First time cutting a thread by hand: outcome oddity

[DaveLaQ]

Total newbie, here; so please be patient with me.

I'm extending the threads on either end of tension rods that run under the steps (one each) of a library-type ladder. I built the ladder narrower than spec, so the rods need shortening, and, it turns out, longer threading on either end so that T-nuts can come in far enough to reach the outside of the rails of the ladder.

I found a metric die that seems to be the only one that fits the existing thread (M6 course thread), and I turned it for an additional quarter inch of threading on either end of a rod, backing it up every quarter turn to release the chip. All seemed to go well, and the T-nuts go on fine, but my new thread peaks aren't sharp like the existing threads; they look like they're squared off, looking fairly flattened and wide. Looking at the threaded rod end in profile, I can see that the originals are nice and pointy, while the new ones don't reach out as far and are, indeed, "flat-topped."

Any thoughts on what may be causing this? Seems odd that it's leaving the existing threads untouched, but lopping off tops of the new ones it's cutting.

Admittedly, I'm using an inexpensive Harbor Freight tap-and-die kit (I only have a very infrequent need; I actually bought it just for this project), but I gotta think it still should cut normal-looking threads. The only other thing I can think of is that I forgot to pick up cutting oil, so I was using WD-40, spraying it into the top of the die occasionally.

Thanks in advance for any wisdom.

 

[???]

Threads are not supposed to be nice and pointy, they should be truncated.

 

[L Vanice]

I suspect the original threads were rolled, not cut. Can you see that the original thread outer diameter is larger than the diameter of the unthreaded portion of the rod? Thread rolling is a forming process that does not remove any metal and results in a fully formed thread that has a major diameter larger than the diameter of the unthreaded stock. Using a die to cut threads on under-sized stock will produce shallow (weak) threads.

I am curious what you mean by T-nut. In machinist language, a T-nut would not be used to fasten the ends of a rod to a ladder frame. The other kind of T-nut, used in woodworking, is fixed in the wood so it cannot rotate and does not seem to be applicable to this application.

Larry

 

[DaveLaQ]

I suspect the original threads were rolled, not cut. Can you see that the original thread outer diameter is larger than the diameter of the unthreaded portion of the rod? Thread rolling is a forming process that does not remove any metal and results in a fully formed thread that has a major diameter larger than the diameter of the unthreaded stock. Using a die to cut threads on under-sized stock will produce shallow (weak) threads.

I am curious what you mean by T-nut. In machinist language, a T-nut would not be used to fasten the ends of a rod to a ladder frame. The other kind of T-nut, used in woodworking, is fixed in the wood so it cannot rotate and does not seem to be applicable to this application.

Larry

Looks like you are correct, sir! The original threads do indeed extend beyond the diameter of the rod itself. And so it must be undersized and would explain, then, why my threads are not very deep and are flat-topped.

Yes, now that you mention it, I have used T-nuts for other applications in the past (putting levelers in the bottoms of my workbench legs comes to mind). It was the first term that came to mind, here. No doubt the wrong one. Apologies. Attaching photos.

What would you call this kind of nut?

Many thanks for the education. :-)

 

[DaveLaQ]

Threads are not supposed to be nice and pointy, they should be truncated.

Right. I guess I meant relatively. See pics in my other reply.

Thanks.

 

[L Vanice]

M6x15mm Female Thread Hex Socket Head Barrel Nut​

Amazon.com

M6 x 10mm Socket Joint Connector Barrel Nuts​

M6 x 10mm Socket Joint Connector Barrel Nuts - Zinc Plated Steel

Buy M6 x 10mm Socket Joint Connector Barrel Nuts - Zinc Plated Steel from Accu's Nuts range. Manufactured by AccuScrews. In stock with express worldwide delivery available.

accu-components.com

That type of nut is seldom seen, so whoever makes them can select what to call them. The resulting name could be something translated to English from the maker's language. But "barrel nut" may be as goad a name as any.

