drill bit for 1/8 tap??????

[maddboy32]

ok, i tried to find the answer myself. but couldn't. soooo............ what is the drill bit size for a 1/8 tap.

i have the tap, i'm going to drill into a tapped hole so i can get out the other side. so i need to find out which one to actually size down to.

do i need a really small 90* drill to start from the top instead???????

[mag79]

what kind of tap 1/8-27? Give me the # on the tap.

[maddboy32]

what kind of tap 1/8-27? Give me the # on the tap.

yeah the tap is a 1/8-27

[ElPanda]

whatever bit is just slightly smaller than 1/8 would be my guess, I ususally just eye it up

[MoeMag]

1/8"-27 is an NPT tap. You use an R drill. or ~.339"

Look up Drill & Tap charts.

I have a really big one on my wall.

Here is a good one....

http://bobmay.astronomy.net/misc/drillchart.htm

[luke]

I use "R".

[maddboy32]

I use "R".

can i get thru a threaded hole without damaging the threads with that bit???

if i had a block and i had a threaded hole half way thru it, and i wanted to thread it the rest of the way.....but couldn't drill thru the top. would this "R" bit damage the threads that are already there????

i would post a pic of what i'm talking about but its a secret

[luke]

Chances are you wil bugger up the existing threads.

[Runamok]

Rule of thumb is the drill is 75% of the tap size if your drilling for an air fitting the tap is tapered to seal and running the bit through the hole will fubar your threads. What kind of project are you making? This morning I started work on my standard or reverse valve. Why settle for an either/ or situation? I'll let you guys know if it works. But all I did was run a smaller bit through then drilled the larger hole from the other side. Now to tap it and see if I have any leaking issues.

[questionful]

cool stuff, runamok. can't wait to see a thread on that!

[sffudapparel]

I used a 7/64ths. At home depot they had a package of a 7/64 bit and a 1/8th tap

[cyberave68]

I used a 7/64ths. At home depot they had a package of a 7/64 bit and a 1/8th tap

I think your a little off here. He is looking for the drill size to a 1/8"-27 thread NPT tap. it's more like something in this chart i found.... Here is a link. Just scroll down an you will see a decent tap/bit chart....

http://images.search.yahoo.com/images/view?back=http%3A%2F%2Fimages.search.yahoo.com%2Fsearch%2Fimages%3Fp%3Ddrill%2Bindex%2Bchart%26fr%3Dyfp-t-501%26toggle%3D1%26cop%3Dmss%26ei%3DUTF-8&w=578&h=881&imgurl=www.toolvice.com%2Fimages%2Fa%2520drill%2520and%2520tap%2520index%25202.jpg&rurl=http%3A%2F%2Fwww.toolvice.com%2Fdrill-tap-chart.html&size=82.8kB&name=a+drill+and+tap+index+2.jpg&p=drill+index+chart&type=JPG&oid=fce8bb369e809b00&no=7&tt=19&sigr=11c8ustle&sigi=11tkndfvs&sigb=1373am6b9

[RangerX]

running the drill bit through the already threaded portion shouldn't bugger the threads up. AS LONG as its centered to the threaded hole.

After all the drill bit is smaller than the peak diameter of the thread, otherwise you wouldnt be able to cut any threads with the tap afterwards.

I have a set up NPT taps at work from 1/8" up to 1" IIRC they say what size drill bit to use for each one. I'll look tomorow if you havent found the answer already

Wow didnt realise the original was from months ago