# Choosing Length of Cut for Endmills?



## Michael303 (May 27, 2021)

I'm looking to buy some endmills in 1/16" increments from 1/8" to 1/2" for an upcoming machine shop class and just for general use, not a specific job.

Is there a consensus or theory on whether it's better to spend a little more to get end mills with a longer length of cut or would it be beneficial to buy more stubby length tooling because (I'm assuming?) it's probably a little less likely to break?

Any feedback is appreciated.


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## benmychree (May 27, 2021)

You got it nailed!  The longer they are, the easier to break.  Use the shortest tooling that will do the job.


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## mikey (May 27, 2021)

Best practice is to use the shortest flute length possible to reduce deflection. This improves accuracy and finishes. However, given that each work piece is different, it will be insanely expensive to have an end mill that just fits the bill every time. So, practically speaking, I would buy end mills in 1/4" increments. Buy centercutting when possible, sharp corner radius unless a radius is called out and have 2 or 3 flute end mills for pockets and slots and 4-6 flute end mills for profiling. Buy high helix 3 flute end mills for aluminum if you can afford them and please, please buy roughing end mills. Get coarse pitch roughers for slotting and fine pitch for profiling - they run 20% faster on both feeds and speeds and will help your finishing end mills last much longer. Buy HSS or cobalt for most jobs and get carbide for deeper cuts or when you have to hold really tight tolerances.


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## RJSakowski (May 27, 2021)

Longer end mills also flex more and are more prone to chatter.  You can only choke up so much before the you hit the flutes.  
sometimes you need a longer reach and it's nice to have it available but longer end mills wouldn't be my first choice in building an inventory.


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## markba633csi (May 27, 2021)

If I could have just one endmill it would be a HSS 3/8", 2-flute, double ended endmill made in USA with about 1" flutes
Of all the ones I have I reach for that one the most
-M
Oh and I forgot to say centercutting


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## Winegrower (May 27, 2021)

markba633csi said:


> If I could have just one endmill it would be a HSS 3/8", 2-flute, double ended endmill made in USA with about 1" flutes
> Of all the ones I have I reach for that one the most



That’s an interesting thought.   For me, it’s a 1/2” 4 flute carbide from YG1.   There was some special awhile ago, and I got a half dozen for around $10 each.   These guys are terrific.  Yes, I keep them in their tubes.


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## markba633csi (May 27, 2021)

Carbides are nice too, I have a few
I have an embarassingly small endmill collection,  but I make the most of it 
I did snap a 3/16" chinese one yesterday, no big loss (2$) they are brittle as glass


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## rabler (May 27, 2021)

Winegrower said:


> That’s an interesting thought.   For me, it’s a 1/2” 4 flute carbide from YG1.   There was some special awhile ago, and I got a half dozen for around $10 each.   These guys are terrific.  Yes, I keep them in their tubes.


1/2" 4 flute carbide would be my goto endmill if I don't have a specific size need.  It tends to be a good price point, big enough to be sturdy.   I don't keep 'em in their tubes, I have a board with blind holes drilled to keep them out where I can see them easily, same board that keeps the drill chuck, collets, and toolholders for the mill.  Tubes for the infrequently used or where I have multiples.


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## BGHansen (May 27, 2021)

My go to in my Tormach 1100 is a 1/4" 4-flute carbide.  Go with 4-flute 3/8" or 1/2" on the Bridgeport.  Not adding anything but the shorter the stick-out, the more rigid the set up.  

I think of it much like turning on a lathe.  My dad was a shop teacher and told kids to not run stock more than 3 diameters outside of the chuck unless they were turning between centers.  I violate it all of the time, but manage it by depth of cut and feed rates.  Imagine sticking a 1/2" steel round out of a lathe chuck 10" and trying to take 0.040" off a side.  You'd be taking a trip to "Chatter City, USA" or "Buckle Town, USA".  Same principles hold true for tool stick out.  You can get away with a deep end mill but need to be careful with the feed rates, width of cut and depth.

