What would a good tap size be for a 1/4" pilot hole.

[Marker]

I am looking for a tap and die set were the hole that you need to drill for the tap is 1/4" I am sure that there can be more than one size depending on how course the threads are.

I would like to find one with fairly fine threads.

it can't be any bigger than 5/16" after I cut the threads.

How do you determine the depth of the threads in sae taps?

In short....I am looking for something that requires a 1/4" pilot hole that is not too course.


Thanks

 

[joefyffe]

You have managed to confuse the hell out of me!:biggrin::biggrin:

 

[Marker]

do you think that a 5/16x 18 will work? I see in a chart that it calls for a 0.2570" drill

It says in the chart...."tap drill size for 75% .dia" = 0.2570" dill size.

also it says........ "tap drill size for 50% .dia" = 0.2770" drill size.

Whatever 75% and 50% means.



Even though it calls for a drill size of 0.2570" do you think that I can get away with 0.25"??? I mean it is only seven thousandths of an inch difference? most drill bits tend to drill a-bit bigger that what it says anyway.



Joefyffe, basicly what I am doing is....

I have a 1/4" hole drilled in something, and I need to tap it. I am just trying to fine the right size tap for a 1/4" pilot hole, and a die to match it.


I have been looking at different tap and drill size charts on the internet, and it seems like none call for a drill size of exactly 1/4"

 

[mikespenturningz]

I bet most people use 1/4" drill for that. 7 thousandths isn't much when you are working with wood!

 

[rherrell]

A 7mm x 0.75 tap will work, it uses a 6.25mm drill which is .0039" smaller than the hole you have, but it will work. It's also considered a "fine" thread.

 

[rherrell]

do you think that a 5/16x 18 will work? I see in a chart that it calls for a 0.2570" drill

It says in the chart...."tap drill size for 75% .dia" = 0.2570" dill size.

also it says........ "tap drill size for 50% .dia" = 0.2770" drill size.

Whatever 75% and 50% means.


It means how much of the male threads will engage the female threads. The SMALLER the hole you drill, the more the threads will engage, or 75%.

I use 75% on soft stuff like plastic , Delrin, aluminum or brass and 50% threads on steel ....make sense?:biggrin::biggrin::biggrin:

 

[frank123]

M7 x .5 will probably work with a .25 drill hole, but if you can get by with a slightly smaller hole and need an inch size tap a 1/4 x 28 would be better.

 

[KenV]

Mark --

The better answers will come with a more complete description of what you are tapping. Coarse vs fine threads are relative to the material being tapped, and loading on the threads.

0.070 is not a big deal in plastics, and is a really big difference in some steels.

Guestimates are pointing to NF, NC, and Metric threads.

So ---what'ca up to?

 

[KenV]

Mark --

The better answers will come with a more complete description of what you are tapping. Coarse vs fine threads are relative to the material being tapped, and loading on the threads.

0.070 is not a big deal in plastics, and is a really big difference in some steels.

Guestimates are pointing to NF, NC, and Metric threads.

So ---what'ca up to?

 

[Marker]

I will be tapping 6061 Aluminum at first, and later 303 stainless steel.

Mark --

The better answers will come with a more complete description of what you are tapping. Coarse vs fine threads are relative to the material being tapped, and loading on the threads.

0.070 is not a big deal in plastics, and is a really big difference in some steels.

Guestimates are pointing to NF, NC, and Metric threads.

So ---what'ca up to?

 

[Marker]

Thanks everyone....I have decided to go with a m7x0.5. I just order 2 sets, one from china, and the other from the U.K.

M7 x .5 will probably work with a .25 drill hole, but if you can get by with a slightly smaller hole and need an inch size tap a 1/4 x 28 would be better.