Is It Possible To Face Mill Hardened 4140?

[Cody Killgore]

Hey guys,

I'm wanting to face mill the end of a piece of 5" square 4140. It is sitting at 55 HRC. Is this possible and, if so, what tool would you guys recommend?

Cody

 

[JimDawson]

It kind of depends on how much material you need to remove and maybe more importantly how big is your machine. If you have a benchtop mill then a 3/8 solid carbide endmill would probably do it. Maybe a small insert type face mill or flycutter with a carbide bit run at low speed would work. Reasonably high feed rates and slow spindle speed would be in in order, don't let it work harden. If you have a heaver machine, then a larger cutter would work.

In either case, be prepared to destroy a cutter or two.

 

[Wreck™Wreck]

Hey guys,

I'm wanting to face mill the end of a piece of 5" square 4140. It is sitting at 55 HRC. Is this possible and, if so, what tool would you guys recommend?

Cody

Yes, you will not like the cost of the ceramic inserts however, if the rigidity of the machine is questionable all bets are off.

Do a google search for hard machining, it mostly applies to turning however, I do a 50 peice lathe part every month or so, material is RC 45-50, NO COOLANT, the finish is exceptional and holds dimension very well. It sparks a good deal and the chips are glowing a dull red when they drop.

 

[Cody Killgore]

My mill is an Enco 100-1525. It is a "knee" style mill so it is heavier than the benchtop types. I want to take off about 0.035"

 

[chips&more]

55RC is pretty darn hard. Does a file just zing across it or does the file dig in at all? I would grind it. Maybe even go as far as to set-up a grinding cup wheel on your mill. Wrap every part of your mill to keep out the grinding swarf/crap and try it that way…Good Luck, Dave.

 

[Wreck™Wreck]

My mill is an Enco 100-1525. It is a "knee" style mill so it is heavier than the benchtop types. I want to take off about 0.035"

I would not try that with a facemill, but it may work well, have never done it that way, I would try a milti-insert face mill with only one insert installed which is a fly cutter.
If .035" is all that needs to come off buy a cheap fly cutter and one or two brazed carbide tools, knock .005" off at a time, grind tool and repeat, when you get down to ,005" or so left sneak up on it.002" at a time, grind tool again and take a slow finish cut .001" big. It won't work harden because it is already hard. This should result in an excellent finish.
Do not grind the tool sharp at the point, put a bit of flat on it.
Good Luck

 

[randyc]

Hi Cody, no offense but are you sure that it's at Rc 55 ? (If it is pre-hardened 4140 hardness, it's usually considerably lower than that.)

 

[Cody Killgore]

Thanks for all the tips guys! I think I may try a fly cutter and see how it goes from there.

Hi Cody, no offense but are you sure that it's at Rc 55 ? (If it is pre-hardened 4140 hardness, it's usually considerably lower than that.)

I had it professionally heat treated. They tested it after heat treat at HRC 55.

 

[JimDawson]

The one tool that nobody has mentioned yet is a surface grinder. It would take off 0.035 off in a few minutes.

 

[randyc]

Thanks for all the tips guys! I think I may try a fly cutter and see how it goes from there.

I had it professionally heat treated. They tested it after heat treat at HRC 55.

Sounds good Let us know how the flycutter works - I'd be wondering if all that pounding would chip the carbide. But might be OK for the small amount you're removing. I machine hardened O-1 with solid carbide end mills often with no difficulties - just another alternative.