Scratches, feed lines and spiral marks
Scratches, feed lines, and spiral marks ruin surface finish and can signal coolant or dressing problems that will worsen if ignored.
How you can tell
- Visible lines across the part spaced equal to the crossfeed or traverse step
- Curved comma-shaped or fish-tail scratches scattered randomly on the surface
- Barber-pole spiral stripes running along cylindrical or roll surfaces
- Thread-like helix pattern where the pitch matches the feed per work revolution
- Scratch marks that appear even after a fresh dress, pointing to coolant contamination
Causes, most common first
Dirty coolant recirculating swarf and loose grains
Abrasive particles and chips larger than the finish scale get dragged through the contact zone and cut comma or fish-tail scratches into the part.
How to check: Hold a sample of coolant from the return line in a clear jar and let it settle; visible grit or grey sludge confirms the filtration is not keeping up. Also inspect the coolant tank for settled swarf bypassing the filter.
Fixes:
- Upgrade or service the filter media (paper/fleece band or cartridge) to achieve 10–25 µm filtration for precision grinding.
- Clean out the settling tank and check the magnetic separator is removing ferrous swarf before fluid reaches the filter.
- After dressing, flush the wheel with coolant or brush it before the finish pass to clear loose grains.
- Clean the wheel guard and machine enclosure regularly so debris cannot fall onto the part.
Wheel edges not chamfered — sharp edge prints lines
A square wheel edge acts like a cutting tool corner, printing a step or line at every crossfeed or traverse increment.
How to check: Run a finger carefully along the wheel edge after dressing; a sharp, un-broken corner confirms the problem. Inspect the part surface — lines will be evenly spaced equal to the crossfeed step.
Fixes:
- Break (dub) both wheel edges slightly with the diamond or a dressing stick immediately after every dress.
- Dress a very slight convex crown across the wheel face so the edges blend smoothly into the surface.
Traverse or crossfeed rate too high for finish pass
When the part advances more than about one-third to one-half of the wheel width per revolution (surface grinding) or the traverse is a large fraction of wheel width per work revolution (cylindrical), the wheel cannot blend successive passes and leaves a helix or feed-line pattern.
How to check: Measure the spacing between visible lines on the part; if it matches your current feed-per-revolution setting, the feed rate is the culprit.
Fixes:
- Reduce crossfeed to one-eighth to one-quarter of wheel width for the finish pass on surface grinding.
- Reduce traverse speed so the part advances well under one-half the wheel width per work revolution during finishing.
- Add two to three spark-out passes at zero infeed and very low traverse rate to blend peaks flat.
Worn, loose, or overheating dressing diamond
A dull or poorly seated diamond chatters across the wheel face, leaving a slight helix or uneven surface that then transfers spiral marks to the part.
How to check: Inspect the diamond tip under magnification for a flat wear spot or cracking; wiggle the dresser holder to check for any movement. A squealing or uneven sound during dressing is another sign.
Fixes:
- Rotate the diamond to a fresh cutting point, tighten the holder securely, and apply coolant to the diamond throughout dressing.
- Replace a cracked or badly worn diamond rather than continuing to use it.
- Ensure the dresser arm has no play; tighten or replace the mounting if any flex is felt.
Dressing in both directions leaves uneven wheel face
Reversing the diamond traverse direction creates a slight helix or double-lead on the wheel face; one edge digs deeper each revolution, printing spiral or barber-pole marks on the part.
How to check: Ask the operator whether dressing was done in one consistent direction or back-and-forth. Inspect the wheel face under a light at an angle for a screw-thread texture.
Fixes:
- Always dress in one direction only; make the final pass a slow, light traverse in that same direction.
- Reduce the dressing traverse rate to a slow, steady pace to leave a finer wheel face.
Wheel face or spindle misaligned to work axis
When the wheelhead or spindle is not square or parallel to the table or work axis, one side of the wheel cuts deeper than the other, printing consistent feed lines or a spiral pattern that a redress alone will not fix.
How to check: Grind a test block or part and look for lines or a step that is always on the same side regardless of dress. For cylindrical work, check whether spiral pitch matches traverse-per-revolution; if marks persist after a good dress, measure spindle parallelism with a dial indicator.
Fixes:
- Check and correct wheelhead or spindle alignment to the table using a dial indicator on a test bar.
- Verify the wheel is true and running concentric before blaming alignment; eliminate wheel runout first.
Wheel too soft — shedding grains into the zone
A wheel grade too soft for the material sheds abrasive grains prematurely; those loose grains roll through the contact zone and cut random scratches or comma marks.
How to check: After the pass, wipe the part with a clean cloth and look for tiny embedded grain fragments. If the wheel loses its shape quickly and grains appear in the coolant filter, the grade is too soft.
Fixes:
- Switch to a slightly harder wheel grade for the finishing operation so grain shedding is reduced.
- Flush the wheel thoroughly with coolant after dressing to clear any loosely bonded surface grains before the finish pass.
Safety
If any fix requires mounting a replacement wheel, confirm the wheel's maximum operating speed (marked on the blotter or ring) meets or exceeds the spindle speed before starting the machine.
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