ER Collet Chucks for BT MAS, DIN69871 & ISO Systems

An ER collet chuck is a spindle toolholder that uses a tapered spring collet to clamp cylindrical tool shanks. The collet is a slotted, spring-steel sleeve with a matching taper and is placed inside the chuck body with the tool shank inserted through it. A clamping nut is then threaded onto the chuck body and as the nut tightens it draws the collet into the taper, compressing it radially inward to grip the shank uniformly around its full circumference.

The design gives ER collet chucks several key properties:

• Diameter flexibility: each collet accepts a 1mm range of shank diameters (e.g. a 10mm ER32 collet grips from 10mm down to 9mm). A full collet set covers all common shank sizes from a single chuck body

• Interchangeability: the same chuck body is reused indefinitely and only the collet and nut need replacing or changing between tool sizes

• Moderate runout: typically <15µm (standard), <10µm (high precision), or <5µm (ultra-high precision) depending on collet grade selected

• Broad tool compatibility: accepts drills, end mills, reamers, taps, boring heads and any round-shank tool within the collet capacity range

ER is the universal standard and the ER series was developed by Rego-Fix and is now manufactured to DIN 6499 / ISO 15488 by many companies. Collets and chucks from different manufacturers are fully interchangeable when they carry the same ER designation!

Yes, the MT3 Morse taper series is specifically listed as suitable for use with coolant-sealed collets.

Coolant-sealed collets have an O-ring or sealing groove that prevents coolant from leaking back up through the collet and out of the back of the chuck and they direct coolant through the tool shank to the cutting zone.

For BT, SK and HSK chucks with through-spindle coolant (TSC) the coolant path runs through the spindle drawbar, through the pull stud and through the hollow body of the chuck. All chucks in the range support this configuration when used with coolant-sealed collets.

It is worth noting that coolant-sealed collets have a slightly reduced clamping range compared to standard collets so you must always verify the sealing collet covers your tool shank diameter before ordering.

HSK (Hohlschaftkegel / German: "hollow taper shank") is a fundamentally different interface from the 7:24 solid taper used in BT and SK systems, here's why:

• Dual contact: HSK achieves simultaneous contact at both the taper face and the flange face of the spindle. The BT/SK 7:24 taper relies on taper contact only and the flange does not contact the spindle. HSK's dual contact gives it superior bending rigidity and much better behaviour under high cutting forces at high speed

• Higher clamping force: the internal clamping mechanism engages inside the hollow shank — clamping force increases with spindle speed (centrifugal effect) rather than decreasing as in 7:24 tapers

• Better repeatability: face contact means the axial position of the tool is more precisely repeatable at each tool change

• Higher dynamic stiffness: critical for high-speed finishing as the vibration is better controlled.

HSK63A-ER collet chucks in stock:

• Available in ER16, ER25, ER32, ER40 at 100mm gauge length

• Balanced to 15,000 rpm G6.3

Choose HSK when your machine has an HSK spindle (they are not interchangeable with BT/SK), your spindle speed regularly exceeds 12,000-15,000 rpm, you require maximum tool position repeatability between ATC tool changes or if the job demands the highest possible dynamic rigidity.

Straight shank ER collet chucks do not have a taper, they have a plain cylindrical shank that is clamped in another chuck or holder.

Common applications include:

• Lathe turret use via VDI ER collet chuck: a straight shank ER chuck fits in a VDI ER holder on a CNC lathe turret allowing ER-held tools (drills, taps, reamers) to be used in the lathe's static or driven turret

• Milling attachment on a manual lathe: straight shank ER chucks can be held in a drill chuck or a boring head arbor for light milling/drilling on a lathe

• Grinding machines and other equipment that clamp a cylindrical shank rather than an ATC taper

For CNC machining centres, always use the appropriate taper shank (BT, SK, HSK). Straight shank chucks are not suitable for machining centre spindles and will not be retained by the machine's drawbar.

No they do not, pull studs are sold separately.

The collet chuck body is supplied as shown and the pull stud (also called a retention knob) that secures the holder into the machine's drawbar must be ordered separately from the Tool Holder Accessories section.

Pull stud specification depends on two things:

1. The toolholder standard (BT40, SK40, etc.): determines the thread and shank geometry of the pull stud

1. The machine's drawbar specification: within the BT40 standard different machine builders specify different pull stud engagement lengths and flange configurations meaning a Mazak pull stud may not be correct for a Doosan machine even though both are BT40!

If you are unsure which pull stud your machine requires contact the team with your machine's make, model and year and they can confirm the correct pull stud variant from stock.