[How-To] Using dies

DavidR8

DavidR8

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As part of my RF alignment build I need a pair of 1/2-20 cap screws.
Have some but they are 5” long and 1/2-13.
I thought I’d cut of the threaded portion and try threading them with my 1/2-20 die.
According to my research the major diameter should be .4675. The unthreaded portion mic’ed out at.4925.
So I chucked one up, parted off the threads and turned it down to .4673.
Chamfered the end and tried the die.
Went fine but it didn’t cut a fully formed thread.
Wondering what I did wrong.


Sent from my iPhone using Tapatalk
 
francist said:
Yikes, where did you get a major diameter of 0.4675” from? Usually it’s just a shade under nominal.
Click to expand...

From here:

Tap Chart UNC/UNF Threads - provides tap sizes, drill sizes, pitch, (threads per inch) basic major diameter, basic effective diameter, basic minor diameter of external threads, and basic minor diameter of internal threads for UNC/UNF threads

Tap Chart UNC/UNF Threads
www.carbidedepot.com

Though I just figured out that I read the wrong column on my phone. Should be .500” right?


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Where did you find that major diameter ??
I have always started at .500 -.495
 
Yeah, or a bit less. You have a Machinery’s Handbook, right? Look there for standard thread forms UNF — I’m seeing 0.4865 as absolute smallest on a 1A fit, 0.5000 on a 3A maximum diameter.
 
Yes, I think that's right. The basic effective diameter looks like the stock size for forming or forging the threads. Get new stock. It's cheap. If you want a ready made head, that's what the tig welder is for.
 
Oh, I see you looked at the effective dia. which is the lowest effective size that will work (kinda)
Caint say I aint done that when it comes to reading charts................... .500 is right
 
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