Bits breaking? Here are a few reasons you might not have thought of.

• Possible Cause: Deflection- cutting edge too long: 
  Possible Solution: Select a tool with cutting edge not more than ¼” longer than material thickness.
• Possible Cause: Bad or worn collets
  Possible Solution: Check tool shank for evidence of chatter marks. When visible, replace collets.
• Possible Cause: Over-torquing
  Possible Solution: If tool breaks in the shank area, tightening the collet nut to incorrect torque can cause tool breakage. Invest in a setup-fixture and torque wrench.
• Possible Cause: Overheating 
  Possible Solution: If signs of heat buildup are in the tool flute, check chip load and adjust feed/speed.
• Possible Cause: Part Movement
  Possible Solution: Improve vacuum hold-down.
• Possible Cause: Too much pressure on the tool tip
  Possible Solution: For rebates, grooves, and slots, use the shortest length to avoid tool breakage.
• Possible Cause: Tool slippage in the collet
  Possible Solution: Replace static collet nut with a bearing nut.

Source: CNC-Tool.com. For information, call 636-447-3439 or visit CNC-Tool.com.