As Professor Scott Smith from UNC Charlotte likes to say, "Random processes produce random results". If you have been following our posts you will have learned that a milling tool is a flexible beam and that changing the length of that beam, even a small amount, will change its frequency and can impact the tool's performance. You will also have learned that rotating a spiral fluted endmill in a toolholder can change the balance of the assembly significantly. If you have something running really good, you want to keep it that way.
Most toolholders other than side-locks use friction to hold the endmill shanks. So you need help to get repeatable tool changes. We found these wrench-free aluminum shaft collars from Ruland Manufacturing. The aluminum won't damage the cutting edges and holds up to the heat of shrinkfits. You can also use steel set screw collars or drill stops.
Set the tool projection from the tool tip, not the back end. Overall length is not a tightly controlled spec in ISO or ANSI, so measuring from the back or using backup screws will not give you a repeatable tool stick-out. You can use a caliper depth rod or depth micrometer to set the projection, just subtract the collar thickness.
Also, use the slot in the collar to orient the tip of one tooth, like a gunsight. This will retain balance. Look through the slot and rotate the tool until the tip lines up with the slot. If you are using variable pitch endmills, identify tooth #1 and set to that each time. Put a witness mark on the end of the toolholder and use that as your target when orienting the new tool with the collar's slot. Balance the tool assembly first, place the collar on the tool while still in the holder and line up the slot to a tooth. Mark the toolholder at the slot with a center punch or drill point. For a collet chuck, torque the nut to the proper value, then mark the nut just as above.
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