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BPF or BPT? A Quick Guide to Choosing the Right Unclamping Cylinder for Your Spindle

2026/ 09/ 22

The single most common question we hear from machine builders is simple: BPF or BPT? The answer depends entirely on one thing — how the spindle itself is driven, not on tonnage or brand preference.

I. The One Question That Decides It

Ask: does the spindle have a separate motor connected by a belt or gears, or is the motor built directly into the spindle housing?

  • Belt-driven or gear-driven spindle: the unclamping cylinder sits directly on top of the spindle and pushes the drawbar. This is a direct mechanism — choose from the BPT family.
  • Direct-drive or built-in-motor spindle (usually with through-spindle coolant): there is no room for a cylinder on top of the spindle, so a hollow hydraulic cylinder (HUC) sits at the spindle and a booster mounted nearby drives it through a hose. This is an indirect mechanism — choose from the BPF family.

II. Inside the BPT Family (Belt- and Gear-Driven Spindles)

  • BPT — standard, three sizes: 3.5T / 4.5T / 7T, matched to drawbar force.
  • BPTQ — the high-speed version, with the HINAKA quick-exhaust valve.
  • BPTH / BPTHQ — the high-tonnage version (code 70, 7-tonne output) for large gantry machines and heavily loaded spindles.
  • DJ2A — all-pneumatic, no oil near the spindle bearings, for drawbar forces up to 1,000 kg; interchangeable with BPT via an adapter plate.
  • BPT-D — the Dual-Oil version, for horizontal mounting or humid environments.

III. Inside the BPF Family (Direct-Drive and Built-In-Motor Spindles)

  • BPF — standard, single-casting aluminium oil chamber, boost ratios 6.25:1 to 51:1, oil volume 50 to 220 cc.
  • BPFQ — the high-speed version, with the HINAKA quick-exhaust valve.
  • BPF-D — the Dual-Oil version, for horizontal mounting or through-spindle-coolant spindles.
  • HUC — the hollow hydraulic cylinder every BPF drives, available with or without through-spindle coolant.

IV. Still Not Sure?

If you are not sure which mechanism your spindle uses, the drawbar force and stroke on the spindle maker's data sheet are usually enough for us to confirm. Tell us your spindle type and model, taper (BT30/40/50), required drawbar force and whether it has through-spindle coolant, via Contact Us — we will size the cylinder for you.

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