214 Module 18 • Surface grinding machines
18.6 Grinding faults Fault
Scratching (fishtails) of workpiece
Care must be taken when removing (not sliding) the workpiece off the dirty magnetic chuck as this could scratch the finished workpiece.
Te following can also cause scratch marks: • Swarf or dirt in the coolant/grinding fluid. • Swarf or dirt dripping from the wheel guard. • Low grinding fluid.
• Grinding wheel too soſt, abrasive grains will roll between the grinding wheel and workpiece.
Chatter (vibration) marks on workpiece Chatter marks can be the result of:
• interrupted cutting due to the wheel being out of balance wheel or out of true
• a worn or insufficiently lubricated wheel spindles • grinding wheel not concentric to spindle • a skipping grinding wheel that is loaded or glazed • external vibrations by other machines nearby • lack of dense (solid) grinding machine foundation • wheel too hard.
Burning (discolouration) of workpiece
Tis grinding fault is quite common and can be caused by various erroneous actions.
Tese actions include: • insufficient grinding fluid • the grinding wheel may be too fine or too hard
• there is a concentration of heat because the cut is too heavy in a small area.
Loading of grinding wheel
Te grinding wheel in the sketch on the next page has been loaded. Te small metal bits are imbedded in the wheel pores in its grinding face. Te grinding wheel is undoubtedly too dense in structure or possibly has too fine an abrasive grain.
Remedy
• Clean or flush out the inside of the wheel guard.
• Clean grinding fluid/coolant.
• Clean the magnetic chuck before removing the workpiece or tilt the workpiece up on the edge rather than sliding it off the chuck.
• Same operators place a thin page of paper between the workpiece and the chuck.
• Relocate grinding machine and isolate from external vibration.
• Reinforce grinding machine foundation
• Rebalance the wheel
• True and redress grinding wheel.
• Speed up the table travel. • Take lighter cuts. • Reduce the area of contact.
• Dress the grinding wheel more regularly.
• Increase the coolant in speed and volume and direct it on both the grinding wheel and the workpiece.
Use either an open structure or a coarser grit wheel to obtain more chip clearance or a soſter grade wheel that will break down more easily.
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