# How to check for dull end mills??



## Ageless (Feb 2, 2010)

Sounds simple but more to this than it seems!
Yes, one can wait until the cutter just burns its way through steel, but then the cutter is ruined.
I have been told to check for a valley across between the tips with a small steel ruler and to look for shiny spots 
on the cutting edge of the end mill. This is however very subjective.
Could some of you experts please give me a description of what to look for so that the tool can be resharpened.

Thanks to all!


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## gbritnell (Feb 2, 2010)

It's just the same as looking at a sharp knife. If you can't see the edge, it's sharp. If you get a reflection from along the edge it has dulled. When the bottom gets dull you can see where the tips of the flutes have polished up because the clearance has been worn away. The easiest thing to do is get a new or like new end mill and study it under a magnifying glass and then check a dull one. You'll see the difference immediately.
gbritnell


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## ieezitin (Feb 2, 2010)

Good advice from George.

Another way is to run your finger down the cutting edge, if you feel thats its going to cut your skin its sharp.

Blunt edges will show ware. Rounded tips are another sign. All tooling should be sharp and profiled. If its not It will not do the job you are asking of it.

Sharp well maintained tooling is 100% of our hobby. Dull bits = failure. And no untold head aces. 

Any questions please ask         all the best     Anthony


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## toolsrul (Feb 4, 2010)

Usually the first thing that gets dull are the corners or edges if it is a square end end mill. That is the weakest part of the end mill, next look at both the sides & the bottom to see if there are any chipped areas. Wear on the bottom would look like a sanded surface maybe .005" to .01" wide, this would be the same for ball end mills. The wear on different areas of the cutter, depending on depth of cut - DOC, start to produce more pressure during cutting so you'll be able to see heavier burrs, different surface finish on the part & possibly moving the part in your vise. If you get too much wear on the outside of the cutter & want to have it re-ground you may want to take it to an experienced cutter grinder that understands the geometry in end mills because of primary & secondary clearances. That gets involved & costs big $$, your better off buying new unless it's an expensive carbide end mill. Usually smaller end mills aren't worth to be re-ground due to cost of a new one.


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## doc1955 (Feb 4, 2010)

I will scrape my thumbnail but that will not tell the whole story as you may have just spots that are dull and not the total length. The best way is to get familiar with looking at the edge as mentioned.I know thats not much help but with time you will develop a feel for it.


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## Ageless (Feb 11, 2010)

Hello All;
Thank you very much for the feedback.


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