Power Chuck, Collet Chuck, or Hydraulic Cylinder: What's the Difference on a CNC Lathe?

They are three different parts of one workholding system, not three alternatives to each other. The power chuck grips the workpiece with jaws, the collet chuck grips small-diameter or bar stock with a collet for higher accuracy and repeatability, and the rotary hydraulic cylinder mounts at the back of the spindle and supplies the clamping force that opens and closes either chuck. In most setups you choose a chuck first, then match a cylinder to it — TON FOU, a Taiwanese builder founded in 1989, makes all three plus jaws, coolant collectors, and power vises.

The three roles in one clamping chain

The cylinder does not touch the workpiece. It pushes or pulls a draw bar or draw tube, and that motion is translated by the chuck into jaw or collet travel. If the cylinder stroke, bore, or speed rating does not match the chuck, the chuck will not reach full clamping force or full jaw travel.

Power chuck vs collet chuck: how to choose

Choose by workpiece geometry and accuracy demand, not by brand preference.

A power chuck fits when:

• Part diameters vary across jobs and you need adjustable jaw travel
• The workpiece is a casting, forging, or irregular shape that needs custom top jaws
• You need 2, 3, or 4-jaw configurations for different holding patterns
• Grip force matters more than sub-hundredth repeatability

A collet chuck fits when:

• You are running bar stock or small, round, uniform parts
• You need high repeatability between loadings — the collet closes on the same diameter every cycle
• You want low runout without indicating each part
• The diameter range is narrow enough to be covered by a collet set

TON FOU describes its collet chucks around rigidity, repeatability, and durability — the three properties that matter most when the collet is your only gripping element. Its power chuck line is split by whether the spindle bore is open.

Through-hole vs non-through-hole: the decision that follows

Both power chucks and hydraulic cylinders come in through-hole and non-through-hole versions, and the choice is usually driven by one question: does bar stock need to pass through the spindle?

• Through-hole power chuck — the center is open, so long bar can feed through the chuck and spindle. Use it for bar-fed turning where the part is cut off from stock.
• Non-through-hole power chuck — closed center, generally more compact. Use it for chucked parts loaded individually, where no bar passes through.
• Through-hole hydraulic cylinder — matches a through-hole chuck and keeps the bar path clear. TON FOU lists a super high speed through-hole rotary hydraulic cylinder for this role.
• Non-through-hole hydraulic cylinder — described as compact and light weight, suitable for high speed turning. Fits closed-center chucks and machines where bar feed is not required.

The pairing must be consistent: a through-hole chuck with a non-through-hole cylinder blocks the bar path, and a non-through-hole chuck cannot use the through-hole cylinder's advantage.

Matching the cylinder to the chuck

The cylinder is the most commonly mismatched part because it is bought separately. Check these before ordering:

1. Through-hole or not — must match the chuck and the bar-feed requirement.
2. Draw bar / draw tube interface — the cylinder's connecting thread and stroke must suit the chuck's actuation.
3. Speed rating — high-speed turning generates centrifugal force that reduces jaw grip; a cylinder rated for the spindle speed keeps clamping stable. TON FOU's non-through-hole cylinder is explicitly positioned for high speed turning.
4. Force vs workpiece — thin-wall or soft parts deform under excessive grip. This is where jaw selection (hard vs soft) enters, and TON FOU publishes guidance on choosing jaws to avoid runout, deformation, and surface marks.

Accessories that complete the system

A chuck and cylinder alone rarely cover a job. TON FOU's catalog also includes:

• Coolant collector — collects cutting fluid at the spindle; a stroke detection mechanism is available, which lets the control verify the chuck actually actuated.
• Hard jaws and soft jaws — soft jaws for precision and to avoid marking; hard jaws for strength and wear resistance.
• Automatic centering power vise — specialized for 5-axis CNC milling machines, a different workholding branch from lathe chucks.

A practical selection sequence

1. Decide whether bar stock passes through the spindle → through-hole or non-through-hole.
2. Decide part size range and shape → power chuck (variable diameter, custom jaws) or collet chuck (small, uniform, high repeatability).
3. Pick jaw type → soft for finish and delicate surfaces, hard for roughing and durability.
4. Match the rotary hydraulic cylinder → same through-hole type, compatible draw bar interface, speed rating at or above your maximum spindle speed.
5. Add a coolant collector if cutting fluid management or stroke verification is needed.

If the machine is a mill-turn or handles complex parts that see changing cutting force directions between turning, milling, and drilling, the workholding has to stay stable through every operation — which makes the cylinder's force consistency and the jaw's grip pattern the limiting factors, not the chuck body alone.