With machine tool capability a given, and the proper choice of cutting tool and toolholder being made, HSM is a snap, right? Not exactly. Particular focus must be given to the assembly of tool and holder.

The fact that each may be inherently balanced doesn’t translate into them being balanced as an assembly. Balancing must therefore be done after the tool and holder are connected. That holds true for whatever combination you choose, and is really a key to effective and efficient machining even in lower speed, heavier cut applications, but ultimately critical for HSM.
To produce fine finishes and maintain long and predictable tool life while performing high-speed applications, you must run balanced tooling. Part of understanding the balance issue is knowing what the maximum “un-balance” your machine can withstand.

As a general rule of thumb, it is accepted that a maximum of 3 grams per millimeter of unbalance is permitted in HSM toolholders. But, at very high spindle speeds (30,000+ rpm); it is not uncommon to require closer to just 1 gram per millimeter. This can be compared to a standard, generic endmill holder, which can have as much 250 grams per millimeter unbalance. Depending on the actual rpm used, this can be the difference between catastrophic failure and complete success. Balanced tooling will yield better results at any rpm, but becomes an absolute necessity when considering HSM, having the ultimate impact on productivity, quality, consistency,