Tap and Die question

I've worked with tap and dies often throughout the years (more tap than die). The charts which come with tap and die sets provide drill bit/hole size for tapping but if I want to thread a rod, what is a required diameter for a specific thread? For example, if I have a 3/4" rod and want to thread it, what size die do I use? Also the opposite, if I want to thread a rod 3/4 - 16, what diameter rod do I use? If this is on the same chart in the set, then I'm oblivious to how to read it.
Thanks
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On 5/20/2014 8:59 PM, Meanie wrote:

19.05 millimeter rod
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wrote:

The nominal thread size is the diameter of the un threaded rod as far as I know.
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snipped-for-privacy@aol.com wrote:

Actually it is slightly smaller than the nominal diameter . Look up major diameter and minor diameter . BTW , SAE threads have several classes of fit . They range from "is this nut just going to just fall off" to "get a bigger wrench , this is tight" .
--
Snag



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'Meanie[_4_ Wrote: > ;3238444']

If you have a 3/4 inch diameter rod, you would use a 3/4 inch die.
Download the following PDF file from Sigma Fasteners: http://www.sigmafasteners.com/catalog/section-15.pdf
There are two ways of making the threads on bolts; cutting and rolling. Cut threads are made with dies, and as such, the maximum major diameter of a 3/4 inch cut thread can be no greater than 3/4 inch. Rolled threads are made by extruding the steel bolt between two plates. So, for example, one would use a steel bar of 0.912 inches in diameter to roll threads that have a 1.000 inch major diameter.
In the example you cite, for a 3/4 inch bar, you could cut a UNC coarse thread with 10 threads per inch, or an UNF fine thread with 16 threads per inch. In that Sigma Fasteners chart you see that there are 3 different classes (1, 2 and 3) for external or "A" type threads, and 3 different classes (1, 2 and 3) for internal or "B" type threads. Class 1 threads are cut with higher than normal tolerances for fasteners that are intended for rapid assembly. Class 2 threads are what you find most of the time. They're a good compromise between cost and accuracy. Class 3 threads have the smallest tolerances and are used in safety equipment where maximum thread holding strength is desired.
Looking at that Sigma Fasteners chart, you'll see that the maximum major diameter for both 3/4 inch coarse (10 tpi) and 3/4 inch fine (16 tpi) thread is 0.7500 inches, which is what you'd expect. So, the answer to your question is that you'd use a 3/4 X 10 tpi or a 3/4 X 16 tpi die.
'Meanie[_4_ Wrote: > ;3238444']

> do I use? If this is on the same chart in the set, then I'm oblivious to > how to read it. From that Sigma Fasteners chart, if you want to make a threaded steel rod with a 3/4 X 16 tpi thread, you would use a 0.7500 inch diameter rod and thread it using a 3/4 X 16 tpi die. That's because on the Sigma chart, the maximum major diameter for a 3/4 X 16 tpi threaded bolt is 0.7500 inches.
--
nestork


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Meanie posted for all of us...
And I know how to SNIP

I read the posts but I'm going to say what I think anyway...
Why thread 3/4 rod when you can go buy lengths of it? To me threading a rod is a waste of resources. I am not criticizing you as I don't know what you are doing but speaking for myself. Whatcha got cooked up?
--
Tekkie

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