cutting shafts for threading

7

777mechanic

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ok so i was playing with making some tools with a shaft that needs a die run on it for a 1/2-13 . per the 29th machinery handbook it state that major diameter is 0.4985 . so with that measurement being known do i turn the shafts to that or a couple thou over , reason for my question is after running snapon die on first shaft that was a few thou over . the shaft tapped just fine but when i tried to screw it into 1/2-13 tapped hole it bound up after about 4 threads . any help would be great :whiteflag:
 
Always turn the Dias slightly under the thread size for OD threads, slightly bigger for ID. For a 1/2-13 the max size you would want on a OD would be the .4985". I always go .005" under for the home stuff.
 
MH gives the limits for the major and minor diameters for all the standard threads and common classes of fit. There is a high and low limit for each. Also, there are many charts available online. Here is one that shows the limits for 1/2-13.

http://www.engineershandbook.com/Tables/threadlimits2.htm



I never stay on the high end for die cutting, but you should remember, the die does not control the major diameter so much, but sets the PD and minor. Are you sure this die is good? Have you measured the major after threading? It could have burred up a little.
 
Last week when I was trying my hand at making a couple shoulder bolts to mount steel wheels onto my snow blower I ran into a similar problem. I was necking down 1/2" bolts to 5/16" and had trouble getting the die to start cutting. I read the sizing I was supposed to be at, but, when I sized a working 5/16" it was definitely smaller. And when I tried the die on the "working" 5/16 bolt it fit very well of course.. So I continued to cut the shoulder down to almost match the size of the working 5/16" bolt. I don't recall the exact size I cut it to, but, I was then able to run the die on the shoulder bolt and thread it and the nut fit.
Maybe you can work it this way with success also. Good luck. And Happy New Year.
NodakGary
 
There are three classes of clearance/tolerance for threaded fasteners - 1A, 2A and 3A for external threads and 1B, 2B and 3B for internal threads.
1 would be the looser fit while 3 would be the tightest fit.
So, if you pair class 3A externally thread bolt with class 3B internally threaded nut you would end up with a very tight fit of matching fasteners.
Use different classes of tolerances for the bolt and the nut so that you won't encounter the problem you have just encountered.

Going back to the Handbook table again for the size of threaded fasteners under certain classes of tolerances you should be able to determine the major diameters appropriate for your nut and bolt.
 
thanks for the replies , one i only use top grade tools such as snapon taps and dies . hopefully there still made here in the usa , fat chance of the but you never know . i went back and reread class of fits now i get that part . i also see from diagram that major is on the flattened peak , so that means i have a interferance fit on my peak by turn it a few thou over . so i'll try it a little under , again thanks i really like trying things from the handbook to get it right but there's a huge learning curve for me .
 
If you have a lathe chuck up the one you already did and run a file over the threads to get them on size. a little at a time untill the nut fits .
 
Yes 2-5 thous under will not effect the hold by much, but 2-5 over can make the fit to tight.

Now you say you buy Snap-on dies but you are not sure if they are made here. Look at the package. If that does not tell you ask the dealer. If the tool you are looking to buy is made here. Then complain to him and on their web site about every tool that is not. I can not see me paying Snap-On price for imports. you would do better buying from Enco's better grade and probably cheaper. Don't get me wrong I think Snap-On has great tools, and if I was working in the auto business or in a shop I would buy them.

Mark
 
I have found that everytime I turn diameters according to the atlas how to run a lathe book a generic nut from home depot will never screw on. Ever. Lol so what I do is use my calipers on pre manufactured nuts and bolts and turn to those dimension. They work everytime. Like you said I could get a nut to thread on two turns then it stopped..... and the calipers were right on for the minor diameters stated in the book.....so I have many nut and bolt combos that I use for gaging the diameters then I make my cuts. Also if allowable I leave a nub at the end of a shaft thats turned to the minor and put layout die on so that when I see it cut the die its done...
 
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