Selecting self-lubricated plastics requires balancing performance, cost, and manufacturability. With 15+ years machining precision components across aerospace, medical, and audio sectors, material choice directly impacts both part reliability and production costs.
Choose self-lubricated plastics based on motion type, operating temperature, mating materials, and load conditions. PTFE-filled grades work best for dry running against steel, while graphite-filled options handle higher loads. Always match lubricant type to your specific application requirements rather than selecting premium grades unnecessarily.
Learn self-lubricated plastic selection criteria: PTFE vs graphite-filled performance trade-offs and cost optimization from real CNC production experience.
Table of Contents
What Types of Motion Work Best with Self-Lubricated Plastics?
Self-lubricated plastics excel in sliding motion, low-speed rotation, and oscillating applications where external lubrication creates contamination risks. PTFE-filled grades machine cleanly and work well for frequent motion, while graphite-filled materials handle higher loads but require sharper tooling to prevent surface smearing during CNC operations.
CNC Machining Considerations by Motion Type
| Motion Type | Best Material Grade | Machining Notes | Surface Finish Target |
|---|---|---|---|
| Linear Sliding | PTFE-filled POM | Finish cuts perpendicular to slide direction | Ra 1.6–3.2 μm |
| Continuous Rotation | Graphite-filled Nylon | Concentric finishing critical, avoid chatter | Ra 0.8–1.6 μm |
| Oscillating Motion | Either type works | Chamfer all edges, avoid tool marks parallel to motion | Ra 3.2 μm acceptable |
CNC-Machined Parts from Our Shop
| Part Application | Motion Requirements | Material Used | Key Machining Challenge |
|---|---|---|---|
| Linear actuator housing | Smooth sliding motion | PTFE-filled POM | Achieving consistent bore finish |
| Rotary selector bracket | Low-speed rotation | Graphite-filled Nylon | Preventing graphite smearing on tools |
| Pivot joint component | ±90° oscillation | PTFE-filled PEEK | Managing material’s tendency to gum tools |
From our CNC experience, the self-lubricating properties only work if we machine these materials correctly. PTFE-filled grades can gum cutting tools at high speeds, requiring slower feeds and sharp carbide tooling. Graphite-filled materials produce abrasive chips that wear tools faster but machine to better surface finishes. Tool marks direction matters—cuts parallel to sliding surfaces create wear channels, while perpendicular cuts help retain lubricant.
CNC Design Guidelines for Self-Lubricated Plastics: Specify generous corner radii (≥1mm) to prevent tool breakage and stress concentration. Avoid thin walls under 2mm where possible—self-lubricated grades deflect more during machining than standard plastics. Include machining allowances for secondary finishing operations on critical sliding surfaces.
Design Takeaway: When designing CNC-machined parts with self-lubricated plastics, consider both the motion requirements and how our machining process affects lubricant distribution. We’ll help optimize your design for both performance and manufacturability.
How Many Types of Self-Lubricated Plastics Are Available?
Four main types of self-lubricated plastics are available: PTFE-filled, graphite-filled, MoS2-filled, and oil-impregnated grades. Each type offers different cost-performance trade-offs, with PTFE-filled being most common for general use, graphite-filled for high-load applications, and specialty grades for extreme conditions.
Performance and Cost Hierarchy
| Performance Tier | Representative Grades | Cost Level | Best For | Availability |
|---|---|---|---|---|
| Standard | Delrin AF, PTFE-filled POM | $ | General machinery, prototypes | Stock sizes, 1-2 week lead |
| High Performance | Nylatron GSM, Iglidur G | $$ | Industrial equipment, automotive | Standard sizes, 2-4 week lead |
| Extreme Performance | Iglidur X, PEEK with PTFE | $$$ | Aerospace, medical devices | Custom orders, 6-8 week lead |
Quick Elimination Criteria:
- Food contact required → Only PTFE-filled (FDA compliant)
- Load >25 MPa → Eliminate PTFE-filled options
- Outdoor/dirty environment → Eliminate oil-impregnated
- Temperature >200°C → Only PTFE-filled handles extreme heat
PTFE-filled grades dominate because they’re versatile and clean-operating. When we machine medical device housings, clients consistently specify Delrin AF because it meets ISO 13485 requirements and leaves no contaminating residue. The most common mistake is over-specifying premium Iglidur grades when standard PTFE-filled materials would work fine—they cost half as much and deliver 80% of the performance.
Start with readily available PTFE-filled options for prototyping. You can always upgrade after testing if you need better load capacity, but many applications never require expensive specialty grades.
Design Takeaway: Use the elimination criteria above to narrow your options quickly, then prototype with standard PTFE-filled grades unless you have proven extreme requirements.
How Do I Choose Between PTFE-Filled vs Graphite-Filled Plastics?
