Grinding wheel care and safety

◉Care and inspection

• Store and handle wheels correctlyWheel

  Observe "do not roll, do not drop, do not knock". Keep wheels on a rack in a dry place

  A shock can cause invisible cracks, and the wheel will burst while spinning^[1][2](1 source, for reference)

• Do a visual inspection and a ring test before mountingWheel

  Look for cracks, fractures and chips, then tap the wheel and listen. OSHA method: with the wheel dry, tap it lightly with a nonmetallic light tool (a screwdriver handle for light wheels, a wooden mallet for heavy ones) about 45° either side of the vertical centerline and 1 to 2 inches from the periphery. Rotate the wheel 45° and repeat. A clear metallic ring means it is good; a dull sound means a crack, so do not use it

  Find cracks made during transport or storage before mounting. Visual inspection and the ring test are also part of the special training curriculum (Special Training Rules for Occupational Safety and Health, Japan). Organic-bond wheels such as resinoid do not ring as clearly as vitrified wheels (OSHA)^[3][1][4]

• Check that the wheel markings match the machineWheel

  Compare the wheel marking (maker, bond type, maximum operating speed) with the grinding machine marking (usable wheel diameter, thickness and bore, direction of rotation, no-load speed) and the guard marking (maximum operating speed, thickness and diameter of usable wheels). Calculate the surface speed from the wheel spindle speed and do not exceed the maximum operating speed

  Using a wheel above its maximum operating speed is prohibited by Article 119 of the Ordinance on Industrial Safety and Health (Japan). The marking requirements are set by Article 29 of the Structural Standard for Grinding Machines (Japan). For wheels under 75 mm in diameter, marking on the smallest package unit is also acceptable (Structural Standard)^[5][6][1][3]

• Do not force on a wheel with the wrong boreWheel

  Do not force it onto the spindle. Do not modify it, for example by grinding out the bore. The wheel should fit loosely on the spindle, and stay loose during grinding

  A tight bore puts large pressure on the wheel from mounting and from thermal expansion of the spindle (OSHA)^[1][3]

• Stop the coolant, then let the wheel spin idle to throw off the fluid before stopping itWheel

  Keep the wheel turning after the coolant supply is stopped, to throw off the coolant soaked into the wheel

  If the wheel is stopped while soaked with coolant, the uneven distribution of water causes unbalance (JTEKT, Noritake). UNITED GRINDING also lists this idle spinning as a countermeasure when chatter occurs^[1][7][8][9]

  Publisher	Applies to	Time
  Noritake	Grinding wheels in general	Spin until it is completely thrown off before stopping (no time given)
  JTEKT Grinding Tools	Wheels that may be used again when the wheel is changed	Run about 10 minutes after stopping the coolant
  UNITED GRINDING	General wheels to be removed before a long shutdown	Spin idle for 20 minutes or more to dry the wheel before removing it

• Use flanges of the same diameter and the same contact width on both sides, with no deformation, scratches, dirt or rustFlange

  Make the diameter and contact width of the fixed-side and movable-side flanges equal. For a straight flange, the diameter must be at least 1/3 of the wheel diameter and the relief at least 1.5 mm (Article 16 of the Structural Standard for Grinding Machines, Japan). Do not use a flange without relief. If the contact faces are worn or deformed, correct or replace them

  If the diameter or contact width differs between the two sides, bending force is applied to the wheel and it cracks. Deformation or foreign matter on the flange face makes the clamping pressure uneven. A safety flange is for straight wheels and must be at least 2/3 of the wheel diameter (Article 18, Structural Standard). OSHA also specifies flanges of at least 1/3 of the wheel diameter, equal on both sides with equal contact faces, with worn or deformed contact surfaces to be corrected^[5][1][3]

• Use the blotter (paper label) that comes with the wheelFlange

  Use a blotter larger than the flange diameter, clean and untorn, covering the whole flange contact face

  The blotter spreads the clamping pressure of the flange evenly (OSHA). The Structural Standard for Grinding Machines (Japan) requires rubber blotters when mounting with a safety flange on a straight wheel. Some types, such as diamond wheels, do not use blotters (OSHA)^[1][3][5]

