Troubleshooting guide for Centreless Grinding

Below, are listed problems, which may be encountered whilst grinding. Under each are listed probable causes, and under each cause, possible corrections. Possible corrections are used advisedly here. It is practically impossible to establish hard and fast rules for turning out perfect grinding. There are many variables, which must be correctly attuned, and variables which must be correctly attuned, and an apparently irrelevant one may prove to be cause of trouble experienced. Also, the same cause may produce a varied number of grinding problems.

SCRATCH MARKS ON WORK

 

Improper work support blades
Change blade to a softer material; if tungsten carbide was used,
try steel, cast iron or aluminium bronze.

Wide irregular marks, varying in depth, from too soft a wheel
Use harder grade wheel.

Widely spaced spots on work piece due to oil or glazed spots on wheel
True spots out of wheel, balance and redress.
Avoid getting oil on wheel.

Even fine spiral diamond lines
Dress at slower traverse rate. 
Turn diamond frequently. 
Diamond cracked or broken; replace. 
Turn diamond frequently. 
Diamond cracked or broken; replace.
Diamond holder loose; tighten clamping screw.
Try lighter diamond cuts.
Make final dressing in opposite direction to initial runs.

Even spiral lines on work piece whose lead corresponds to feed rate.
Dress wheel face parallel to work piece to prevent leading or trailing edge from digging in.
Use crowned cam when dressing grinding wheel.
Cut back front of face of wheel approximately half of stock removal over 1" distance for a six-inch wheel (relatively more on wider wheels)
Increase or decrease successive traverse rates to break pattern of diamond lines. When throughfeed grinding, make certain guides on regulating wheel side are parallel and even with wheel face.

Uneven fine lines on work piece due to faulty dressing
Do not allow diamond to dwell on wheel. Barely contact wheel face at high spot—dress across face only, starting at an edge, do not start on face. Maintain diamond traversing at an even rate.

Uneven, or evenly spaced lines on work piece due to extraneous vibrations
If impossible to change machine location, mount grinder on some vibration insulating material. Be certain insulation is thick enough to be effective.
If it is not sufficient, the natural frequency of grinder normally damped out by rigid construction may be emphasised and combine with external vibration to make conditions worse.

Wavy traverse lines due to faulty dressing, leaving ragged wheel edges.
Round off wheel edges nicely—chamfering or dressing back is not sufficient.

Irregular grit marks as result of wheel bond’s disintegrating. ("Fish Tails".)
Try a different coolant, or if soluble oil used, cut down soda content of coolant. High soda concentrations attack resinoid and shellac bonds. Wheel too soft—use harder grade.

Coarse grains or foreign matter in wheel face.
Dress these out of wheel.
Determine whether caused by type of wheel, dull diamond, dirty or too strong a coolant.

Irregular scratches of various lengths and sizes due to dirty coolant. ("Fish tails.")
Empty and clean tank, lines, guards, etc. Flush guards and wheel after each truing. Use coolant filter for fine finishes.

Too great a difference in grain size between roughing and finishing wheels.
Dress roughing wheel at slower traverse rate. 
If this doesn’t help, try a finer cut with roughing wheel.

Deep irregular marks caused by loose wheel.
Use one standard paper washer (blotting paper if other not available) under flanges and tighten down.

Isolated deep marks due to improper dressing.
Rotate or change diamond to—get sharper dressing. Wash wheel thoroughly with coolant after dressing. Reset gib on truing device.

Grain marks due to too soft or coarse a wheel.
Substitute harder grade or finer grained wheel

Rough uneven finish.
Diamond cracked or broken; replace.

Regulating wheel too hard.
If regulating wheel too hard, work will spin and score on blade but it would be practically impossible to grind.

Wheel too smooth.
Reset diamond or use new one. Use coarser or softer wheel.

Roughing wheel breaks down too fast.
Rough grind with more and smaller cuts, or use harder wheel for roughing.

   
VIBRATION  

Loose levelling screws.
Set all screws so they bear evenly on floor.

Grinding wheel out of balance.
Inspect spindle and collet—remove burrs if present. Use only one standard or blotting paper gasket under each flange.
Make sure balancing stand is level both ways before attempting to balance wheel. Always balance wheel in following sequence:

  1. True wheel.
  2. Run wheel long enough to throw off coolant.
  3. Balance wheel on same mount as used for grinder.
  4. True wheel after mounting on spindle

Motor bearing defective or armature out of balance.
Renew motor bearings or balance armature.

   
MARKS ON WORK  

Work too high above centre.
Lower work support blade.

Too great an angle on workrest blade
A 3O° angle should be a good average starting angle for most work. Long blades will cause chatter unless blade angle is reduced. Also for small diameter work it will generally be necessary to reduce angle.

Work support blade too thin
Use a heavier blade. Blade length must be slightly longer than wheel width. Blade thickness should be under work diameter just enough so that it doesn’t cause wheel interference.

Work support blade loose.
Tighten clamping screws.