If your load is under 25 MPa and cleanliness matters, choose PTFE-filled. If you need maximum load capacity above 25 MPa and can tolerate dark residue, choose graphite-filled. The key decision factor is contamination tolerance—PTFE transfers a clean film, while graphite creates visible dark markings on mating parts.
Decision Filters:
- Mating with hardened steel shafts → PTFE performs better
- Load >25 MPa contact pressure → Graphite-filled required
- Food/medical/clean applications → PTFE-filled only
- Outdoor/harsh environments → Graphite-filled preferred
We’ve seen the consequences of wrong choices. One customer used PTFE-filled parts for high-load conveyor applications—parts needed replacement every 6 months instead of the expected 2 years. Another client specified graphite-filled bearings for clean room equipment and faced contamination issues from dark transfer residue.
PTFE-filled materials excel in enclosed systems with moderate loads. They handle temperature extremes (-200°C to +260°C) and provide excellent chemical resistance. Graphite-filled grades work best for heavy-duty outdoor applications where maximum wear resistance matters more than appearance.
Validation Method: Test both materials in your actual operating conditions for 100-500 cycles. Watch for excessive wear (PTFE overloaded) or contamination issues (graphite in clean environments).
Design Takeaway: Start with PTFE-filled for clean, moderate-load applications. Switch to graphite-filled only when load testing confirms you need the extra capacity and contamination isn’t a concern.
Do Self-Lubricated Plastics Work Against Steel Shafts?
Yes, self-lubricated plastics work excellently against steel shafts, especially hardened steel with Ra 0.8-1.6 μm surface finish. PTFE-filled grades perform best against hardened steel (50+ HRC), creating a thin transfer film that reduces friction and wear. A roughness average (Ra) of about 0.8 to 1.6 micrometers is often recommended for small bearings, while larger bearings may require a roughness of 1.6 to 3.2 micrometers.
Steel Grade Compatibility:
- 4140/4340 hardened steel: Excellent with all self-lubricated plastics
- 304/316 stainless steel: Good, requires longer break-in period
- Chrome-plated shafts: Poor lubricant adhesion, use graphite-filled only
Drawing Specification for Your Shaft Supplier: Specify “4140 steel, heat treated 50-55 HRC, ground finish Ra 1.6 μm max” on your drawings. For outdoor applications where abrasive dirt and contaminants are present, a surface hardness rating of minimum 50+ HRC is ideal. From our CNC experience, this finish requirement adds 15-25% to shaft cost but prevents premature bearing failures we’ve seen with rougher surfaces.
Validating Existing Shafts: Use a surface roughness tester or compare against Ra reference standards. If existing shafts exceed Ra 3.2 μm, consider shaft sleeves—we machine these regularly as retrofit solutions. Hardness testing with a portable durometer confirms HRC levels before committing to self-lubricated plastic bearings.
When Hardening Isn’t Feasible: Hard chrome plating provides surface hardness but works only with graphite-filled plastics. Alternatively, we’ve machined stainless steel sleeves for corrosive environments where carbon steel can’t be used. These approaches cost more initially but avoid complete redesigns.
Design Takeaway: Specify hardened 4140 steel with Ra 1.6 μm finish on your shaft drawings. For existing equipment, validate shaft condition first—retrofitting is often more cost-effective than complete redesign.
What Wall Thickness Do Self-Lubricated Plastics Require?
Self-lubricated plastics require minimum 2mm wall thickness for reliable performance, with 3mm preferred for loads above 15 MPa. From our CNC machining experience, thinner walls deflect during both cutting operations and service, creating uneven contact that compromises lubricant distribution and dimensional accuracy.
Wall Thickness by Load Requirements:
- Light duty (0-10 MPa): 2mm minimum
- Medium duty (10-25 MPa): 3mm minimum
- Heavy duty (25+ MPa): 4mm+ required
Calculating Wall Thickness for Your Application: Use basic beam deflection formulas: thinner walls under radial loads create stress concentrations that exceed plastic yield strength. We’ve machined 1.5mm prototypes that failed after 500 cycles, while 3mm versions ran 50,000+ cycles under identical loads—the material’s lower modulus requires adequate section thickness.
Tolerance and Assembly Considerations: Wall thickness directly affects achievable tolerances. Below 2mm, we struggle to hold ±0.05mm bore accuracy due to workpiece deflection during machining. Press-fit forces also increase with wall thickness—design clearance fits for thin-wall applications to avoid stress cracking during assembly.
Cost-Benefit Reality Check: 3mm costs 50% more material than 2mm, but prevents field failures and warranty claims. Consider total system cost including replacement labor. For critical applications, the extra material cost is negligible compared to downtime costs.
Design Review Checklist: Ask these questions: Can loads create stress above 15 MPa? Is maintenance access difficult? Are replacement costs high? If yes to any, specify 3mm minimum wall thickness.
Design Takeaway: Design with 3mm wall thickness unless space absolutely prohibits it. The extra material cost pays for itself through reliable operation and reduced field service calls.
