Page 12 - Parlec Catalog
P. 12
Concentricity, Rotational Speed, & Balance
10 Selection Guide
SELECTING THE PROPER TOOLHOLDER TYPE
Friction Drive vs. Positive Drive
The most common positive drive toolholder is the Weldon end mill holder. This type of system requires flats
or some other feature on the cutting tool shank raising the cost of the cutting tool. The positive drive nature
virtually eliminates pull out or spinning potential during a cut.
Friction drive such as Collet Chucks and Shrink Holders are more likely to result in concentric and higher
speed operations. Clamping relies on either compression, as in power milling and hydraulic chucks, or
wedging, as in collets, to do the clamping on the round shank. In the case of friction drive, the question is how
much torque, vibration , force or combination of these will it take to allow slipping.
Types of friction drive holders include ERos , heat shrink, ER collet chucks, power milling chucks,hydraulic
®
chucks, single and double angle collet chucks.
Variables
Reduction bushing systems consume some of the clamping force to absorb the clearance between the holder and the
reduction bushing as well as the reduction bushing and the tool shank. This results in much less performance when
not used on size.
Collets use linear travel to create a wedge to generate the clamping force. Most collet systems are designed to
collapse a considerable distance. When the collet collapses below its nominal size the od and id of the collet are no
longer matched to the holder seat and the cutter shank diameter lessoning the contact area. This results in reduced
concentricity and grip force.
Heat shrink utilizes thermal expansion to give a clearance to insert the tool. The cooling of the holder shrinks the
body back to the original size. The cutting tool interference with this movement creates the clamping force. There is
no action in this process to make up for variables in bore or cutting tool shank diameters.
Collet Style vs. Bore Style
Collet style tools are made to be more flexible than a tool with a sized bore such as heat shrink or Weldon
style. This can be more cost effective but adds complexity to the assembly process and requires better and
more defined cleaning and storage techniques. Collets or reduction bushings allow a common holder to be
used on many size applications. This is especially valuable to a job shop environment where the jobs may
change many times.
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