Comparison
UHMW vs acetal
Two of the most common plastics for machined wear parts: how they differ, which parts suit each, and how they machine.
Properties
Side by side
Typical published values for unfilled grades. The longer bar in each row is the higher value, which isn’t always the better one.
| UHMW | Property | Acetal |
|---|---|---|
| 3,100 | Tensile strength psi | 9,800–10,000 |
| 110,000 | Stiffness flexural modulus, psi | 370,000–420,000 |
| 18.0* | Impact strength notched Izod, ft-lb/in | 1.0–1.5 |
| 0.10–0.20 | Friction dynamic coefficient | 0.20–0.21 |
| Slight | Water uptake 24 h immersion | 0.20–0.25% |
| 11.1 | Heat expansion in/in/°F × 10⁻⁵ | 6.1–6.8 |
| 180 | Max continuous service in air, °F | 185–195 |
| 0.93 | Density g/cm³ | 1.41 |
*UHMW tested with a double 15° notch. Acetal values span copolymer to homopolymer. Typical published values; grades vary.
- Acetal is about three times as strong and three to four times as stiff.
- UHMW takes knocks that would crack acetal, and slides with less friction.
- Both take up little water, and both top out around 180–195°F.
Conditions
What decides it
The conditions a part runs in usually point to one or the other. General guidance: if your drawing names the plastic, we machine to it.
| Condition | UHMWBothAcetal | Why |
|---|---|---|
| Impact and knocks | UHMW | UHMW. It absorbs repeated impact without cracking. |
| Grit, slurry or bulk product | UHMW | UHMW. Abrasive particles embed in its soft surface instead of gouging it. |
| Strong acids, caustics and chlorine | UHMW | UHMW. It resists most cleaning chemicals. Strong acids and oxidizers attack acetal. |
| Steady load, or a fit that must stay put | Acetal | Acetal. It resists creep. UHMW slowly gives under a constant load. |
| Threads, gear teeth and small bores | Acetal | Acetal. It’s hard enough to hold fine detail. UHMW is too soft for it. |
| Long parts through temperature swings | Acetal | Acetal. It grows about half as much as UHMW with heat. Size-change calculator |
| Wet service and washdown | Both | Both. Neither takes up much water, so both hold size when wet. Acetal vs nylon |
Parts
Parts in each
The plastic each part is most often made in. We machine any of these in either plastic, or another one, to your drawing.
Usually
UHMW
Either, depending on the job
UHMW or acetal
- Star wheels
UHMW for large wheels that take container impact. Acetal where the pockets must hold a precise size.
- Rollers
UHMW for light, wet duty. Acetal for a hard surface that stays round under load.
- Sprockets
UHMW for quiet, lighter-duty chain. Acetal for stiffer teeth that hold their profile.
- Timing wheels
UHMW for a light, impact-resistant wheel. Acetal where the spacing must stay exact.
In our Aurora shop
How they machine
We machine both every day. They behave very differently under the cutter, and that shows in the tolerance each one holds.
UHMW
Toward ±0.005"
- Under the cutter
- Soft and waxy. It gives under clamping and cutting forces.
- Chips and edges
- Long, stringy chips and soft, fuzzy burrs.
- Heat
- Grows readily, including from the heat of the cut.
We support long guides and thin parts so they stay straight, bring parts to size at room temperature, and finish the edges clean.
Acetal
Toward ±0.002"
- Under the cutter
- Hard and stiff. It cuts cleanly and holds its shape.
- Chips and edges
- Short, clean chips and small burrs at edges and bores.
- Heat
- Moves about half as much, but thin walls still need care.
We machine threads, small bores and gear teeth directly in acetal, keep thin walls cool as we cut, and deburr every edge and bore.
Reordering a part
Telling them apart
Both come in white and black, so color won’t tell you which one an old part is made of. These differences usually will.
| UHMW | Acetal | |
|---|---|---|
| In water | Floats. Its density is 0.93, lighter than water. | Sinks. Its density is 1.41, heavier than water. |
| Feel | Waxy and slippery, almost greasy. | Hard, smooth and slightly glossy. |
| Surface | Soft enough for a fingernail to leave a mark. | Too hard for a fingernail to mark. |
Filled and specialty grades can differ.
Still not sure? Send the old part anyway. Tell us how it runs, and we’ll suggest suitable plastics with your quote.
Reverse engineeringQuestions
UHMW and acetal FAQs
Something else? Call (630) 904-2525.
Many parts are. We machine the part in the plastic you choose, and if the drawing leaves it open, we’ll suggest suitable plastics with your quote.
UHMW stock usually costs less than acetal, and it’s lighter, so a part of the same size uses less material by weight. The price of a machined part depends mostly on the machining.
Yes. Both come in food-contact grades and in metal-detectable grades. Compliance comes with the grade’s supplier documentation, so tell us the requirement and we’ll suggest suitable grades.
Detectable plasticsHave a part in UHMW or acetal?
Send a drawing, a sample or the worn part. We machine in either plastic, and suggest one with your quote if the drawing leaves it open.