Can you explain this?

Awl --
I got a hardware-store eye-bolt, 1/4-20, garden variety, not welded or cast.
The thread measures .246 -- no pro'leng. But the part of the rod that forms the eye measures .210-.215.... !!
Shouldn't the eyebolt measure .246 *everywhere*?
Or did they form-thread .215 rod, with the threads now deformed out to .246? I figger that's gotta be the explanation? I know about form tapping, just never heard of form-threading, which I assume must exist.

Existential Angst wrote:
  Quoted Text Here  
Standard procedure just look up thread rolling. You can get tools to do it on a normal lathe. Have a look at youtube for videos of the process. Things like the splined drive shafts on many vehicles have been formed in a similar manner for decades. It's a cold forming process.

On Wed, 06 Jan 2010 19:57:44 +0000, David Billington
  Quoted Text Here  
Back in the good old days (prior to '82) when I worked from an on site office rather than in the regional cube farm, whenever I came up with a bright idea, be it work related or personal, I just went to the maintenance shop and did my thing with available materials. One day I grabbed a handful of 1/4-20x1 cap screws and, after trying for some time to start the nut on one, took a closer look. The nicely formed threads looked great except for the fact that they were half way between RH and LH, i.e. they were just ridges around the shaft! Apparently, the blank hit the rolls at the wrong angle. Gerry :-)} London, Canada

  Quoted Text Here  
Assuming the threads were cut, they'd have to begin with a blank that had the thread area larger than the rest.
But that's not the standard way "screw machine" equipment works on cheap fasteners. Not only does roll forming exist, it is the standard way by which its done in mass-production.
They don't even use a "forming die", they use flat forming plates between two of which the stock is rolled under extreme pressure to create the threads.
LLoyd

"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message
  Quoted Text Here  
Mystery solved! Heh, but boy, the threads sure do *look* like cut threads!
So much for traditional machining, eh?

On Wed, 6 Jan 2010 16:21:39 -0500, "Existential Angst"
  Quoted Text Here  
Not only that but the fastener is supposedly stronger than if the threads were die cut. Gerry :-)} London, Canada

On Jan 6, 3:00 pm, "Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:
  Quoted Text Here  
Not just cheap fasteners, though? I thought roll-formed threads were stronger than cut.
Dave

  Quoted Text Here  
They are.

On Wed, 6 Jan 2010 14:42:16 -0500, "Existential Angst"
  Quoted Text Here  
=============see http://video.google.com/videosearch?hl=en&newwindow=1&as_epq=thread+rolling&as_oq=&as_eq=&num 0&lr=&as_filetype=&as_sitesearch=&as_qdr=all&as_rights=&as_occt=any&cr=&as_nlo=&as_nhi=&safe=images&q=%22thread+rolling%22&um=1&ie=UTF-8&ei=VaNHS62EB4TOM6auvJAJ&sa=X&oi=video_result_group&ct=title&resnum&vedDUQqwQwCQ http://www.efunda.com/processes/metal_processing/thread_rolling.cfm
The only problems are cosmetic in that the crests of the thread may not not be perfect, but the crests don't effect the functionality of the thread. Unka George
(George McDuffee)
The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).