Machining Delrin: Feeds, Speeds, Tolerances and Fixes

Delrin (POM-H acetal) machines on standard equipment with few special requirements [6].

What goes wrong is not the cutting. It is heat, clamping, stress release and thermal growth.

This guide gives published speed and feed ranges, worked examples, tool geometry, tolerance and thermal growth numbers, stock and porosity checks, and an ordering checklist, with the source named for every range.

Quick answer

• Starting ranges for acetal homopolymer: milling 920 to 1,640 ft/min; turning 980 to 1,960 ft/min at 0.004 to 0.015 in/rev; drilling 165 to 650 ft/min at 0.004 to 0.012 in/rev with peck cycles; sawing 1,640 to 2,600 ft/min [1] [2] [3] [21].
• Tolerance: one service publishes ±0.005 in as standard and ±0.002 in for precision work. Thermal growth is 0.00068 in per inch per 10 °F [9] [10] [13].
• Check first: centerline porosity in thick stock, and heat and fumes if chips smoke or discolor.

Where to start

• Machinist: Speeds and Feeds, then Troubleshooting.
• Designer: Tolerance and Thermal Growth, then Design Rules.
• Buyer or QA: Stock Form and Porosity, then Ordering Machined Delrin Parts.
• Part out of tolerance: go to Tolerance and Thermal Growth first, then Troubleshooting.

Speeds and Feeds

Published starting ranges

Curbell’s tables list acetal homopolymer and copolymer with identical values. These are published starting ranges, not a guarantee for your machine, tool or stock.

The sources agree on the principle even where numbers differ.

Emco says slow feed/fast speed and slow speed/fast feed both machine well.

DuPont says cutting speed is the critical factor to watch. 

The Cambridge design cookbook says a high speed and coarse feed throws chips away and prevents the rubbing that dulls the tool [6] [7] [8].

In practice, avoid slow feeds at high rpm: rubbing makes heat, and the chip should carry it away.

Spindle speed for the published range

RPM = surface speed (ft/min) × 3.82 ÷ tool diameter (in). For the milling range of 920 to 1,640 ft/min:

This is our arithmetic. Small cutters often cannot reach these speeds on a standard spindle.

Engineering note: run the spindle’s maximum and keep feed per tooth up, rather than slowing the feed to compensate.

Worked examples

These apply the published ranges. They are arithmetic, not recommendations for your setup.

One machinist reports that 0.003 in per flute is easy on Delrin and that a 1/2 in cutter at 6,000 rpm (about 800 ft/min) gave clean parts. That is a single anecdote [20].

Tool Geometry, Coolant and Work holding

Tool geometry

Carbide or HSS

Curbell says HSS tooling works well for most thermoplastics and carbide is recommended for reinforced materials, while recommending carbide inserts for turning.

Polished surfaces reduce material build up [1] [2].

Single flute or more

Sources differ. Emco recommends single-flute mills for lower friction heat and more chip clearance, Boedeker lists 2 to 4 flutes, and Curbell finishes with 2 or 4 flutes depending on chip behavior [2] [5] [6].

Start with 1 or 2 flutes in pockets and deep slots, and test.

Coolant

Boedeker says coolants are generally not required except for drilling and parting off.

Emco says oils or water are typically unnecessary but may help at very high speeds, and recommends coolant when drilling at high rates [4] [6].

Work holding

Curbell warns that clamping needs care to avoid deforming or springing the stock [2].

Boedeker notes that plastics are much more elastic than metals [4], and Fictiv advises clamping thin parts down with fasteners [12]. Use light, distributed clamping and support thin sections.

Sawing

Curbell recommends relatively thin blades for thick-walled parts to avoid frictional heat, and well-sharpened, strongly offset blades [21].

Boedeker lists carbide-tipped, triple-chip blades with a low positive hook of 5 to 10°, 4 to 10 teeth per inch depending on thickness, and lower speeds to prevent melting [22].

