# How long before end mill dulls out?



## tkitta (Nov 14, 2014)

Well I got this set of 6 HSS (I assume M2) end mills made in China and branded by Grizzly - all 3/8 shank.

I run them all on my mini mill which is the top model of X2.

Now I calculated that my small 5/16 end mill removed at most a single cubic inch of mild steel before it is clearly dull - still workable but now it doesn't cut like a sharp knife - it now requires more "persuasion" and also starts to heat up - before it was cold when cutting. Also unable to take as large of a cut as before - it starts to "chatter" vs. before I could take 1mm cut now I cannot take 0.5mm. I think I can still get it to cut little more but its close to an end.

Is the 1cu of mild steel normal amount? How much should I expect? I know a tool life of an end mill run at proper speed and not overheated should be around 90min but its not like I time my cutting - I can tell how much I cut through somewhat easily.

I know I can re-sharpen the end mill with some good optics and a dremel tool but can I instead just grind the end of the end mill and make it into a standard end mill vs. center cutting - I mean I only dulled the 1mm of the end mill + center cutting part - the rest is fine.

Finally, is it normal for a lathe tolling to cost at least 10 x less (more like 20 or 30) then the mill? I mean my lathe HSS tool bits require occasional sharpening for pennies spent and my brazed carbide bits, for less than $2 a peace also last super long time + I can re-sharpen these rather easily on the green wheel on the grinder if I want to => its seems for each dollar spent on tooling on the mill I can only remove grams of mild steel while on the lathe I can remove pounds - is this normal? My lathe is much bigger than my mill its a 12 x 24.


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## JimDawson (Nov 14, 2014)

That is a really good question.  And you are correct that an endmill should last for about 90 min, and sometimes they do.

This is just my experience, but it seems that if you over speed them just once or do not feed fast enough then the life drops off dramatically.  If conditions are perfect, then they last quite a while.  I also think that the cheap Chinese endmills are not very consistent in heat treat or overall quality and sharpness.  Some of them seem to last a lot longer that others under the same conditions. I buy a lot of Harbor Freight endmills for general use.  I bring out the good stuff for precision work.

As far as cost difference, if you look at the manufacturing process for endmills, there are a lot of steps to get a finished product.  A lathe tool bit is just a ground square, so not much manufacturing process there.


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## Harvdog42 (Nov 14, 2014)

How many RPM were you running the 5/16" endmills?  RPM or SFPM is 
an important factor in how long a HSS cutter will stay sharp.

Harvdog42


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## Karl_T (Nov 14, 2014)

You dulled it, don't do that again   Better than schmucking it 

Suggestions

Use ME consultant to set your speed and feed
http://www.portablefreeware.com/?id=389

get a coolant mister, many have made their own.

Shop eBay for quality tooling. A good cutter lasts light years longer. But the more expensive the cutter, the bigger chance you will schmuck it. DAMHIKT

Karl


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## spaceman_spiff (Nov 14, 2014)

tkitta said:


> Well I got this set of 6 HSS (I assume M2) end mills made in China and branded by Grizzly - all 3/8 shank.
> 
> I run them all on my mini mill which is the top model of X2.
> 
> ...



I'm not sure where the 90 minutes number comes from, but those estimates dont mean much, as you have discovered. Tool wear depends on actual usage including machine rigidity, spindle runout, material, rpm, depth of cut, etc..etc...its really where every real world parameter comes to play. 

Likewise a "worn out" tool is a relative idea too, and depends on what is acceptable for your operation. Perhaps you could throw several things at it at once, such as increased diameter, more flutes, carbide, hog flutes, less stickout, and experimenting with rpm/feed?

Cutting steel with a small diameter HSS tool on a hobby mill is pretty much maximum difficulty level for a hobby machinist and is very unforgiving. I'm impressed you got 1 cu. in. out of it!


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## eightball (Nov 15, 2014)

We bought some kool-mist systems at work and they work great. Tool life is greatly increased. We have a big cincinatti millatron, and its got oil flow for coolant. Its great but the machine is too big for any kind of fine work.  We mostly use it for big keyways (1 1/2 -3") and we use a 8" facemill on it. I actually run the facemill at 600 rpm and 50 ipm taking .125 deep cuts.  After a cut the workpiece is still cool to the touch, so thats usally a good indicator your speeds and feeds are correct. We use the kool-mist on the bridgeport knee mills and its such an improvement. I even use them when i broach keyseats in our Davis key seater.


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