Making a 1″ NPT Tap For A One-off Use

I am in the process of reconfiguring the plumbing at the bottom of the hydroelectric system (more about why later) involving increasing the size of the final flow route from 3/4″ to 1″, a dimensional increase of 33% and, more beneficially, a volumetric increase of almost 80%.  But in order to accomplish this I needed to fabricate some fittings with 1″ NPT female threads, requiring a 1″ NPT tap.  Ever priced one of those?  The number is exceedingly off-putting so instead I made my own using a $3 piece of  1″ NPT pipe fitting from the hardware store.  Since I was cutting threads in Schedule 40 PVC it was more than robust enough for the task.

I first tapered the end of the pipe with a file, then sawed four kerfs into the surface of the threads with a hacksaw.

With files I then reduced the cross-section of the threads such that each of the four kerfs became four cutting faces for the new threads which were being cut into a slightly oversized 1-1/8″ hole drilled in the PVC.

The “tap” handle was just an assemblage of plumbing pieces, and the thread cutting could commence.

This allowed me to screw in the fitting I needed for the radiator hoses that connect the penstock to the turbine valves/nozzles/impeller.

It took about an hour to make the tap, and it saved many, many dollar$.