Problem: No Spindle Taper Available for a Face Driver
A Haas SL-30 fitted with a Kitagawa power chuck is actuated by a hydraulic cylinder through a cylindrical draw tube. That draw tube passes straight through the spindle bore, so the spindle nose does not present a usable internal Morse taper for a conventional taper-shank face driver. The classic shop solution — knock a Morse-taper face driver into the spindle and back it up with a drawbar — is not available.
The requirement is unchanged: drive a shaft-type workpiece from the face so the full outside diameter can be turned between centers in one operation, with no jaw marks and no re-clamping for the second end.
Three Mounting Strategies
| Strategy | Interface | Strengths | Limitations |
|---|---|---|---|
| Flange-mount face driver | Bolted to spindle nose or a purpose-made adapter plate (chuck removed) | Highest rigidity and repeatability; best for heavy roughing cuts | Chuck must come off; changeover is slow; adapter plate must match the spindle nose standard |
| Shank-type face driver clamped in soft jaws | Cylindrical body of the driver gripped by bored soft jaws | Chuck stays on the machine; setup and teardown in minutes; the same driver moves to another lathe | Concentricity depends entirely on how well the jaws are bored; grip force limits torque transmission |
| Dedicated boring-bar / stub-arbor holder | Driver shank held in a hardened bushing or arbor gripped by hard jaws | Repeatable indexing if the bushing stays with the machine | Extra part to make and store |
Face drivers with a mounting flange instead of a taper shank are catalogued by tooling suppliers including Sandvik, Hoffmann and Neidlein. Shop experience on Kitagawa-equipped lathes shows that a shank-type unit clamped in bored soft jaws is the fastest route back to production and is the option most commonly used in practice.
Soft-Jaw Clamping Procedure
This is the low-cost, no-teardown route. Bore the jaws in place, at the pressure you will actually run, so the bore is round when the driver is gripped.
- Fit a matched soft-jaw set. Use jaws that are new or have not been bored to a smaller diameter. Torque the jaw mounting screws to the chuck manufacturer's value and record the serration position so the set can be re-installed identically.
- Set clamping pressure before boring. Choose the hydraulic pressure you will use in production for the face driver, and bore at that pressure. Boring at high pressure and running at low pressure (or the reverse) produces a three-lobed bore and runout.
- Load a boring ring or plug. Grip a boring ring on the jaw step opposite the intended clamping step so the jaws are loaded outward in the same direction as when the driver is clamped. Without this, the jaws bell open and the bore is tapered.
- Bore to the driver body diameter. Bore a straight bore to a light interference-free fit — target the measured shank diameter with a small negative offset so the jaws close slightly onto the shank. Bore a length at least equal to the intended grip length; the deeper the grip, the better the resistance to tipping moments.
- Bore relief for the shoulder. If the driver has a shoulder or flange behind the body, either bore a counterbore in the jaws for it or plan to seat that face against the jaw front faces — seating a shoulder squarely helps axial location and repeatability.
- Install the driver, clamp, and index. Scribe or mark the driver body against jaw #1 so that after any removal the driver returns to the same angular position.
Alignment and Runout Verification
A face driver only works if its center point is on the spindle axis; otherwise the workpiece runs out at the tailstock end and the drive pins load unevenly.
- Center point radial runout: mount a dial or test indicator on the turret/carriage, contact the driver's center point close to the tip, and rotate the spindle slowly by hand or in low RPM jog. Record total indicator reading (TIR).
- Body runout: repeat on the ground cylindrical body of the driver to separate a bent/damaged center from a poorly bored jaw set.
- Face squareness: indicate the driver's front face to check it is perpendicular to the axis; a cocked mounting shows up as face wobble even when the OD runs true.
- Acceptance limit: set the limit from the part tolerance you must hold, not from a generic number. A practical rule is that the driver's runout should be a small fraction of the diametral tolerance of the turned feature, because runout at the drive end transfers directly into taper and concentricity error along the shaft.
- Re-check after the first cut: take a light skim pass along the workpiece OD, then measure at both ends. A diameter difference between headstock end and tailstock end indicates axis misalignment, not just driver runout — check tailstock alignment before re-boring jaws.