• Keep foreign matter out between flange and wheel, and tighten the bolts evenly with a torque wrenchFlange

  Make the contact faces (wheel, blotter, flange) flat and clean before assembly. For flanges with several bolts, use a torque wrench at the torque in the work standard so that every bolt carries an equal load. Do not overtighten even when there is a single nut

  A CNC cylindrical grinder wheel burst, believed to be caused by a piece of metal between flange and wheel and by uneven torque from tightening with a hex wrench and a hammer (MHLW case; the 5-minute test run showed no abnormality)^[10][1][3]

• Clean the wheel spindle taper and the flange bore taper, and remove raised edgesFlange

  For a new mounting, clean the taper of the wheel spindle and the taper of the flange bore, and lightly use an oilstone to remove burrs and the raised edges of scratches

  A small amount of dirt can cause unbalance (JTEKT)^[7][10]

• Decide when and how to balanceBalance

  Balance when the wheel is changed and when problems such as chatter appear. Wheels with flanges (general wheels and superabrasive wheels alike) are statically balanced; superabrasive wheels without flanges are generally dynamically balanced (JTEKT)

  Causes of wheel unbalance: uneven distribution of abrasive grain and bond or voids inside the wheel, misalignment between wheel and flange, uneven wear of the wheel, and chips or cracks that soak up coolant (Marposs). Superabrasive wheels without flanges are often dynamically balanced by the maker before shipping. If the wheel is stored assembled on its flange and already adjusted, static balancing at the time of change can sometimes be skipped (JTEKT; depends on surface speed and required accuracy)^{[7][11][12][1]}

• Static balancing (balancing stand)Balance

  JTEKT procedure: (1) check that the balancing stand is level with a spirit level; (2) put a balancing arbor on the flange and set it gently on the stand; (3) let go, and when it comes to rest, mark the flange with chalk at the top (the lightest point); (4) put balance piece 1 at the mark and loosely fit pieces 2 and 3 at 120° from it (do not tighten them fully); (5) move only pieces 2 and 3 a little at a time (toward the lighter side, opposite the side that drops) until the mark stays put at 0°, 90° and 45°; (6) finally check again that it stays at every position and fix the pieces with a hex wrench

  Even a slight weight imbalance becomes runout while rotating, leading to vibration, chatter marks, poor surface roughness and shorter wheel life. If the balancing stand is not level, the wheel cannot be balanced correctly however carefully you work (JTEKT)^[7][1]

• Dynamic balancing on the machine (portable balancer, automatic balancer)Balance

  A portable balancer measures the dynamic balance of the whole grinding machine including the wheel and shows where to put the balance weights (Noritake). An automatic balancer measures vibration while running with a vibration sensor (accelerometer) and moves weights in the balancing head to cancel it. It runs automatically at operating speed between grinding cycles and repeats when vibration exceeds the set value (Marposs)

  Grinding while unbalanced lowers quality and productivity and damages the grinding machine itself (Noritake). Balancing heads come in types built into the spindle, types fitted to the flange (easy to retrofit), and liquid types that balance by putting coolant or oil in chambers in the flange (Marposs)^[2][12][11]

• After mounting a wheel, always true it (remove runout and correct the shape)Dresser

  After mounting, measure the runout of the rotating wheel surface with a dial indicator and make the periphery concentric with the spindle by truing. Also do it when a problem caused by a wheel out of shape appears, such as chatter, feed marks or scratches

  If the wheel center is off the rotation axis from mounting, vibration appears during grinding (JTEKT). Truing (shape correction) removes runout of the periphery and corrects the shape; dressing (sharpening) crushes worn grains to expose new cutting edges and clears loaded chips (Noritake)^[7][13][14]

• Mount a single-point dresser at an angle, turn it from time to time, and apply plenty of coolantDresser

  Set a mounting angle of 10 to 15° in both the direction of wheel rotation and the direction of dresser feed, and bring the tip against the wheel. Turn it around its axis from time to time so the same part of the tip does not wear flat. Apply plenty of coolant to the diamond tip

