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pipe tap what design?

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fixerupper
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PostPosted: Fri Feb 15, 2019 5:05 pm    Post subject: pipe tap what design? Reply to specific post Reply with quote

I have used pipe taps for a long time but not often enough to need to know what kind of tap is better than the other.

I'm shopping on line for a 1/8" pipe tap to thread holes in a cylinder head. The Grainger website has a long list of 1/8" taps and now i'm getting confused. They have a choice of 3, 4, or 5 flutes and taper vs semi-bottoming taps though most are bottoming. Taper must be something special because they offer only three choices of taper, two in NPTF and one in NPT. They offer 18 choices in semi-bottoming, some in Npt and some in NPTF.

I am working with plain NPT so I have that worked out. What is the advantage to 3,4,or 5 flutes? What amount of flutes do you guys recommend for cast iron, 3,4,or 5? How is the taper tap design different from the semi-bottoming tap? Thanks
 
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fixerupper
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PostPosted: Fri Feb 15, 2019 5:08 pm    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

fixerupper wrote:
(quoted from post at 18:05:28 02/15/19) I have used pipe taps for a long time but not often enough to need to know what kind of tap is better than the other.

I'm shopping on line for a 1/8" pipe tap to thread holes in a cylinder head. The Grainger website has a long list of 1/8" taps and now i'm getting confused. They have a choice of 3, 4, or 5 flutes and taper vs semi-bottoming taps though most are bottoming. Taper must be something special because they offer only three choices of taper, two in NPTF and one in NPT. They offer 18 choices in semi-bottoming, some in Npt and some in NPTF.

I am working with plain NPT so I have that worked out. What is the advantage to 3,4,or 5 flutes? What amount of flutes do you guys recommend for cast iron, 3,4,or 5? How is the taper tap design different from the semi-bottoming tap? Thanks


And I forgot to mention, one of the reasons for the large listing is three different brands are shown.
 
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leroy in ne
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PostPosted: Fri Feb 15, 2019 5:37 pm    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

I'm not going for my books but I believe NPT stands for National Pipe Taper, NPTF is for National Pipe Taper Dryseal which is a modified thread crest that crushes when the joint is made and will not seep as easy as flank sealed NPT. They also make what is called NPS which is National Pipe Straight and is used in things like nuts for tank nipples, bulk head fittings, electrical fittings, ect. it does not seal and requires gaskets ect. then to make things interesting you can through in metric pipe, as an example 1/8 metric is 28 threads per inch not 27 as NPT is, also 1/4 or 3/8 metric is 19 threads per inch instead of 18 as NPT is. as far as the number of flutes, the more flutes the less chip load and reduced chipping due to load as you are cutting a tapered thread. It's been 15 years since I had to deal with this so memory is not what it was.
 
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Roger Tomfohrde
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PostPosted: Fri Feb 15, 2019 5:53 pm    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

Generally speaking the taper is for if there is enough room below the hole standard dimension for pipe thread for that size. 1/2 Inch pipe it was seven threads usable.So a bottoming tap is shorter and will be harder to use because there is in effect no precut for the tap and it will not find its path as easy. Three flute is easier in my mind to cross thread and is the cheapest to buy but it will allow for larger chips. Machinist wise the more flutes will let you cut harder materials. This is mostly how I feel they work but there is more to it than that. Quality makes a huge difference on how good they are to use.
 
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Oregon Tractor Jack
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PostPosted: Fri Feb 15, 2019 5:57 pm    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

Don't know for a fact, but in my opinion the number of flutes would have to do just how much you would need to use the tap and the material it would be used in. I would think that for a once up use in cast iron just about any tap would work. If you were planing to tap a ton of heads then you would want as many flutes as you could get just to cut faster and longer.

OTJ
 
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fixerupper
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PostPosted: Fri Feb 15, 2019 6:32 pm    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

I made a typo when I said most are bottoming. I meant to say semi-bottoming.
 
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Ralph, Ohio
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PostPosted: Fri Feb 15, 2019 6:51 pm    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

If you need to get threads near the bottom of a blind hole it works well to start with a standard tapered tap & finish with a bottoming tap.
 
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Ken(Ark)
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PostPosted: Fri Feb 15, 2019 7:05 pm    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

I use a pipe tap to replace the welch plug with a pipe plug on the front oil galleys on small block chevy's .

A standard pipe tap is too long but it starts the hole . I use a second tap that I cut short with a cut off wheel on a hand held angle grinder , to finish the hole .

