What Are the Best Toolholders?

May 17, 2010 // by Bob Warfield // Blog, Techniques // No Comments

According to Google Analytics, one of the most popular pages on this site is the one about surface finish for milling. As a result, I am busy updating the page to include a bunch of newer information I’ve come across since I first wrote it.

For example, as part of the research, I recently read a fascinating analysis of toolholder efficacy in a graduate thesis out of the University of British Colombia (“Mechanics and Dynamics of the Toolholder Spindle Interface”) that raised some good data I hadn’t seen before:

- HSK toolholders are as much as 4x stiffer than equivalent sized CAT40 holders. This is mainly due to the dual-face contact of the HSK design.

More interesting was the comparison of the performance of milling chucks, shrink fit, hydraulic chucks,and collet chucks. The most important characteristic for finishing operations is modal stiffness. In order of best to worst performance, here is how the different toolholders ranked:

Tool Holder Type	Modal Stiffness	Dyamic Stiffness
Shrink-fit	0.89	0.065
Collet Chuck	0.75	0.155
Hydraulic	0.53	0.196
Milling Chuck	0.52	0.184

Surprising that the lowly collet chuck performed nearly as well as finicky shrink fit tooling and quite a bit better than more expensive hydraulic and power chuck-style holders!

However where roughing is concerned, the Dynamic Stiffness is important for suppressing chatter. For maximum material removal rates, we want to maximize Dynamic Stiffness. Here the Collet Chuck also performs pretty darned well, and it is in hogging out lots of material that the hydraulic and milling chuck style holders start to come into their own.

Lemme see, looks like I need to order some more collet chucks!