San Diego Plastics
2220 McKinley Avenue
National City  CA  91950
800/925-4855   619/477-4855   FAX 619/477-4874

PLASTIC MACHINING TIPS

Cutter Guy

General Fabrication Guidelines
 

The following guidelines are presented for those machinists not familiar with the machining characteristics of plastics. They are intended as guidelines only, and may not represent the most optimum conditions for all parts. The troubleshooting quick reference in this section should be used to correct undesirable surface finishes or material responses during machining operations.

Most quality stock shape materials are stress relieved to ensure the highest degree of machinability and dimensional stability. However, the relative softness of plastics (compared to metals) generally results in greater difficulty maintaining tight tolerances during and after machining. A good rule of thumb for tolerances of plastic parts is +/- .001 per inch of dimension although tighter tolerances are possible with very stable, reinforced materials.

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 localized 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.

Getting Started
 

  • Positive tool geometries with ground peripheries are recommended
  • Carbide tooling with polished top surfaces is suggested for optimum tool life and surface finish. Diamond coated or polycrystalline tooling provides optimum surface finish when machining Duratron® XP or Vespel®
    PI or Celazole* PBI.
  • Use adequate chip clearance to prevent clogging
  • Adequately support the material to restrict deflection away from the cutting tool
Turning
Operations require inserts with positive geometries and ground peripheries. Ground peripheries and polished top surfaces generally reduce material build-up on the insert, improving the attainable surface finish. A fine grained C-2 carbide is generally best for turning operations.

 

Drilling
The insulating characteristics of plastics require consideration during drilling operations, especially when hole depths are greater than twice the diameter.

Small diameter holes (232" or 1mm to 1.0 or 25mm)
High speed steel twist drills are generally sufficient for small holes. To improve swarf removal, frequent pull-out (peck drilling) is suggested. A slow spiral (low helix drill will allow for better swarf removal.

Large diameter holes (1.0” or 25mm and larger)
A slow spiral (low helix) drill or general purpose drill bit ground to a 118° point angle with 9° to 15° lip clearance is recommended. The lip rake should be ground (dubbed off) and the web thinned.

It is generally best to drill a pilot hole (maximum 1/2” diameter) using 600 to 1,000 rpm and a positive feed of 0.005” to 0.015” per revolution. Avoid hand feeding because of the drill grabbing which can result in microcracks forming. Secondary drilling at 400 to 500 rpm at 0.008 to 0.020” per revolution is required to expand the hole to larger diameters.

A two step process using both drilling and boring can be used on notch sensitive materials such as Ertalyte® PET-P, Torlon* PAI, Duratron® XP, Vespel® PI, Celazole* PBI and glass or carbon reinforced products. This minimizes heat build-up and reduces the risk of cracking.

  1. Drill a 1” diameter hole using an insert drill at 500 to 800 rpm with a feed rate of 0.005” to 0.015” per revolution.
  2. Bore the hole to final dimensions using a boring bar with carbide insert with 0.015” to 0.030” radii at 500 to 1,000 rpm and a feed rate of 0.005 to 0.010” per revolution.

Threading and Tapping
Threading should be done by single point using a carbide insert and taking four to five 0.001” passes at the end. Coolant usage is suggested. For tapping, use the specified drill with a two flute tap. Remember to keep the tap clean of chip build-up. Use of a coolant during tapping is also suggested.

Milling
Sufficient fixturing allows fast table travel and high spindle speeds when end milling plastics. When face milling, use either high positive or high shear geometry cutter bodies.

Sawing
Band sawing is versatile for straight, continuous curves or irregular cuts. Table saws are convenient for straight cuts and can be used to cut multiple thicknesses and thicker cross sections up to 4” with adequate horsepower. Saw blades should be selected based upon material thickness and surface finish desired.


 

Machining Tips
 
  • Rip and combination blades with a 0° tooth rake and 3° to 10° tooth set are best for general sawing in order to reduce frictional heat.
  • Hollow ground circular saw blades without set will yield smooth cuts up to 3/4” thickness.
  • Tungsten carbide blades wear well and provide optimize surface finishes.

