Page 41 - CNC West Oct-Nov 2021

So, if runout is tricky to identify, what’s the bottom line? If a drill or mill doesn’t run concentric to its centerline, more forces are generated in the direction of the biggest margin. This causes just one side of a tool to work. Even if this results in on-spec parts, and it can, the cutting tool is essentially being wasted.
Each tooth should hit at the exact same spot along the workpiece. If one tooth is hitting the workpiece more frequently, it’s doing the bulk of the work. In other words, if you have six teeth on a cutter but the tool is runout out by more than a thousandth of an inch, you’re likely only using three of the teeth.
To calculate the impact of this on tool, we use the One Tenth = 10% Rule. That is, one tenth (.0001”) of runout will increase or decrease tool life by 10%. In other words, if five tenths of runout is your baseline and you swap in a holder that that reduces runout to one tenth, tool life should improve by 40%.
What’s more, if you’re worried about carbide costs, you’ll want to use the whole cutter. Remember, runout uses certain teeth or flutes more than others. If you’re using carbide cutters larger than about a quarter inch in diameter, tool wear can get expensive quickly. There
are significant carbide savings to be had by changing to a lower runout holder.
What many shops believe is acceptable runout is actually unacceptable if the shop wants to improve tool life. A manufacturer basing a tool holder purchase decision solely on the price of the tool holder may end up choosing a more expensive alternative, based on tool life and cost per cut, while sacrificing quality and accuracy. Runout accuracy pays. We’ve done the math.
CNC WEST October/November 2021
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