How Long Do Self-Lubricated Plastic Parts Last?
Self-lubricated plastic parts typically last 50,000-100,000 cycles in moderate-load applications, with CNC machining quality significantly affecting actual service life. From our shop experience, how we machine these parts directly impacts their longevity—poor surface finish or machining-induced stress concentrations can cut service life in half.
We’ve learned that tool marks parallel to sliding surfaces create wear channels that accelerate failure, while perpendicular cuts help retain lubricant. When machining PTFE-filled housings, maintaining consistent feeds prevents heat buildup that can degrade the lubricant particles embedded in the material. Sharp carbide tools are essential—dull tools create torn surfaces that compromise the transfer film formation these plastics rely on.
CNC Process Impact on Longevity:
- Surface finish quality: Ra 1.6 μm or better extends bearing life significantly
- Machining direction: Perpendicular tool marks retain lubricant better than parallel
- Heat management: Excessive cutting heat degrades embedded lubricants
- Stress relief: Parts with machining-induced stress fail earlier under load
Graphite-filled materials machine to better surface finishes but wear our tools faster, requiring more frequent tool changes to maintain the surface quality that ensures long bearing life. We’ve seen parts with excellent material selection fail prematurely because machining quality wasn’t properly controlled.
Design for CNC Longevity: Specify adequate wall thickness for rigid machining setups, design generous radii to prevent tool breakage that creates surface defects, and allow machining allowances for finish operations on critical bearing surfaces.
Design Takeaway: Material selection is only half the equation—CNC machining quality determines whether you’ll achieve the expected service life from self-lubricated plastics.
Are Self-Lubricated Plastics Worth the Extra Cost?
Self-lubricated plastics cost 2-4x more in material but often justify the premium through simplified CNC machining and eliminated secondary operations. From our machining perspective, the real cost equation includes reduced setup complexity, eliminated lubrication grooves, and simpler part geometries that these materials enable.
Standard bronze bushings require precision lubrication grooves, multiple machining setups, and careful coolant management to prevent contamination. Self-lubricated plastics eliminate this complexity—we machine straight geometries without lubrication features, reducing both machining time and setup costs. Recent jobs showed 30% reduction in machining hours when switching from grooved bronze to self-lubricated plastic designs.
CNC Cost Factors:
- Material premium: Higher raw material cost offset by simpler machining
- Eliminated operations: No lubrication grooves, oil galleries, or grease fittings
- Reduced setups: Simpler geometries require fewer operations
- Tool life: PTFE-filled grades are easier on cutting tools than bronze
However, graphite-filled grades wear our tools faster, requiring more frequent changes that add cost. We help clients balance material performance needs against total machining costs—sometimes standard PTFE-filled materials are more economical than premium grades when machining costs are included.
Geometry Simplification Benefits: Self-lubricated designs eliminate complex internal channels and multiple drilling operations. Parts that required 4-5 setups for bronze can often be completed in 2 setups with self-lubricated plastics.
Design Takeaway: Factor total machining costs, not just material costs, when evaluating self-lubricated plastics. The simplified geometries often offset higher material prices.
Conclusion
Self-lubricated plastics offer excellent performance when properly specified and machined, with material choice depending on your specific motion, load, and environmental requirements. Success depends on matching the right grade to your application while ensuring proper CNC machining quality for optimal performance and longevity. Contact us to explore manufacturing solutions tailored to your self-lubricated plastic component requirements.
Frequently Asked Questions
Specify material grade (e.g., “Delrin AF PTFE-filled POM”), surface finish requirements (Ra 1.6 μm typical), and note “CNC machined to maintain lubricant integrity.” Include machining direction callouts for critical sliding surfaces and avoid specifying unnecessarily tight tolerances that increase cost.
Avoid thin walls under 2mm, sharp internal corners that cause tool breakage, and deep narrow pockets that trap chips. Don’t specify lubrication grooves—these materials are designed to work without them. Keep geometry simple to maximize the cost benefits over traditional lubricated designs.
Both machine similarly, but graphite-filled grades handle slightly thinner walls better due to higher strength. PTFE-filled materials are more forgiving of design variations. Either way, design generous radii (≥1mm) and adequate wall thickness (3mm preferred) for reliable CNC manufacturing.
±0.05mm is achievable and sufficient for most applications. Avoid over-tolerancing—self-lubricated plastics accommodate some dimensional variation through their compliance. Focus tight tolerances only on critical mating surfaces and allow standard tolerances elsewhere to control costs.
Simple geometries with minimal setups cost least. Complex internal features, multiple drilling operations, and tight tolerances increase cost significantly. Design parts that can be completed in 1-2 setups to maximize cost savings versus traditional lubricated bearing designs.
Self-lubricated plastics deflect more than metals during press-fitting, potentially creating stress cracks. Design clearance fits when possible, especially for thin-wall applications. If press-fits are required, specify generous chamfers and conservative interference levels.
