threading formula

[skipper]

Hi All,

Well I've asked this question before and got links to the efunda site that has a table that is really confusing. I am trying to cut threads on my lathe, I am looking for what size of diameter to machine down to so I can thread a rod. Like I mentioned, I've seen some tables but it is rather confusing with all the different choices. Can someone give me a easy to read table or better yet let me know what they use for these standard sizes. Whats the magic formula for figuring this out?

Thanks,
skipper

6-32
8-32
10-32/24
1/4-20
5/16
3/8
1/2-13

[chucker]

try this link
http://www.engineersedge.com/screw_threads_chart.htm

[valmet58]

In a book i bought it says that you basically can take the nominal diameter
minus 1%.So with a 1/2 inch bolt which is 500 thousand you remove 5 thousand which would be .495 inch to start to thread..hope this helps

[tauntdesigns]

Also posted this in your other thread,
Here's an online site with a chart showing thread per and such
http://www.engineershandbook.com/Tab...readlimits.htm

[skipper]

Thanks for the replys guys so, to answer my question from the tables (there are seven different column). Do I take the Max Major, subtract the Max Minor and is that the diameter needed? What is the Minor Diameter value that is given?

thanks
skipper

[tauntdesigns]

I may have mis-read your question. I was thinking that you needed the major diameter of the material before turning the threads.

Are you wanting to know how much to dial in on a lathe to cut the threads to size?

If so, are you using the compound slide at 30degree for in feed or are you plunging in with the cross slide?

[tauntdesigns]

Here's a pdf with some general info:
http://www.frappausa.com/PDF/Article...the/150235.pdf
IIRC
p = pitch
p = 1 divided by # of threads
in feed = p times .6
compound feed = p times .866

I couldn't find my notes from 1980 on threading. the old brain ain't as good as it used to be........

[g-codeguy]

Sounds like you are asking for the major thread diameters. These dimensions are for 2B threads, which are the norm.

6-32 .1372/.1312
8-32 .1631/.1571
10-32 .1891/.1831
10-24 .1890/.1818
1/4-20 .2489/.2408
5/16-18 .3113/.3026
5/16-24 .3114/.3042
3/8-16 .3737/.3643
3/8-24 .3739/.3667
1/2-13 .4985/.4876
1/2-20 .4987/.4906

HTHs