Newbie (HELP!) -- problems threading 5/32 rod

Craig,

Sounds like you are a beginner at this. I see several problems with what you are trying to do.

First, a 5/32" rod is 0.156" in diameter while a #8 screw has a major diameter of 0.164" so your stock is 0.008" small to begin. That difference will show up as half that or 0.004" on each side. This is true if your 5/32" stock is accurately sized; but it could be a few thousandths smaller so you could be losing even more. A 32 TPI thread will have a full height of about 0.020". Subtract that 0.004" from that and you are left with 0.016" of thread engagement.

Nuts are made by tapping. Generally an internal, tapped thread is around 65% of the full thread height. In the case of an 8-32 thread this translates to about 0.013". So you lose at least another 0.007" in the nut. And again, that is true only if the manufacturer of the nut used the 65% thread factor. Smaller factors have been used. I have seen nuts so poorly made that they have only two or three thousandths of engagement on a standard screw.

So, at a minimum you are working with a loss of 0.004" + 0.007" = 0.011" of the full thread engagement. That leaves you with only 0.009" of engagement. And that is the maximum engagement you will have: chances are you had less - a lot less.

Harbor Freight die = pure garbage. I have no idea what size thread it would cut. And I would not expect it to last very long if you are cutting a hard music wire. Hardware store dies (Ace brand? Craftsman? etc.) are only good for cleaning up existing threads, not cutting new ones.

Another problem with cutting small diameter threads with a die is that the die can wander from side to side while cutting. This gives you a drunken thread. This is hard to control when using a die alone for thread cutting and once it starts, the part is ruined.

Normally I would try to cut an external thread in a lathe, leaving it a few thousandths large and only finish it with a die. This prevents the drunken thread problem and can give very good results. But you need a good quality die, NOT Harbor Freight. You can purchase good quality dies from places like McMaster-Carr (on the web) and other tool supply companies. Avoid import ones. For a small diameter like a #8 you will probably need to back up the rod with a follow rest in the lathe.

And start with full diameter stock, not 5/32". Or, if you must thread the 5/32" rod, it would be better to roll the thread. By PROPERLY rolling the thread the OD of the 5/32" rod will be built up to the full diameter of the #8 thread. But that is not a simple or inexpensive process; not a hand process for beginners.

You could also look for better quality nuts. Again, McMaster-Carr would be a good source.

On the cutting oil, I like Tap Magic. But there are other good brands. Again, McMaster-Carr and other tool suppliers will have a variety of them.

EPAIII pretty much covered everything.
The only thing I can add is, pro quality dies will be split and have an adjustment screw for dialing in the size. Tightening the screw will open the die, making it cut bigger.

This will probably be ok if you're just going for a tighter fit to the nut. But as mentioned, you don't have a very high percentage of thread engagement, so it will be prone to stripping out.

The above responses provided a lot of good information. Not really emphasized was the importance of alloy selection of the rod as a determinant of ease of threading and quality of thread. (Again a reliable source like McMaster-Carr vs Home Depot may be a big help.). If you provided a few more details concerning the end use of the threaded rod, suggestions for selection of alloy could also be helpful. There are also a few post-threading things to do that might make your threads work better and look and feel better.

Denis

Would there be a metric or numbered drill rod available that would be better suited to give a better fit?

Sent from my SAMSUNG-SGH-I337Z using Tapatalk

FYI that Harbor Freight Die probably wore out after cutting the first thread. Most cheap dies and taps are carbon steel which was replaced by harder High Speed Steel around 1900. Note that sears and most hardware store dies are mostly carbon steel.
You can anneal hardened steel by heating and plunging in water.
Bill D

heres what you do....if that die has an adjustment screw in the side by a slit....unscrew it a tad...then try nut again...too loose...unscrew more...then only use that die for those now since its out of spec but good for what you need....also if have lathe put rod in drill chuck in tailstock and die in lathe chuck to make sure its straight and doesn't wobble as you thread

Assuming that you need some unthreaded portion of the rod (that is, that all thread won't work), I agree with folks above: get the right size rod for the thread, get a good die (or find a friend with a lathe to single point this). A critical success factor is centering. You should use a centering die stock.

It may be easier to buy a long bolt and cut the head off, although a 1 1/2" threaded section may be hard to find on a bolt.

Good luck. Keep Austin weird, and hook 'em.

bosleyjr said:

Assuming that you need some unthreaded portion of the rod (that is, that all thread won't work), I agree with folks above: get the right size rod for the thread, get a good die (or find a friend with a lathe to single point this). A critical success factor is centering. You should use a centering die stock.

It may be easier to buy a long bolt and cut the head off, although a 1 1/2" threaded section may be hard to find on a bolt.

Good luck. Keep Austin weird, and hook 'em.

Click to expand...

Buy an 8-32 stud from.....wait for it......wait for it...........McMaster.