  Heating carbonizes and wears the diamond (Noritake). Heating and wear of the dresser cause feed marks (UNITED GRINDING). The larger the mounting angle, the finer the surface finish, but the angle is set for each grinding machine (Noritake)^[13][2][8]

• Decide the depth of cut for dressingDresser

  General vitrified wheels: as a guide, a depth of cut of 0.03 mm or less on diameter, about 1/10 of the average grain size (1/20 for wheels with ceramic grain). Noritake technical support gives about 5 µm on radius for precision grinding, 10 to 30 µm on radius for general grinding, and about 40 µm on radius for rough grinding. Do not take a large cut at once

  A smaller depth of cut flattens the grain faces and gives a finer finish but a duller wheel; a larger one gives a sharper wheel and a rougher finish (Noritake). If the total depth of cut (the sum of several passes) is too small, performance does not come back; if it is too large, grain protrusion may be insufficient (Noritake). An SME article advises starting with a depth of cut of 0.0005 to 0.001 inch with a fixed dresser on centerless wheels^{[14][13][2][15]}

• Decide the dressing lead (dresser feed per wheel revolution)Dresser

  As a guide, the dresser should pass over each grain 2 to 3 times (about 2.5 cutting-edge peaks per grain). Dresser feed rate F (mm/min) = average grain size d (mm) × wheel speed N (min⁻¹) / 2.5. Guide values: 0.05 mm/rev for grit 100, 0.1 for grit 60, 0.22 for grit 36 (Noritake)

  In general, changing the dressing lead affects grinding performance more than changing the depth of cut. To fix accuracy, review the lead first (Noritake). A smaller lead gives a finer surface finish but higher grinding force and easier loading; a larger one gives a sharper wheel but a rougher surface. UNITED GRINDING recommends dressing in one direction only and lowering the feed when a spiral pattern appears^{[14][13][2][8]}

• Check the dresser for wear and cracks, and replace it when the tip is flatDresser

  Check for cracks in the diamond, loose mounting and too much shank overhang. Replace a flat-tipped dresser with a new one

  A dresser with a flat tip risks cracking the diamond from heat, and also glazes the wheel face so it cuts less well (Noritake). UNITED GRINDING also lists inspecting and replacing the dressing tool as a countermeasure for a wheel that does not cut (is glazed)^[13][2][8]

• Decide the rotation direction and speed ratio of a rotary dresserDresser

  Vitrified CBN wheels are conditioned with a rotary dresser (a single-point dresser distorts the shape and flattens the cutting edges). Guide values for CBN: depth of cut 1 to 7 µm on diameter, lead 0.01 to 0.2 mm/rev. With the dresser and wheel turning in opposite directions (moving in the same direction at the contact point = down-cut), the wheel cuts more freely; in the same direction (up-cut), the surface is finer. In down-cut, a speed ratio (dresser surface speed / wheel surface speed) of 0.4 to 0.9 is used, and 0.75 or more is common when sharpness is the priority (Noritake)

  For rotary dressers, rotation direction and speed ratio change grinding performance greatly. An SME article (by a Norton engineer) says that in centerless grinding, rotating the diamond roll so that it moves in the same direction as the wheel at the contact point, at 80% of the wheel surface speed, gives the best cutting action. This is the same direction as Noritake's down-cut and speed-ratio guide^[14][16][15]

• Dress the regulating wheel to a shape that matches the tilt angleRegulating wheel

  In through-feed grinding, the regulating wheel is tilted to feed the workpiece. Dress the regulating wheel to the machine maker's offset so that the grinding wheel, workpiece and regulating wheel touch in a straight line (the shape is often a "dog bone" that is thicker at both ends). Guide values from the SME article: feed 5 to 10 inches/min (rough), 1 to 2 inches/min (finish), depth of cut 0.001 inch

  The faster the regulating wheel turns and the larger its tilt angle, the faster the workpiece is fed (Micron Precision). If the contact is not a straight line, feed and accuracy are disturbed (SME). In through-feed grinding the regulating wheel is often tilted about 3° (SME)^[15][17]