• Speed and pitch: 1,640 to 2,600 ft/min, with tooth pitch 0.078 to 0.197 in (about 5 to 13 teeth per inch, our conversion)[21].
• If the cut edge melts: feed faster or slow the blade speed, and watch for dulling teeth [23].
• Start with relieved stock: residual stress in plastic is the enemy during sawing [23].

Heat Limits and Fumes

Temperature limits

On the Plastics International Delrin 150 sheet, long-term service is 185 °F, heat deflection at 264 psi is 257 °F, and melting is 347 °F [13].

We found no published “smear temperature.” Treat the 264 psi heat deflection figure as the point where a loaded or clamped part loses stiffness.

Fumes and exposure

An acetal safety data sheet reports heavy formaldehyde fuming above 230 °C (446 °F) [18].

OSHA’s formaldehyde limits are 0.75 ppm (8-hour average) and 2 ppm (15-minute short-term) [19].

If chips smoke or discolor, stop, fix the cause and ventilate. Do not use smell as your monitor.

Tolerance and Thermal Growth

Published tolerances

Delrin 150 values are from the Plastics International data sheet [13].

Boedeker notes that the relative softness of plastics makes tight tolerances harder to hold during and after machining [4].

Thermal growth

This is our arithmetic from 6.8 × 10⁻⁵ in/in/°F. A 4 in part measured at 85 °F and again at 68 °F (a 17 °F difference) changes by 0.0046 in.

What this means. A 10 °F swing moves a 3 in feature by 0.0020 in, as much as a ±0.002 in tolerance on that dimension.

State the inspection temperature on the drawing, and let the part reach it before you measure. For tight fits in wet service, ask for dimensions after moisture conditioning, since saturation uptake is 0.9%.

Stress, annealing and moisture

DuPont says most stock shapes are pre-annealed, and that for high tolerance parts an annealing step may be necessary before light finish machining.

Fictiv notes Delrin is highly susceptible to warping on large flat parts or thin walls [7] [12].

Need a tolerance held on a specific feature? Upload your STEP, IGES or DXF file for a tolerance check and quote

Stock Form and Porosity

Stock sizes and listings

Delrin 150 NC010 shapes are listed in rod from 0.187 to 10.00 in diameter and plate from 0.031 to 5.00 in thick, with ASTM D6100 and FDA 21 CFR 177.2480 listings on the natural grade [14].

Centerline porosity

The same data sheet warns of a low-density center, especially in large cross-sections [14].

Boedeker describes it as interconnected micro-porosity of about 100 to 150 microns in homopolymer stock, and one distributor says 150 is not USP Class VI compliant because of it.

Copolymer (POM-C) stock is reported to have little or no centerline porosity [15] [16] [17].

Rule of thumb: if a bore, seal face or fluid passage runs through the center of thick Delrin stock, get a porosity statement from the supplier first, or compare POM-C.

Design Rules for Machined Delrin

Walls

Protolabs lists 0.020 in as the practical minimum turned wall.

Xometry advises against going below 0.060 to 0.080 in for acetal because thin walls are hard to fixture and can flex, warp or chatter.

Fictiv advises avoiding thin walls, or clamping the part down with fasteners [10] [11] [12].

Inside corners

The cutter radiuses sharp inside corners, and Curbell recommends rounded corners in pockets. One machinist notes acetal can chip on sharp corners [2] [10] [20].

Cost levers

Acetal is one of the more expensive plastics, and Fictiv advises limiting setups, inspection dimensions, tight tolerances, and deep pockets with small radii [11] [12].

Tolerance only the features that need it.

Threading, Tapping and Finishing

We found no authoritative published tap-drill, thread-engagement or deburring table for acetal.

One machinist reports rarely having problems drilling or tapping Delrin, notes the material can push away instead of cutting a chip, and suggests single-flute cutters [24].

Prove threads and edges on a coupon before committing, and check thread engagement and fit on the real part.

Troubleshooting

Ordering Machined Delrin Parts

• Material and form: Delrin 150 NC010 extruded shape per ASTM D6100, or POM-C if the part is porosity sensitive.
• Porosity statement for the diameter or thickness if a bore, seal face or fluid path crosses the center.
• Critical features marked individually, with tolerance on each. The published default is ±0.005 in.
• Inspection temperature stated on the drawing.
• Annealing requirement for tight tolerance or thin parts.
• Certificates: match FDA or NSF statements to the exact form and color you are buying.

