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Troubleshooting Tips

  • Avoid sharp “internal” corners.  Recommend a minimum radius of .060” to provide added strength and toughness.
  • A typical surface finish achievable with most plastics is a 32 RMS.  With extra care and the right approach, surface finishes can be achieved down to about 20 RMS for certain materials.  Below 20 RMS, secondary polishing will be required.
  • To achieve a surface finish down to 16RMS, one could try buffing with a simple “Scotch-brite®” style pad.

Machining Tips

  • Carbide cutting tools with polished top surfaces are suggested for optimum tool-life and surface finishes.  Use of coatings is not recommended.           
  • Poly-crystalline Diamond Tipped Cutting Tools are recommended when machining polybenzimidazole (PBI) and other extremely hard polymers including those filled with glass and carbon fibers.  This practice will improve tool life resulting in improved surface finishes and better tolerance control.  Use of coatings is not recommended.
  • Use of water soluble coolants are recommended for optimal surface finishes and close tolerance machining.  General purpose petroleum based cutting fluids, may contribute to stress cracking of amorphous plastics.
  • Use adequate chip clearance to prevent clogging and increased heat generation.
  • Adequately support the material to restrict deflection away from the cutting tool and to prevent breakout when drilling.     

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Troubleshooting Quick Reference

Issue or Difficulty Common Cause Machining Activity
Tapered hole 1. Incorrectly sharpened drill
2. Insufficient clearance
3. Feed too heavy		 Drilling
Burnt or melted surface 1. Wrong type drill
2. Incorrectly sharpened drill
3. Feed too light
4. Dull drill
5. Web too thick
6. Not peck drilling		 Drilling
Chipping of surfaces 1. Feed too heavy
2. Clearance too great
3. Too much rake		 Drilling
Chatter 1. Too much clearance
2. Feed too light
3. Drill overhang too great
4. Too much rake		 Drilling
Feed marks or spiral lines on inside diameter 1. Feed too heavy
2. Drill not centered
3. Drill ground off-center		 Drilling
Oversize holes 1. Drill ground off-center
2. Web too thick
3. Insufficient clearance
4. Feed rate too heavy
5. Point angle too great		 Drilling
Undersized holes 1. Dull drill
2. Too much clearance
3. Point angle too small		 Drilling
Holes not concentric 1. Feed too heavy
2. Spindle speed too slow
3. Drill enters next piece too far
4. Cut-off tool leaves nib, which deflects drill
5. Web too thick
6. Drill speed too heavy at start
7. Drill not mounted on center
8. Drill not sharpened correctly		 Drilling
Burr at cut-off 1. Dull cut-off tool
2. Drill does not pass completely through piece		 Drilling
Rapid dulling of drill 1. Feed too light
2. Spindle speed too fast
3. Insufficient lubrication from coolant		 Drilling
Melted surface 1. Dull tool
2. Insufficient side clearance
3. Insufficient coolant supply		 Cutting Off
Rough finish 1. Feed too heavy
2. Tool improperly sharpened
3. Cutting edge not honed		 Cutting Off
Spiral marks 1. Tool rubs during its retreat
2. Burr on point of tool		 Cutting Off
Concave or convex surfaces 1. Point angle too great
2. Tool not perpendicular to spindle
3. Tool deflecting (use negative rake)
4. Feed too heavy
5. Tool mounted above or below center		 Cutting Off
Nibs or burns at cut-off point 1. Point angle not great enough
2. Tool dull or not honed
3. Feed too heavy		 Cutting Off
Burrs on outside diameter 1. No chamfer before cut-off diameter
2. Dull tool		 Cutting Off
Melted surface 1. Tool dull or heel rubbing
2. Insufficient side clearance
3. Feed rate too slow
4. Spindle speed too fast		 Turning & Boring
Rough finish 1. Feed too heavy
2. Incorrect clearance angles
3. Sharp point on tool (slight nose radius required)
4. Tool not mounted on center		 Turning & Boring
Burrs at edge of cut 1. No chamfer provided at sharp corners
2. Dull tool
3. Insufficient side clearance
4. Lead angle not provided on tool
(tool should ease out of cut gradually, not suddenly)		 Turning & Boring
Cracking or chipping of corners 1. Too much positive rake on tool
2. Tool not eased into cut (tool suddenly hits work)
3. Dull tool
4. Tool mounted below center
5. Sharp point on tool (slight nose radius required)		 Turning & Boring
Chatter 1. Too much nose radius on tool
2. Tool not mounted solidly
3. Material not supported properly
4. Width of cut too wide (use 2 cuts)		 Turning & Boring
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