Bruce


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## Aukai (May 28, 2021)

I have been adding to my inventory by looking on ebay for endmills new. I will not buy pre owned now, but if you keep looking at the new, and keep the brand names in mind, very good deals pop up.


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## markba633csi (May 28, 2021)

Bruce your dad was pretty generous- I think even two diameters is pushin' it
Depends on the size of the chuck tho and the stock


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## Michael303 (May 28, 2021)

Thanks, everyone, for the replies.  This feedback has clarified things for me quite a bit.



mikey said:


> So, practically speaking, I would buy end mills in 1/4" increments. Buy centercutting when possible, sharp corner radius unless a radius is called out and have 2 or 3 flute end mills for pockets and slots and 4-6 flute end mills for profiling. Buy high helix 3 flute end mills for aluminum if you can afford them and please, please buy roughing end mills. Get coarse pitch roughers for slotting and fine pitch for profiling - they run 20% faster on both feeds and speeds and will help your finishing end mills last much longer. Buy HSS or cobalt for most jobs and get carbide for deeper cuts or when you have to hold really tight tolerances.


Why are 2-3 flutes preferred for slots and does it apply to steel and aluminum?  I hadn't thought about roughing endmills.  Thanks.  What advantages can HSS and cobalt have over carbide?


markba633csi said:


> If I could have just one endmill it would be a HSS 3/8", 2-flute, double ended endmill made in USA with about 1" flutes
> Of all the ones I have I reach for that one the most
> -M


Thanks for the insight.  Do you have any go to brands for HSS?


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## markba633csi (May 28, 2021)

Cutting clean slots is difficult because the chips tend to bind up in the slot and give a rough, choppy finish.  So fewer flutes works better, gives the chips someplace to go
Good question about USA endmills.  I think Cleveland and Niagara are still making them here.  Brubaker, Morse, SGS are some others. I'd do a search
Most of mine are old brands that are out of business now like Putnam and Do-all, I purchased an estate sale lot with new and nearly new ones but they are quite old. They don't have a "use by" date tho


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## Michael303 (May 28, 2021)

markba633csi said:


> Cutting clean slots is difficult because the chips tend to bind up in the slot and give a rough, choppy finish.  So fewer flutes works better, gives the chips someplace to go
> Good question about USA endmills.  I think Cleveland and Niagara are still making them here.  Brubaker, Morse, SGS are some others. I'd do a search
> Most of mine are old brands that are out of business now like Putnam and Do-all, I purchased an estate sale lot with new and nearly new ones but they are quite old. They don't have a "use by" date tho


That makes sense.  I would have guessed more flutes would clear the chips better.  Thanks for the info.


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## mikey (May 28, 2021)

Michael303 said:


> Why are 2-3 flutes preferred for slots and does it apply to steel and aluminum?  I hadn't thought about roughing endmills.  Thanks.  What advantages can HSS and cobalt have over carbide?



As Mark said, fewer teeth for better chip clearance primarily but you are also able to feed faster given that feed rates are rated by inch per tooth. Edit: I meant that 2 flutes clear faster but 3 flutes can be fed faster while still clearing well.

HSS and HSS-cobalt end mills are cheaper, very sharp, less brittle and work for most materials. Carbide is much stiffer than HSS so it deflects less ,which helps accuracy. It can also go deeper so for deep cuts or where there is a lot of edge contact, carbide end mills work better. You can also run them at higher speeds and feeds so they are more efficient. However, they are more expensive and brittle - push too hard and you'll hear a "tink" and the end mill is gone. Hobby guys tend to think that throwing money at a process is the way to go but HSS-cobalt end mills are far and away the most useful in the hobby shop.


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## Janderso (May 28, 2021)

In my experience, an aluminum 2 flute extended end mill did a beautiful job milling out 80%ers. (deep channel)
I'd blow the Kool mist to help evacuate the mountain of chips.
I would finish with a 3 flute finishing end mill high speed.


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