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Master Apprentice
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This is a true bottoming tap, but its not what your looking for and a little expensive.

McMaster # 2659A56

I would try a modified bottoming tap, they are a little cheaper. Mcmaster has them too but not in NPT
 

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There is no production bottoming NPT tap made that I've ever found.

Take a little at a time (so you don't get it hot enough to hose the hardness) and grind off ~3/8" off the tip of a standard tap, flat across. Then use it to chase the hole after you've tapped it (not deep enough) with the standard tap.
 

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There is no production bottoming NPT tap made that I've ever found.

Take a little at a time (so you don't get it hot enough to hose the hardness) and grind off ~3/8" off the tip of a standard tap, flat across. Then use it to chase the hole after you've tapped it (not deep enough) with the standard tap.

And after you do this you will have a " shallow-hole NPT tap" for the next box you do. Just remember that once you modify a taper pipe tap it can't be used as anything other than what you modified it to do...
 

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Discussion Starter #6
Thank you guys for the suggestions. Guess I will grind mine down very slowly. If I trusted my tig welding I would just tig it to the box but I'm also lacking SS rods.
 

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are you refering to a pipe thread or a bolt thread the one you show is a pipe tap.????????
 

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Isn't asking for a bottoming tap for a pipe thread indicative of a lack of knowledge of what a pipe thread is? The only pipe thread where this would be appropriate would be something like a British Parallel Pipe thread, but I don't think I'd want to use one with the types of pressures encountered in hydraulic steering applications.

If you cut the lead end of a pipe tap off, you will end up with a tap that only taps the largest dimension of a tapered thread. Doesn't sound like a good thing to me if you want it to withstand high pressures and not leak. Now, OTOH if you are trying to cobble a bulkhead type fitting, you might want a pipe tap with only the major diameter so the matig fitting can pass completely through whatever you tapped.
 

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Isn't asking for a bottoming tap for a pipe thread indicative of a lack of knowledge of what a pipe thread is? The only pipe thread where this would be appropriate would be something like a British Parallel Pipe thread, but I don't think I'd want to use one with the types of pressures encountered in hydraulic steering applications.

If you cut the lead end of a pipe tap off, you will end up with a tap that only taps the largest dimension of a tapered thread. Doesn't sound like a good thing to me if you want it to withstand high pressures and not leak. Now, OTOH if you are trying to cobble a bulkhead type fitting, you might want a pipe tap with only the major diameter so the matig fitting can pass completely through whatever you tapped.
???

The part you are cutting off a NPT plug tap to make it a bottoming tap are the initial tapered cutting edges (IE removing the first 3-4 threads leaving a 1-2 thread chamfer) which assist in aligning and starting the tap into an untapped hole.

The "lack of knowledge" part comes when someone runs a NPT tap in far enough to produce parallel threads; most of us that have some experience chose to test the tapped threads with the fitting that is going in them at least for the first few holes tapped. Running a NPT tap in past the major diameter and producing parallel threads is going to be an issue whether it is a bottoming tap, a plug tap or a taper tap, the same goes for a NPT die set.

Using a NPT bottoming tap is a very common practice in blind holes where you need threads throughout the material but are unable to get a plug tap engaged far enough to provide a complete thread throughout.

Depending upon how clearance you have in the hole you are tapping you may need to take a few passes at trimming a NPT plug tap back enough to work as a bottoming tap but it easier to trim the tap twice than buy a new one when you trim too much the first time.
 

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Using a NPT bottoming tap is a very common practice in blind holes where you need threads throughout the material but are unable to get a plug tap engaged far enough to provide a complete thread throughout.
I agree!
This is where the 'short projection tap' or 'bottoming tap' comes in.
On a thru hole or deep hole, we run the NPT tap in 1/2 to 3/4 the length of the the tap. Check it, and make any adjustments.
If the hole is shallow we use the short taps, and keep checking it with the fitting till we like it.
 

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Running a NPT tap in past the major diameter and producing parallel threads is going to be an issue whether it is a bottoming tap, a plug tap or a taper tap, the same goes for a NPT die set.
Not necessarily. When I was building process equipment and wastewater treatment equipment, it was very common to run pipe taps through vessels to allow using a nipple as a welded bulkhead fitting.

While there may be special situations requiring special taps, the vast majority of pipe threads do not.
 

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I think we're loosing track of the fact that anything less than 75%-80% of the fitting making thread contact is less than desirable. The fittings length usually has a direct correlation with it's intended pressure range.

I'm sure most of the guys here that have dealt with very high pressure NPT and there tight fit requirements know that they have to be run in a taper reamed hole... tap only cuts threads not sizing the minor dia.


Most of these "Redneck-ram" box modifications require you to put a NPT in a non-boss area of the casting... not optimal.


Tap it- run it- break it- fix-it...:grinpimp:
 
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