making 8-32 threads question

T

Terry_Dodson

Joined
Jul 10, 2002
Messages
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I wanted to thread the end of a tang on a knife i am making out of 1080 steel. I cut the tang down to about the size i thought it should be and rounded it. i wanted to make the rounded part as soft as i could so it would thread easier, so i wrapped the blade in a rag and submerged it in a bucket of water and took a propane torch and heated the rounded part til it was red and then let it cool. it seemed to file easily. So i took an 8-32 die and started twisting it onto the round part. i sprayed the die and tang with wd-40 hoping it would go smoothly. It was going but seemed a little hard to rotate and from time to time would squeak. I finished the threads, about 3/4 inches worth. I got an 8-32 bolt and nut package from lowes and wanted to try those nuts to make sure the threads were OK, but the nuts will not screw onto the treads. The threads seem to be too thick or something. What did i do wrong or what can i do to fix the threads?
 
you can test to make sure your nuts and bolts are the same pattern as your die or tap by running your tap through one of the nuts you have and make sure it spins properly.

sometimes a nut or two will be bad and re-tapping them can solve your problem

Or you can just run the die again and clean off the metal chips in between.

wd40 is not really a lubricant and lite oil would do much better. you can use olive oil in a pinch.


Reuben
 
How do your threads mic out versus the screws from Lowes?
 
Reuben i have run the die down the threads several times and it goes down smoothly now, but the threads don't look as sharp as the threads on the bolts i got from lowes. The bolts will go into the die, but i can wobble them easily in the die.

fitzo i dont have anything that can measure them with, that was why i bought the bolt and nut pack just to make sure the threads should be the same. Could i have messed up the die when it squeaked?
 
It is a good idea to pic up a 1" micrometer and a 6" caliper if/when you can afford them. Even the Harbor Freight cheapies aren't too bad, Terry. they can come in pretty handy for things like this.

Sounds like the die is a bit oversized. Does this die by chance have a slot cut into it and screw in the side? Check your threads close (magnifiying glass if you have one) and see if they're flat a little on the outside. Is there prinitng on the die other than 8-32?

I don't think you'd screw up the outside part of the threading die but more likely the edge that cuts the teeth in.
 
I don't know what more to tell you, sorry. :( Some older dies had a screw in them that allowed for some adjustment. That's obviously not the case here, though. Sounds like a bad die.

One thing you could do is tap a hole in a piece of scrap with the corresponding tap out of the set and if your threads fit, you at least have a matching pair and can make a buttcap threaded to the same thread.

They might have been in the flea market because they were mis-sized at the factory in China and seconded out. Some of these imports aren't too good.

I wish I could help more, Terry, but I'm fresh out of ideas. :( Good luck with it.
 
For everybody's knowledge:

A bit of a flat on the outside of the thread is normal and is supposed to be there. A very sharp thread is incorrect except for pipe threads.

WD-40 is about useless as a tapping fluid. Any other oil is better, Moly-dee from Castrol is the best.

You can not directly measure how "tight" or "loose" a thread is with just calipers. You must measure the pitch diameter by using something called "the three wire method". You will need something like The Machinery's Handbook for tables to tell you what the pitch diameter is supposed to be for a particular thread and how to extrapolate if from a given wire size. Using a good nut or bolt is more practical in most instances.

If the threads on the die are the same as the threads on the bolt you are using, and they don't screw together, the most likely explanation is the die is worn. WD40 didn't help that... If this is what happened, a new die will fix the problem.

8-32 is not the only size 8 thread, though it is the most common.
 
You can measure the outside diameter of the thread. That simple. No more, no less. There might be something one can learn, there. I know how to read thread tables, too, Nathan.

He was using a new die, the way I read. Something's odd about the die if the ordinary 8-32 screw wobbles so badly in it. Could be major or minor diameter or the pitch. Could even be a M4.5 die that the factory in China subtituted to meet a deadline. If the thread's round instead of flat on the outside, that says something too, doesn't it?

Hard to tell without having the die in hand. Thanks for the info.
 
