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Getting rid of the air from a coal era steam heating system as quickly as possible is the secret to making them work so much better!
There is very little commentary on this video because this process has to be done right the first time and requires the worker to be focused and not distracted.
The fitter first drills an 1/8" pilot hole in the chosen location, roughly in the middle of the last tee on the system.
A slightly bigger hole is drilled using a standard drill bit.
A step bit (1/8" to 1/2") is used to widen the hole.
Notice the oscillating motion of the 1/4" impact driver by the operator and the slight upward angle of the drill.
The process is repeated using a larger step bit up to 3/4"
A 1/2" NPT tap in a socket of the correct size and a 1/2" ratchet makes the threads in cast iron.
Please notice the steam fitter carefully tapping the 1/2 NPT threads to just the right depth.
This process takes several times to dial it in, as threading too deep would make it much harder to make a good seal on the 1/4" thick cast iron fitting.
No cutting oil is used as the old cast iron has plenty of lubricating graphite already in the metal and any oil may contaminate the boiler water.
The technician pipe dopes a short 1/2"steel nipple (off screen) and installs a recovered 1/2" cast iron 90.
Finally, he installs it in the newly formed hole using a short pipe wrench so as not to over-torque the iron and threads on a Gorton #2 in the 90 fitting.
During the coal era, main vents on these small systems were thought not to be needed (& it kept the install price low) because the coal fire would burn for hours and hours and hours and eventually the air was driven from the system and the radiators would finally heat.
Always keep in mind that Steam and Air are invisible gasses that Do. Not. Mix.
Where there is trapped air, steam cannot flow and do its magic of making radiators warm.