Thread: machining pre-heat treated 4140

I've never used any of this before. I've got carbide insert tooling for the lathe which should be fine, but I just realized I didn't buy a carbide center drill when I ordered the 1.5" OD bar of steel. Will using an HSS center drill just burn up the drill without making a center hole in the steel?

thanks,
Michael

HSS will work. Cobalt is better. It's really not that bad to work with it. It likes heavy cuts and it's possible to get a beautiful finish when pushing it (when using carbide).

Keep the surface speed around 60 FPM with HSS and you will be fine.

Dan

I cut a lot of this with WNMG KC9010 inserts. I get great insert life out of it at 450SFM, .080 deep, and .014"/rev. Makes a nice chip and I leave about .02 for finishing and do that at .003"/rev.

i use HSS drills and feed about .003/rev, beyond that is rough on the edges.

Thanks for the advice. I've seen people mention that the 4140HT stuff machines nicely with carbide and I wasn't sure if that had an implied "and burns up HSS."

I figured there was no sense destroying a HSS center drill if I could avoid it.

cheers,
Michael

I've worked with it in the past. In my experience, it's easier to get a good finish on the pre-hard than on soft 4140. It doesn't have as much of a tendency to tear.

You have to reduce the cutting speed a little but other than acting a little abrasive, 4140 HT machines ver well with HSS.

I've machined mounds of it with M2 cheapo HSS. Better tool steel will last longer in a given application but a quick stoning will put a fading tool back in service without removing it from the holder.

4140 is what we buy as EN19, preheat treated would have "T" suffix. My data says that EN19T has a hardness of 250 - 300 Brinnel and Tensile strength of 850-1000 MPa, therefore about double that of mild steels, but like Dave says it doesn't tear and you can really get good results. I use plenty in the T condition and find that I get great finishes. Virtually all my tools are insert type but I only have HSS centre drills and don't have a problem with the 4140.

The 4140PHT (pre heat treated) I buy machines as good or better than regular 4140. The PHT is "resulpherized", which makes machining fairly straightforward. Sulfer is like lead or tin...they're added to increase machinibility of steel.

Keep your HSS tools below 60 sfm and you'll be fine.

Interesting.

My limited experience was that it ate an HSS tool's edge every pass, past the point of stoning. But each pass was about 12" of 1 1/2" round, pulling off bright blue chips. Probably was running the HSS too fast.

Carbide was good, even with my lower powered smaller machine.

From the answers here I assume it will be ok to cut gears out of this with HSS gear cutters too ?

Originally Posted by Panza

From the answers here I assume it will be ok to cut gears out of this with HSS gear cutters too ?

I've done it several times, no issues. Just keep the SFM down, take a decent cut, and flood coolant.

Regards.

Mike

I used to write a lot of cnc programs for milling, often simple parts, but I used 50 sfm for all ferrous stuff. O1, D2,A2, 4140HT, S7, H13, M4, M42.

If you look them up you CAN go faster than that, but as a "one size fits all" speed that worked well to do (SFM*4/dia) formula in your head and have a simple job running without a calculator it worked fine. The Machine (Fadal) was not super rigid, so carbide ran at 150sfm, again conservative...but always worked with that machine.

Bill

4140 pre-heat treat machines very nice. It's not going to cut like 1018 CRS, but you can get aq really nice finish on it with taking your time. As far as the Suffix, 4140-PHT is pre-heat treat. 4140-HT is already heat treated.