# Are End Mills Tapered?



## JPMacG (Dec 30, 2015)

I am reducing the size of a small 1/4 inch thick steel plate using an end mill.   I got lazy and started cutting the full 1/4 inch thickness in one pass, rather than taking a number of smaller cuts.

I notice that when taking the full thickness cut I am getting a tapered surface. - maybe .010 over the .250 thickness.   It is like the mill is larger in diameter at the end and it tapers down gradually  toward the shank.  It does not matter how aggressive the cut is.   I can take a .003 inch cut and I still get the taper.   I don't think anything in my set up is flexing.

Is this normal?   I thought end mills were a constant diameter.  This is a cheap 5/8 inch diameter 2-flute mill from Harbor Freight.   It cuts well otherwise.


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## ronzo (Dec 31, 2015)

Mic it.


Sent from my iPad using Tapatalk


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## JimDawson (Dec 31, 2015)

Not normally tapered, but it is a HF end mill.  I assume you are using your Atlas, so is the work piece square to the spindle?  Does the table run true to the spindle?  Is the table square to the spindle?  Just a few things that need to be confirmed in the trouble shooting process.   And as ronzo suggestes, mic the endmill.


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## coolidge (Dec 31, 2015)

They do make tapered end mills, they are for mold making where you need a taper so that the part will release from the mold.


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## Billh50 (Dec 31, 2015)

They make tapered endmills with different tapers. I have a couple different tapered ones. They would be marked with the degrees instead of the diameter. I would make sure everything is square first. The endmill also may not have been sharpened properly causing a taper on it.


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## kingmt01 (Dec 31, 2015)

Take a spring pass to see if it goes away.


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## Billh50 (Dec 31, 2015)

Also if the endmill is already dull it may be deflecting. You would be surprised how much a dull endmill can be deflected without it breaking.


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## RJSakowski (Dec 31, 2015)

coolidge said:


> They do make tapered end mills, they are for mold making where you need a taper so that the part will release from the mold.


I believe the OP said it is cutting as if it were tapered in the wrong direction, more like a dovetail cutter.  Deflection of the endmill is possible with a heavy cut but it would also cut as if it tapered toward the end rather than the shank.  

I would suggest checking runout of the endmill. If the endmill were bent, it would cut as if it were tapered as the OP describes.


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## planeflyer21 (Dec 31, 2015)

JimDawson said:


> Not normally tapered, but it is a HF end mill.  I assume you are using your Atlas, so is the work piece square to the spindle?  Does the table run true to the spindle?  Is the table square to the spindle?  Just a few things that need to be confirmed in the trouble shooting process.   And as ronzo suggestes, mic the endmill.



This is what I was wondering too.



kingmt01 said:


> Take a spring pass to see if it goes away.



Taking a spring pass (don't change any settings and run over the part again) gives amazing results sometimes.


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## RJSakowski (Dec 31, 2015)

Make a pass with another endmill, preferably a different brand..   It will tell you whether it is the endmill or the mill  Have you tried cutting from both the left and the right side, front and back sides, with the same results?   If it is a tram issue, the results will be different.


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## JPMacG (Dec 31, 2015)

Thanks guys!

Yes, this is with my Atlas MFC.
I did take a spring cut.... no difference.
The tip and the shank (beyond the flutes) both mic at .624.   In between is about the same, although it is more difficult to position the mic.  
I checked movement in the X and Y directions with a dial indicator with its magnetic base stuck onto the head.   X and Y are not bad:  better than +/- .001 over about 3 inches of travel.  
Rolling the end mill on a counter top and sighting the edge, it does not appear to be bent.  But this is not much of a test.
I still need to check the Z movement.   It might be that the jaws of my vise are not perpendicular to its base. It is a cheapo import from Little Machine Shop, but it fits the MFC nicely.  Or it might be that the head casting is somehow misaligned.
I do have some old American-made end mills.   I will run one of those for comparison.  
I'll figure it out from here.  When I first noticed the problem I thought I was being an idiot and that end mills might be tapered by design for some reason.


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## Paul in OKC (Dec 31, 2015)

Definitely sounds like an alignment issue to me. Since there is no change with a spring pass I would bet something is a bit skewed in either the vise kicking the part up, or head not trammed in to the table.


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## John Hasler (Dec 31, 2015)

Sounds like runout.  Could be the cutter, the holder, or the spindle.


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## joshua43214 (Dec 31, 2015)

Can you help us all get on the same page. Since you have a horizontal mill, things are a bit different.
We could really use a pic of your set up.

It would be nice to have no confusion about where the problem might be.


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## Andre (Dec 31, 2015)

My Bridgeport M head bearings are shot, so on heavy cuts I get quite a bit of spindle deflection that leads to a tapered surface.


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## JPMacG (Jan 2, 2016)

Well....    I changed to another end mill and now I am getting good results.   But I changed some other things too, so I don't know for sure that it was the end mill.   This is approximately the setup I was using.   At any rate, I'm happy now.   Thanks for all the good ideas!


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## kingmt01 (Jan 2, 2016)

It's always easy enough to toss the end mill back in later & run a test cut to see if it is still there. Now that you got it true is get done with making the more pressing chips then you can come back to the test piece when you have a slow moment.


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## joshua43214 (Jan 2, 2016)

I see I spy a...
Tool holder...

Tool holders are great when you absolutely must have your cutter run off center.
Is using a tool holder the only option for using an end mill in your machine?


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## JPMacG (Jan 2, 2016)

With the vise I have, oriented the way it is shown, a collet and end mill will not reach far enough.    But I agree, I would prefer not to use the tool holder.   A better option might have been to set up the arbor and use a horizontal cutter.


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## joshua43214 (Jan 2, 2016)

JPMacG said:


> With the vise I have, oriented the way it is shown, a collet and end mill will not reach far enough.    But I agree, I would prefer not to use the tool holder.   A better option might have been to set up the arbor and use a horizontal cutter.



Better to have your set up than no mill at all 

Dunno if you have run into it or not, but you might come across "imperial" mills that are actually metric. It will cause problems with your tool holder. Might not hurt to put a caliper on your HF mill and make sure it really is the right size for your holder.


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