×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

NPT pipe plug set beneath the surface
3

NPT pipe plug set beneath the surface

NPT pipe plug set beneath the surface

(OP)
i have to machine a few standard NPT thread for exaple 1/8 27tpi and a few others i was supplied the standars plugs, if i mill a standard 1/8 27 internal the plugs sit above the part, does anybody have an idea of where i could compensate to make the plug sit beneath the surface. any help would be appreciated!!

RE: NPT pipe plug set beneath the surface

How thick is the material you are threading into? Would it be possible to spotface the hole and re-tap the NPT threads?

RE: NPT pipe plug set beneath the surface

There are standardized pipe plugs readily available without the hex heads, which sit below the surface.  I use them all the time.  They have the socket head recessed into the top of them and suited for a key.

I believe they are referred to as "internal" pipe plugs.

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

RE: NPT pipe plug set beneath the surface

(OP)
what if i already have the plugs which cannot be remachined but i have not yet machined the hole i was wondering if i could do something with the program on the mill so the plug would go lower into the part, i think maybe change the major dia couple thou.? i dunno please help?

RE: NPT pipe plug set beneath the surface

threading, If they are ever going to have to come out I would be very leery of sinking square head plugs below the surface. Bite the bullet, buy the socket head plugs.

Regards,

Mike

RE: NPT pipe plug set beneath the surface

You would have to counterbore the holes before tapping if you want them recessed, We used drill, counterbore, and then tap. I think the c'bore was .81 dia. x .62 deep.  You have to c'bore large enough for the socket wrench to drive these.

RE: NPT pipe plug set beneath the surface

(OP)
say the plug has an alen wrench head recessed into the plug and they just want it to sit a little below the surface, i cant buy new plugs they were given to me with the part, i never though of a counter bore, might look a little funny? but maybe. does anyone think if i change the major thread diameter the plug will go futher into the whole?

RE: NPT pipe plug set beneath the surface

(OP)
why should i worry if they have to come out, for example an oil drain on an engine i guess it could also be square plud either way , i dunno how to get it to lay beneath the hole!

RE: NPT pipe plug set beneath the surface

threading, yeah, you don't have to worry if they have to come out, or if they leak someday or...

Regards,

Mike

RE: NPT pipe plug set beneath the surface

They make pipe plugs instead of grease fittings if that is what you want.  If they still stick out an option would be to c'sink maybe .56 @ 120degrees.  I am fairly certain your tap drill is .344 dia.  The other option is simply to c'bore .56 x .12 deep if you are using pipe plugs.  They do make a flush type pipe plug, but I forget the part number now.  Check with Alemite or whoever.

RE: NPT pipe plug set beneath the surface

2
I think I know what you are saying.  NPT threads are tapered and the depth that a fitting tightens to is dependent on how deep you tap and how tight you make the joint.

Do you just drill a hole and then tap with a pipe tap, or do you also taper ream first?  For a 1/8-27 NPT you should drill with an 11/32" bit, then ream with a taper pipe reamer (3/4 in. to the foot).  The deeper you ream, the deeper the tap will go and the deeper the plug will seat.  

As long as the female material is thick enough and the plug is tightened to the same torque, it will seal the same.  What you don't want is to go so deep that the plug protrudes on the inside wall, since this means that some of the threads aren't mating and you might not get a good seal

Don
Kansas City

RE: NPT pipe plug set beneath the surface

(OP)
cnc milling machine, i dont know how to tell you guys this but again but i cant buy any new plugs they were supplied to me!! but now i came across a new idea, i mostly just need to increase the diameter of the tapered hole and thread in the program, thus allowing the plug to sit lower, while retaining the same taper! i guess ill try this first! unless u guys see something wrong with this idea!!

RE: NPT pipe plug set beneath the surface

since NPT's tend to leak (& thus be retightened, is there any chance of "falling of the end" (i.e. running out of taper) after you go oversize? What's the wall th'k you're tapping into?
{how about Lee plugs if it doesn't need removing, or SAE O-Ring seals if you don't want leaks?}

RE: NPT pipe plug set beneath the surface

Have you thought about buying new plugs?

Actually, I think eromlignod's advice to use a tapered ream is the most sensible.

RE: NPT pipe plug set beneath the surface

We have some spots where we have to plug an oil gallery, but the plugs have to be below the surface because some customers use the surface to attach their drives to. As far as I know, they just run the tap a little deeper. I don't think there is any special procedure other than checking it with the pipe tap gages.

RE: NPT pipe plug set beneath the surface

We never used a taper for any pipe tapping in the lower sizes.  The pipe plugs and/or grease fittings come with a taper, but we tap straight threads in the bores.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources