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Username Post: tapping stainless        (Topic#364530)
"5th Year" Platinum Supporting Member
Posts: 680
Loc: Ohio
Reg: 12-17-06
03-06-21 06:12 AM - Post#2815642    

Hi, I want to enlarge a fuel log from 1/4" to 3/8"IPS that is made of SS. Its probably 3/8" to a 1/2" thick and my worry is that hand tapping may turn ugly rather than a machine shop doing it where I think their equipment is better suited. Has anyone had to do similar tapping.


65' Impala SS, 65' Belair, 89' Silverado Z71, 95' Silverado Z71, 12' Silverado, 15' Silverado LTZ, 16' Tahoe LTZ

Edited by 995jim on 03-06-21 06:14 AM. Reason for edit: No reason given.


Senior Member
Posts: 495

Loc: CA
Reg: 07-18-00
03-06-21 05:06 PM - Post#2815676    
    In response to 995jim

Disclaimer: I'm not a machinist or tool maker.

Tapping for NPT "by the book" calls for drilling the hole and then reaming the hole with a taper reamer before cutting the threads.

I would think that for a fuel log you don't have to thread all the way to the bottom of the hole. If this is the case, you can probably get away with skipping the reaming operation. I've gotten away with skipping the reaming operation, but YMMV.

There's lots of "getting ugly" when tapping holes. If you're worried about breaking the tap, NPT tapes are pretty thick in the shank and would take a lot for it to break off in the hole. Starting the tap in straight prevents breakage; I've used a drill press (turned by hand) to help with this.

Edit: Use some kind of cutting fluid and avoid hardware store taps.

1987 IROC-Z 5.0L
1992 Lumina Euro 3.1L
2003 GMC Safari

Edited by paulo57509 on 03-06-21 05:09 PM. Reason for edit: No reason given.

Super Senior Member
Posts: 5790

Loc: paradise
Reg: 09-05-03
04-22-21 07:30 AM - Post#2818546    
    In response to 995jim

gonna depend on how hard the metal is. i would do a practice peice, and taper ream it. maybe get a new tap too.

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.

"4th Year" Silver Supporting Member
Posts: 2307
Age: 66
Loc: Altavista, Va.
Reg: 07-05-08
04-26-21 03:48 PM - Post#2818851    
    In response to bobb

When tapping stainless always remember to go SLOW and use a good tapping lubricant such as Tapfree


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