Step 6: Drilling the holes and tapping the threads
This section assumes some very basic knowledge of how to use a vertical milling machine. It also assumes that you have already fabricated the tooling necessary to hold the delrin stopper during this step, or its equivalent. Fabrication of the tooling is described in Appendix A.
1. Use a deburring tool or file to remove any nub left by the parting-off on the lathe.
2. Mount the stopper in the tooling and tighten down the screws, making sure that the clamp on the top is level.
3. Mount the tooling in the vise of a milling machine, and use an edge-finder to locate its corner, setting both digital read-outs to zero.
4. Use the drawing to center a Q-sized drill bit over the large hole. Drill through.
5. Put a spring-loaded tap guide in the check to keep a 1/8-27 NPT (tapered) tap oriented vertically while you tap threads for the hose barb.
6. Use a #30 drill to make the hole for the hypodermic tubing.