• Watch the wear of the centerless wheels and set the dressing intervalWheel

  When wear spoils the surface shape, correct it by dressing. In production centerless grinding, a rotary dresser is more stable (SME)

  With a lot of wear, contact between workpiece and wheel decreases and workpiece accuracy gets worse. The more dressing, the sooner the wheel reaches the end of its life, so holding down the loss of shape and lengthening the interval is what lengthens wheel life (Noritake). Centerless wheels are large and take time and effort to change (Noritake)^[18][15]

• Remove chips, burrs and dents from the holding faceMagnetic chuck

  Wipe the holding face and remove burrs and small dents with a smooth oilstone (IMI Walker says to remove small marks on the chuck mounting face this way)

  Holding force varies greatly with the workpiece material, thickness and area, and also with the roughness of the holding face (Kanetec). With burrs or foreign matter, the workpiece does not sit tight and both holding force and accuracy fall^[19][20]

• Mount the chuck on the table correctlyMagnetic chuck

  IMI Walker procedure: clean the table mounting face and check that it is flat and free of burrs (correct it if it is not flat or not aligned with the machine axes). Also check the flatness of the chuck bottom and clean it just before mounting. For a rectangular chuck, tighten the clamps just enough that it still does not move at first; once it is aligned to the table, tighten alternately a little at a time up to 10 ft·lbf, and finally add torque to 15 ft·lbf on one end only (to allow for expansion when it warms up)

  Dirt or distortion on the mounting faces shows up directly in the accuracy of the chuck face. Kanetec's quality standard says the chuck mounting face "must not be crowned". Check that the electromagnetic chuck body is grounded before energizing it (IMI Walker)^[19][20]

• Energize an electromagnetic chuck and let its temperature stabilize before finishingMagnetic chuck

  After mounting, energize it and, with coolant running, let it come to the average temperature of the machine before grinding the face (IMI Walker)

  The coil heats an electromagnetic chuck. In Kanetec's standard, the temperature rise of the chuck working face is 15 °C or less (3 hours energized). A permanent magnetic chuck does not generate heat, but it also needs time to come to the machine temperature (IMI Walker)^[19][20]

• Regrind the chuck face (face grinding, self-grinding)Magnetic chuck

  After mounting, grind the chuck face to align it with the machine's axes of motion. IMI Walker's guide: a medium-hard, open-structure (many pores) general-purpose wheel of grit 36 to 40, wet grinding (coolant free of nitrite, or with an inhibitor). True the wheel before each grinding pass. Do not spark out after the final pass (a normal grinding finish makes workpieces slide less). The guide for stock removed from the top plate is up to 1/3 of its thickness

  Grinding with a loaded wheel heats the chuck, makes its center bulge and badly damages flatness (IMI Walker). When grinding the bottom face, do not clamp the chuck by energizing it; hold both ends with blocks (IMI Walker). Do not grind dry^[19][20]

• Choose a coolant that does not damage the chuck, and prevent rustMagnetic chuck

  For chucks with brass or resin separators, choose a coolant that is less corrosive to them (consult the coolant maker, Kanetec). IMI Walker specifies a coolant free of nitrite or with an inhibitor

  Corrosion of the separators or bonded parts lowers holding force and surface accuracy^[20][19]

• Remove residual magnetism (demagnetizing) and demagnetize workpiecesMagnetic chuck

  With an electromagnetic chuck, switching off the current alone leaves residual holding force that makes the workpiece hard to remove. Weaken the residual magnetism with a demagnetizer (alternating decaying field) before removing it. If the workpiece itself is magnetized, run it through a degausser. Pass it slowly over the face of a table-type degausser and keep moving it until it is about 20 cm or more from the edge (recommended 3 to 5 m/min, about 5 seconds to pass)

