How are set screws made? 1

[steris]

So this is something that I have been curious about for a long time and never figured out. When you use a metal or plastic set screw, they can have a hex recess for an Allen wrench. How is recess this made? I would have guessed that the hex is punched in while the part is just a cylinder. I know that the threads are roll formed so punching the hex head (I think) would cause mushrooming and hinder the thread rolling. Intuitively, it seems that machining it in would be way too expensive given the cost of these parts. The metal parts are obviously not cast or forged. Also, is the process different for metal fasteners versus plastic ones? Just something that had been bothering me since college. Sorry if this isn't exactly the right forum but it seemed to be the most appropriate one. Thanks!

-Steris

 

[MiketheEngineer]

Google??

 

[steris]

You'd think the answer is that easy but I didn't find anything that talked specifically about the formation of hex. If you found something that explains this, I would love to learn about it.

 

[rb1957]

how about a robertson head screw ? (a square recess)

i suspect punching th ehead is the answer. maybe look at a "How is it made" episode on Discovery ??

 

[btrueblood]

something like this machine would be one option:

http://www.google.com/imgres?start=...6&tbnw=169&ndsp=38&ved=1t:429,r:0,s:235,i:137

 

[MintJulep]

http://www.youtube.com/watch?v=7PQyant3mCc&feature=related

 

[CorBlimeyLimey]

Google for Rotary Broaching

 

[steris]

Hi All,

Thanks for all of the replies. It would seem that cold forming is preferred way for mass production. I thought that may have been the case. Mushrooming really isn't an issue when you have a head on the fastener - I guess I just assumed that since set screws don't have a head then the mushrooming would have prevented cold forming.

 

[Screwman1]

You run the part on a cold former with the entire length buried down in the die so there is no expansion except axially. After heading, both ends are shaved to clean up the point and OA length and then the parts are tube fed into a dual spindle roll threader (regular flat dies tend to squeeze the recess down).

 

[steris]

That makes perfect sense! Thanks everyone for the help - now that's one less thing that will bother me on my death bed.

 

[rb1957]

man ... that was easy !

 

[drawoh]

steris,

There is a documentary, possibly up on YouTube on W.L.Robertson the inventor of the Robertson screw. They do explain how the screws are fabricated, including the Robertson socket. It is cold formed. I don't see why they would fabricate a hex socket any other way.

I do not know how popular Robertson screws are outside of Canada.

--
JHG

 

[steris]

Thanks for the heads up - I think I may have found the video that you were referring to:

http://www.youtube.com/watch?v=Td7GjAMAY7Y

 

[chicopee]

I have seen machine shops use muliple spindle screw machines to fabricate hex heads of machine screws.

 

[JohnRBaker]

I do not know how popular Robertson screws are outside of Canada.

I've run into them on occasion, however, the last set of 'accessory bits' I bought for my Ryobi cordless drill/driver came with 3 or 4 different size square-head bits so it's not like they're being completely ignored here in the Colonies ;-)

BTW, my understanding is that the Phillips-head screw was developed primarily to enhance the assembly of products via the use of automation, either hand-held power-drivers or full-on automated systems due the ability of the driving bit to 'self-center', and that normal 'civilian' use with non-powered tools was never a driving factor (excuse the pun).

John R. Baker, P.E.
Product 'Evangelist'
Product Engineering Software
Siemens PLM Software Inc.
Industry Sector
Cypress, CA
Siemens PLM:
UG/NX Museum:

To an Engineer, the glass is twice as big as it needs to be.

 

[Cockroach]

In the old days, the recess was pre-drilled to depth and then broached. If you look closely at the recess, you can see the stand-off between the hex and the bottom of the drill. That's because you can't broach to full depth due to tooling configuration.

Regards,
Cockroach

 

[drawoh]

JohnRBaker,

Where I work, we use Phillips machine screws here most of the time, and we are very happy with them.

Here in Canada, self tapping wood screws are Robertson. I do not understand how people manage with anything else, outside of Canada. We did ship a system to a customer in California in a wooden crate assembled with Robertsons. We had a good chuckle over that. It was easy enough for them to make a square bit.

--
JHG

 

[steris]

According to the video about Robertson screws, Robertson wouldn't license the screw to Henry Ford so the Phillips screw became his fall back. I agree that Robertson style is far superior and less likely to strip/fall off the bit but Phillip heads are now the standard in the US and Robertson is a specialty.

 

[KENAT]

I thought Phillips were designed to deliberately Cam Out to prevent over torquing or something.

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[TenPenny]

Kenat, I remember reading that, too, I think it was in the book about the Roberston screw, probably by Witold Rybczynsky (sp?).