tap size, npt 1/8" Options

[rjbibeau]

i can't find the right drill bit size for the 1/8" npt anywhere. i checked the interent and found some charts and every single chart the i found has got either an R or a C for some reason. what the heck is up with that??? does anyone know the right size drill bit to use??

[rjbibeau]

bump it up

[wind]

since i work on a manufacturing floor and re-work is my specialty i can help you out....

measure the tap size, then find a bunch of drill bits. You usually want to drill a hole slightly smaller then your tap size. you want to have it small enough so that the teeth of the tap will be able to dig in and leave a thread.

in canada we use metric not imperial, so i cant help you with exact drill bit sizes.... if you use metric then i could help

1/8" is 3.175mm. So you would be using roughly an m3 tap.

when drilling metric you would go one mm less then your tap (unless your threads are large). so its an m3 hole you would us a 2mm to 2.5mm drill bit.

so you should be using a drill bit that is roughly .08 inches... drill bits that are close to that are 1/12" drill bit.... test it on scrap metal first.... you dont want to bust your tap on your car.... oh and use tapping oil and go slow!

one last thing.... all the holes on your car are metric... mabey you should get a metric set

This post has been edited by wind: Jan 12, 2005 - 2:43 PM

[rjbibeau]

ahh good info man i appreciate it. i gotta go buy a drill press now. i'm just tapping threads on a custom flange that i made for the turbo oil and coolant lines. i made it outta 1/2" aluminum.

This post has been edited by rjbibeau: Jan 12, 2005 - 2:46 PM

[rjbibeau]

here's my flanges custom made by mua

[rjbibeau]

what do you guys think of em?

[presure2]

id say nice try..but a little on the crude side..

[rjbibeau]

man i did that with an angle grinder give me some credit. i'm not done yet i still have to round up the edges a lil bit more i took those right after i was done cutting them.

[97GTinKC]

My tap set calls for an 11/32 drill bit for 1/8-27 pipe tap, I'd go with 5/16 and try it, some bits can wobble out the hole while drilling and you can always go larger if you need to, do a test hole in some scrap material, also remember pipe threads are tapered, so they get tighter as you screw them in, so you have some leeway as to how far you run the tap in.
also double-check your fittings, as there is a 1/8-28 bsp british/metric pipe thread, same drill size .

This post has been edited by 97GTinKC: Jan 14, 2005 - 2:18 PM

[rjbibeau]

ya i know of the bsp thread. i think we have 1/8" bsp thread for our oil pressure sender unit. i took a 1/8" npt tap set at work it comes with a drill bit as wells as the tap and it doesn't say what size it is on the drill bit so i got the drill bit card thingy to measure diameter holes and the drill bit was a lil small in the 5/16" hole but i'm sure it would work becuase it tapers off. thanks for your help man

[rjbibeau]

i just tapped a 1/8" npt hole and the threads are all jacked. i went in straight and for some reason the hole is actually bigger than the 1/8" fitting. it slips rights in. the threads aren't even that thick either.