IPM = RPM. x IPR
CHIP LOAD = IPM / (RPM x F) or IPR / F

For mild steel and 1/2" tool, I would guess around 80 feet per minute surface speed which gives around 600rpm.

You have make the tool cut, don't let it rub, taking tiny cuts is the best way to blunt a tool, it needs to work within a window of speed/feed/depth of cut combinations.

Check out eBay for small cuts of mild steel, something like 230m07 one EN1A in old style is a pretty safe bet to play with.

If you can find a slide-rule type speed and feed tool on eBay, they are great.

A simple test is to take a file or hacksaw to it.  If it files reasonably easily and generates filings it's probably machinable too.  If you are going to buy some steel to practice on, I'd suggest (in the UK) some free machining mild steel, or just some CRS.  You can get a cheap/free app for an iPad or iPhone called FSWizard Lite that will give you feeds and speeds for a given material, cutter etc.