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We need to talk about tool holders and some of the considerations that go with tool holders when dealing with hardened materials.

The mill chuck is a very effective roughing tool holder for 60 Rockwell materials. When I am roughing I am creating vibration. That vibration has to be absorbed somewhere. This tool holder is very good in absorbing that energy because it has ball bearings on the inside of the tool holder.

The next type is a collet type holder a collet chuck holder. These are good for roughing. Not as good as the milling chuck but still very good for roughing. Good for semi finishing and in some cases are good for finishing as well. It just depends on the range and the type of tool holder. All types of different sizes and shapes of collets that can be put inside of these tool holders. So multiple tool sizes can be acceptable and multiple shank diameters can be accepted in these types of collet holders.

Shrink fit holders are great for finishing because the run-off characteristics on these tools are much better than other systems. With a high quality shrink fit system you can easily cut under two microns. So we are talking 80 millionths of an inch or less. If you take a two micron or a one tenth indicator on a shrink fit holder you will not see the dial move. It will stay pegged at zero. Ultimately, I recommend to not use these for roughing whatsoever. Only use these for finishing when milling 60 plus Rockwell materials.

No matter what tool holder you use, make sure you check the run-out. This is especially important if you are concerned about having predictable tool life. If you are trying to use tool life management, for example, you should make sure that all of your tool holders are checked. I do my checking in two places. I check the tool at the shank, provided that I can get in close enough to the shank and check it, and I check the cutting edges.

We check the run-out to make sure we won't run into any unexpected issues. If I do have any run-out issues in a colleted system it will allow you to easily move the tool around, maybe you spin it a couple degrees to try to dial it in. If it is a shrink fit you are kind of stuck. You kind of get what you get. The other thing about checking the run-out is you can also check the tool holder, especially in a shrink fit, to make sure that the tool is the tool holder is still good. Eventually in a one piece or an induction heat system you will start to get deformation. The longer you use the shrink fit the more deformation you will get. Checking the run-out is a great way to verify whether the tool holder is still in good working condition.

As far as balancing is concerned, we recommend all tool holders are balanced to G 2.5. I also strongly recommend that you balance tool holders to the maximum rpm and that you will run on that tool holder, map the holders to that rpm, and mark the tools so you know they have been balanced and mapped. You ultimately want have predictable tool life and make sure that your bearing life is going to be extended, balancing and checking run-out will aid this greatly.