rssteve

got a 1/8" sensor that i need to make a thread in my inlet manifold. The metal is about 5mm thick, so i have brought a 1/8" tap, what size should i drill the hole to before tapping it? would be easier if i could drill a hole measured in mm as i have the sizes here. Cheers

Christian and Beccy

iTrader: (14)

I usually use a drill bit just slightly larger than the end of the tap.

I think for 1/8NPT or 1/8BSP, the drill bit is around 8.5mm, from memory (so I might be wrong!!)

richard_syko

75% of the tap size as rule of the thumb

rssteve

ok i will probably test it on a spare piece first, the sensor is made of what looks like nylon? What is the best way to insure this is sealed well as it will be on my FRS, is there some kin of paint you put on the thread first or should screwing it in do the trick.

wirralphil

where's me zues book......

richard_syko

Cant see a bit of thread lock hurting

trevCOSS

iTrader: (6)

http://www.newmantools.com/taps/bsp.htm#drills

that should give your answer

rssteve

thanks

GARETH T

thats what i was going to say

gotta love the zues book,,, for anyone who hasnt got one ! GET ONE

paul16v

The engineers bible

st3v3

Tis actually "Zeus" but im splitting hairs.

To be as accuratte as i can be,after a few beers,you take the addendum and dedendum of the thread and adding them up thus giving the thread depth or .86603xp to give the fundimental triangle minus the basic crest radius,minus the basic root radius.
Take about 2/3 of this depthx2 then take this figure away from the tap diameter, that should be about right for the hole size to be drilled.



And yes i make all sorts of threads,taps,cutters milling hobs yada,yada,yada.

GARETH T

ooow all that sounds very accurate

maybe not

st3v3

yeah you still use the Zeus book m8,i'll use my head

GARETH T