Lathe chuck care

◎Care and inspection

• Greasing intervalHydraulic power chuck

  Around once a day (once per shift) is common. Shorten it for high-speed rotation or heavy use of water-soluble coolant

  The most common cause of chuck trouble is insufficient or unsuitable lubrication. Wear progresses, and the workpiece can come loose for lack of gripping force (Howa Machinery). Haas's maintenance schedule RD0035 says "weekly". For one shift a day, Kitagawa, Howa, and RÖHM are about the same, while SCHUNK NCO2 and Haas are longer^{[1][2][3][4][5][6][7][8]}

  Publisher	Applies to	Interval
  Kitagawa	Standard power chucks (BR, B-200, etc.)	Daily (once at the start of work). Shorten for high speed or heavy use of water-soluble coolant
  Howa Machinery	Power chucks (H011MC, H01MA, etc.)	Once every 8 hours. Once every 4 hours if cutting fluid is constantly applied
  RÖHM	Manually lubricated power chucks	Every 8 operating hours or 1000 grips (about 0.5 cm³ per nipple)
  SCHUNK	ROTA NCO2 (wedge type)	Every 24 operating hours
  SCHUNK	ROTA TB (pneumatic)	Normally daily or every 16 hours; with heavy coolant use, every shift or every 8 hours
  Hurco	Chuck on TM-series CNC lathes	Daily
  Haas Automation	Chuck on CNC lathes	Grease the jaws weekly

• Amount of grease per pointHydraulic power chuck

  Kitagawa BR, per master jaw nipple: BR05: 3 g, BR06: 4 g, BR08: 6 g, BR10: 10 g, BR12: 12 g

  Without a guide for the amount, too much or too little gets put in. RÖHM uses about 0.5 cm³, which is an order of magnitude different. Follow the manual for each model for the amount, and do not generalize^[2](1 source, for reference)

• How to greaseHydraulic power chuck

  Turn off the main power, set the jaws to the specified position, and apply grease to the nipple of each master jaw with a grease gun. After greasing, open and close the jaws several times without gripping a workpiece to spread the grease

  If it goes into only some points, it does not reach the sliding surfaces, and uneven distribution causes imbalance. The jaw position for greasing differs by model. Kitagawa BR, Howa H3KTA, and RÖHM use the "open" state; Howa H011MC and SCHUNK ROTA TB use the "closed (retracted)" state. For the Howa H011MC, greasing in the open state may not reach the sliding surfaces, or overfilling may keep the jaws from closing^{[2][4][3][5][7]}

• When you have put in too much greaseHydraulic power chuck

  Remove the plug of the grease relief hole on the chuck body's outer circumference, and open and close the jaws to push out the excess grease

  Overfilling makes the draw sleeve move heavily^[3](1 source, for reference)

• Grease to usePower chucks and manual chucks

  Use the grease specified by the chuck manufacturer. Howa and Hurco use Molykote EP grease, SCHUNK uses LINOMAX plus, RÖHM uses the lithium soap-based F80, and Kitagawa uses its dedicated CHUCK GREASE PRO

  Using a non-specified grease has bad effects on gripping force, friction, and wear. Kitagawa says that ordinary lithium grease tends to squeeze out of the contact surfaces under high loads^{[3][8][6][5][2][9]}

• Occasionally move the jaws from end to endPower chuck

  If you keep using the chuck with a short stroke (less than half of the full stroke), move it through to the end several times at least every 500 grips

  Returns grease to the force-transmitting surfaces and keeps the gripping force high^[6][10](1 source, for reference)

• Measure the gripping force with a gripping force meterPower chuck

  Measure the actual gripping force periodically with a gripping force meter. Measure under the same conditions as in use (same jaws, same step)

  Even chucks of the same specification vary greatly in gripping force depending on the condition of the grease, the shape of the jaws, and the viscosity of the hydraulic oil. An unexpected drop leads to the workpiece being thrown (Kitagawa)^{[11][7][6][3][5]}

  Publisher	Frequency
  Kitagawa	Not specified (recommends control with a gripping force meter, and checking after reassembly)
  Howa Machinery	Depending on use, it needs to be measured periodically (cites the guidelines of ANSI B11.6)
  RÖHM	Weekly at the start of operation, and just before the next greasing
  SCHUNK	The user decides. Also before new production and between maintenance
  RÖHM (DURO-A RC)	6000 hours or once a year

