View Full Version : characteristics of end cutting mills

old mart
05-02-2016, 02:22 PM
Iv'e just twigged the differences between two, three and four flute end cutting mills. Not just the number of flutes, but the way they cut, particularly slotting in one pass. I wonder how many inexperienced mill users like me, don't know?

05-02-2016, 02:42 PM
53,494 as of noon today.
Globally as a whole (as opposed to just inexperienced machinists), 6,954,833,761 +/- 5.

05-02-2016, 03:18 PM
Two flute for aluminum, four flute for steel, three flute for either.

In practice I use whatever I have on hand, but if I'm ordering end mills that's what I go by.

old mart
05-02-2016, 03:33 PM
I was thinking of the way they cut at the end of the slot.

05-02-2016, 03:35 PM
That's a little oversimplified. The two characteristics to pay attention to IMO are whether it's center cutting and whether a slot you're cutting needs to be an accurate width.

Two flute cutters are commonly center cutting. With more flutes they might or might not. So if you're plunge cutting into a pocket you need a center cutting mill or you need to ramp down to a cutting depth rather than plunging straight down. If the mill isn't center cutting it will only go a few thousandths straight down before it quits.

Next is number of flutes versus slot width. If I need a slot to be an accurate width there can be two strategies. A four flute re-ground cutter will make an undersize slot that I can then whittle out to width. If the four flute is the same diameter as the slot I need it will cut oversize from deflection. Think about it. As the cutting edge moves into the cut in the direction of feed there will be a reaction that will try to push the cutter in the opposite direction of the rotation. Thus the oversize. A two or three flute cutter doesn't have one flute cutting the side at exactly the same time as another cutting in the feed direction. I presume this is why Brits often call two flute cutters slot drills. They will drill straight down and they're good for slot width.

old mart
05-02-2016, 03:44 PM
That's exactly it, TGTool.

05-02-2016, 08:23 PM
particularly slotting in one pass.

not saying I never do it, but unless its a bill gates quality slot (quick and dirty) its best not to cut in one pass. Do the finish cut on each side after measuring so you know the slot is on size, where its suppose to be and with a good finish.

05-02-2016, 11:47 PM
Quickest and easiest is a roughing cutter, usually full depth, finished for size and shine with a standard endmill. If dimension and finish have .002 leeway, one pass with a fine tooth rougher is almost always enough. The cutting pressures and therefore deflection are minimal with this type cutter even with four flutes.

old mart
05-03-2016, 08:12 AM
So far I've never had to produce a tight tolerance slot, I will definitely creep up on it if I do.

05-03-2016, 01:08 PM
It works best when you creep up on the mill from behind the lathe. It can clearly see you coming if you start by the drill press.