Cutter body steel selection

[tcncj]

Hi
I need to make a few custom cutter bodies for inserts.
Which steel is generaly used for cutter bodies?
Most of the time i make them out of 4140 PH. But maybe there is a better option?
Just curious from which steel they are made.

 

[jscpm]

The alloys used by insert companies are proprietary. That is part of their secret sauce for getting money out of you.

Anything rigid will work. Cast iron. Carbide. Hardened tool steel. A steel alloy that flexes will be more like to vibrate and chatter. If it were me, I would try an ordinary tool steel like A6 and temper to purple, which is a compromise between rigidity and toughness. Insert companies don't use tempered steel because that would be expensive and cut into their profits.

 

[Milland]

The alloys used by insert companies are proprietary. That is part of their secret sauce for getting money out of you.

Anything rigid will work. Cast iron. Carbide. Hardened tool steel. A steel alloy that flexes will be more like to vibrate and chatter. If it were me, I would try an ordinary tool steel like A6 and temper to purple, which is a compromise between rigidity and toughness. Insert companies don't use tempered steel because that would be expensive and cut into their profits.

Not to be a jerk (but I am), but this has been gone over many times. All steels have essentially the same stiffness. Hardness, which does not factor significantly in stiffness, can vary with alloy and heat treatment. With more hardness typically more deflection of a given section of steel can be withstood before permanent (plastic) deformation takes place.

Flexing itself is a matter of geometry over material. You can change stiffness characteristics vastly more with design than changing out steel alloys.

Tempering is typically a function of drawing down the steel hardness after HT and furthering a desired metallurgical structure, it's part of the cost of heat treating and isn't expensive in and of itself.

4140 PH is around RC 28-32 (some variation exists), it's fine for your needs. The big advantage is you can machine it and go, no need to worry about HT or additional cutting or grinding afterwards.

 

[jscpm]

Not to be a jerk (but I am), but this has been gone over many times. All steels have essentially the same stiffness. Hardness, which does not factor significantly in stiffness, can vary with alloy and heat treatment. With more hardness typically more deflection of a given section of steel can be withstood before permanent (plastic) deformation takes place.

Flexing itself is a matter of geometry over material. You can change stiffness characteristics vastly more with design than changing out steel alloys.

Tempering is typically a function of drawing down the steel hardness after HT and furthering a desired metallurgical structure, it's part of the cost of heat treating and isn't expensive in and of itself.

4140 PH is around RC 28-32 (some variation exists), it's fine for your needs. The big advantage is you can machine it and go, no need to worry about HT or additional cutting or grinding afterwards.

Hmm, I never knew. Damn, to think of all that time I wasted hardening boring bars and mandrels. This knowledge is going to save me a lot of time.

 

[Milland]

Hmm, I never knew. Damn, to think of all that time I wasted hardening boring bars and mandrels. This knowledge is going to save me a lot of time.

Cool. You'll get more wear life with a hardened part, but the stiffness will be pretty much identical up to the plastic deformation limit. If the part will see a lot of stress it may still be worthwhile to harden it.

 

[Hardplates]

Not to be a jerk (but I am), but this has been gone over many times. All steels have essentially the same stiffness. Hardness, which does not factor significantly in stiffness, can vary with alloy and heat treatment. With more hardness typically more deflection of a given section of steel can be withstood before permanent (plastic) deformation takes place.

Flexing itself is a matter of geometry over material. You can change stiffness characteristics vastly more with design than changing out steel alloys.

Tempering is typically a function of drawing down the steel hardness after HT and furthering a desired metallurgical structure, it's part of the cost of heat treating and isn't expensive in and of itself.

4140 PH is around RC 28-32 (some variation exists), it's fine for your needs. The big advantage is you can machine it and go, no need to worry about HT or additional cutting or grinding afterwards.

^Correct, this is measured in Young's modulus of elasticity

 

[Nerdlinger]

^Correct, this is measured in Young's modulus of elasticity

Yeah, it's really weird...if you pull on two cantilevered beams, one hardened and one not, with the same amount of force they will both deflect the same amount as long as you do not exceed the elastic limit of either. The hardened one will just be able to deflect further while still being able to relax to its original position.

We've got a bar of prehard 4340 that we've been using for our homemade cutter bodies that we use almost every day...seems to work pretty well.

 

[richard newman]

I posted a query about this years ago, for a boring bar I was going to make. Took a while to get my head around it, just seems so counter intuitive...

 

[john.k]

A commmon mode of failure of boring bars is wear by chip abrasion.....so the surface around the insert should be hard as you can make it.....commercial tooling is generally very hard .

 

[gbent]

What is the life expectancy of the tool? If chip wash is a problem, use a steel that can be heat treated to a higher hardness. However, that will make it more difficult to do weld repairs.

How have previously made bars failed? If they have failed because of obsolesce, better steel will be a waste.

 

[dian]

if the screws mushroom into a soft toolholder its no fun.

