4140 P/H vs. 1144 S/P machinability

[Barefoot]

Would like to hear your opinions on how 4140 pre-hard cuts compared to 1144 stress-proof on a milling machine.

I've milled plenty of 1144, 1018 CRS, 304, 303, but not one chip of 4140 ph. I'd like to use some on a project or two, but the whole pre-hard thing makes me want to run for the hills. Would hate to buy material only to find out it eats up cutters.

[Mcgyver]

The HT stuff is no big deal to machine, go a little slower perhaps, but I can't say I really notice much difference. Fast with carbide for a good finish, I'd put it halfway between 1018 and 1144 finish wise

[knedvecki]

What kind of milling are you talking about? End, side, face, and what type of tooling, carbide or quality HS such as T-15 or M-42? Are you using flood or mist coolant? And of course you know, that if you dwell too long in one place, it will work harden

[Bob La Londe]

4140HT is ok to mill. Not as easy as 1144, but you can make good parts if you are reasonable with the stuff.

On the lathe 1144 is easier to turn, but I can get a quality surface finish easier with 4140QT.

Never understood why they say HT vs QT vs PH. All of those tend to be 28-32 RC.

[754]

Just a guess but Likely similar to milling stainless..

[eKretz]

Don't worry about it. Lower your cutting speed and it will be just like cutting any other steel. Be conservative if you're not getting paid for the work: 250 SFM for carbide inserts, 50 SFM for HSS. You'll get plenty good tool life that way.

[Barefoot]

What kind of milling are you talking about? End, side, face, and what type of tooling, carbide or quality HS such as T-15 or M-42? Are you using flood or mist coolant? And of course you know, that if you dwell too long in one place, it will work harden

All 3...side, end, and facing with most likely a flycutter with micro 100 brazed bits. Far as end mills go, roughing with probly M42 and finishing with 4 flute carbide. No flood or mist here as either one causes rust under the vise before I have time to blink. Usually brush on a tap magic or molly dee w/ a light air nozzle to keep chips cleared..

[Barefoot]

By the replies so far, it doesn't sound as bad as I thought. Thanks to all.

Should've asked about this one as well. Does 4140 "move" like the other steels do, like if a hundred thou is taken off one side of a piece of 1/2 x 2 flatbar that's, oh, say 6" long? I've learned the hard way to allow for skimming the bowed material off after any kind of heavy one sided stock removal.

[nickel-city-fab]

I figured theres a reason why 4140HT is so popular. I haven't heard any bad stories about it moving.

[knedvecki]

Don't worry about it. Lower your cutting speed and it will be just like cutting any other steel. Be conservative if you're not getting paid for the work: 250 SFM for carbide inserts, 50 SFM for HSS. You'll get plenty good tool life that way.

Without coolant this will work fine. Conventional cuts with end mills, unless cutting off an end upright. There are always stresses built up in rolled stock which can / will cause movement if not following proper machining procedures.

[eKretz]

Any steel can move. The particular alloy isn't usually to blame, it's the forming process. The worst culprit is almost always cold-rolled. Hot rolled will move too, but not nearly as much. The worst movement is usually when the first "skin" is taken off. Less afterward but it can and will still move. If you have something very fussy, you should rough complete and then spring the work, reset with lighter clamping pressure in a relaxed position and then finish. Very large work needs to be roughed complete, then stress relieved, then clamped in a relaxed position and finished.

This movement has little to do with machining procedures. Poor practice can make it a little worse, but it happens regardless. The movement occurs when internal stresses are relieved by material being cut away - this happens no matter what procedure is used.

As regards work hardening - very uncommon with 4140 in my experience. And I've machined many thousands of pounds worth. Don't use dull tools and you should never have a problem with that in 4140. Climb or conventional mill at your leisure. If you're cutting stainless, then you need to watch out for tool dwell time and be sure to keep the tool cutting.

[dian]

" Conventional cuts with end mills":

why are you saying that?

[Sparky_NY]

Nobody mentioned it but the type of machine being used makes a difference too. Being tougher materials, higher cutting forces are at play. 4140PH machines beautifully on a reasonably rigid machine. Years ago I remember having lot of issues on a real light lathe. A 100lb table top mill may not like it either. I love the finishes obtained with 4140PH, mirror like if you use the right speeds/feeds etc.

[knedvecki]

" Conventional cuts with end mills":

why are you saying that?

Conventional VS Climb milling. Climb milling is where if the table was let free to move, the cutter would walk along on the stock.

[CCWKen]

I'm working on a chunk of 4140 PH right now. Just finished the lathe work and will move to the mill to finish some keyways and holes. What I've found is it machines great on my 12x36 Atlas/Craftsman late with carbide but it will eat HSS for breakfast. It's coming out like the surface of CD. I may have to sand blast it to get rid of the shine! My lathe really isn't large or heavy enough to take much of a cut. I could only manage .015" on a pass. .020 would chatter and slip the belt. (You can only get a link belt so tight.) And I was working at the maximum of 6" diameter stock. Even that took a special setup for the tool post.