Question
Most of our collets for our CNC are what you call range collets, where each one can be used for a variety of bits. (12-13mm range for 1/2" and 6-7mm for 1/4".) Recently a tooling salesman was insisting we should have dedicated collets (1/2" collet for a 1/2" bit). Supposedly this will be easier on the spindle, and increase tool life, among other things. Can anyone confirm this, or is it just another pitch?
Forum Responses
(CNC Forum)
From contributor M:
From my experience, range collets should not be used. Buy either metric sizes for metric shanks, or inch sizes for inch shanks.
Contributor A hit on something. The PS2000 chucks that we [Leuco Tooling] carry as well as the Tribos chucks are simplicity in action, as well as being highly precise. These not only make setup a great deal faster, but also have running tolerances that are greatly superior to the standard collet chucks.
You will have a tool holder (for specific sizes only, the "close enough" approach will not work here) and when the tool is set to a specific height, you turn a lock screw which will create pressure in a chamber surrounding the bore in which the tool is set, the bore will contract, thereby locking the tool in place very securely.
Physics dictates that the pressure applied will be evenly distributed if given even points of distribution. This means that the same amount of pressure will be applied over the entire shank of the tool, thereby holding it with equal amounts of pressure as well as centering the tool as accurately as possible.
Just as a note: If one were to try to mount a 12mm shank tool in a 0.500" (12.7mm) hydro chuck, it may return to its pre-pressurized state, but most likely, it will go beyond the locking point and not return to a useable state, at least as far as the 0.500" tool is concerned.
There are a few other options as well. Keep your applications in mind when shopping for tool holders. Standard collet chucks do have a place, but you really need to make sure you use the right collets for the tools you are holding. I wouldn't use anything that was close enough unless I had a real production emergency.
I use ISO30 tool holders with ER32 collets specifically sized to the bit shank (typically 1/4", 3/8" and 1/2" along with a scattering of other sizes). I cut solid wood typically held in place with vacuum pods. My primary tools are a 3/8" downcut spiral 2-flute HSS bit on a 1/2" shank and the same in carbide as an upcut spiral with a 3/8" shank. Both have a 1 1/4" cutting length. I also frequently use a HSS upcut spiral 1/2" bit with a 1/2" diameter x 1 1/2" long cutting length. We rarely break bits... They usually wear out first.
So, do the hydraulic holders work with ISO30 setups? If not, then that is the end of this for me.
If they do, though, then what would be the typical comparison cost to a tool holder, collet and nut? What is the longevity factor? I know I at least am delinquent in disposing of collets, holders, and nuts that may be beyond their useable life, and probably others out there tend to do the same.
Finally, in a standard collet and nut system, the idea is that as the collet tightens, it becomes perfectly parallel with the shank of the bit as it closes in, thus properly holding the bit in place. What is the oil in the hydraulic holder pressing against that then presses against the bit shank? It would seem there must be some sort of pressure plate involved that matches the bit shank radius.
The way it works is the bore where you put the tool is, in reality, a thin steel wall machined to be slightly larger than the O.D. of the router bit. When the bit is inserted, you turn the locking screw and it pressurizes the grease chamber, forcing that thin steel wall to compress inward. The only moving part is the screw itself. When the screw is released, the pressure is released, and the wall flexes back to its original shape.
Yes, is does come in ISO30 style. I won't show pricing here as I think it would be in bad taste, but I can tell you that our ISO30 hydro chuck costs about 40% more than our ISO30 collet chucks.