 

[CarbideBob]

Most decent lathe holders are 4140 hardened to mid 40s to low 50s.
Problem here is that shanks warp in heat treat so the process is to make the shank .010 oversize and then finish it to the insert pocket after heat treat to bring in the F an H dimensions.
Milling cutters are often made of PH as this finish step difficult with multiple pockets.
For added help with chip wash and such nitriding, hard chrome, or even PVD Tin is applied to the finished tool.
Boring bars are done both ways.

IMO Pre-hard 4140 is just fine and a good compromise for one offs. Does not machine as nicely as dead soft but the heat treat and finish step is skipped.
In a softer holder with time the insert will brinnell itself into the pocket and ends up sloppy. Not a problem lower usage tool.
Pin locks also care a whole lot about that tiny cone being harder.

Opinions will vary, I've see S7, 8620 and you name it making OEM holders.
Bob

 

[Hardplates]

Most decent lathe holders are 4140 hardened to mid 40s to low 50s.

Thats kind of what I thought since I've cut many bars on a bandsaw. For the hell of it I just threw a Sandvik 1 1/4" bar on the hardness tester and it came back right at 47C

 

[Phil in Montana]

I use 8620, and heat treat when done, very easy to machine and is one of the most forgiving to heat treat and very weldable before heat treating...Phil

 

[ygolohcysp]

Not to be a jerk (but I am), but this has been gone over many times. All steels have essentially the same stiffness. Hardness, which does not factor significantly in stiffness, can vary with alloy and heat treatment. With more hardness typically more deflection of a given section of steel can be withstood before permanent (plastic) deformation takes place.

Flexing itself is a matter of geometry over material. You can change stiffness characteristics vastly more with design than changing out steel alloys.

Tempering is typically a function of drawing down the steel hardness after HT and furthering a desired metallurgical structure, it's part of the cost of heat treating and isn't expensive in and of itself.

4140 PH is around RC 28-32 (some variation exists), it's fine for your needs. The big advantage is you can machine it and go, no need to worry about HT or additional cutting or grinding afterwards.

I'm not sure all of this is correct. I'm no metallurgist here, but all steels don't have the same stiffness. Correct that hardness doesn't change the shape of the slope in the graph for the modulus of elasticity, it just raises the amount of strain the material can take before the deformation happens. So if you want something more rigid, you have to choose a more rigid material. Though you're also right in that geometry can also change that. Kind of like how lifting bars are better hollow. Solid is easier to bend.

 

[Milland]

I'm not sure all of this is correct. I'm no metallurgist here, but all steels don't have the same stiffness. Correct that hardness doesn't change the shape of the slope in the graph for the modulus of elasticity, it just raises the amount of strain the material can take before the deformation happens. So if you want something more rigid, you have to choose a more rigid material. Though you're also right in that geometry can also change that. Kind of like how lifting bars are better hollow. Solid is easier to bend.

Sorry, for all reasonable compositions (I.E. not calling an alloy with 50% tungsten a "steel"), all steels have roughly the same stiffness:

Metal Strength and Stiffness: What’s the Difference?

"All steel has approximately the same stiffness, but comes in many different strengths depending on the alloying metals used."

[Approximately 15% down the page]

Search for the statement yourself, you'll find plenty of references.

 

[ChipSplitter]

I'm not sure all of this is correct. I'm no metallurgist here, but all steels don't have the same stiffness. Correct that hardness doesn't change the shape of the slope in the graph for the modulus of elasticity, it just raises the amount of strain the material can take before the deformation happens. So if you want something more rigid, you have to choose a more rigid material. Though you're also right in that geometry can also change that. Kind of like how lifting bars are better hollow. Solid is easier to bend.

Nooope........ Young's Modulus of Elasticity for Metals and Alloys

The three top lines are all steel. There is some variation at 100 deg. (27.5 - 30.5) but the general theory holds true. If you look at carbon steel vs. Cr-Mo steel you have about half of that. (29 - 30.5)

Yes, it makes a difference......like 4%. Not enough to be meaningful.

 

[ygolohcysp]

Thanks for the responses. I uh ... have kind of already read up on the subject.

Also, as for the non-meaningful 4% difference. That's only what's listed on that chart. And it's a difference of 4 units. 4GPa is not the same as 4%.

But, whatever.

 

[Milland]

Thanks for the responses. I uh ... have kind of already read up on the subject.

So, should we, uh, take your word on this, or all the references available, and the established knowledge of metallurgists and engineers?

 

[ChipSplitter]

Thanks for the responses. I uh ... have kind of already read up on the subject.

Also, as for the non-meaningful 4% difference. That's only what's listed on that chart. And it's a difference of 4 units. 4GPa is not the same as 4%.

But, whatever.

Ummm........nooooooooooo.........

30.5 minus 29 equals 1.5 GPa

1.5 divided by 30.5 equals 4.9% (so 5% instead of 4%....) What part of numbers don't you understand?

I can guarantee that other factors like insert type, speeds/feeds/DOC, tool projection, and harmonics will make more than a 5% difference.