Back to Top of Page
Coolant Recommendations

Coolants are generally not required for most plastic machining operations (not including drilling and parting off). However, for optimum surface finishes and close tolerances, non-aromatic, water soluble coolants are suggested. Spray mists and pressurized air are very effective means of cooling the cutting interface. General purpose petroleum based cutting fluids although suitable for metals and some plastics, may contribute to stress cracking of amorphous plastics such as Acrylic, Polycarbonate, Polysulfone, Ultem® PEI, and Radel® R PPSU.
Coolants Tips
  • Coolants are strongly suggested during drilling operations, especially with notch sensitive materials such as Ertalyte® PET-P, Torlon® PAI, Duratron® XP, Vespel® PI, Celazole® PBI and glass or carbon reinforced products.
  • In addition to minimizing localized part heat- up, coolants prolong tool life. Example (flood) coolants suitable for most plastics include: A generally suitable mist coolant is Astro-Mist 2001A (Monroe Fluid Technology, Hilton, NY).

Back to Top of Page

 
FABRICATION GUIDELINES - TURNING AND DRILLING
MATERIALS REL.
MACHIN-
ABILITY
(1 to 10
1=easiest)
TURNING DRILLING**
Depth of cut Speed
Feet/Min.
Feed,
In./Rev.
Nominal Hole Dia. Feed,
In./Rev.
Acetal copolymer
Delrin®, Delrin® AF
Delrin® AF Blend
Nylon 101
Nylatron® GS, GSM
Nylatron® GSM Blue
Nylatron® NSM
MC® 901, MC® 907 Nylon
Polycarbonate
Polysulfone
Ultem® 1000 & 2300 PEI
1
1
1
1
1
1
1
1
3
3
7
.150”
.025”
500-600
600-700
.010-.015
.004-.007
1/16"
1/8"
1/4"
1/2"
3/4"
1"
1 1/2"
2" or >
.007-.015
"
"
.015-.025
"
.020-.050
"
"
Fluorosint® 500
Fluorosint® 207
1
1
.150”
.025”
350-500
500-600
.010-.015
.003-.008
1/16"
1/8"
1/4"
1/2"
3/4"
1"
1 1/2"
2" or >
.007-.015
"
"
.015-.025
"
.020-.050
"
"
PEEK™, unfilled
PEEK 30% GF
PEEK 30% CF
5
7
7
.150”
.025”
600-1000
600-700
.010-.016
.004-.007
1/16"
1/8"
1/4"
1/2"
3/4"
1"
1 1/2"
2" or >
.002-.005
"
"
.004-.008
"
.008-.012
"
"
Ertalyte® PET-P
Ertalyte® TX
Hydex® 4101 PBT-P
  .150”
.025”
500-600
600-700
.010-.015
.004-.007
1/16"
1/8"
1/4"
1/2"
3/4"
1"
1 1/2"
2" or >
.002-.005
"
"
.015-.025
"
.020-.050
"
"
Techtron® PPS
Ryton® PPS
Ryton® BG PPS
  .150”
.025”
100-300
250-500
.010-.020
.005-.010
1/16"
1/8"
1/4"
1/2"
3/4"
1"
1 1/2"
2" or >
.007-.015
"
"
.015-.025
"
.020-.050
"
"
Torlon® 4203 PAI
Torlon® 4301 PAI
Torlon® 4501 PAI
Torlon® 4503 PAI
Torlon® 4540 PAI
Torlon® 5530 PAI
Duratron® XP
Vespel® PI
  .025” 300-800 .004-.025
 
1/16"
1/8"
1/4"
1/2"
3/4"
1"
1 1/2"
2" or >
.007-.015
"
"
.015-.025
"
.020-.050
"
"
Celazole® PBI   .150”
.025”
100-150
150-225
.005-.010
.002-.006
1/16" to 1/4"
1/2" or >
.005-.015
.015-.025

