Sample holders (and grabber)

This is our 3D-printed sample holder, printed in metal as a base piece and two clamping pieces. The clamps pivot on ¹⁄₃₂” spring pins (from McMaster-Carr) and derive clamping force from extremely small 0.057” OD stainless steel compression springs (from, of all places, Amazon.com).

We use a magnetically coupled linear-rotary motion feedthrough to move samples in and out of the microscope. The sample grabber here has pincers that hold onto the back knob of the sample holder. (As in the sample holder, these pincers pivot on spring pins; clamping is through extension springs.) Rotating the sample locks it into place (or unlocks it, if already locked), after which linear motion engages or disengages the grabber from the back knob.

The quatrefoil shape of the sample holder and sample grabber also appears in the microscope body, the in-vacuum sample tree and load-lock block, and the tip grabber. It’s a relic of the first iteration of the microscope, where the indents allowed clamping screws to move closer into the center and therefore minimize the size of the assembly. Later versions of the microscope use an external clamping mechanism instead, which means there’s no reason sample holders and everything else couldn’t have a square cross section, or even one that’s somewhat convex. We have too many pieces designed and printed to make the change, but if we were starting fresh, a larger cross-section on the sample holder would make designing the little clamps and other mechanisms substantially easier.

Both the pincers of the sample grabber and the clamps of the sample holder are tiny pieces that are grouped together for printing multiples. A sharp cutting pliers (perhaps followed by sanding) will cut through the sprues to separate the parts.

Autodesk Inventor files are here. STL files (for 3D printing) are here.

Assembly instructions can be found in this post.