View Full Version : End Mill ? 2 Flute, 4 Flute.

Big T
01-01-2010, 01:47 PM
I have a few questions about various end mills. I have a 2hp, round column mill/drill. (Yes i know not the best, but it's what I got). What end mills do you use for mild steel?
2 flute are for keyways and slotting, but can you slot with a center cutting 4 flute?
I have some Chinese made HSS 2 and 4 flute end mill, but they dull quickly, and some corners break off. 1/2" end mill usually run 500 rpm with DOC .050".

Picked up some 4 and 5 flute US made carbide end mills, and they sure can cut. Should these be run dry? Should they be used at all on a mill/drill? Some guys told me that HSS should only be used on these machines. Is this right?

I usually climb mill for heavier cuts, and down mill for a light finishing pass. Is this proper?

01-01-2010, 02:45 PM
Narrow slots and keyways (1/8-1/4") I use four flute carbide spun up near max running dry.An air jet is nice to remove chips from the cut.One thing you want to avoid is recutting chips,that tends to chip the cutting edges reducing EM life considerably.

I pretty much use two flute for everything else.I do keep a sharp four flute in the common sizes,they are good for reaming accurate sized small holes in the mill.

Wet or dry?Carbide likes either flood or dry,but not intermittant as in a cup and brush application.Coolmist works,but I don't use it unless there is a vaccum hose nearby to remove the mist.Stuff can be rough on the lungs.

01-01-2010, 03:30 PM
4 flute endmills are not very good for cutting slots. The reason is, they like to wander off center. You will end up with a crooked slot.
2 flutes stay on center because both flutes are in contact at the same time. A 4 flute endmill has 3 flutes in contact, therefore 2 flutes are pulling 'left' , so it will wander.
4 flute endmills are best used for side milling.
2 flute for slotting.

01-01-2010, 03:44 PM
I don't use or have a lot of use for three or four flute endmills. I use two flutes for almost everything. I will use three or four flutes for a side cut but I do use four flute roughing mills a lot and their great for hogging out metal.

For keyways it's two flute only. I seldom use carbide, to expensive and they chip easy. I use cutting oil with endmills and with carbide air blast or a mist coolant system. Sometimes I use the mist with the HSS mills.

You need oil or coolant on endmills all the time.

Undercut for heavy cuts and climb cut for finish cuts. Just the opposite of what your doing.

01-01-2010, 04:16 PM
I have heard some guys say 3 flute end mills are good for keyways.
Myself, I prefer to use an undersize 2 flute cutter right down the middle of the keyway
and then finish both sides individually.
It takes a little longer but you get a nice keyway that is on center.


01-01-2010, 04:31 PM
Here is a link to a video on climb milling and some charts for end mill selection
that may help.


01-01-2010, 08:52 PM
That is a demo of a horizontal cutter but still relates to climb cutting with an endmill on it's side.

You need a very tight mill to climb cut because the cutter is always trying to pull the work into the cutter. That can lead to severe problems with a heavy cut and loose machine. Most mills do best undercutting on heavy cuts. To get a nice finish you can climb cut with a .001-.002" DOC at a reasonable feed and higher than normal rpm.

Three flute endmills will not cut an accurate width keyway. It will be over size as it will be with a four flute. Depending on how tight the quill is in the housing and the spindle bearings are will determine the oversize.

Even the two flute will cut oversize depending on how fast the feed is and the rpm. The faster the feed the more the mill is pushed to one side as it advances in the keyway. To slow an rpm will cause oversizing also. Reversing the feed the mill will then cut on the other side of the keyway and that further widens the keyway. Always cut a keyway in the same direction for each pass. Only take a reverse pass on the last cut with no depth of cut only cleaning up the slot.

If a keyway is cut with a two flute at reasonable rpm and feed the width is usually within specs. The key may not have to be hammered in the keyway but it will fit without slop, at least that is my experience.

Using an undersize endmill to cut a keyway works but it requires careful offsetting on each side to get the right width and takes a lot more time and is best done using a DRO.

