Within your toolholder assembly, one of the most important factors that can affect or limit your machining potential is the runout of the cutting tool. Albeit .0005 to .001” may not seem to be a lot, nothing affects tool life, predictability of tool life, cutting ability, surface finish, and part tolerances more than runout. To add more fuel to the fire, in many cases, runout doesn’t only cause just one of these issues, but many, if not all at the same time. This often results in longer part production time, and can lead to unnecessary down time to change out cutting tools more frequently.
Let’s take into account a simple formula to calculate your feed rates: Feed Rate= RPM X number of teeth X chip load per tooth
Now, let’s give an example of how runout can slow production under the guise of optimal machining capability. Assume we’re in the process of setting up a job to run into production. With all things being equal with RPM and the number of teeth on the cutting tool, if we were to use a chip load per tooth of .005”, a .001” runout adds 20% more cutting force unnecessarily to one tooth unevenly. Unknowingly to the circumstances of the runout, the operator will proceed to make adjustments with the feed dial during machining operations concluding his optimal feed rate is where the squeals, sound and load meter are at a comfortable level. In addition, if the operator continues to use a toolholding system that provides inconsistent runout (some good and some bad), cutting tool life predictability becomes variable, often resulting in the operator picking the lowest quantity produced as a safe benchmark of when to change cutting tools. To the detriment of the business utilizing the equipment, this example shows how costly such a small issue can not only limit the true machining productivity of your machining center, but also limit the ability to get the full cutting capability of the cutting tool.
The solution goes along the saying, “Prevention is better than a cure.” For starters, although this may take a bit more time on your set up, make an active effort to verify that cutting tools are running true prior to machining operations and see if improvements can be seen. As one may also realize how runout may vary each and every time a cutting tool is replaced, the value in investing in a quality toolholding system that provides accurate and consistent runout will become apparent.