PSC (Capto) or HSK-T? Choosing the tool interface for mill-turn and multi-axis lathes
On a mill-turn machine the milling spindle also has to hold turning tools, so its interface must lock the tool at a defined centre height and take a sideways cutting load. Two interfaces are built for that: PSC, the ISO 26623 polygon coupling whose sizes correspond to Capto C3 to C10, and HSK-T, the turning form of HSK. Both use taper and face contact. The machine spindle decides which one you use; where a machine is offered with either, the tool stock you already have usually decides.
The two interfaces side by side
PSC (Capto sizes)
HSK-T
Standard
ISO 26623 (polygon taper with flange contact)
ISO 12164-3, the turning form of HSK
Geometry
Tri-lobe polygon taper
Hollow 1:10 taper with drive slots
Contact
Polygon taper and flange face at the same time
Taper and face at the same time
Torque
Carried by the polygon shape itself — no keys
Carried by drive keys in the slots
Angular position for turning
Set by the polygon
Set by drive slots made to tighter tolerances than HSK-A
Sizes
PSC32, 40, 50, 63, 80, 100 = Capto C3 to C10
HSK40T, 50T, 63T, 100T
Where you find it
Mill-turn milling spindles, and lathe turrets fitted with PSC clamping units
Mill-turn and multi-axis milling spindles
Why turning needs a different interface from milling
A milling tool spins, so it does not care where its cutting edge points when the spindle stops. A turning tool does: the cutting edge has to sit exactly at centre height and stay there under a cutting force that pushes sideways on the tool, not around it. On a mill-turn machine the milling spindle is locked and becomes a tool holder for turning. That only works if the interface holds the tool in a defined angular position and takes the turning load through a stiff contact. PSC does it with the polygon; HSK-T does it with drive slots made to tighter tolerances than standard HSK-A, so a turning tool sits at a defined centre height.
What interchanges and what does not
PSC and Capto of the same size
Yes — PSC sizes are the ISO 26623 coupling sizes that Capto C3 to C10 correspond to. Unit-for-unit interchange with a specific third-party cutting unit is confirmed at the quotation.
PSC in an HSK-T spindle, or the reverse
No. Different coupling geometry. An adaptor is possible but adds length and costs stiffness.
HSK-T and HSK-A
Related, not identical. Same basic taper and clamping, but HSK-T has tighter drive-slot tolerances. Whether they may be mixed in a spindle is set by the machine builder.
HSK-T and HSK-E or -F
No. Different flange and drive forms.
How to choose
The machine spindle decides first. Like BT and HSK on a machining centre, you cannot choose the interface when buying tools. Check the spindle on the machine specification sheet.
If the machine is offered with either, look at what is already in the tool room. Shops that already run HSK-A milling tools on machining centres often stay with HSK; shops with PSC on their lathes often stay with PSC.
Turret and spindle together. With PSC clamping units on the lower turret, the same PSC tool body can be used in the turret and in the milling spindle. That reduces the number of different tools to stock and preset.
Size by load, not by habit. Heavy turning on a large mill-turn machine calls for PSC63 / C6 or larger, or HSK100T; light work on a small machine runs on PSC40 / C4 or HSK40T and HSK50T.
Mongtec range
PSC: PSC32 to PSC100, the sizes that correspond to Capto C3 to C10 — clamping units for VDI and BMT turrets, extensions and reducers, and external and internal turning tool bodies across 50 ISO 5608 styles. PSC (ISO 26623) tool holders →
HSK-T: HSK40T to HSK100T — boring bar holders for bores of 6 to 50 mm, square-shank blocks 20 × 20 to 32 × 32 mm, and 38 integral ISO turning tool types. HSK-T turning tools →
Coromant Capto® is a registered trademark of Sandvik Coromant / Sandvik AB. Mongtec Precision Inc. is an independent tooling brand and is not affiliated with, endorsed by, or a licensee of Sandvik Coromant. The trademark is used only to identify the ISO 26623 coupling sizes.
PSC is the polygon shank coupling standardised in ISO 26623. Its sizes 32, 40, 50, 63, 80 and 100 correspond to the Coromant Capto sizes C3 to C10. Capto is a Sandvik Coromant trademark; Mongtec PSC is an independent product built to the ISO standard.
Can HSK-T tools be used in an HSK-A spindle?
HSK-T is derived from HSK-A and shares the hollow 1:10 taper and the clamping principle, but it is made with tighter tolerances on the drive slots so that a turning tool sits at a defined centre height. Whether HSK-A and HSK-T tools may be mixed in a given spindle is set by the machine builder; check the spindle specification before you do it.
Which is better for turning on a mill-turn machine, PSC or HSK-T?
Both are designed for it: both have taper and face contact and a defined angular position for turning tools. The machine spindle decides which one you use. Where a machine is offered with either, the existing tool stock and whether you also want the same tools on the lower turret usually decide.
Can I use the same PSC tool in the turret and in the milling spindle?
Yes, when the turret has PSC clamping units of the same size. That is one of the main practical reasons shops choose PSC: one tool body, two places on the machine.
Does Mongtec make both?
Yes. Mongtec makes PSC32 to PSC100 clamping units, extensions and turning tool bodies, and HSK-T turning tools from HSK40T to HSK100T, including boring bar holders and square-shank blocks.