Big T
01-01-2010, 09:28 PM
Thanks for the replys. Now I am getting confused with milling directions.
Up milling and climb milling are the same, right?
So is down milling also called conventional milling?
To get a smooth finishing pass you should climb mill?

01-01-2010, 10:26 PM
The terms I am used to is undercut and climbcut.

If you look at the video in post #6 you will see the teeth of the cutter are moving like it would pull the cutter along the surface of the work as the feed pushes the work toward the cutter and that is climb cutting.

Undercutting is when the cutter teeth would be pushing the work away from them while the feed is pushing the work toward the cutter.

What happens with climb cutting is if there is any slop in the lead screw and nut the cutter can pull the work in and climb on top of the work. When that happens the cutter gets broken and if it is on an arbor it may bend the arbor. If it's an endmill in a BridgePort it may knock the head out of tram and break the endmill and tear up the work.

Since undercutting is pushing the work away from the cutter it is less likely to damage anything.

Climb milling will most the time give a better finish but you have to be careful. You have to snug the gib clamps and feed the work very carefully to keep the cutter from sucking the work into it.

If you use the terms climbcutting and undercutting any machinist would know what your saying but they may not know what you mean if you say up milling or down milling.

01-01-2010, 10:37 PM
Thanks for the replys. Now I am getting confused with milling directions.
Up milling and climb milling are the same, right?
So is down milling also called conventional milling?
To get a smooth finishing pass you should climb mill?

Sorry to confuse you. Watch the video's again the first video is how you want to finish your cut.
The second video is how you want to machine.
Climb milling (first video) is not good for machining. Use this method for your finish

01-01-2010, 10:42 PM
If you use the terms climbcutting and undercutting any machinist would know what your saying but they may not know what you mean if you say up milling or down milling.

A guy in the UK made the video's Up Milling & Down Milling I also use the turm climb & undercutting.

Maybe the Up & Down is a UK thing

01-01-2010, 10:44 PM
That could be. Maybe John will chime in.

Big T
01-01-2010, 10:53 PM
A guy in the UK made the video's Up Milling & Down Milling I also use the turm climb & undercutting.

Maybe the Up & Down is a UK thing
I have the book Milling a complete course by Harold Hall. That is where he talks about up milling (climb milling) and down milling.

01-01-2010, 11:00 PM
Climb vs conventional milling is intresting as you can actualy feel the cutter try and feed the table with climb milling and resist it with conventional.

4 flutes are great for general perpose mild steel milling (with the mentioned exception of slots) as you can't take deep cuts in mild steel, you won't be generating a ton of chips, so 4 flutes lets you extract more material and have an endmill that (idealy) lasts 2x as long due to 2x as many cutting edges.

2 and 3 flutes are great for general perpose milling of aluminum, because its much softer you can take much deeper cuts and the amount of chips generated could start cloging the flutes of a 4 flute endmill, so 2 and 3 flute endmills actualy can extract more aluminum (endmilling that is. Side milling typicaly has enough free room that 4 and even larger 6 flute endmills can be used for better removal rates and finishs)
Aluminum also does not dull endmills as fast so the extra cutting edges of the 4+ flute endmills is not a great benifit.

01-01-2010, 11:06 PM
As long as you can keep it straight in your mind you can call it anything you want. If you start asking questions about it then you have to explain what you mean by any terms not familiar to others.

There are machining terms for the same operation that are different all over the world.

The people in one state I had a shop called a nut that goes on a bolt a tap. Well, to me it is a nut and when he asked for a 3/8" coarse tap I gave him a 3/8" coarse tap. He said, this is not a tap and I said it most certainly is. After he did some more explaining he got a 3/8" coarse nut for his bolt.

Big T
01-01-2010, 11:26 PM
Carld you are absolutly right about using the correct terminology. It really does vary a lot from region to region.

I will try and figure it out, but I thought that up milling and climb milling were the same.

Big T
01-01-2010, 11:34 PM
[QUOTE=Black_Moons]Climb vs conventional milling is intresting as you can actualy feel the cutter try and feed the table with climb milling and resist it with conventional.