• Grease when the gripping force drops to 80% of the maximumPower chuck

  If periodic gripping force measurement shows only 80% of the maximum gripping force, apply grease (SCHUNK)

  The greasing interval can be set to suit actual use^[6][7](1 source, for reference)

• Check that the gripping force is maintainedPower chuck

  Leave the gripping force meter gripped for more than 10 minutes and check that the gripping force does not fall. At least every 5000 grips (SCHUNK)

  Check whether gripping force is being lost through leaks in the cylinder or seals^[7](1 source, for reference)

• Disassembly and cleaningPower chuck

  Disassemble and clean it from time to time, and replace worn or damaged parts

  Even when greased, fine chips and scale collect inside and hinder movement (Howa). Coolant washes the grease away (SCHUNK)^{[2][12][9][3][4][6][7][5]}

  Publisher	Interval
  Kitagawa	6 months or 100,000 strokes (2 months when machining castings)
  Howa Machinery	1000 hours
  SCHUNK	ROTA NCO2: once a year or 2500 hours; ROTA TB: when needed or 1200 hours depending on how dirty it is
  RÖHM	Decide at the shop. At the latest when the movement becomes heavy or the gripping force drops

• Chips insidePower chuck

  If a lot of chips have gotten inside, disassemble and clean it

  When chips build up, gripping force drops and the jaw stroke becomes insufficient. Machining in that state lets the workpiece come loose^[3][7][13]

• Check the jaw strokeHydraulic power chuck

  Before work, open and close the jaws without gripping a workpiece and check that the master jaw reference line moves through the full stroke. When gripping a workpiece, the reference line should be within the proper range (1 to 2.7 mm for Kitagawa BR). Howa says to grip within the range that excludes 1/4 of the stroke at each end

  If the stroke is insufficient because of chip buildup or a loose draw nut, there is a danger that the spindle turns without gripping the workpiece^[2][14][4]

• Clean the chuck at the end of workPower and manual

  Blow chips off the body and sliding surfaces with an air gun or similar (Kitagawa)

  Prevents chips from getting inside. RÖHM cautions against blowing air into the jaw guides and gaps (it pushes chips deeper). Hardinge and HAINBUCH also say not to use compressed air on some parts^[2][15](1 source, for reference)

• Check for loose boltsHydraulic power chuck

  Check every 3 months that the bolts on each part are not loose (Kitagawa BR, B-200)

  Spinning with loose bolts throws the jaws and the workpiece^[2][12](1 source, for reference)

• Clean the mounting surfaces when changing jawsPower and manual

  Clean the mounting surfaces and serrations of the top jaws and master jaws (base jaws) before fitting them. For dirt that compressed air does not blow off, loosen it with cleaning oil and brush it (Howa)

  Leftover debris reduces runout accuracy^[3][7][2]

• Tighten the jaw mounting bolts to the specified torqueHydraulic power chuck

  Tighten the supplied bolts to the specified torque with a torque wrench. Kitagawa: M8: 33, M10: 73 N·m (strength class 12.9); Howa H01MA: M8: 29.4, M10: 57.9 N·m. Use 2 bolts per top jaw (Howa)

  Insufficient tightening, too few bolts, or wrong length leads to bolt breakage and jaws and workpieces being thrown. SCHUNK says that insufficient tightening causes large runout. Use the tightening torque for each model^{[14][2][4][7]}

• Bore soft jaws under the same conditions as for machiningPower and manual

  Bore with the same hydraulic pressure as in machining for power chucks (Kitagawa says the same or slightly higher), and with the same handle torque for manual scroll chucks

  If the gripping conditions differ between boring and machining, poor accuracy and slipping result^{[3][7][2][15]}

• Jaw position when gripping a workpiecePower chuck

  Howa says to grip near the middle of the stroke. SCHUNK says to use only up to 2/3 of the stroke and keep the rest as a margin

  Gripping at the end of the stroke leads to missed grips and insufficient gripping force^[3][7]

• Do not extend the jaws too far outPower chuck

  Soft jaws should preferably not stick out beyond the chuck's outer diameter (MHLW manual). Howa says to keep the top jaw adjustment within the range in the dimension table, and Kitagawa says to use it with the T-nut not protruding from the outer circumference side of the master jaw

  Extending them out increases centrifugal force and leads to damage to the master jaws and jaw nuts^[16][4][14]

