Broken an Endmill in Aluminum



let me first start out by saying that I am new to CNC.  I have a Tormach PCNC1100 machine.  I used the GWizzard Feed / Speed Calculator and the CADCAM function of the GWizzard to calculate my rate of feed / speeds for a part that I am trying to cut.  My part is made out of Aluminum 6061, and I was using a 3/8″ center cut HSS End mill.  I  say using because after calculating my feed rates with GWizzerd my freshly opened never used before lasted for about 30 seconds before it snapped in half…sadly I could not hit the “OH CRAP” red button in time.  The calculations from GWizzard was to cut .25 at a rate of 35ipm.  when I set up the CAM software to do this… my brand new end mill bogged the machine down and snapped in half.


My question here is even after I enter things in Gwizzard it is still reporting that I should be able to move my part around at the same IPM.  I am fear full that running this pass at this speed again would yield the same results…



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Keith, there’s not enough information in your question for me to tell what all is going on.  Best thing is to email me a screenshot when you ask this sort of question so I can see all the various settings.

However, from what you describe, and especially when you mention the endmill broke quickly after the spindle bogged down, there are a few possibilities:

  1.  Where you using coolant?  You really need to use either flood or mist with aluminum, because it will weld to your cutter without the lubrication very quickly. It’s also important to aim it fairly well to clear the chips and make sure plenty of the coolant reaches into the cut.
  2. TTS Pullout is a possibility with these symptoms.  What happens in that case is the endmill is pulled out of the holder, which results in a deeper than expected cut, and that will often break the endmill too.
  3. If there’s any error setting part zero (the Z) or tool length, the cutter can wind up going deeper than expected and again, you will get this result.

I’d check on things in that order to look for answers.

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