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How much can you bend an end-mill before it breaks?


How much can you bend an end-mill before it breaks?

I am spending Christmas getting to know G-Wizard.  I bought it a while back and it has been very helpful but I know there is much more than I’ve been using.

Anyway, I’ve been playing with the cut optimizer and it has led me to a question, mostly out of curiosity.

How much can you bend a carbide end mill before it breaks off?  I’m pretty sure it doesn’t matter since long before that point one would have an intolerable deflection error.  But I’m still wondering.



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Mark, as you suspect, how far you can bend an endmill before it breaks isn’t the important issue.  It’s a number that will vary–the point where it breaks instantaneously 100% of the time?  80% of the time?  After 10 minutes of use?  30 minutes? 60?

Here’s the thing–you don’t want to get anywhere close to that point.  Think about bending a paper clip too many times–that’s the kind of repetitive stress you’re putting the endmill through every single revolution of the spindle.  Before you break it instantly, you will radically shorten its life.  But it gets even worse.  You mention the error in the cut from deflection, that’s a problem.  But another problem is that too much deflection makes chatter more and more likely and chatter is terrible for tool life and surface finish as well–worse in fact to chatter at a particular deflection than not because that vibration is the sound of destructive energy being injected into your tool.

G-Wizard’s deflection limits are chosen largely with the idea of minimizing the risk of chatter.  If you want to get aggressive, you can change them–there’s a % you can apply under Setup Other.  I wouldn’t get too carried away, experiment with it a bit if you want to drive maximum MRR.  It will vary from one brand endmill to the next.  And you’ll have to be much more prepared to deal with chatter as it will be more likely.

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