Pull Studs (Retention Knobs) and Reduction Sleeves are vital for securely clamping tool holders and tools on CNC machining centres and lathes.
Watch Temak Teknik’s video below explaining the selection, use and maintenance criteria for pull studs and lathe reduction sleeves:
1. Pull Stud (Retention Knob)
On a CNC machining centre, the pull stud allows the tool holder to be drawn into and locked in the spindle by the ball-type pneumatic/hydraulic clamping mechanism [00:11], [00:22].
- Coolant-Through (Bored) vs. Closed (Solid): If through-tool coolant (internal coolant supply) is used on the machine, a pull stud with a through bore should be selected. If there is no internal coolant supply, closed types are preferred [00:43], [00:51].
- Wear and Accuracy Checks: The taper and shoulder surfaces of the pull stud wear or become damaged over time. Damaged or worn pull studs harm the tool holder and the spindle clamping mechanism [01:07], [01:15].
- Correct Type Selection / Clamp-Unclamp Failure: A pull stud with an angle and dimensions that exactly match the machine brand and spindle standard (MAS BT, DIN SK, CAT, etc.) must be used. If the wrong pull stud is fitted, the spindle may clamp the tool but be unable to release it (the unclamp mechanism jams), and the spindle head will need to be dismantled manually and repaired [04:45], [04:53].
2. Reduction Sleeve (for Lathe Tool Holders)
Reduction sleeves are used on CNC lathe turrets or block tool holders to clamp boring bars, drills and other tools with different shank diameters [02:06].
- Choose Hardened and Ground Products: Unhardened, unground raw or low-quality sleeves mark the tool shank over time and cause axial misalignment [02:38]. For high precision and long service life, ground and hardened sleeves should always be used [02:46].
- Coolant Direction: Quality reduction sleeves feature coolant holes. These ensure that coolant is sprayed onto the bar or tool shank at exactly the right angle [03:31], [03:45].
- Clamping Sequence: When fitting the sleeve, the tool should first be inserted into the sleeve, then the first locking screw followed by the remaining screws should be tightened in sequence to ensure the shank is fully seated [03:11], [04:11].