NPT pipe plug set beneath the surface 3

[threadmaster]

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!!

 

[scastillo]

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

 

[Cockroach]

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

 

[threadmaster]

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?

 

[SnTMan]

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

 

[dimjim]

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.

 

[threadmaster]

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?

 

[threadmaster]

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!

 

[SnTMan]

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

Regards,

Mike

 

[dimjim]

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.

 

[eromlignod]

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

 

[threadmaster]

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!!

 

[arto]

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?}

 

[dvd]

Have you thought about buying new plugs?

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

 

[EngJW]

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.

 

[unclesyd]

You might want to take a look at this approach to plug your hole if a threaded connection isn't needed.

http://www.theleeco.com/PLUGWEB2.NSF/Plugs!OpenView

 

[dimjim]

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.