Torque, Pin Penetration and Tailstock Force
Face drivers transmit cutting torque through hardened pins that bite into the workpiece face while a spring-loaded center holds the part on axis. Three variables must be balanced:
| Variable | Effect if too low | Effect if too high |
|---|---|---|
| Tailstock thrust | Pins do not penetrate; part slips and pins polish/skid on the face | Excessive deflection of slender shafts; center and pin wear; part bows and turns barrel-shaped |
| Depth of cut / feed | Long cycle time | Torque demand exceeds pin grip — the part rotates relative to the driver, scoring the face |
| Chuck hydraulic pressure (soft-jaw mounting) | Driver body slips or shifts in the jaws | Jaw bore distortion, driver body marking, and loss of the bored-in-place concentricity |
Follow the face driver manufacturer's published thrust and torque ratings for the specific model — pin count, pin diameter, pin circle diameter and center spring rate all vary by unit and determine the transmissible torque. Do not extrapolate a torque figure from a different driver size.
Choosing Between Flange-Mount and Soft-Jaw Mounting
- Run a flange-mount driver when the job is a long production run, cuts are heavy, and the machine can be dedicated — removing the Kitagawa chuck and bolting the driver (or an adapter plate) to the spindle nose gives the stiffest, most repeatable setup and removes the chuck mass from the front of the spindle.
- Run a shank-type driver in soft jaws for mixed work, prototype and short runs, or when the same driver must serve several lathes. Keep one dedicated soft-jaw set bored for the driver, stored as a matched set with the jaw positions marked; reinstalling that set restores the setup without re-boring.
- Keep a spare bored jaw set if the driver moves between machines — each machine's chuck will need its own bored jaws, since the bore is only true on the chuck it was bored on.
Common Failure Modes
| Symptom | Likely cause | Corrective action |
|---|---|---|
| Part end runs out at tailstock | Driver center not concentric with spindle axis, or tailstock offset | Indicate driver center; re-bore soft jaws with a boring ring at production pressure; check tailstock alignment |
| Circular scoring / smeared marks on part face | Pins slipping — torque demand exceeds grip | Increase tailstock thrust within the driver rating, reduce depth of cut/feed, verify face is flat and not case-hardened |
| Taper along turned OD | Excessive thrust bowing a slender shaft, or headstock/tailstock misalignment | Reduce thrust, support with a steady rest, verify alignment with a test bar |
| Driver shifts in the jaws mid-cycle | Insufficient clamping pressure or too short a grip length | Raise chuck pressure within chuck and driver limits; increase bored grip length; add a shoulder stop |
| Bore in soft jaws is bell-mouthed or lobed | Bored without a boring ring, or bored at a different pressure than used in production | Re-bore with a boring ring in the opposite jaw step at the production clamping pressure |
Why can't I use a Morse taper face driver on a Haas SL-30 with a power chuck?
The hydraulic chuck is actuated by a cylindrical draw tube running through the spindle bore, so there is no usable internal Morse taper or drawbar arrangement at the spindle nose to retain a taper-shank driver. You need a flange-mount driver or a shank-type driver clamped in the chuck.
Can a face driver be clamped in chuck jaws instead of the spindle?
Yes. Clamping a cylindrical-body face driver in soft jaws bored to the driver diameter is a proven setup on Kitagawa-equipped lathes. It keeps the chuck on the machine and allows the driver to be moved between lathes, provided each lathe has its own bored jaw set.
How do I bore soft jaws for a face driver?
Load a boring ring on the opposite jaw step, set the hydraulic pressure to the value you will run in production, then bore a straight bore matching the driver body diameter over the intended grip length. Boring without a ring or at a different pressure produces a lobed or bell-mouthed bore.
What runout is acceptable on a face driver center?
Derive the limit from the part tolerance rather than a generic figure: the driver's TIR at the center point should be a small fraction of the diametral tolerance you must hold, because drive-end runout translates directly into taper and concentricity error along the shaft.
The pins are skidding and scoring the workpiece face — what do I change?
Torque demand is exceeding pin grip. Increase tailstock thrust up to the driver's rated limit, reduce depth of cut and feed, and confirm the workpiece face is flat, clean and not hardened so the pins can penetrate evenly.
