End Mills...2 Flute or 4 Flute

[snub]

I am looking at purchasing a set of large center cutting end mills ( 3/4" to 1-1/2"). I will only be using them on 6061 aluminum. They are offered in 2 flute and 4 flute so I am wondering which would be better. Do the 4 flute offer a better surface finish?  Any and all advice is appreciated.

[Chazz]

Actually, for Alu (6061 T6) I use 3 flute carbide mills at high RPMs.  I've found that 4 flute mills don't give me enough chip clearence time and 2 flute mills don't remove as much material (for the same given time) as the 3 flute mills.

My 2 pesos,
Chazz

[DaveH]

Snub,

Generally a 4 flute end mill used for profiling will give a better finish than a 2 flute.

For slotting a 2 flute cutter is the better option.

So it does depend on what they will be used for.

Maybe a compromise would be a 3 flute end mill. (Centre cutting)

 
DaveH

[Divided he ad]

I've always been of the notion (possibly wrong?) that


Endmills are 3/4 flute and will not plunge cut (well not very deep) and remove materials at differing rates. (Also there are roughing cutters too! .... Ribbed sides if you're looking.)

Slot drills are the 2 flute cutters that will plunge cut. (I.E. drill down into material as well as travel along)


Then some 3/4 flutes if they have a centre relief ground into them will plunge cut (I have a few 2nd hand ones ground like this.... They still shake if you try to go too deep though!)



That's what I've been led to believe through things I've read and what I can recall of what I've been told.....

Now for one of the trained machinists to correct all that and enlighten us all    


 




Ralph.

[Paddy OFernichur]

Aluminum needs chip clearance in the flutes. The most common failure of four-flute end mills in aluminum is chip packing in the flutes.

I don't necessarily advocate solid carbide, but it can be nice. The reason is that on most home shop machines you can never reach even 10% of the recommended range of cutting speeds. I do agree that 3-flute end mills can be very good, and there are many that are developed specifically for aluminum. Weldon (brand) "Ski-Kut" are an example of good parabolic flute HSS end mills, the first on the market with aluminum in mind.

I have some Cleveland (brand) HSS-PM (High Speed Steel-Powdered Metal) 3-flute end mills that were also made for milling aluminum. I believe that's PM T-15 steel they are made from. Wow, is all I can say! They PLOW through aluminum and I can't clog them if I tried. I have some carbide ones too, but I'd feel much worse if something happened to those. The carbide ones want to run at 10,000rpm and up, my Bridgeport tops out at about 2750. ;) Strange though, because the PM HSS end mills cost almost as much as good carbide, and are more money than cheap Chinese carbide.


The TiCN-coated PM-HSS Cleveland's are the 3 on the right. The longest is a Ø3/4", then 2 different length Ø5/8", all 3-flute and in the middle of the array are two 1/2" 2-flute ones.

One thing I would be wary of doing is to buy the "weekly special" kits from Chinese sources. One of those top-quality made-in-USA HSS-PM end mills may cost more than a 7-piece set of TiN-coated carbide, but it will outlast and out-perform the whole set.

Three-flute end mills can indeed plunge, and do it quite well. Look at how the end gashing is done on this 3-flute solid carbide end mill I have is done. Notice that ONE flute is coming across the center and will do most of the cutting on a plunge. Works GREAT! Not cheap!

[snub]

Thanks to all for the info. Much appreciated!

[Chazz]

One thing I forgot to mention, when it comes to mill cutters, or inserts for that matter  "You Get What You Paid For!" 

Like a lot of "First-time-on-a-budget-starting-a-hobby" machinist, I got those 'On Sale' 20 piece 2 or 4 flute mill cutter sets from 'Parts Unknown', since then, I was introduced to companies such as Kennametal, Sandvik-Coromat & Iscar (I'm not saying these are the 'only good ones') and when you do the math, (as an example) an 'Import' 1\2" x 2 flute mill lasted an afternoon, nay, 20 minutes on T6061-T6 before EBU, (Edge Build Up), since then, about a year and a half ago, I got a $65.00, 3 Flute Kennametal Mill and guess what?  I'm STILL using it! 

Another musing, regardless, mills or inserts, I'm (coming out of the closet)  I go both ways, less expensive HSS for roughing or interupted cuts and my carbides for continues or 'uninterrupted' cuts.

Enjoy,
Chazz


   

 

[steamman]

 :hammer:Hi I would indeed agree that you only get what you pay for,Dont be tempted by price and offers .you say you want to use the cutters on Aluminium ,due to the size range, are you using them for a project for yourself,also will they be used frequently or only occasionally  or on a Profit /non profit job that will be repetitive?all these factors should help to decide what outlay you can justify.With regard to the type of cutters if you are doing holes or slots then you need either a 2 flute slot drill or even better a 3flute you can use both these to advantage as you can both plunge and mill with just 1cutter,if you are to use them in the future consider getting a indexable cutter it will allow you greater scope as you can buy the inserts in various grades for different materials but beware these cutters are quite expensive but with care and forethought can save you time and money in the future providing you have the work for them and the Machine to give the Feeds and Speeds you need.

[PekkaNF]

Why set? Are you slotting for certain sizes and want to do without traverse? There are slot drills that will get you close enough for keyways.

I have very little experinece on aluminium, but I can tell that carbide stumpy mills are fine if your setup is rigid and you can run it fast. HSS works better for me because sometimes I need long relaitively slender cutters, mill is slow and some parts end up looking more like lace.

Buy least one good one, no matter what type it is and use it with seriousness. You don't want to break it, but if you'll have trouble you don't need to guess "is it the cheap tool of unknown properties" or "is me who can't use it".

Then I have one more consideration: I don't sharpen endmills, therefore coated are fine. If you sharpen, coating does not offer it's fullest. Then again quite a few better endmills are solid/polished for aluminium.

I don't actually know much, but I email my regular supplier (always the same person) and describe what I need and what is the envelope of my machine. I'll buy several different tools at the time and pick them up for 100-300 € every time. I need exact change, they don't keep change. I know it is peanuts for an industrial supplier, but I hope it least amuses them. But after I have broken half a dozen normal dormer drills and then get the 40€ drill that actually cuts it...very nice. Not so nice after that M12 special tap broke only after 10 uses when it finnaly met just a tad too tough MT3-shank - my false economy to buy cheap metal for good tools.

PekkaNF