Is Machining the Right Route for your project?

FAQ

Related Guides

• Delrin (Acetal Homopolymer): Properties, Grades and Applications
• Laser Cut Delrin: Is It Safe, and What Settings Work?
• Delrin 3D Printing:Challenges, Print Settings and Best Alternatives
• Delrin 100 vs 150: Which Grade for Machining and Molding?
• Delrin vs. Acetal: Are They Even Different Materials?
• Delrin vs. Nylon: Which Engineering Plastic Should You Choose?
• Delrin vs. ABS: Strength, Machining, Cost & Selection

Sources

All sources last checked October 9, 2026. Ranges and typical values are published guidance, not guarantees for your machine, tool or stock.

1. https://www.curbellplastics.com/services-capabilities/fabrication-machined-parts/plastic-machining-guidelines/plastic-turning-machining-guidelines/
2.  https://www.curbellplastics.com/services-capabilities/fabrication-machined-parts/plastic-machining-guidelines/plastic-milling-machining-guidelines/
3. https://www.curbellplastics.com/services-capabilities/fabrication-machined-parts/plastic-machining-guidelines/plastic-drilling-machining-guidelines/
4. https://boedeker.com/Technical-Resources/Technical-Library/Plastic-Machining-Guidelines
5. https://www.boedeker.com/Technical-Resources/Plastic-Machining-Guidelines/Plastic-Milling-Machining-Guidelines
6. https://www.emcoplastics.com/delrin-machining-and-fabrication/
7. https://www.plasticsintl.com/media/xgmka1p3/machining_glass_reinforced_resins.pdf
8. https://wwwmdp.eng.cam.ac.uk/web/library/enginfo/cookbook/manufacturing/plastics/machining.html
9. https://www.protolabs.com/de-de/ressourcen/design-tipps/bessere-cnc-teile-durch-feinabstimmung-der-toleranzen/
10. https://www.protolabs.com/services/cnc-machining/cnc-turning/design-guidelines/
11. https://www.xometry.com/material-cnc-machining-plastic-delrin
12. https://www.blog.fictiv.com/materials/cnc-machining-delrin
13. https://www.plasticsintl.com/media/05oith4t/delrin-150-data-sheet.pdf
14. https://plastics.tridentplastics.com/Asset/TDS_Delrin150%20NC010.pdf
15. https://www.boedeker.com/Portals/0/Documents/Acetals-Understanding-the-Differences-POMC-POMH-Boedeker-Technical-Guide-Acetals-New-Logo.pdf
16. https://professionalplastics.com/Acetal-Delrin
17. https://sterlingplasticsinc.com/product/delrin-150-homo-polymer/
18. https://www.mcam.com/mam/29867/MCAM-ACETRON-POM-H-AF-EN-SDS-1000-220818.pdf
19. https://ehs.prod.fbweb.psu.edu/sites/ehs/files/formaldehyde_-_osha_fact_sheet.pdf
20. https://forums.autodesk.com/t5/fusion-manufacture-forum/mill-cutting-delrin-speeds-and-feeds-anyone/m-p/6350924/highlight/true
21. https://www.curbellplastics.com/services-capabilities/fabrication-machined-parts/plastic-machining-guidelines/plastic-sawing-machining-guidelines/
22. https://www.boedeker.com/Technical-Resources/Plastic-Machining-Guidelines/Plastic-Sawing-Machining-Guidelines
23. https://modernplastics.com/?p=2370
24. https://www.emastercam.com/forums/topic/99237-drilling-tapping-pvc-and-acetal/

Last Reviewed: October 2026

Usama Ayub

Usama Ayub is the founder of PlasticSpec and a polymer manufacturing engineer with eight years of hands-on industrial experience in PET, PA6, and PA66 fiber and filament yarn production. He writes material property and selection guides for Delrin, Nylon, PEEK, PTFE, UHMW, Polycarbonate, and ABS.