npt

[smokey_44]

I don;'t have alot of experince with NPT ,trying to do a 1/2-14 NPT for water line , I looked up the tap drill size and says .703 on 1 chart and .718 on another. The only drill I have is .730 dia ...is that ok ? I want to make sure I don't go to big and the fitting wont sit right. Can anyone please tell me if I drill at .730 I think it should be ok ???

 

 

Dave Ferraro

[Mcam Nut]

I guess that depends on the psi of the fitting, if its for aerospace, it will probally be too big, if its for your kitchen sink it will probally be ok. can you not just drill .687, and mill the rest?

[Mike@Dive Lab Inc.]

I agree with Shawn, if it's a B.S. part It otta seal o.k. with a little extra tape. If it has to seal anything other than l.p. water go with the proper drill .703

[smokey_44]

Its just a waterline ,I dont have a smaller drill long enough (or one at all that will do) Its on a cnc HORZ ,which I do not know at this time (lol) just trying to get the job done when the boss is away , So I'm not even sure I will be able to get a program goin on it or not , if not I was just goin to drill it manualy.

 

 

Dave

[john316]

.

 

I'd say scrounge up 10 bucks and go buy a 45/64 drill and do it right.

 

.

[David from FN MFG.]

+1 to doing it right

[smokey_44]

I'm kinda looking at it like this ...one of the charts I have says to drill @ .718 dia ...So if I drill .730 dia ,I'm really only over by .006 /side ..on a thread I don't really think that it matters all that much ,but I want to make sure that my thinking is correct ,I still think that it will seal off ok and everything like that ...Ps I want to "do it right" too thats why I'm asking if .006 /sdie really matters that much on a taper thread anyways?

 

 

Dave

[heavychevy2155]

on npt threads alittle goes along way, have you ever thread milled a npt. .0005-.0015 to big and wow its way oversized.

[Mcam Nut]

quote:

---

.0005-.0015 to big and wow its way oversized.

---

Yeah that is a pain, we have scrapped a few parts over that(operatior bumping the dia by -.005 increments)

[David from FN MFG.]

.006/side for low pressure (water line or even low air pressure) is not that bad. basically you will be drilling a hole for a NPS thread(straight pipe thread). It should still seal but it will require additional tape or thread dope. (personally i have always had to use tape or thread dope to seal properly anyways). JM2C

[Mcam Nut]

If your in a jam, and its not a production run, and wont be inspected very closely by your customer, then go for it I guess. I know I couldnt do that where I am at (they reject parts over a scratch on a part) but I know alot of places that they would let that slide.

[smokey_44]

thanks for the advice guys. I'm still trying to figure out the damn machine (no manual ,no book ,NO BODY lol ....Long way to go before I start anyways just trying to get a heads up on the NPT thread ...again thanks for the advice

 

 

Dave

[john316]

.

 

Maybe you should be asking for advice on the machine.

 

What type of horizontal is it, and what do you need to know?

 

.

[Kevangel]

Ok, I miked one of my taper reamers for that size and about where I would stop on depth, it is about .730 which means that your threads would be pretty correct near top of hole but shallow at bottom. personally I would prefer to drill it with a smaller long drill that you may have in stock then bore the thread area to proper size (if the pipe has a .5 i.d then a .5 drill will not restrict water flow, etc)...if $$$ part I would buy a drill.

[WWFCAM]

+1 JOHN316,

our charts say 45/64" other charts show 23/32"

 

we always use 45/64", we have a better chance of fixing if it gauges too deep, we just spotface and then chase to proper gauge depth by hand

 

jm2c, hth

[smokey_44]

Well its done , everything went fine and thanks for all the replies and advice ...I used the .73 drill and everything went fine , The machine is old (1979) SHIBAURA TOSHIBA BMC 8B ,ETA-17 SYSTEM-01 ,if anyone know about this machine let me know ,the boss says he is goin to get someone in here that knows the machine.

 

 

Dave