• Lower the conditions when using heavy or tall jawsPower chuck

  Do not use top jaws heavier than the standard soft jaws (Howa). For heavy jaws or jaws with the center of gravity far out, calculate the gripping force loss from centrifugal force and reduce the input and the spindle speed (Kitagawa)

  The heavier the jaws, the more gripping force is lost when spinning^[3][17][2]

• Do not exceed the maximum permissible speedPower chuck

  Review the spindle speed for each job and do not exceed the maximum permissible speed. Decide the required gripping force and rotation speed by test cuts, and confirm that the gripping force is there before machining (Kitagawa)

  In outside-diameter gripping, gripping force decreases with rotation by the amount of centrifugal force, and when the limit is exceeded the workpiece suddenly comes loose. Howa sets the maximum speed as "the speed at which the gripping force falls to 1/3 of that at standstill". Kitagawa (citing JIS B 6150) and SCHUNK (citing EN 1550) say "keep the loss from centrifugal force to 2/3 of the static gripping force or less", which is the same idea^{[3][17][2][6]}

• Lock valve and solenoid valve circuit for the rotating cylinderHydraulic power chuck

  Use a cylinder with a built-in lock valve (check valve), and use a circuit in which the solenoid valve keeps the grip even if power is cut. Do not stop the hydraulic pump or operate the switching valve while the spindle is rotating

  Prevents gripping force from being lost instantly in a power failure or pump failure. Kitagawa presents this as a requirement of JIS B 6150:2015^[14][18][4]

• Manage the hydraulic oil of the rotating cylinderRotating hydraulic cylinder

  The hydraulic oil should be an anti-wear, anti-foaming oil equivalent to ISO VG32 (32 mm²/s at 40°C). Kitagawa SR: change about every half year and wash the strainer every 2 to 3 months; Howa C1TA: change about once a year, strainer about once a month, and drain water from the tank bottom about once a week

  Contamination or deterioration of the hydraulic oil affects the cylinder's heat generation, drain volume, and operating speed. Howa says cleanliness matters most because the drain oil cools and lubricates the bearings^[19][18]

• Reset the hydraulic pressure when you change the chuckHydraulic power chuck

  The slope of "hydraulic pressure vs. gripping force" differs by chuck type, so recalculate the pressure from the input that gives the same gripping force as before the swap. Example: what was 1.7 MPa with BB208 + SR1566 needs 2.0 MPa with BR08 (Kitagawa)

  Even at the same hydraulic pressure, the gripping force changes^[11][20](1 source, for reference)

• Check the chuck pressure gaugeHydraulic power chuck

  Hurco's TM series sets the upper limit of chuck hydraulic pressure at 40.8 kg/cm², raising it for hard materials and lowering it for soft ones. In an exercise example in the MHLW CNC lathe manual, you check that the pressure gauge reads about 1 MPa after gripping

  Hydraulic pressure determines gripping force^[8][16]

• Lubricate the manual scroll chuckManual scroll chuck

  1 to 2 times a day. Increase the frequency for high speed or heavy use of water-soluble coolant. For Kitagawa's JN type, use a grease gun on the nipple; for the SC type, use ISO VG32-equivalent oil in the ball cup

  Poor lubrication leads to malfunction, reduced gripping accuracy, seizure, and workpieces being thrown because of lost gripping force^[15][21](1 source, for reference)

• Disassembly and cleaning of manual scroll chucksManual scroll chuck

  Every 6 months or 20,000 grips (at least once every 2 months for castings and similar). If chips get into the scroll or gears, disassemble and clean immediately. To disassemble, remove the knock pin and pinions first, then take off the cover

  Prevent wear of the scroll and pinions^[15](1 source, for reference)

• Always remove the chuck keyManual chuck

  Remove the key after tightening. Do not push a pipe onto the key handle to force it tighter (Kitagawa). Hardinge also says to remove the chuck wrench before starting. Do not defeat SCHUNK's mechanism that keeps the key from remaining inserted

  Spinning with the key left in throws the key^[15][22][10]

• Gripping accuracy of scroll chucks and part replacementManual scroll chuck

  Kitagawa adjusts its chucks to a gripping accuracy of 30 µm or less in the assembled state before shipping. Replacing even one part may keep it from returning to its factory accuracy

  For an old scroll chuck, replacing it may be more economical than repairing it^[11](1 source, for reference)

• Inspection after a crashPower and manual

  If a tool or turret hits the chuck, stop immediately, disassemble and clean it, and check for damage and cracks (Kitagawa). SCHUNK says to crack-test the chuck and jaws after a collision before use