  With residual magnetism the workpiece is hard to remove, and chips and iron dust stick to it, causing scratches and defects. In Kanetec's terms, electrically reducing the residual magnetism of an electromagnetic chuck is "demagnetizing", and forcibly reducing the residual magnetism of tools and workpieces is "degaussing". The face of some degaussers gets quite hot by electromagnetic induction and metal objects nearby also heat up, so keep 5 cm or more from the face (30 cm or more for tunnel types). Some materials are hard to degauss depending on their heat treatment^[21][22][23](1 source, for reference)

÷Calculating wheel surface speed and spindle speed (checking that the maximum operating speed is not exceeded)

1. Read the maximum operating speed (m/s) from the wheel marking (older markings are in m/min)
2. Check the wheel spindle speed n (min⁻¹) of the grinding machine and the outside diameter D (mm) of the wheel
3. Surface speed v (m/s) = 3.14 × D × n / 60000 (divide by 1000 for m/min)
4. v must be at or below the maximum operating speed. Conversely, the upper limit of speed is n = maximum operating speed (m/s) × 60 × 1000 / (D × 3.14)

Speed (Noritake's formula)

Speed (min⁻¹) = surface speed (m/s) × 60 × 1000 / (wheel outside diameter (mm) × 3.14)

m/s and m/min

1 m/s = 60 m/min (Noritake's conversion table: 33 m/s ≒ 2000 m/min, 45 m/s ≒ 2700 m/min, 60 m/s = 3600 m/min)

Worked example: conditions

Surface grinder in MHLW case 101224: wheel outside diameter 405 mm, maximum operating speed 1800 m/min, motor speed 1450 min⁻¹

Worked example: result

Surface speed = 3.14 × 405 × 1450 / 1000 ≒ 1844 m/min, which exceeds the maximum operating speed of 1800 m/min (the case also judged it to be exceeded; the calculation is an estimate from these figures)

Fitting a wheel with a larger outside diameter, or changing the motor or pulley, changes the surface speed. Article 119 of the Ordinance on Industrial Safety and Health (Japan) prohibits use above the maximum operating speed^[24][25][6]

▦Grinding wheel speed conversion table (Noritake, unit min⁻¹)

Each value is the speed that gives that surface speed. Do not run faster than the speed in the column for the maximum operating speed. The calculation uses 3.14^[24](1 source, for reference)

▦Limits of ordinary working surface speed for grinding wheels (appended table of the Structural Standard for Grinding Machines, Japan; unit m/s)

This is the upper limit treated as "ordinary speed"; there are also high-speed wheels above it. The speed you may use is, in the end, the maximum operating speed marked on each individual wheel. For imported wheels marked in feet per minute, convert 6500 = 33, 8500 = 45, 9500 = 50, 12000 = 60, 16000 = 80 and 20000 = 100 m/s (from the notes to the same table)^[5](1 source, for reference)

▦Straight flange dimensions (Article 16 of the Structural Standard for Grinding Machines, Japan)

Make the diameter and contact width equal on the fixed and movable sides (Article 15). A safety flange must be at least 2/3 of the wheel diameter for straight wheels and at least 1/2 for double-tapered wheels, with a contact width of at least 1/6 of the flange diameter (Article 18). Sleeve flanges and adapter flanges use a different formula (Article 17). Example: for a wheel 305 mm in diameter, a straight flange must be about 102 mm or more in diameter^[5](1 source, for reference)

÷Calculating the dresser feed rate (Noritake's guide: about 2.5 cutting-edge peaks per grain)

1. Read the average grain size d from the table for the wheel's grit size
2. Check the wheel speed N (min⁻¹)
3. Dressing lead f (mm/rev) = d (mm) / 2.5
4. Dresser feed rate F (mm/min) = f × N = d × N / 2.5

Worked example: conditions

Grit 60 (average grain size 0.25 mm), wheel speed 1800 min⁻¹

Worked example: result

Lead = 0.25 / 2.5 = 0.1 mm/rev, feed rate = 0.1 × 1800 = 180 mm/min (estimate)

Grain size is a reference value treating the grain as a sphere (Noritake catalog). For a finer surface roughness, make the lead smaller; for a sharper wheel, make it larger. Depth of cut: 0.03 mm or less on diameter^[14][13][2](1 source, for reference)