I need to make to a hole to tap for pipe, NPT, what size drill(s) are needed?
I've google-fu'd but the answers/charts seem to make the drill size too big.
I need to make to a hole to tap for pipe, NPT, what size drill(s) are needed?
I've google-fu'd but the answers/charts seem to make the drill size too big.
These work
Nominal pipe size is based on internal diameter. (i.e. 1.5" pipe has an OD of 1.9"...approx)
Drill size is for the OD.
That may be where the confusion lies.
jamscal said:Nominal pipe size is based on internal diameter. (i.e. 1.5" pipe has an OD of 1.9"...approx)
Drill size is for the OD.
That may be where the confusion lies.
No, the one chart I have says that for 1/2NPT, I need a 23/32" bit. That just seems rather large for something needing the tapered thread.
Those numbers sound about right. Keep in mind that it's a taper pipe thread, so if you don't have the exact size bits you have a little room to play with.
In reply to Ranger50 :
That's what my chart shows, OD of 1/2 NPT is approx. 27/32.
The correct way to create a female NPT thread is to drill, ream with a tapered reamer and then tap. The way most of us do it is to just drill and tap. If you're going to do that you should use the drill size recommended by the tap manufacturer for tapping without reaming. It's often marked right on the tap.
What others said here. Reamers aren't necessary. Don't try to fudge drill size by 'close enough'. If it calls for letter drills, 32nds or 64ths get it, you'll likely save yourself trouble of a broken tap, especially smaller sizes. Good cutting oil too. Fastenal should have all this stuff.
That's right. Don't want to risk breaking that 1/2" NPT tap ;)
In reply to Zomby Woof :
1/2" oughta be OK unless junk tap, smaller sizes meaning 1/4" and under. You'd be surprised the E36 M3 I seen over the years. Stick w/ the correct drill size, just do it.
Journeyman pipe fitter since '83, I seen a thing or two.
For 1/2 npt i've drilled with a 3/4" (24/32) bit and it went fine. Lots of people already have 3/4" bits and just don't realize it. It happened to be the biggest size on one of my stepper/unibits. 
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