Machining 1020 Steel with Inserted Cutter

[Machine1]

I am face milling 1020 steel with an inserted cutter with a positive rake. Its all I got right now. I am having problems with finish and inserts chipping. I am looking to get a new cutter with a neg rake around 2 1/2 to 3. Do you have any suggestions on a new cutter or if I should go with a neg rake? Any comments would be much appreciated.

[HuFlungDung]

What brand and number is the tool you are using now? There are so many different kinds, it is tough to give any advice without knowing what it is. It could be due to choice of insert, the insert coating, overspeed, underspeed, overfeed, underfeed................and the moon isn't blue today, either.

[Machine1]

It is a SPKN 42 Iscar insert. The cutter is a no name. We have tried numerous feeds, speeds, DOC. And I messed up on the material, it is Cast Iron. Should I use a neg rake tool machinig Cast Iron and why if you know?

[HuFlungDung]

I'm not the expert in cast iron, but yes, a negative rake insert with no chipbreaker would be my choice. Cast iron is brittle, and will not benefit from a chipbreaker.

You may always suffer some breakout of the base metal where the cutter exits the work, so sometimes a special precautionary cut needs to be taken all around the part, so that the tool exits somewhere along the center of a side, rather than at an edge.

If you are milling cast iron near the surface of the casting, there may be some hardness, or inclusions that are hard on tool edges, too. Talk to your tool dealer about the proper grade of insert. There is so many changes in insert grades, I don't even attempt to keep up. I just ask for a higher grade number than was on the old box of inserts

[wms]

Machine 1,

Here is some info from the Iscar Book:..


First choice grade = IC910
second choice = IC4050
last choice = IC20 (uncoated)



speeds:
IC910 Grey cast = 1310 to 720 sfm
Nodular = 790 to 410 sfm

IC4050 Grey = 980 to 660
Nodular = 660 to 410.


chip load :

IC910 .004 to .012
IC4050 same

Feed:
IC910 .0028 to .0039 for finish up to .315 doc
IC4050 same

No info on IC20 but it would be less as it is uncoated.

Hope this is of some help.

[mrainey]

Hi,

It's been my experience that positive rake is vastly superior to negative for all milling. You get fewer cutting edges for your money, but get much higher productivity while being easier on the machine and workpiece. At the end of the month, you'll usually make more money with positive.

Of course, there will always be certain specialized exceptions to any rule.

[Machine1]

Thanks guys!! I ended up going with the Iscar TangMill with the I4050 grade insert. And they where having a special deal where I buy 30inserts and give them my old cutter and I get the new cutter head free. So hopefully it works out...Thanks