As I am a hobbist, the only time cost is equal to my enjoyment.

I have been playing with a bar of 4140 in my bridgeport

I found the finish and the feed rate to be GOOD and SLOW... I'll be playing with this billet awhile, but who knows, I may come to like this steel

jeffe

Most of the machining I do is with 4140.or 4340. It does machine nice..Easy to get a good finish on a lathe even with a light depth of cut..Tough stuff too,the heat treated kind anyways..

If you're running a screw machine you'll not appreciate 4140 as you're probably used to 12L14 and there's a world of difference.

For a tool maker even prehardened 4140 isn't a challenge because these guys are used to tough steels....A-2, D-2 O-1 etc...

Keep the RPMs down and feed about .002" per tooth per Rev and use a little cutting oil and you'll have a fine finished product.

Read your posts and decided to add my .02 cents. When you take your time 4140 and even 4340 are not that bad to machine, nothing like P-20, Inconel, titanium, 316l or even 300M. However, when you start cutting this stuff commercially, speed becomes of the essence and thats when the headaches start. The list of "problem" alloys would startle most of the guys here who don't do this for a living..

Toolmaker

Thanks guys...

on 4140, i went into it prepared for D2 like machining.. and was pleasantly surprised to find it VERY much harder than 01 (is that stuff REALLY just plastic until it's heattreated? ?)

Like I said in my starting post, i KNOW it's fine and dandy for a hobbiest to take all the time required... as it does eat up a bunch of time... I am running it a 9/16"/m on the powerfeed, which is NOT problem, other than time... Hopefully it'll machine nearly as nice at 1.5" or 2" pm

thanks guys

jeffe

4140 is a fine steel and it has been available at least in the past in a free machining grade. The microstructure of 4140 and O1 in the annealed condition is quite different therefore machines differently.Heat treated the 4140 has a excellent combination of strength toughness cost etc and that's why it's used in so many ways from guns, high strength bolts ,aircraft tubing ,etc.

You'll appreciate 41L40 even better, due to it's added lead content. Surface feet can be upped over 1/2 again the normal rate. Coatings like TICN and TIAN are making the machining of 4140 much better for the production oriented machine shops. We've been able to achieve as much as 800 SFM on 416 stainless with these new coatings on Hanita endmills. Tool life is phenominal and I'm usually pushing .004-.006" per tooth on a 5 flute endmill in 3/8 diameter. In other words, 130 IPM is all too common and over 160 IPM with 1/2" endmills.
Tooling has come a long way in just the last 6 or 7 years, and it just keeps getting better.
I've been able to run as many as 3500 extractors on a single endmill that's roughing the outside contour. To say they are cost effective is an understatement.