What Size Rod To What Size Die

Bob Korves said:
This is why we have machine tools
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That's what I keep telling my wife! :)

Most times that I have needed to thread smaller sizes it has been something turned anyway like a shoulder bold or spacer with threaded ends so stock needed to be larger anyway. The only exception that I can remember was a replacement electric motor thru bolt #8. I ended up using all-thread.
 
Fairly often I would like to put a thread on the end of a piece of stock, for instance a 1/2-13 thread on a 1/2" rod. It would seem to be easy, just take a die and cut the thread. But it is not usually that easy, because the rod is too big to cut a thread on it with a die, as it it a bit too large and can jam up and break something if you try to force it. So the rod needs to be turned down a little to the correct size for an easy to thread size. No problem on a 4" piece of stock, but I have needed to do it to an 8 foot piece of 1/4" stock, for instance. I was able to get it done by properly supporting the rod along the entire length that stuck out of the left side of the spindle. It was a good thing I placed the lathe with this in mind. So, I do understand the OP's frustration. We just need to deal with it the best we can.
 
Humor- i found the main problem. I mistook harbor freight dies for dies that actually can cut carbon metal. Bought a simple 6 dollar die and work accomplished.


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Another issue with all this is getting the die not wander away from 'true'. Countless times I've mounted the part to be threaded in the lathe & backed up my die holder with the tailstock & turning by hand... I still end up with a jake legged thread. Not square, true, parallel with the rod at all. Once I get my BXA tool holders to fit my lathe: I'm making die feeders (sorry can't think of their proper name).

At this rate I will never be considered a Machinist; but I will have been a Tool Maker!

I hope this is not considered too inappropriate as I'll paraphrase: You can climb poles your whole life & Never be called a Lineman; but suck just 1 (fill in the blank) & you're labeled for life. Point is, we are All learning And sharing = we learn from each other. But, yeah gotta reduce your overall dimension before threading. Think of it this way: The nominal size, like 1/4" requires a bit of give from the bolt & also from the nut. Charts given above by others should have you on your way! & a few YouTube videos should help me to have my new tool for cutting those threads straight as well!
 
Brockwood, you are referring to a Tailstock Die Holder - useful tool.

This is an old thread but on the off chance that some new guy will see it, I'm attaching the best chart I've seen for sizing the rod before screw cutting or using a die. You need to determine the class of fit because this determines the rod size used before cutting the thread. Note that a class 2a is a looser fit than a 3a and the starting diameter ranges are tighter. The stock is turned to the OD limits for the class you need and this allows you to obtain the needed pitch diameter range you need for that fit.

For example, for a class 2a, 1/4-20 external thread, you would turn the work to a diameter between 0.2489 to 0.2408. Then you put a 30 degree chamfer on the end and thread it or screw cut it. Then you check with three wires or a pitch micrometer to be sure your pitch diameter is between 0.2164 and 0.2127" and this should allow that work piece to fit any class 2b nut.
 

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CluelessNewB said:
So besides #5 (1/8" rod) nothing under 1/4" seems to be a standard off-the-shelf rod size. How convenient ;). And #5 isn't a very common size.
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OH, they're standard sizes, all right, but from the age of uncalibrated tooling. #0 through #12 are
from a standard published 1907 by ASME. Wire sizes were likewise
various; salesmen would have a book of samples, and you'd match diameters and
order the 'gage' you needed. Fit-and-try, not measure, was the common practice

#5 is not such an uncommon size, actually: it's 1/8 inch diameter. I once needed to
thread some tubing 1/8"-40tpi lefthanded, and the die was available off-the-shelf. But, it
came labeled "#5-40 LH".

Granddad's old threading tools are adjustable; you'd keep tightening the
die plates against the thread and working it until it fit into your nut. Any blacksmith
could harden the thread to make a new tap, or file a rod, for cast iron and wrought iron; the grinding
of HSS tooling came later.
 
mikey said:
Brockwood, you are referring to a Tailstock Die Holder - useful tool.

This is an old thread but on the off chance that some new guy will see it, I'm attaching the best chart I've seen for sizing the rod before screw cutting or using a die. You need to determine the class of fit because this determines the rod size used before cutting the thread. Note that a class 2a is a looser fit than a 3a and the starting diameter ranges are tighter. The stock is turned to the OD limits for the class you need and this allows you to obtain the needed pitch diameter range you need for that fit.

For example, for a class 2a, 1/4-20 external thread, you would turn the work to a diameter between 0.2489 to 0.2408. Then you put a 30 degree chamfer on the end and thread it or screw cut it. Then you check with three wires or a pitch micrometer to be sure your pitch diameter is between 0.2164 and 0.2127" and this should allow that work piece to fit any class 2b nut.
Click to expand...

Nice chart Mikey! Thanks for sharing!! Thank you: Yes, tailstock die holder is the term I was suddenly at a loss for.

Whitmore filled in the blanks on the history of it all. Thanks! I do remember the reason electric wire actually uses a backwards gauge reference, as compared to metal, is because it was believed that wires would only get smaller way back then. Now 4/0 copper (0000) is considered small for many applications. Thank you all for sharing & maybe the Op will rejoin his thread & catch us all up on his progress.
 
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mikey said:
Brockwood, you are referring to a Tailstock Die Holder - useful tool.

This is an old thread but on the off chance that some new guy will see it, I'm attaching the best chart I've seen for sizing the rod before screw cutting or using a die. You need to determine the class of fit because this determines the rod size used before cutting the thread. Note that a class 2a is a looser fit than a 3a and the starting diameter ranges are tighter. The stock is turned to the OD limits for the class you need and this allows you to obtain the needed pitch diameter range you need for that fit.

For example, for a class 2a, 1/4-20 external thread, you would turn the work to a diameter between 0.2489 to 0.2408. Then you put a 30 degree chamfer on the end and thread it or screw cut it. Then you check with three wires or a pitch micrometer to be sure your pitch diameter is between 0.2164 and 0.2127" and this should allow that work piece to fit any class 2b nut.
Click to expand...


Thanks for the chart Mikey. I have to cut some 2 1/4-8 threads and couldn't find the info I needed until I found this. I have an old machinery's handbook with a 1948 copyright date and couldn't find it in there either. It may be in there but the book is the small size version and its hard on the eyes.
schemer
 
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