Conventional Wisdom, right or wrong?

[KC2IXE]

I was doing some thinking today on "conventional wisdom" and milling machines

The conventional wisdom is that if you are slot milling, and need an accurate slot, you have to use a 2 flute end mill due to deflection of end mills that have More than 2 flutes

Today, we can use solid carbide end mills, and our mills themselves are often quite a bit more rigid than when the classic HSM authors were writing. How many of the old timers would have loved to have a machine as well built as one of our mill drills, never mind a Bridgeport (or better, a Bridgeport with ballscrews)?

I can't really see a solid carbide end mill "deflecting" enough to be measurable in the average shop

 

[greenlight]

Your title is misleading, but, in general, conventional wisdom is usually right. Any brainiac can figure out a better way to do a lot of things.

 

[kromeke]

I don't know if there is a firm "conventional wisdom" Lots of 6 of one and a half dozen of the other. There is more than one way to skin a cat.

I find that I believe that 3 flute mills work best, because two flutes are not engaging the sides of the slot at the same time. I think that an even # fluted mill tends to chatter more easily in slotting applications. A 5 flute might get too crowded, but it depends on the application.

This is mostly anecdotal evidence on my part. Of course, any slotting should be done with and undersized end mill, to allow for finish passes to clean up the sides.

I did some slots, roughly 5/8" in width in some 1" thick 304 stainless. I used a solid carbide 1/2" three flute mill (long LOC for the diameter). No problems. Worked as expected. Paid extra for a AlTiN coating. I think the coating helps prevent chip build up. And it is a hard coating.

Edit: in general, the more flutes, the stiffer the end mill. A 4 flute end mill is stiffer than a 2 flute. Slots are troublesome sometimes.

 

[precisionworks]

Paid extra for a AlTiN coating. I think the coating helps prevent chip build up. And it is a hard coating.

+1

That's my favorite ceramic coating, as the hotter it's run (within operating parameters) the better it does. Very nice for Type 316 & Ti 6-4, as well as most other tough to mill materials.

 

[gadget_lover]

I thought the reason for the two flute when cutting slots was that there was better clip clearance. It looks like two flute mills generally have deeper flutes.

I could, of course be wrong. 🙂

Daniel

 

[kromeke]

Two flute mills have deeper flutes, which makes them less stiff. I find 3 flute mills to be a better compromise.

In general, 2 flute for aluminum and plastics, 4 flute for steel. 3 flute works good for all three, but sometimes you want the extra stiffness of a 4 flute.

This is my general rule for end mills 3/4" diameter and less. Bigger end mills have more flutes, typically.