Machinist60
Plastic
- Joined
- Sep 17, 2004
- Location
- Ottawa, Ontario, Canada
I have an old aluminum cylinder head with a spark plug plug hole that was repaired with a bronze pinned threaded insert. This insert has come loose allowing gas to leak. The pins have been ground out and the insert threaded out easily as it was loose. No standard replacement insert can be found because of space restrictions a custom insert has to be made. For this I need to make a m25 1.25 tap. There is not space for a more coarse thread. The spark plug is m18 1.5.
Pictured is a tap made from water hardening steel. It will not bite and pull in aluminum, even pushed with the tailstock. I have tried 2 taper angles, 5 and 3 degrees, no difference. The scraping angle in the flute is 90 degrees or a little under. I have made smaller taps in the past with good results.
Any advice or help will be much appreciated.
Thanks.![IMG_1915.JPG IMG_1915.JPG](https://www.practicalmachinist.com/forum/data/attachments/361/361197-6ca2ee5b4909bc5f1d2d0810c7f146f2.jpg)
Pictured is a tap made from water hardening steel. It will not bite and pull in aluminum, even pushed with the tailstock. I have tried 2 taper angles, 5 and 3 degrees, no difference. The scraping angle in the flute is 90 degrees or a little under. I have made smaller taps in the past with good results.
Any advice or help will be much appreciated.
Thanks.
![IMG_1915.JPG IMG_1915.JPG](https://www.practicalmachinist.com/forum/data/attachments/361/361197-6ca2ee5b4909bc5f1d2d0810c7f146f2.jpg)