Two flute v. four flute end mills

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KellyJones
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Two flute v. four flute end mills

Post by KellyJones » Sun May 10, 2020 6:05 pm

Thought I would post something I learned on anther forum here today.

Being a newbie, I went to machine some aluminum the other day. I selected a 3/16 diameter, 4 flute end mill. The job was to simply hog out a lot of material in a relatively small part. The part was too small to hold and use a bigger end mill.

As I got braver in increasing the depth and width of cut, something weird happened. The machine started vibrating and the feed got harder to turn. When I turned off the machine, imagine my surprise at finding all flutes filled with aluminum welded to
the cutter.

A google search for "welded aluminum cutter" quickly revealed that the 4 flute cutter wasn't allowing the chips to escape and the heat build up was welding the chips to the cutter. In addition to using a two flute cutter on aluminum, I found recommendations to increase feed and decrease speed when cutting aluminum. There was a comment that this is exactly the opposite of what newbies (like me) tend to do.

I share this for all the other newbies lurking here. I know Harold has tried to tell us about chip load before, but it never stuck with me until I saw the welded chips myself.
Kelly Jones, PE
A life spent making mistakes is not only more honorable, but more useful than a life spent doing nothing.
George Bernard Shaw
(1856-1950)

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GlennW
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Re: Two flute v. four flute end mills

Post by GlennW » Sun May 10, 2020 6:49 pm

A little WD-40 or coolant on the cutter will do wonders for the chip welding as well.
Glenn

Operating machines is perfectly safe......until you forget how dangerous it really is!

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SteveM
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Re: Two flute v. four flute end mills

Post by SteveM » Sun May 10, 2020 9:06 pm

The other thing that a 2-flute does for you is that if you are cutting a slot, it will come out closer to the diameter of the cutter than with a 4-flute.

Reason is that a 2-flute can cut in front OR on the sides, but not both.

A 4-flute is going to be cutting the sides while the flute cutting the front is cutting and deflecting the cutter sideways.

Steve

Harold_V
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Re: Two flute v. four flute end mills

Post by Harold_V » Mon May 11, 2020 1:49 am

Yeah, a four flute is generally a poor choice for aluminum, as it not only has limited space in the flutes to deal with the generated chip, but they are often finished, which encourages chip welding. If you're doing a lot of aluminum, it's not a bad idea to invest in an end mill made specifically for that material, as it not only has the proper relief for aluminum, but also polished flutes, which discourages chip welding.

If you must use a four flute, make sure you lessen the feed, and follow Glenn's advice. Aluminum behaves far better in the cut when it's lubricated. You can use WD-40 or kerosene. I often just use some used solvent (paint thinner) applied with an acid brush. You need not flood the cut.

If you tend to machine dry, you'll see an instant improvement in the finish and the way the cutting tool deals with the cut the moment you apply the brush. Give it a go if you haven't already. You'll be instantly convinced.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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SteveM
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Re: Two flute v. four flute end mills

Post by SteveM » Mon May 11, 2020 7:20 am

Harold_V wrote:
Mon May 11, 2020 1:49 am
...but also polished flutes, which discourages chip welding.
If I have a 2-flute end mill without polished flutes, could I use a dremel and polish them?

I'd have to stay away from the very edge to make sure I don't dull it.

Steve

rkcarguy
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Re: Two flute v. four flute end mills

Post by rkcarguy » Mon May 11, 2020 10:21 am

Yep, use two flute cutters for aluminum. I still have my bottle of A9 cutting oil I use for aluminum it must be 20 years old, a little goes a long way.
For blind slots, I always used a little air to clear the chips from the slot while I was cutting.
If you put that cutter back into a cut on a scrap piece of aluminum and lubricate it well with cutting oil, the flutes will probably clear and it will be ok.

Harold_V
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Re: Two flute v. four flute end mills

Post by Harold_V » Mon May 11, 2020 4:33 pm

SteveM wrote:
Mon May 11, 2020 7:20 am
Harold_V wrote:
Mon May 11, 2020 1:49 am
...but also polished flutes, which discourages chip welding.
If I have a 2-flute end mill without polished flutes, could I use a dremel and polish them?

I'd have to stay away from the very edge to make sure I don't dull it.
It stands to reason that anything you can do to the flute surface to decrease friction would be beneficial, but I strongly suspect that you'd have a little trouble avoiding the cutting edge. A great deal depends on one's approach, but you'd have to polish right up to the edge in order to make an acceptable difference. Might just be easier to use them as-is, and to procure one that is polished (and often with a different helix angle of the flute) when necessary. I can say that in my case, I usually get by nicely with a standard two flute and lubrication.

Now if a guy happens to have an air spindle and finger setup, the cutting edge could be restored easy enough. However, even that is not a great solution as rake angle of end mills is generated by the original making of the flutes. As you reduce cutter diameter, positive rake reduces, but that's just part of the problem, as, in effect, you are reducing the useful life of the end mill, and may even render it useless, depending on how much the cutting edge is rounded in the polishing process. When the edge is restored, if one removes enough material you've not only lost positive rake, but you've appreciably reduced chip clearance, so the end mill fails to perform acceptably. That's especially true of small diameter end mills, where the removal of even a few thou will render the end mill somewhat useless.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

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mcostello
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Re: Two flute v. four flute end mills

Post by mcostello » Mon May 11, 2020 9:16 pm

Cutting on a piece of steel will remove the aluminum, just remember to change speeds. :)

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