How Are Manifold Flanges Machined After 3D Printing?

The flanges are machined in one setup from the mounting interface as datum, with 1.0 mm of stock on the faces and 0.4 mm on the bolt holes. Sealing faces finish at a 0.05 mm target flatness and Ra 1.6 µm.

Which datum is used?

The datum is the mounting interface — the face that bolts to the head or the test fixture — not the CAD origin. The printed part is set on that face, and the machine cuts the opposite flange and the bolt pattern from it.

The datum is taken after stress relief, not before. A datum measured on the constrained part moves once the supports are cut, and every feature cut from it inherits the error.

One setup is the rule. Re-clamping a manifold to reach a second face adds a fixturing error that no CMM can separate from the machining error, and the report then records a number nobody can act on. Fixtures are built around the measured part, not the model: a printed manifold can sit off its datum by a few tenths, and a fixture cut from CAD would hold that error in place.

How much stock is left on each face?

Faces are cut from 1.0 mm of stock, holes from 0.4 mm. The face stock covers the movement left after relief and the skin left by blasting; the hole stock covers the drill wander in an as-built boss.

The split matters. A part with 1.0 mm on the face but 0.2 mm on the holes will clean the face and break into the hole, so the shop checks both before the first cut.

Sealing faces finish at a 0.05 mm target, with 0.05–0.10 mm accepted across the face, and Ra 1.6 µm. The acceptance band is wider than the target because a printed flange can spring slightly after unclamping, and the band keeps that movement from turning into a reject. The first article is measured on a CMM against the drawing; the same features are checked on the parts that follow, so the band can be compared between builds.

The general tolerances that are not on the drawing follow ISO 2768; the printed surfaces themselves are not held to that band, which is why the cut faces are called out separately.

How are threads cut?

Threads are milled, not tapped, on printed bosses. Milling cuts a clean profile without the tearing a tap can leave in an as-built hole, and it keeps the axis on the same setup as the face.

The thread is cut after the face, so the axis and the face stay square to each other. Blind holes stop two threads short of the bottom, which keeps the tap from breaking out through the far wall.

Engagement is at least 1.5×D. A 1.0 mm wall around the boss is not enough for that, which is why threaded bosses are thickened to at least 2×D before the machining step is quoted. Engagement is checked with go/no-go gauges, not by eye, because a short thread looks the same as a full one until it strips.

When does the machining plan not apply?

It does not apply when the flange has no stock left after relief. The part is re-relieved or scrapped, not machined to a thinner flange — cutting a flange that has already moved past its allowance just moves the leak path.

It does not apply to precipitation-hardening grades that will be aged after machining. The ageing distortion has to be planned into the stock or the sequence changed, or the finished face will move after the final cut.

And it is not a guarantee of a leak-free joint. Machining gives flatness and surface finish; gasket choice and bolt torque sit outside the machine, and the tolerance risk guide covers the parts of that stack the shop controls.

Send the flange drawing and the gasket type to Neway; we will confirm the stock, the datum and the thread callout before quoting the machining. Stainless steel 3D printing supplies the blank; the cut is what makes it an interface.