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More About Spring Collets

Spring Collets for HSK & ISO Tool Holders

CNC Collets in various styles
Collet Style Selection

In the wood industry, the vast majority of collet styles in use are ER32, ER40 and SYOZ25 (also called RDO35). Several other (smaller) sizes are common in specialty applications such as CNC aggregate heads or Weeke BHX Hydro clamping system system, but on the most common CNC machines, one of the three styles, mentioned above, will be found in use. The tool holders do not allow interchanging collet style within the same tool holder, but the tool holder itself (mostly HSK-F 63) is interchangeable with any machine that has the HSK interface. So, a machine using ER32 style which accepts a maximum diameter of 20mm, can simply move up to an ER40 style tool holder, if a 25mm or 1″ tool shank calls for a larger diameter collet. It’s noteworthy that the ER style (both ER32 and ER40) are usually standard on Italian-made CNC machines such as SCM and Biesse, whereas the German and Austrian machines use the SYOZ style, as does US manufacturer Onsrud Machine. The table below shows the diameter range for the ER and SYOZ collet range, as well as their clamping tolerance range.


The 462E collet shown above, is the SYOZ25 standard. Regular replacement of collets should be considered part of good machine maintenance as worn collets will directly reflect upon the tool life as well as quality of product finish. Collets that are worn and dirty will create vibration during the cutting process. A good rule of thumb is to replace them about every 500 machine hours!

Inspect your cutting tools to see if any marks are visible on the tool shank (like fingerprints that show where the collet was gripping). If so, that is an indication of vibration occurring during the cut and it could either be time to replace the collet, it might have a bad toolholder nut, or the nut may not be torqued to the correct torque. Proper torque values are:
RDO35 (SYOZ25) collets 90ft/lbs
ER 32 collets 100 ft/lbs
ER 40 collets 130 ft/lbs.

Finally, we have learned not to take proper mounting of the collet and securing it into the collet nut for granted. We recently had a seasoned woodworker stop by with a new surfacing tool that wasn’t performing to his expectations. Luckily, he brought the entire assembly on the tool holder which immediately showed the problem! The collet was just placed into the nut as opposed to properly locked down. Below is a quick video showing proper mounting.

Proper collet mounting into collet nut / tool holder

Precision Collets for SCM, Biesse, HolzHer, Homag, Weeke, Onsrud, Laguna, Felder and others
SYOZ / RDO35 collets

Did you know that in addition to the standard collets with a tolerance of 0.5 mm, GUHDO also offers premium collets with a tolerance of 0.15 mm? If you want to improve your finish, please call or email us to discuss!