How Deep To Tap??

-
mopowers

mopowers

Well-Known Member
Joined
Feb 15, 2006
Messages
8,663
Reaction score
4,878
Location
West Sacramento, CA
I need to drill and tap the 1/4" NPT hole just left of the water neck in my Air-gap manifold to accept a 3/8" NPT fitting. Since I've never tapped a NPT hole before, I've got a quick question...

Seeing how the threads are tapered, how deep do I need to run the tap??? I've heard 12 threads deep is the go-to number. Or should I tap it and keep test fitting the fitting until I'm happy with the depth?

20140407_202439_zps9e980a3d.jpg
 
Tap it and keep test fitting. You can adjust the height of the sensor by doing this. Just for looks, I like the sensors deep, with only a few threads showing.
 
Most pipe taps are tapered pipe taps.


They also make straight pipe taps. Those are better as they are not "sensitive" to the depth that you tap.

I would recommend using a straight pipe tap. You should be able to find them at a local Grainger or Production Tool Supply store.
 
krazykuda said:
Most pipe taps are tapered pipe taps.


They also make straight pipe taps. Those are better as they are not "sensitive" to the depth that you tap.

I would recommend using a straight pipe tap. You should be able to find them at a local Grainger or Production Tool Supply store.
Click to expand...

I've never heard of a straight pipe tap. interesting...

I've already got a tapered 3/8"-18 NPT tap though. Thanks for the input.
 
Try and get 3 to 3-1/2 turns of engagement and you should be good.
 
mopowers said:
I've never heard of a straight pipe tap. interesting...

I've already got a tapered 3/8"-18 NPT tap though. Thanks for the input.
Click to expand...


What Chrysler does is to use a straight pipe tap for the female threads, then use a tapered pipe thread for the "male"/"plug" portion. Then it wedges itself in like a cork and does not leak.

You have to find a specialty tool store to get straight pipe threads. It's the best way to go.
 
ESPECIALLY in an aluminum (or other soft alloy) I'd do as above, tap a few threads and test it. Just did this myself, some bean brain hay wired a t gauge into a manifold. Had a nice time getting the fitting out. Of course Edelbrock "can't afford" to give us any spare tappings LOL

I've never heard of using a straight pipe tap for conventional tapered pipe fittings which is what this is. A straight pipe tap would be for special stuff, I would think.

My recent "down that road

http://www.forabodiesonly.com/mopar/showthread.php?t=271617&highlight=npt,+tap

attachment.php


attachment.php


attachment.php


attachment.php


attachment.php


My old taps had since the early 70's and some way before that. An old friend taught me that sometimes, it's better to do without a tap wrench. You experiment with nut sizes, put them in a vise, and press the nut on the end of the tap drive square.

attachment.php
 
I start by going about 1/2 way down the tap and then test fit. Minimum is about 3 turns of the fitting or sensor by hand before the threads bind up.
 
Also, don't get carried away tightening a pipe thread. The sensor can split the aluminum, like a wedge if you force it in too tight. I have been coating the threads with gasket sealant (purple stuff that dissolves in ethanol). Teflon tape seals well, but I don't like the little bits that get into things when you unscrew the sensor. Also, your sensor must cut thru the sealant to get a good ground.
 
I always tap her as deep as she can stand it. And then a little more.
 
RRR, I'm not sure that yer talkin about the same thing as they are. Jist sayin......

Second on the teflon tape. I prefer PTFE-bearing pipe dope. When nothing else would reliably seal them, the pipe dope sealed my slant's manifold studs.
 
You must log in or register to reply here.
-

Back
Top