Back to Top of Page

 
FABRICATION GUIDELINES - MILLING
MATERIALS End Milling / Slotting Face Milling
(C-2) Carbide Tool
high speed
steel (m2,M7)
Depth
of cut
Speed,
ft./min.
Feet,
in./tooth
Depth
of cut
Speed,
ft./min.
Feet,
in./tooth
Acetal copolymer
Delrin 150, Delrin AF
Delrin AF Blend
Nylon 101
Nylatron® GS Nylon
Nylatron® GSM,
Nylatron® GSM Blue,
Nylatron® NSM
MC® 901 Nylon,
MC® 907 Nylon
1/4"
1/2"
3/4"
1", 2"
1/4"
1/2"
3/4"
.250
"
"
"
.050
"
"
270-450
"
"
"
300-500
"
"
0.002
0.003
0.005
0.008
0.001
0.002
0.004
0.150
0.060
1300-1500
1500-2000
0.020
0.005
Polycarbonate
Polysulfone
Ultem® 1000 PEI
Ultem® 2300 PEI
1/4"
1/2"
3/4"
1", 2"
1/4"
1/2"
3/4"
.250
"
"
"
.050
"
"
270-450
"
"
"
300-500
"
"
0.002
0.003
0.005
0.008
0.001
0.002
0.004
0.150
0.060
1300-1500
1500-2000
0.020
0.005
PEEK™ 1/4"
1/2"
3/4"
1", 2"
1/4"
1/2"
3/4"
.250
"
"
"
.050
"
"
270-450
"
"
"
300-500
"
"
0.002
0.003
0.005
0.008
0.001
0.002
0.004
0.150
0.060
500-750
"
0.020
0.005
Fluorosint® 500
Fluorosint® 207
1/4"
1/2"
3/4"
1", 2"
1/4"
1/2"
3/4"
.250
"
"
"
.050
"
"
270-450
"
"
"
300-500
"
"
0.002
0.003
0.005
0.008
0.001
0.002
0.004
0.150
0.060
500-700
550-750
0.010
0.005
Techtron® PPS
Ryton® PPS
1/4"
1/2"
3/4"
1", 2"
1/4"
1/2"
3/4"
.250
"
"
"
.050
"
"
270-450
"
"
"
300-500
"
"
0.002
0.003
0.005
0.008
0.001
0.002
0.004
0.150
0.060
1300-1500
1500-2000
0.020
0.005
Torlon® PAI 1/4"
1/2"
3/4"
1", 2"
1/4"
1/2"
3/4"
.250
"
"
"
.050
"
"
270-450
"
"
"
300-500
"
"
0.002
0.003
0.005
0.008
0.001
0.002
0.004
0.035 500-800 .006-.035
Ertalyte® PET-P
Ertalyte® TX
Hydex® 4101 PBT-P
1/4"
1/2"
3/4"
1", 2"
1/4"
1/2"
3/4"
.250
"
"
"
.050
"
"
270-450
"
"
"
300-500
"
"
0.002
0.003
0.005
0.008
0.001
0.002
0.004
0.150
0.060
1300-1500
1500-2000
0.020
0.005
Duratron® XP
Vespel® PI
Celazole® PBI
1/4"
1/2"
3/4"
1", 2"
1/4"
1/2"
3/4"
.50



