Tapping my first thread into Cast Iron

[Anonymous]

These cylinders have a lot of blind tapped holes:

All holes drilled and tapped (using spiral flute taps) on the vertical mill. For cylinder and valve covers it was worth setting up the Tapmatic. For other holes, after drilling, I put the tap in the drill chuck, put the mill in 'neutral' and tapped a few threads deep turning the drill chuck by hand. The threads can be finished later by hand on the bench.

For cast iron I work on a thread depth of approximately 70%, or a little deeper on fine pitch ME threads. All drilling and tapping is done dry.

Tapping by hand is easier with taper hand taps, as the taper helps to align the tap. When tapping by hand I judge perpendicularity in two directions by eye after a turn or so and bias the force on the tap accordingly. I normally only buy taper and bottom hand taps, never use second taps.

Andrew

[Author]

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