  Using a damaged chuck leads to chuck breakage and workpieces being thrown^[14][6]

• Warning signs before failurePower chuck

  If slipping, chatter, worsening accuracy, increased vibration, or gripping force that does not rise even when hydraulic pressure is raised appears, take the countermeasures in the manual, and if it does not fix the problem, stop using the chuck (Kitagawa)

  Stopping chuck breakage before it happens^[14](1 source, for reference)

• Chuck standards—

  JIS B 6151:2015 Scroll chucks (three-jaw scroll chucks), JIS B 6150:2015 Safety requirements for workholding chucks (identical to ISO 16156:2004), JIS B 6152:2008 Test conditions for manually operated self-centring chucks with one-piece jaws (identical to ISO 3089:2005)

  ISO 16156 is out for ballot on a draft revision as of November 2025 (MTA, the UK machine tool trade association)^{[23][24][25][26]}

÷Calculating gripping force and hydraulic pressure for power chucks (Kitagawa Iron Works procedure)

1. From the height of the jaw gripping center, read the chuck's maximum static gripping force from the figure in the manual, and set the static gripping force at or below that
2. Find the mass moment = mass of one jaw × radius of its center of gravity × number of jaws, and read the gripping force loss at the machining speed from the figure
3. Dynamic gripping force = static gripping force − gripping force loss
4. Gripping torque = dynamic gripping force × friction coefficient × gripping radius; moment resisting tipping = dynamic gripping force ÷ number of jaws × (2/3 × gripping length + k × friction coefficient × 2 × gripping radius)
5. Cutting torque = depth of cut × feed × specific cutting force × cutting radius; tipping moment = depth of cut × feed × specific cutting force × distance from the gripping center to the cutting position
6. Check that the gripping torque and the moment resisting tipping are sufficiently large compared with the cutting torque and the tipping moment
7. Read the input needed for the required static gripping force from the figure, and find the hydraulic pressure from the cylinder formula

k (coefficient by number of jaws)

2 jaws 1/2, 3 jaws 3/4, 4 jaws 2

Recommended safety factor

Against cutting torque: 2.5 or more for continuous cutting, 3.5 or more for interrupted cutting; against tipping moment: 3.0 or more for continuous, 4.0 or more for interrupted

Cylinder thrust and hydraulic pressure

Working thrust Q = maximum thrust Qmax × (working pressure P − 0.25) ÷ (maximum working pressure Pmax − 0.25). 0.25 MPa accounts for mechanical loss

Gripping force and thrust

Chuck gripping force = maximum static gripping force × (cylinder thrust ÷ permissible maximum input)

Loss from centrifugal force (Kitagawa BR manual)

The loss is proportional to the square of the rotation speed. With jaws heavier than standard, add ΔFc = number of jaws × (m×r − m0×r0) × (2π×n/60)² × 10⁻⁶ [kN] (m and r are the mass in kg and center-of-gravity radius in mm of the jaws in use; m0 and r0 are those of the standard soft jaws)

Inside-diameter gripping

Keep the input at 1/2 or less of the permissible maximum input for outside-diameter gripping

Worked example: conditions

BB208, jaw mass 1.2 kg, center-of-gravity radius 72 mm, gripping center height 60 mm, gripping radius 80 mm, gripping length 15 mm, distance from gripping center to cutting position 20 mm, spindle speed 3500 min⁻¹, friction coefficient 0.1, depth of cut 1.5 mm, feed 0.2 mm/rev, specific cutting force 2100 N/mm², cylinder SR1566 (maximum thrust 45.0 kN, maximum working pressure 4.0 MPa)

Worked example: result

Static gripping force 60 kN, mass moment 259.2 kg·mm, gripping force loss 38 kN, dynamic gripping force 22 kN, gripping torque 176 N·m (cutting torque 50.4 N·m), moment resisting tipping 161.3 N·m (tipping moment 12.6 N·m), required input 24 kN, hydraulic pressure 2.25 MPa

Kitagawa cautions that this calculation is simplified and that the final values should be decided only after confirming with a test cut^[17][2](1 source, for reference)

▦Kitagawa BR series maximum speed and gripping force (3-jaw hydraulic power chuck)

The dynamic gripping force is the value with standard soft jaws mounted flush with the outer circumference. For every model, static − loss = dynamic^[27][2](1 source, for reference)