Terry_Dodson said:
I wanted to thread the end of a tang on a knife i am making out of 1080 steel. I cut the tang down to about the size i thought it should be and rounded it. i wanted to make the rounded part as soft as i could so it would thread easier, so i wrapped the blade in a rag and submerged it in a bucket of water and took a propane torch and heated the rounded part til it was red and then let it cool. it seemed to file easily. So i took an 8-32 die and started twisting it onto the round part. i sprayed the die and tang with wd-40 hoping it would go smoothly. It was going but seemed a little hard to rotate and from time to time would squeak. I finished the threads, about 3/4 inches worth. I got an 8-32 bolt and nut package from lowes and wanted to try those nuts to make sure the threads were OK, but the nuts will not screw onto the treads. The threads seem to be too thick or something. What did i do wrong or what can i do to fix the threads?
Click to expand...


one thing that may have gotten missed here
you said you cut the tang down to about the size i thought it should be and rounded it.
it may have been to big around coupled with the squeaking, not cutting good and rubbing for the most part,, if it turns hard with dull Teech your climbing the steel leaving to much by not cuting it out well. leaving it over sized
.. mike's talking about real dies that you can make differant fits
you have 3 different fits mainly, for nuts and bolts class A B and C
a class A fit being a wrench fit all the way..
a cheap new Die could be bad also .. you may even have a thread chasing set not a die set some guys don't know the differance..

for me I never buy taps and dies from a bargain house, some things you can get away with but don't cut corners there if only you're thinking your saving money, in the long run you won't most of the time.... JMO

Nathan not to get down on you but when you say
'Moly-dee from Castrol is the best" are you saying it's the best you've tried?? :o
to me to say that it's kind of like saying that 5160 is the best steel for all knives..
we have some impressionable new guys here all the time , and to say it's the best,, well you can see what I mean..
you have good info to offer and I for one like that thank you..
 
Thanks guys for all of your info. A LOT of good info. I did not measure the size i cut the tang end down to, i just eyeballed it to an 8-32 bolt and then sanded it round with files and sandpaper. The tool guy sells new things, and i even tried the 6-32 die on a piece of brass rod and it cut good and a regular 6-32 nut goes on smoothly. So i am guessing either i did n ot get the steel soft enough or i had it oversized when i started to cut the threads. So for the next time i go to do this, how should i heat the round end of the tang to soften it the most i can? What size should i cut the tang to round for 6-32 & 8-32 siize according to a caliper (which i will get). And i will use regular cutting fluid instead of wd-40 to help the cut.
 
Terry_Dodson said:
Thanks guys for all of your info. A LOT of good info. I did not measure the size i cut the tang end down to, i just eyeballed it to an 8-32 bolt and then sanded it round with files and sandpaper. The tool guy sells new things, and i even tried the 6-32 die on a piece of brass rod and it cut good and a regular 6-32 nut goes on smoothly. So i am guessing either i did n ot get the steel soft enough or i had it oversized when i started to cut the threads. So for the next time i go to do this, how should i heat the round end of the tang to soften it the most i can? What size should i cut the tang to round for 6-32 & 8-32 siize according to a caliper (which i will get). And i will use regular cutting fluid instead of wd-40 to help the cut.
Click to expand...

see if this will help you Terry
http://www.knivesby.com/drill-tap-chart.html
 
Terry, the nominal "major diameter" (outside diameter) of an 8-32 screw is 0.164".

Here's another nice little set of tables you may want to bookmark:
http://www.metalwebnews.com/howto/drill-tables/drill-table.html

One other suggestion, Terry, is if you plan on making threaded-tang knives much, go to the hardware store and see if you can't replace that specific die with a quality American made one. Just my 2cents worth.
 
fitzo said:
You can measure the outside diameter of the thread. That simple.
Click to expand...

Not to be argumentative Fitzo, but I don't think it is that simple.

I could be mistaken, as most of my experience is internal threads with taps and thread milling. When I do make external threads, it is usually on a lathe, not with a die. So I don't use die too often, but I'm pretty sure they are the same as taps in the respect they do not cut the full thread form, only the flanks and roots. Meaning a properly sized shaft will measure the same after threading as before. Thus the dimension calipers can measure have no bearing on the actual thread size.

For example, you can turn a shaft to .240 (well under 1/4") and thread it 20 TPI, yet it be too tight to fit a standard 1/4-20 nut if the threads are not cut deep enough. Yet measuring the OD with calipers would tell you the thread was undersized, when it was actually oversized.

