I needed a tap to suite to the tyre air valve. I heard taps were available but quite expensive. So I decided to make one by myself. The size of the thread is 0.209”OD X 36TPI or 5.3mm X 0.706mm pitch in metric. Very odd size. The OD was not a problem, but my lathe does not have 36TPI gear. I had to compromise with 0.7mm pitch. Anyway only a couple of threads would mate in this case and this difference should not be a problem.

これは車のタイヤの空気バルブですが、これに合うタップが必要になりました。手には入るようですがえらく高いそうで、自作することにしました。0.209"OD X 36TPIというなんかえらく半端なサイズです。メトリックに直すと、5.3mm X 0.706ピッチ。外径はいいんですがピッチの方は36TPIなんて私の旋盤にはない。そこでピッチは0.7mmで妥協することにします。もともとこのバルブのねじ山は数山しか咬み合ってないので問題ないでしょう。旋盤でのねじ切りは初めての経験です。

This was the plan for the job.


This is the blank for the intermediate tap. The end was tapered at 8 degrees. The material is 6mm silver steel.


This blank is for bottoming tap. The taper is 20 degrees.


I cut the thread following the procedure shown on my lathe text book.


I cut it with 100rpm and 0.2mm cut-in, but the thread was badly torn. I used water base cutting fluid, but it did not work at all for this job. I scrapped the blank.




Cutting intermediate tap thread. I changed the cut-in to 0.1mm and used tapping oil instead. The result was acceptable. I removed the burs by a file.


I cut cutting edges by mill.


Cutting edge grooves were finished, but I think these were too shallow. It would be better to cut them deeper.


All machining finished.


I hardened and tempered it.


Testing the tap. Tapping was bit hard, because the tap did not have any escape angle at cutting edges. Use of tapping oil is essential even for brass.


At first the thread was bit tight, but after removing burs by a drill the air valve mated nicely. I used only intermediate tap, and it was enough. Bottoming tap was not necessary.



inserted by FC2 system