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Flat Screw?

Excuse me if this is a "newbie" question. I am trying to build a small prototype machine, and have need to attach a flat, die-stamped part into a threaded bore. It would be most cost effective if I could stamp the part with the addition of a long tine, thread the edges of the tine, and then screw it into the threaded bore. For a better idea of what I am talking about, imagine slicing down opposite sides of the threaded shaft of a machine screw.

A few questions:

  1. Is this a common fastening device, or have you ever heard of or used it?
  2. Would the threaded tine provide good pullout strength along the axis of the bore, in that the threads would only engage, say, 60-80 degrees of the perimeter of the bore, rather than the 360 degrees that most screws provide?
  3. Any idea as to lateral stability (strenth of tine in resisting forces horizontal to its axis) relative to normal screw?

Any feedback or references you could turn me to would be much appreciated.

-Paul

Reply to
Paul Moe
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My machine shop opinion (I'm not an engineer) is it wouldn't be very strong, and could prove to be a bitch to assemble. I guess it all depends on what you expect from the item.

Harold

Reply to
Harold & Susan Vordos

I've seen screws like this, but I'm blowed if I can remember where. They worked (operation and assembly) very well - surprisingly so - but I seem to recall that they had thread contact for more like 90 deg total, a little more than you are specifying.

Lateral stability? Depends on the orientation of the force. Excellent to poor, I'd suggest. (sorry).

Try it on a sample. I think you'll be pleasantly surprised.

Jeff R.

Reply to
A.Gent

Sounds like a tap to me, but I'm just an engineer.

Richard

Reply to
Richard Lamb

Grin! A tap, but with very limited side support. The typical tap, even a two flute, has greater engagement which helps keep the tap in alignment with the hole. He's talking, at most, 80 degrees total of engagement of the diameter. That's not much to help keep it straight between sides. He'd have a far better shot if it was more than 90 degrees per side. You'll get a better understanding of what I'm talking about if you try to tap a hole free hand using a two flute tap. It brings into sharp focus why hand taps generally have four flutes.

Harold

Reply to
Harold & Susan Vordos

--Sounds like an inside-out application for a Formdrill. If you could redesign the part so that it threads onto a stud then it becomes easier. Alternately you could spotweld a threaded stud onto the bottom of your part and use that to thread it into the hole.

Reply to
steamer

It's similar to an old style (1940s) doorknob spindle. A threaded piece of square stock.

Cheers,

Kelley

Reply to
Kelley Mascher

Reply to
Machineman

Paul What you have described is the "thread" that is used on the old Winchester Model 12 shotgun.

JRW

Reply to
J.R. Williams

Kelley Mascher snipped-for-privacy@comcast.net

That's what I was thinking--having had a knob just pull free of one.

Threads, flutes, and a set screw. It must have been someone's quick fix that made it into general use, somehow--a cheap way out, for mass production. Frank Morrison

Reply to
Fdmorrison

A couple of points here. The threaded square shaft for door knobs has been around much longer than the 1940's. Also the system works fine if you keep the set screw tight. The flat sides of the square spindle allow you to set the screw every 90 degrees. This permits the knob to engage the bearing surface of the escutcheon and allow it to be used on various door thicknesses and trim options.

Reply to
Roger Shoaf

Much much longer indeed. My house has those on the original doors, and it dates back into the late 1800s.

It's tought to keep the setscrews tight, especially in a teenager's room door.

etc.

Next stop is red locktite.

Jim

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Reply to
jim rozen

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