.015
450-650
"
"
"
250-350
"
"
0.005



0.002
0.050



0.015
450-650



250-350
0.005-.010



.002-.006

Back to Top of Page

 
FABRICATION GUIDELINES - SAWING
MATERIALS Sawing
Material
thickness
Tooth
form
Pitch
teeth/in.
Band Speeds
ft./min.
Acetal copolymer
Delrin 150,
Delrin AF
Delrin AF Blend
Nylon 101
Nylatron® GS Nylon
Nylatron® GSM,
Nylatron® GSM Blue,
MC® 901 Nylon,
MC® 907 Nylon
<1/2"
1/2"-1"
1"-3"
3"
Precision
"
Butress
"
10-14
6
3
"
3,000
2,500
2,000
1,500
Polycarbonate
Polysulfone
Ultem® 1000 PEI
Ultem® 2300 PEI
<1/2"
1/2"-1"
1"-3"
3"
Precision
"
Butress
"
10-14
6
3
"
4,000
3,500
3,000
2,500
PEEK™ <1/2"
1/2"-1"
1"-3"
3"
Precision
"
Butress
"
8-14
6-8
3
"
4,000
3,500
3,000
2,500
Fluorosint® 500
Fluorosint® 207
<1/2"
1/2"-1"
1"-3"
3"
Precision
"
Butress
"
8-14
6-8
3
"
3,000
2,500
2,000
1,500
Techtron® PPS
Ryton® PPS
<1/2"
1/2"-1"
1"-3"
3"
Precision
"
Butress
"
8-14
6-8
3
"
5,000
4,300
3,500
3,000
Torlon® PAI <1/2"
1/2"-1"
1"-3"
3"
Precision
"
Butress
"
8-14
6-8
3
"
5,000
4,300
3,500
3,000
Ertalyte® PET-P
Ertalyte® TX
Hydex® 4101 PBT-P
<1/2"
1/2"-1"
1"-3"
3"
Precision
"
Butress
"
10-14
6
3
"
5,000
4,300
3,500
3,000
Duratron® XP
Vespel® PI
Celazole® PBI
3/8"-1"
1"-2"
Precision
"
Butress
"
10
10
3,000
1,500

Back to Top of Page

 
TROUBLESHOOTING QUICK REFERENCE
Drilling
Difficulty Common Cause
Tapered hole 1. Incorrectly sharpened drill
2. Insufficient clearance
3. Feed too heavy
Burnt or melted surface 1. Wrong type drill

2. Incorrectly sharpened drill
3. Feed too light
4. Dull drill
5. Web too thick
Chipping of surfaces 1. Feed too heavy
2. Clearance too great
3. Too much rake (thin web as described)
Chatter 1. Too much clearance
2. Feed too light
3. Drill overhang too great
4. Too much rake (thin web as described)
Feed marks or spiral lines on inside diameter 1. Feed too heavy
2. Drill not centered
3. Drill ground off-center
Oversize holes 1. Web too thick
2. Insufficient clearance
3. Feed rate too heavy
4. Point angle too great
Undersize holes 1. Dull drill
2. Too much clearance
3. Point angle too small
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
Burr at cut-off 1. Dull cut-off tool
2. Drill does not pass completely through piece
Rapid dulling of drill 1. Feed too light
2. Spindle speed too fast
3. Insufficient lubrication from coolant
Cutting Off
Melted surface 1. Dull tool
2. Insufficient side clearance
3. Insufficient coolant supply
Rough finish 1. Feed too heavy
2. Tool improperly sharpened
3. Cutting edge not honed
Spiral marks 1. Tool rubs during its retreat
2. Burr on point of tool
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
Nibs or burrs at cut-off point 1. Point angle not great enough
2. Tool dull or not honed
3. Feed too heavy
Burrs on outside diameter 1. No chamfer before cut-off
2. Dull tool
Turning & Boring
Melted surface 1. Tool dull or heel rubbing
2. Insufficient side clearance
3. Feed rate too slow
4. Spindle speed too fast
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
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)
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)
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)
 

Also see: Guidelines for Machining Ensinger Engineering Plastics
 

Trademark Acknowledgments:

RADEL and TORLON are registered trademarks of Solvay Advanced Polymers.
RYTON is a registered trademark of Chevron Phillips Chemical Company.
DELRIN and VESPEL are registered trademarks of DuPont.
ULTEM is a registered trademark of General Electric Company.
CELAZOLE is a registered trademark of Celanese Advanced Materials, Inc.
HYDEX is a registered trademark of A.L. Hyde Company.
DURATRON, ERTALYTE, NYLATRON, and TECHTRON are registered trademarks of Quadrant DSM Engineering Plastic Products.
PEEK is a trademark of Victrex plc.

The information on this page originally provided by Quadrant DSM Engineering Plastics.
Other stock shape manufacturers have also provided relevant information.

 



Return
To MAIN

Site
Map
Search
Me
Return To
Linecard
Sales
Terms
Contact
Me