Troubleshooting Bit Breakage
From contributor F:
Make sure that the spiral cut in the shank is not below the collet surface. Sometimes with longer bits, an operator may try to put it deeper in the collet, thinking there will be less tension, but this will leave a weak area. Also, your tool selection should work fine, as we routinely cut solid wood with a 1/4 upshear at 18,000 rpm and 200 ipm 3/4" at a time. However, there is no more than 1.75" total bit protruding from the collet.
From contributor B:
Is this a cutting process you've done successfully before and the bit failed this most recent time? Or is it the first time you've made a 1 11/16" deep cut in oak in this manner? I think some more specific guidance can be given if you let everyone know.
From contributor G:
I would say vibration. The collet could have been dirty, thus becoming unbalanced, or your work piece could have lost its hold down.
From contributor I:
It could simply have been a defective tool, too.
From contributor E:
Your rpms are too high and/or feed speeds too slow. I assume that it is an upshear. Slow the rpms down to 14K at that speed. Traditionally, if the tool breaks in the collet, the collect can be dirty with chips or simply worn, and a new one should be installed. The correct type of tool would be a necked down version. Meaning, most of the cutting edge should be engaged in the cut. This will assist the tool from vibration breaks, which has occurred.
From the original questioner:
Thank you all for your responses. I find all of your opinions helpful. I realize that we have many different issues to address. I think the main cause of this particular situation was a worn collet. It is possible there was a bur inside the collet that caused the bit to break when it was tightened.
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