Yes you are right, I have felt that many times.

01-01-2010, 11:40 PM
Carld: Hahahah.
I would of likey grumbled '... I must be working for a tap'

What did they call taps? 'threading thingys'?

01-02-2010, 12:02 AM
I'll agree with you Card, lootsa loost nuts out there running around lookin to get tapped HUH? :D I got another good one. Somebody will come up and say "I want a 1/2 inch bolt this long". I say OK and go get them a 1/2 inch bolt that long and when I give it to them and they say "that's not a 1/2 inch bolt" I'll say yeah it is. Then they will say "well a 1/2 inch wrench won't fit it"!!! Thats when you say something like what you really want is a 5/16 bolt, right?

Anyway, Climb cutting requires a real tight, rigid mill, with ballscrews and a rigid setup, especially in steel or a similar metal. i am of the opinion that if you climb cut in a light machine. Better to have a face shield on and your bullet proof vest cause the shrapnel is a gonna fly!!! :eek:

You can get away with it in a light machine if it's plastic easily, as long as you got a good grip on the workpiece. And even in aluminum as long as you don't get to carried away with it. But in anything any tuffer than that, better make it extremely light cuts. Or even better, leave the climb milling to the CNC machines. They are made for that kind of work. Actually the larger manual mills are set up with back-lash eliminators that make climb milling possible. But bear in mind that these are big heavy rigid machines, and even then you gotta be careful about it.

The only real advantage to climb milling is to get a cutter to last longer anyway. Something that the Home Shop Machinist should really NOT have to worry about.

Awwww hell why should I bother telling anybody this. Just let them try it, they'll know better than to try that one again, won't they?


01-02-2010, 12:10 AM
Climb milling does achive a better finish typicaly, and only needs to take finishing depth cuts to do it. This is generaly the only time you want to climb mill on a non ballscrew machine

Big T
01-02-2010, 01:58 PM
I got it straight now with climb cutting and under cutting. I was milling the right way, just had the terminology wrong!!
I use an air stream when milling with carbide , dont have a coolant system.
Thanks for the replys:)

01-02-2010, 03:33 PM
I'll never forget the first time I tried to climb cut the side of a bar to try to get a better finish when a fellow at work told me it would work. I thought I had it under control until the endmill got a grip on the work and sucked the slop out of the screw and nut and snapped the endmill off and sent it flying past me.

When I got settled down again I put another piece of metal in the mill and started working to get back to where I was before I tried to climb cut.

You can guess that I am not real fond of climb cutting with a BridgePort type mill and my mill is very tight while the one at work was loose. Even cutting a slot across a piece of steel that is open ended, when the mill breaks out of the side it can and usually does jump forward or back and bugger stuff up. I usually snug the gib lock before breaking through the side to avoid damaging the work or endmill.

Big T
01-02-2010, 05:48 PM
I had an end mill grab the work piece, swung the head 90* to the side, and therefore busted the endmill. It happened when I first got this mill/ drill( Just over a year ago). I am geussing I was climb cutting at the time.

Your Old Dog
01-02-2010, 09:06 PM
Most all of my problems early on were when trying to climb cut to get a better finish of to save time with moving the table to the other end. I almost never climb cut now as I don't like surprises!!

This has been a good thread for me. Several of you explained very well the big differences between 2 and 4 flute cutters and I never took the time to analyze it but what you all say makes a lot of sense to me.

01-02-2010, 09:07 PM
I climbed cut on a bridgeport clone all the time, although the backlash was about .006. I never really had any problems, except one time when I tried to use a roughing end mill on SS.

01-02-2010, 09:31 PM
As many have said, climb cutting on standard mills is ok at VERY light depths.

You can feel when its getting too deep because you'll notice it no longer takes any effort to feed the table! It should feel like your just normaly moving the table without cutting, then you know you are not going too deep or feeding to fast to climbcut on a manual mill. if it feels like the cutter is feeding the table for you.. well, it is :)
snugging up the gibs is another well used tatic to incress the force needed to move the table, letting you take slightly deeper cuts.. but at the expense of more wear to your ways.