Since the NPT tap is tappered I have to watch how deep I run the tap or the plug would screw in too deep before getting tight .

Through trial and error , I figured out how deep I wanted to run the tap and marked the teeth that had not gone below the surface ( or still sticking out of the block ) . Then I ground them off . When running the tap in , I stop when the last tooth has become flush with the block .

I think all of my taps are general purpose taps purchased from local hardware stores and they have 4 sides . They have worked fine for dozens of holes and I see no reason I will ever wear them out .
 
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Steve@Advance
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PostPosted: Fri Feb 15, 2019 7:20 pm    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

Taps can be a confusing subject because, just as you mention, there are so many choices!

But most of the choices involve mass production, material being tapped, and tap longevity.

The "semi-bottoming" comes in when the hole being tapped is too shallow for a standard tap to enter far enough.

Unless the depth of the hole is a concern, a standard 4 flute NPT hand tap will work fine.

You may find that even though all those options are listed, very few will be available in stock, and if they have to be ordered there will be a long lead time and very high price.

Just to be on the safe side, I want to ask...

You do know that a taper pipe tap in never run all the way in? General rule, leave about 6 threads showing.
 
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atlarge54
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PostPosted: Fri Feb 15, 2019 7:58 pm    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

fixerupper wrote:
(quoted from post at 02:05:28 02/16/19) I have used pipe taps for a long time but not often enough to need to know what kind of tap is better than the other.

I'm shopping on line for a 1/8" pipe tap to thread holes in a cylinder head. The Grainger website has a long list of 1/8" taps and now i'm getting confused. They have a choice of 3, 4, or 5 flutes and taper vs semi-bottoming taps though most are bottoming. Taper must be something special because they offer only three choices of taper, two in NPTF and one in NPT. They offer 18 choices in semi-bottoming, some in Npt and some in NPTF.

I am working with plain NPT so I have that worked out. What is the advantage to 3,4,or 5 flutes? What amount of flutes do you guys recommend for cast iron, 3,4,or 5? How is the taper tap design different from the semi-bottoming tap? Thanks


I've tapped 100's of 1000's of 1/8 pipe. I'd use a 4 flute NPTF. Run the tap deep enough that the mating part goes in about 3 and 1/2 turns by hand and tighten over 1 turn with a wrench. If the hole is anywhere near being a blind hole the tap will need to be shortened and re-lead. In cast iron it should be a piece of cake.
 
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SDE
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PostPosted: Fri Feb 15, 2019 8:38 pm    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

Tapered taps have about six threads of lead. Plug taps have about three and the bottoming tap has one thread of lead. The length of the tap and the depth of the hole,
will determine which one will or will not work. A bottoming tap will require more effort to tap the hole and the tapered tap will use the least force. Bottoming taps will
dull more quickly and then break. The tapered tap will easily outlast a bottoming tap.
 
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leroy in ne
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PostPosted: Sat Feb 16, 2019 3:30 am    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

sde, you are mixing tap types for making threaded holes for bolts ect. that require straight walls with tapered pipe which I believe requires a tapered wall which if my memory is correct is 1/8 inch per foot. Machinery,s Handbook devotes over 200 pages to thread systems, specs. and methods
 
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flembo
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PostPosted: Sat Feb 16, 2019 4:57 am    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

For depth we always went by leaving 6 or 8 threads showing unless it was a stagger tooth tap which I didn't see mentioned then left 4 threads which was real the same depth. There now I confused a simple matter even more LOL. Like others have said when ever I encountered a shallow hole to tap I cut the end of the tap and re-sharpened. So to cut thru all the confusion go with a standard NPT 4 flute tap and leave 6 or 8 threads showing use tapping fluid unless cast iron then try your fitting and go a thread or 2 deeper if needed. Easy eh. So easy a Caveman can do it.
 
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fixerupper
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PostPosted: Sat Feb 16, 2019 7:36 am    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

Thanks for the great information. I knew you guys wouldn’t let me down. One more question; what is the advantage to a spiral flute tap over a straight flute tap?

I ended up ordering a semi-bottoming 5 flute. $33 and some change. The price is good incentive to take good care of it. Now it’s back ordered with a projected delivery date of 3-1 to 3-15.
 
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Mike(NEOhio)
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PostPosted: Sat Feb 16, 2019 7:47 am    Post subject: Re: pipe tap what design? Reply to specific post Reply with quote

Just to throw in a little more confusion, NPT is normally 3/4 inches per foot but 7/8 per foot is used for certain applications.
 
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