AR Headset Frame — Titanium 6Al-4V

Why This Part Is Hard to Machine

Titanium 6Al-4V has the best strength-to-weight ratio of any common engineering metal, which is exactly why it’s the right material for an AR headset frame. But those same properties make it brutally difficult to machine at the dimensions this part requires.

The frame cross-section varies from 4mm at the temple arms down to just 1.2mm at the bridge — the piece that sits on the user’s nose. At 1.2mm, you’re machining a wall thickness barely thicker than a credit card, in a material that work-hardens when you cut it too slowly and generates extreme heat when you cut it too fast. Tool deflection at these dimensions can push the wall out of tolerance in a single pass.

The waveguide mounting pads are the most critical features. These are the flat surfaces where the optical waveguides — the transparent panels that display the AR image — mount to the frame. If these pads aren’t coplanar within 0.0005", the waveguides tilt relative to each other, and the AR image appears shifted or doubled. The human eye can detect image misregistration down to about 1 arc-minute, so the mechanical tolerances are driven by human perception.

The camera mount bores add another layer of difficulty. The cameras must be pressed into the frame at precise positions and angles to map the user’s environment for mixed-reality overlays. Press-fit bores in titanium at ±0.001" require rigid fixturing and conservative cutting parameters to prevent bore distortion from cutting forces.

How We Solved It

We ran a free DFM review and recommended starting from thin titanium plate stock to reduce machining time, tool wear, and risk of distortion from material removal stresses:

• Thin plate stock for minimal material removal. We started from 6mm titanium plate instead of bar stock. This reduced the buy-to-fly ratio dramatically — less material removal means less heat generation, less residual stress, and less distortion in the finished part. The plate was stress-relieved before machining.
• Micro endmill strategy for thin sections. The 1.2mm bridge section and temple arm profiles were machined with a 0.5mm micro endmill at high RPM (40,000+) with minimal depth of cut (0.05mm per pass). This keeps cutting forces low enough to prevent deflection while maintaining the surface speed titanium needs to avoid work-hardening. Tool life was monitored per part to prevent wear-induced dimensional drift.
• Shared datum for waveguide coplanarity. Both waveguide mounting pads were machined in a single setup referencing a shared datum surface. By never re-clamping between the left and right pad, we eliminated any fixturing error contribution to coplanarity. The CMM verified coplanarity at 0.0003" — well within the 0.0005" spec.

Surface Finish and Post-Processing

The frames were bead blasted for a uniform matte texture that’s comfortable against skin and hides minor handling marks during assembly. The customer then sent the frames out for PVD titanium nitride coating (gold tone) at their own facility. The PVD process adds a hard, wear-resistant layer that also gives the frames a premium gold appearance.

Waveguide mounting pads and camera press-fit bores were masked during bead blast to preserve the as-machined surface finish and dimensional accuracy these features require.

What the Customer Said

“We went through three vendors before RivCut. The first two couldn’t hold the waveguide coplanarity — our AR image was shifting every time we swapped frames. RivCut hit 0.0003" on the first batch, the image registration was within 2 arc-minutes, and the frames weighed 3.5 grams under our budget. We wore them for 8 hours straight with no discomfort. Design frozen.”