Yes, it appears his die is oversized, perhaps due to wear, poor manufacturing, or it could be an adjustable die.
 
Thanks guys, i bookmarked those page.
fitzo i had not really planned on making this one a threaded tang, but i cut the tang shorter than i wanted and thought this would be the best way to fix it. :confused:
 
Nathan, I was fishing for information to try and ask proper questions and narrow in on things. Simple to more complex. If the major diameter was .175, then that would tell me something right there. It would tell me that either too large a rod had been forced through the die, not cut, or the die was oversized. Either way it would tell me it wasn't going to fit in a plated 8-32 nut from Lowes. If the threads weren't properly flat then that too might say it was forced through the die. I had no good way to ask questions about pitches and minor diameters.

I don't disagree with anything you're saying. But I'm not sure you understand where I was headed with my questions. There was a method to my madness. :)
 
1. I'm not a machinest. I was just trying to visualize the tang/die problem, and am assuming the die is correct and not damaged or adjustable; Is it possible that the actual tang, while appearing rounded, may be eliptical or egg shaped when viewed from the end? If so, possibly the die sort of wobbles as it is turned, and although it makes threads, it makes wobbley threads that the nut has a very hard time going over. However, Mike, what you're saying makes sense to me.
 
fitzo said:
Nathan, I was fishing for information to try and ask proper questions and narrow in on things. Simple to more complex.
snip
I had no good way to ask questions about pitches and minor diameters.

I don't disagree with anything you're saying. But I'm not sure you understand where I was headed with my questions. There was a method to my madness. :)
Click to expand...


Ah, I see your point. Sorry if I was being obstinate...

Dan Gray wrote:
"Nathan not to get down on you but when you say
'Moly-dee from Castrol is the best" are you saying it's the best you've tried??
to me to say that it's kind of like saying that 5160 is the best steel for all knives.."


Dan,

5160!? Nope, D2! (oop, there I go...)

While I was in my early 20s I had the good fortune to work as a hack machinist while I was going to school. I had to make a large production automated drill fixture (over ten feet long and half a ton) with many many holes to be hand threaded. Any broken taps in the main fixture was a real problem to deal with. Having used "tap majic" and others and still suffering problems I sought out a very experienced machinist from a different shop who said moly dee was the best he had used.

Since then I have heard similar stories which reinforced my POV. Is it the best in all circumstances? It is relatively expensive, stinky, black and messy and hard to remove from the part. So in a production setting it is certainly not the best choice. But in my experience, when threading a part where you really really don't want a tap failure, it is the best I have been able to find. I have never had a tap fail due to galling while using it.

If a new impressionable new guy reads this and uses it on his knives, I can say, speaking from experience, it will work well, and probably work better than other common tapping oils and pastes that I have tried.

Obviously, I shouldn't have said "the best", because I haven't used everything out there, and currently do relatively little hand threading anymore. But it is in my opinion, and in the opinion of a couple shop owners and other experienced machinists that I have talked to about it.

But I'm being long winded... Your point is taken.
 
But it will work great, no doubt, Nathan. Nasty stanky with all the moly sulfide but good cutting fluid. It's what was recommended to me by the old machinist who owns Taig to use for my small-scale amateur milling, too.

Robert, your idea is another excellent possibility.

The thread problem here is one of those where having the threaded part in hand would lead to a really quick diagnosis. Words alone make it a lot more difficult, since it could be so many things causing the problem. Such is the frailty of the internet and written interaction.

Time for basketball! Go Bulls! :) Hope you folks have a great day.
 
thanks Nathan
no doubt it's good stuff ..
I've worked with the water solubles in the 55 gal drums to the little cans of tap free,, BTW that tap free could be why my brain is burned out :eek:
I was a tool and die maker in the later 70's and been out of it a LONG time now , I think I've forgotten more than I learned back then :o ..

we have such a mass of diverse guys with different knowledge's it's very hard to pin anything down in stone here :D except that I don't know when to keep my trap shut some times..

OK OK MOST of the time :D I can hear that from the peanut gallery from here :rolleyes: ,,,:D :D

nathan keep that good info coming. :thumbup:
 
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