Indexable Milling Inserts For Steel?

[Dan_S]

I made some more progress on this issue tonight, after contacting Korloy directly yesterday. The first interesting thing I found out, is that the X45 chipbreaker is a special one and not normally for-sale. Thus why they are so readily available on eBay wasn't something the sales representative wanted to talk about.

I did however get the corrected milling parameters for the inserts from him.
P
* Vc 200 - 1150 sfm
* Fz = 0.002 - 0.014 ipt
* Ap = 0.004 - 0.235 in

M
* Vc = 200 - 920 sfm
* Fz = 0.002 - 0.014 ipt
* Ap = 0.004 - 0.235 in

With the corrected info in hand, and a scratch pad i set about systematically testing the working envelope of the inserts. The stock I ran the tests with A36, i figured if i could get a good finish on that horrendous stuff, I could get a good finish on just about anything. After almost 4 dozen test cuts, I got what i think is pretty much the best finish possible with these inserts on my machine. The parameters that worked best, are as follows:

I had to remove all the insets except for one so i could get a high chip-load.
Vc = 774 sfm - this is as fast as my machine can spin (1970 rpm) a 1.5" diameter cutter.
Fc = 0.0147 ipt - This is as fast I could feed (rapid traverse ~29 ipm), given the spindle speed. Chipload seemed to have the greatest effect on surface finish.
Ap = 0.010 in - depth of cut seemed to have the least effect on the surface finish. anything above 0.005" (smeared bellow this), and less than 0.040" (started self feeding above this because of the climb cut) worked equally well.

These two photos show the surface finish I got. Though it looks worse than the 4140, it's actually a smoother finish. I cant feel the ridges with my finger tips, and I can just barely feel them with my fingernail if i scratch it just so.



To get a better finish I would need to do the following.

1) switch to an insert with a better edge perpetration, as this "S" style is probably the worst one possible for generating a good shearing action (see diagram). A "T" or ideally an "F" preparation would be better, but more fragile.

2) Use a larger face mill. A 2" would let me run right at the maximum sfm the inserts can handle, and a 2.5" or 3" would let me drop down a spindle speed and still maintain a high sfm. An added bonus would be that I could start using multiple inserts, or still use one insert, and feed slower.

unless I can find something cheaper I'll bite the bullet after xmas, and drop the cash for the iscar insets, as they are the only manufacture i have found so far that uses the F& T edge preparations.
http://www.iscar.com/eCatalog/Family.aspx?fnum=348&mapp=ML&app=61&GFSTYP=I
http://www.iscar.com/eCatalog/Item.aspx?cat=5699770&fnum=1526&mapp=ML
http://www.iscar.com/eCatalog/Item.aspx?cat=5602918&fnum=1526&mapp=ML

 

[Thad]

Too much SFM, did you look at the material group chart in the iscar book? It better defines a sfm parameter for the specific material. In my opinion I wouldnt go over 2" shell mill on R8, slow down your sfm and increase your DOC. It will really improve finish if you can bury the corner radius

 

[AspenM/C]

What's everybody using to get a good surface finish on steel?

I've been playing around with a 1-1/2" 45 degree face mill, that uses SEHT inserts, and while I can get an ok surface finish it's nothing to brag about. If i switch over to the aluminum inserts I get a fabulous finish on every grade of aluminum I've tried.

This is the finish I got in hot rolled 4140, the close up looks worse than it actually is. Sometimes the middle of the cut has a glass smooth finish to the touch. The roughness is always at begging & end of the cut, when only one insert is engaging the work at a time.. I think the issue is that wiper style insert is just to much for my machine in steel.
View attachment 116015

View attachment 116016

this is the face mill & inserts.
View attachment 116017
View attachment 116018

What's everybody using to get a good surface finish on steel?

I've been playing around with a 1-1/2" 45 degree face mill, that uses SEHT inserts, and while I can get an ok surface finish it's nothing to brag about. If i switch over to the aluminum inserts I get a fabulous finish on every grade of aluminum I've tried.

