From 3D Hubs, I have some parts that will hold a mirror and viton o-ring using an SM1 mount in an assembly that will hold a piezo to actuate the length of the cavity. 3D Hubs did not tap the hole, they just made the 1.011" diameter minor diameter pilot hole. For a square-shaped part for the GQuEST Output Filter Cavity, I previously used a 2D Mill to hold and tap the part. Since this part has cylindrical symmetry, I used a lathe.

I place the part all the way in the back of the jaws so that the tap would be perpendicular to the hole. I used the Thorlabs SM1 tap and Anchorlube as my lubricant. Anchorlube is approved by LIGO to machine because it is easy to clean. The tap is mounted on a spring guide. To move the tap clockwise, I used a 20 mm ratchet wrench. See attached photo. To move the tap counterclockwise every so often to break up the chips, I used a 11/16 in open ended wrench. I made sure to tap all the way through such that I can easily spin the tap clockwise with my hand before retracting. I then used an SM1RR to ensure the threads went all the way deep. I then washed the lubricant off with water and dried the parts.

The next step is to clean and bake the parts before installing the cleaned and baked 1/4-20 helicoils.