Plastics Troubleshooting

When machining plastic stock shapes, remember...

  • Thermal expansion is up to 10 times greater with plastics than metals
  • Plastics lose heat more slowly than metals, so avoid localised overheating
  • Softening (and melting) temperatures of plastics are much lower than metals
  • Plastics are much more elastic than metals

Because of these differences, you may wish to experiment with fixtures, tool materials, angles, speeds and feed rates to obtain optimum results.

  • DRILLINGOpen or Close
    Problem Caused Common Cause
    Tapered drill holeIncorrectly sharpened drill - cutting edges not symmetrical
    Drill speed in relation to feed not correct
    Insufficient clearance
    Feed too heavy
    Burnt or melted surfaceWrong type drill
    Drill speed in relation to feed not correct
    Incorrectly sharpened drill
    Feed too light
    Worn flutes on drill
    Check tool clearance
    Chipping of surfacesFeed too heavy
    Clearance too great
    Too much rake
    Material not clamped properly - movement on material
    ChatterToo much clearance
    Feed too light
    Drill over-hang too great
    Too much rake
    Check PRM
    Feed markes or spiral lines
    on inside diameter
    Material not square
    Feed too heavy
    Drill not centered
    Drill ground off-centre
    Oversize holesInsufficient clearance
    Feed rate too heavy
    Point angle too great
    Undersize holesDull drill or worn flutes
    Too much clearance
    Point angle too small
    Holes not concentricFeed rate too heavy
    Spindle speed too slow
    Drill enters next piece too far
    Cut-off tool leaves nib, which deflects drill
    Drill speed too heavy at start
    Drill not mounted on centre
    Drill not sharpened correctly
    Rapid dulling of drill bitFeed too light
    Spindle speed too fast
    Insufficient lubrication from coolant
    Check support under work piece
  • SAW CUTTING Open or Close
    Problem Caused Common Cause
    Melted surfaceBlunt saw blade
    Insufficient side clearance
    Rough finishFeed too heavy
    Saw blade improperly sharpened
    Cutting edge not honed
    Saw blade wrong sided
    Spiral marksSaw blade rubs against material during its retreat
    Burr on point of tool
    Concave or convex surfacesPoint angle too great
    Tool not perpendicular to spindle
    Tool deflecting (use negative rake)
    Feed too fast
    Tool mounted above or below centre
    Nibs or burrs at cut-off pointPoint angle not great enough
    Saw blade blunt or not honed
    Feed too fast
  • TURNING & BORING Open or Close
    Problem Caused Common Cause
    Melted surfaceTool blunt or heel rubbing
    Insufficient side clearance
    Feed rate too slow
    Spindle speed too fast
    Rough finishFeed too heavy
    Incorrect clearance angles
    Sharp point on tool (slight nose radius required)
    Tool not mounted on centre
    Burrs at edge of cutNo chamfer provided at sharp corners
    Blunt tool
    Insufficient side clearance
    Lead angle not provided on tool
    (tool should ease out of cut gradually, not suddenly)
    Cracking or chipping of cornersToo much positive rake on tool
    Tool not eased into cut (tool suddenly his work)
    Blunt tool
    Tool mounted below centre
    Sharp point on tool (slight nose radius required)
    ChatterToo much nose radius on tool
    Tool not mounted solidly
    Material not supported properly