Larry

 

[DaveLaQ]

Yep. You found some. Turns out I was mistaken, by the way. Mine aren't M6's, they're 1/4-20's. FWIW. Thankfully, I was able to use all the original parts and so didn't have to go searching. Good to know they're out there, though. :-)

 

[???]

Not to be picky but a rolled thread does not result in a fully formed thread. If you fully form the crest of the thread you will potentially destroy the tooling. See attached illustration.

 

[L Vanice]

Yep. You found some. Turns out I was mistaken, by the way. Mine aren't M6's, they're 1/4-20's. FWIW. Thankfully, I was able to use all the original parts and so didn't have to go searching. Good to know they're out there, though. :-)

Your rods might be pretty close to 6 mm diameter, so you possibly could use your M6 die on just one cut-off end of the rods and buy some M6 nuts. Micrometers or digital calipers are handy things to have when you need to measure a rod that might be 1/4" or might be 6 mm.

Larry

 

[GregSY]

The use of HF dies/taps is begging for a crummy product. It's like performing surgery with a butter knife.

 

[L Vanice]

Not to be picky but a rolled thread does not result in a fully formed thread. If you fully form the crest of the thread you will potentially destroy the tooling. See attached illustration.
View attachment 396674

Might depend on who did the rolling. I got out a new Holo-Krome/Allen 1/4-20 cap screw and put it under a microscope. I had to zoom in to 30X to see that there was a nearly invisible hairline along the thread crests. Looked like fully formed to me.

Larry

 

[rons]

What would you call this kind of nut?

That is a nut used in fine Danish furniture. It allows for a thicker plank of wood for attachment.
I bought some myself to make a base for a glass table top.

 

[DaveLaQ]

Your rods might be pretty close to 6 mm diameter, so you possibly could use your M6 die on just one cut-off end of the rods and buy some M6 nuts. Micrometers or digital calipers are handy things to have when you need to measure a rod that might be 1/4" or might be 6 mm.

Larry

That's an interesting idea.

Ultimately, I brought a rod and nut into the thread gauge at Home Depot. 1/4-20 is the only one that they fit. As shown, I extended the threads on either end using a 1/4-20 die after shortening the rod to accommodate my "custom" ladder width. After the first couple, I got smart and worked with just one end of each rod—very much like you suggested, above.

I don't know if my new threads are actually engaging the nuts, but at least I can now screw them far enough in to tension the rod between the rails. Maybe the few remaining original threads are doing the "heavy lifting."

I'm just glad I can now snug them up to the sides of the ladder for some decent rod tension under the steps.

And now I know a couple more things about threads. All is well. :-)

 

[DaveLaQ]

The use of HF dies/taps is begging for a crummy product. It's like performing surgery with a butter knife.

Someday maybe I can be just like you.

 

[DaveLaQ]

That is a nut used in fine Danish furniture. It allows a wider plank of wood for attachment.
I bought some myself to make a base for a glass table top.

They come in the library ladder hardware from Rockler. That's where I got mine.

 

[Mechanola]

I found a metric die that seems to be the only one that fits the existing thread (M6 course thread)

Just a sidenote, the concept of coarse, fine, and extra fine does not exist with metric threads. There are regular and fine threads. Without further specification you always have the regular thread such as M 6. A space is left between the M and the number.

 

[GregSY]

Someday maybe I can be just like you.

No matter how bad I ever get, I'll never be a Harbor Freight askhole....

 

[Tyrone Shoelaces]

Someday maybe I can be just like you.

Maybe you need to be patient with us ?

Regards Tyrone

 

[SeeFair]

whoever makes them can select what to call them

Some people call them sex bolts. I don't know why.

Sex bolt - Wikipedia

en.m.wikipedia.org

 

[Doozer]

Because they have always been called sex bolts.
Don't be offended. Sex is what made you.

-D