Ok silly question about using dies

[rustyknife]

Wow I feel like a complete newb and have a silly question about using dies to cut threads. I'm very familiar with taps and tap drill sizes for various percentages of thread.....but I've only used dies to clean up things that were already threaded, and only cut new threads on a lathe. Is there a chart somewhere that will tell me what diameter to turn a piece of stock down to for threading with a die? Fractional and metric? My matco tap set doesnt even mention this and I've never needed this information until now. Strangely enough, I don't even know the right keywords to type in to search for the information. Complete mental blockage here.

Please help lol.

Regards

Eric

 

[rustyknife]

Ok I think I found what I was looking for in the download section ;D

External thread table

Thank you rake60 :bow:

Now off to find a metric version, now that I know what I am looking for.

Regards,

Eric

(I guess I created a post for no reason, so sorry!)

 

[t_ottoboni]

Sorry it's in portuguese
http://www.dallanese.com.br/Servicos/PDF/Servicos_Diam_Barras.zip

 

[rustyknife]

For 1/4" I use a 1/4" piece of rod, same with other standard sizes like 3/8", 1/2", etc.

Pat J

Yes, my confusion set in when I was trying to grasp what kind of diameter say something 10-32 is.....perhaps my mole hill was too big of a mountain.

thanks

Regards
Eric

 

[rkepler]

Yes, my confusion set in when I was trying to grasp what kind of diameter say something 10-32 is.....perhaps my mole hill was too big of a mountain.

The UN numbered screw series has a fairly straight forward formula to calculate the screw moninal size - .060" + .013 * screw_size. Using this a #5 is .060 + .013 * 5 giving .125" nominal. Note that the crest of an external thread will be shortened by 1/8 of the thread height so the real screw size is less than nominal. Thread height can be calculated from the pitch as .866 * pitch where pitch is 1 / threads_per_inch, so a 40 tpi thread would have a height of .022" and be truncated at the crest by approximately .003". So the die would be happiest if fed stock of about .122". (In practical terms it'll be just fine being fed anything near that, it's just that it'll want to cut the crest off above .122" and you'll have less thread under that size. A lot of the time less thread is fine as long as you have enough threads engaged - this is an important point when you're making long threads inside or outside tough materials.)

One thread series that's always confused me is the BA series. Metric pitch with imperial diameter. Odd.

 

[Tin Falcon]

Here is a copy of the chart I like to use. http://littlemachineshop.com/Reference/tapdrill.php imperial one side metric on the other.
I suggest you find a copy of the Machinery handbook probably something between the 13th edition post wwII and the 25 ed or so IIRC 28 is the latest current one.
The older ones contained a bunch of neat stuff that is no longer in them like standard sizes for blacksmith tongs. they also contained many many pages of math tables that are no longer needed since the advent inexpensive scientific calculators.
but any edition is a near must for a machinist.
Tin

 

[Omnimill]

I'm so glad I chose to only use Metric threads except where absolutely necessary - so much easier!

Vic.