This is the finish I got in hot rolled 4140, the close up looks worse than it actually is. Sometimes the middle of the cut has a glass smooth finish to the touch. The roughness is always at begging & end of the cut, when only one insert is engaging the work at a time.. I think the issue is that wiper style insert is just to much for my machine in steel.
View attachment 116015

View attachment 116016

this is the face mill & inserts.
View attachment 116017
View attachment 116018

As you found going to a single point tool will give the most consistent finish, any multiple insert tool will have one insert higher than the rest due to combined tolerances. Add that to an older and somewhat light machine tool. You can step up to a ground high tolerance wiper flat but again only 1insert is actually wiping. Most any cutter is going to load and unload when entering and exiting a cut, this can be mitigated with a light .015" depth as a finish pass. If you have an insert with a 010" edge prep you will essentially be smearing the metal back into to the surface though, the benefit of a ground edge is a better shearing action. Different steels will have varying characteristics, typically lower carbon steels will shear easily and respond to a sharper edge, harder steels will benefit from a somewhat protected edge. Inserts designed for light cuts in stainless will give decent results in most steels given machine and workpiece rigidity. For an older manual knee mill excellent results can still be had with a TPU insert, again using a single insert in a cutter body.
No single method or insert works every time for everything, that's the joy of applying experience and experimenting, and the frustration when doing all the right things and still not getting the desired results.
That was my daily life for near 40 years as a technical rep.

 

[Richard White (richardsrelics)]

Not sure what you are expecting, but I was taught 30+ years ago, that if you are looking for a nice finish..... grind it....Milling is for nothing more that stock removal, grinding is for precision and looks, and then there is polishing if you need it to look really nice. I have yet to get a mirror finish off of a milling machine. It is just plain not intended for that purpose. just my .02 pennies

 

[Dan_S]

I played with this off and on, and the best finish I've gotten was with a single insert, but i attribute that to getting a better chip load than anything else.

I've pondered buying a small left handed turning tool that i can run in my fly cutters, because even hss don't leave a very nice finish.
http://www.shars.com/products/index...-small-screw-lock-positive-insert-tool-holder

I've always gotten an excellent surface finished on my lathe using inserts, and my lathe is a puny little 8x. Even in hot rolled 4140 I get good finishes, I just crank it all the way up, and keep the doc above 0.010"

 

[AspenM/C]

I played with this off and on, and the best finish I've gotten was with a single insert, but i attribute that to getting a better chip load than anything else.

I've pondered buying a small left handed turning tool that i can run in my fly cutters, because even hss don't leave a very nice finish.
http://www.shars.com/products/index...-small-screw-lock-positive-insert-tool-holder

I've always gotten an excellent surface finished on my lathe using inserts, and my lathe is a puny little 8x. Even in hot rolled 4140 I get good finishes, I just crank it all the way up, and keep the doc above 0.010"

A different dynamic occurring with a lathe, different address to an insert etc. Milling throws in so many variables with varying chip thickness, constant entering and exiting cut not to mention the confusing array of insert geometries and edge preps as well as surface area . With a lathe there is generally speed feed depth of cut and insert radius to be concerned with , and a relatively constant chip formation across a smallish area.

 

[Dan_S]

A different dynamic occurring with a lathe, different address to an insert etc. Milling throws in so many variables with varying chip thickness, constant entering and exiting cut not to mention the confusing array of insert geometries and edge preps as well as surface area . With a lathe there is generally speed feed depth of cut and insert radius to be concerned with , and a relatively constant chip formation across a smallish area.

All true,

I've just noticed people getting much better surface finishes in steel using fly cutters with brazed or insert lathe tools.
like this for example, I'd be pleases as punch with this finish. Suburban tolls fly cutter seems to produce good results as well.

 

[Dan_S]

here are some more!

based on a the blue haze around the fly cutter, i think its safe to assume this one is a brazed bit.

and this is the suburban tool fly cutter, though this is way to wide a cut for a Bridgeport imo.

 

[benmychree]

Not sure what you are expecting, but I was taught 30+ years ago, that if you are looking for a nice finish..... grind it....Milling is for nothing more that stock removal, grinding is for precision and looks, and then there is polishing if you need it to look really nice. I have yet to get a mirror finish off of a milling machine. It is just plain not intended for that purpose. just my .02 pennies

Thank you for saying what I have been thinking while reading this post!