Guides / Process

What Tolerance and Finish Can You Hold on a Tungsten Part

Updated September 26, 2026 · Reviewed September 26, 2026

Tolerance and finish questions come up on nearly every tungsten RFQ, because the answer depends more on grade than it does on the shop’s equipment. This guide sets out what is realistic to specify, by grade, by feature type and by the surface finish a given process actually produces.

Tolerance depends on grade first, geometry second

The single biggest factor in what tolerance a shop can hold is which tungsten grade the part is. Heavy alloy behaves like a dense, tough metal and holds tolerance the way hard cast iron would. Pure tungsten is brittle and pushes tolerances toward the looser end of what a shop would normally quote on a similar-sized steel part, unless the feature is finished by grinding. Tungsten copper sits closer to heavy alloy in behavior. Sintered tungsten carbide is not held to milling tolerances at all, since it is shaped by grinding and EDM.

Typical tolerances by grade

Grade	Typical tolerance, milled or turned	Tighter option
Heavy alloy (W-Ni-Fe or W-Ni-Cu)	±0.01 to ±0.025 mm	Grinding on selected features
Pure tungsten	Around ±0.025 mm	Grinding, tighter on flat or round features
Tungsten copper	±0.01 to ±0.02 mm	Grinding for critical faces
Tungsten carbide, ground	±0.005 mm or better	N/A, grinding is already the primary process

These are typical figures, not guarantees. The shop quoting your part confirms what it can hold given your specific geometry, fixture design and inspection capability.

Where the tolerance actually matters

A tolerance callout should map to a real functional requirement: a bore that mates with a bearing or shaft, a face that seats against another part, a thread that must engage correctly, or a feature that affects balance or alignment. Dimensions that do not affect fit or function do not need tight tolerance, and loosening them where possible has a real effect on price and lead time with tungsten, more so than it would with a cheaper, easier-to-machine material.

A drawing with every dimension held to ±0.01 mm regardless of function is not more precise, it is more expensive to inspect and more likely to generate scrap on features that never needed to be that tight in the first place.

Surface finish

Out-of-the-mill or lathe surface finish on heavy alloy is broadly comparable to what the same operation would produce in a hard steel, assuming similar cutting parameters. Pure tungsten can finish rougher directly off the tool because material tends to fracture rather than shear cleanly, which is part of why fine-finish requirements on pure tungsten often move to grinding rather than trying to achieve them with a milling or turning pass alone.

Ground finishes, used for the tightest tolerance features across all grades and as the primary process for tungsten carbide, produce the smoothest and most consistent surface, at the cost of additional processing time compared with machining alone.

Typical surface finish by process

Surface roughness is usually expressed as Ra, a measure of average roughness. The ranges below are typical for the process itself across dense, machinable metals, and give a starting point for deciding what to specify. Confirm the actual achievable finish with your shop for the specific grade and feature.

Process	Typical Ra range	Where it is used
Standard milling or turning, heavy alloy or tungsten copper	Comparable to the same operation on hard steel	General features with no sealing or bonding function
Standard milling or turning, pure tungsten	Somewhat rougher than the same pass on heavy alloy	General features where fine finish is not required
Fine finishing pass (light cuts, sharp tooling)	Noticeably smoother than a roughing or general pass	Faces with a light cosmetic or fit requirement
Grinding, any grade	The smoothest and most consistent of the group	Sealing faces, bearing bores, and all tungsten carbide geometry

If a face has no sealing, bonding or bearing function, it usually does not need a surface finish callout at all. Reserve a specific Ra value for faces where roughness genuinely affects performance.

Features that push tolerance toward grinding

A handful of feature types commonly move from milling or turning to a grinding operation, regardless of grade, when the tolerance is tight enough:

• Flat mating faces requiring flatness beyond what milling reliably holds.
• Precision bores for bearing fits or close-tolerance shafts.
• Any feature on pure tungsten tighter than roughly ±0.01 mm, since the brittleness makes that hard to hold reliably by milling or turning alone.
• All tungsten carbide geometry, since grinding is the primary shaping process, not an exception.

Knowing this in advance helps when deciding whether a tight tolerance is worth the added cost, or whether a slightly looser callout still meets the part’s function.

Common tolerance and finish mistakes on tungsten drawings

• Applying a single blanket tolerance to the whole part. A general note of ±0.01 mm on every dimension treats a cosmetic edge the same as a bearing bore, and costs accordingly.
• Specifying a surface finish on faces with no functional reason for it. A fine finish callout on a face nobody sees or touches adds cost without adding value.
• Not flagging which features are allowed to be ground. If a bore needs to be tighter than milling can reliably hold, say so, rather than leaving the shop to discover it during quoting or, worse, during machining.
• Assuming pure tungsten will hold the same tolerance as heavy alloy on the same drawing. The two grades are not interchangeable at the tolerance level, even when the geometry is identical.

What to ask your shop before you finalize tolerances

A short conversation with your shop before the drawing is locked can save a redesign later:

1. What is your tightest reliable tolerance on this grade and geometry? A shop’s general capability chart is a starting point, but your specific size, wall thickness and fixture needs confirmation.
2. Which of my features would you recommend moving to grinding? A shop that regularly cuts tungsten can usually spot this faster than working it out from a generic tolerance table.
3. Does this tolerance change your blank or process choice? A tight bore, for example, may push the shop toward a different starting stock or a different machine than a looser one would.
4. What is a realistic surface finish on this feature without grinding? If your callout is close to what milling or turning already produces, it may not be worth specifying a number at all.

How to specify tolerance on the drawing

1. Apply tight tolerances only to features that affect fit or function.
2. State the grade clearly, since tolerance expectations differ by grade.
3. Flag features that may need grinding, such as precision bores or flat mating faces, so the shop can plan the process and price accordingly.
4. Ask the shop what it can hold on your specific geometry rather than assuming a blanket tolerance across the whole part.

The whole decision path is in our guide on how to machine tungsten.

When your drawing is ready, send your RFQ and we match it with shops that can hold the tolerances your part actually needs. For the underlying question of what each grade allows, see what is possible when machining tungsten. For heavy alloy specifically, see tungsten heavy alloy machining.

Frequently asked questions

Sources

• Wikipedia - Engineering tolerance
• Wikipedia - Surface finish
• Wikipedia - Grinding (abrasive cutting)

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• Grinding Tungsten Heavy Alloy: Which Wheel, What Finish, How Tight