How to Find Minimum Insertion Depth
Q: I am trying to find the minimum insertion depth for cutting tools in holders. Other than referencing DIN, ISO or NAS standards for shank length to diameter dimensions, is there a rule used to determine the minimum insertion depth of an end mill, thread mill or drill bit into collets, shrink or hydraulic holders?
A: The is no general rule to cutting tool shank insertion as a multiplier for shank diameter. All tool holder types have different requirements. The most important concept is that no matter what tool holder you are using, the cutting tool shank should be past the ground clamping section.
An example of this is with ER32 collets. The smaller clamping sizes (Ø3mm) have an internal recess in the back of the collet. Even though the collet is 40mm long, the ground clamping length is only 19mm. As the clamping sizes get larger, the ground length increases (Ø12mm = 30mm) but is not relative to a set multiplier.
Tool holders like shrink fit, hydraulic and milling chucks typically have the minimum insertion depth listed in catalogs. For holders like these, if the cutting tool shank does not pass through the ground portion of the holder, the bore can be damaged and ruin the entire chuck. Straight collets have the same type of recess. As long as the OD of the collet passes through the ground section of the holder, the cutting tool shanks can be shorter.