Pilot hole for tapping?

[Rubikahn]

What's the easiest way to determine the size of the pilot hole to drill when tapping threads?

 

[tiriaq]

There are tables, matching the size of the drill to the tap, for a given percentage of thread depth. 6-48, the most common sight mounting screw uses a #31 drill. What size tap are you wanting to use?

 

[Rubikahn]

It's actually for a steel fence so accuracy isn't that crucial. I figured this was the best place to find out. I haven't figured out the size yet. I remember seeing a formula somewhere. I guess I'll google it.

 

[Ripstop]

When I'm too lazy to figure it out (especially on non-critical stuff), I match up a drill with the tap. I lie the tap on top of the drill and look to see if there is any drill showing. Go the biggest you can go without the drill showing behind the tap.

Not very effecient but you can't be anal all the time.

 

[winchester_070]

Simple , Screw size less pitch . Pitch is found by 1 divided into # of threads per inch . IE: 16TPI 1divided by 16 = .0625
so a 3/8 unc is 3/8-16tpi 3/8"(.375) - .0625 = .3125 tap drill size

Hopefully that helps

 

[Rubikahn]

Simple , Screw size less pitch . Pitch is found by 1 divided into # of threads per inch . IE: 16TPI 1divided by 16 = .0625
so a 3/8 unc is 3/8-16tpi 3/8"(.375) - .0625 = .3125 tap drill size

Hopefully that helps

That's the one I was looking for. Thanks

 

[rennugliat]

tap drill

or.................

http://www3.telus.net/public/aschoepp/tapdrill.html

for a chart

 

[zuke]

I like to use a center drill then go to a 1/8 (pop rivet size) and then go to the tap drill size.

 

[sunray]

Do a net search for tap drill sizes. Mind you, for a fence post, I'd just drill a hole and use a nut and bolt.

 

[guntech]

Mind you, for a fence post, I'd just drill a hole and use a nut and bolt.

I would use a post hole auger and concrete.

 

[Rubikahn]

Mind you, for a fence post, I'd just drill a hole and use a nut and bolt.

That's plan B

 

[SignGuy]

I would use a post hole auger and concrete.

i just hire someone from off the street corner for 5 bucks and get them to do it for me lol its much more entertaining