Socket headed cap screws

Hi David

Most bolts are made by cold-heading and then thread rolled. A coil of wire of the appropriate diameter is fed through from the back of a collet type chuck which then grips tightly while a shaped heading 'hammer' whacks down onto the free end to hob the hex/philips/cheese head form. The collet then releases and feeds the wire forward to the required thread length, then a chisel type head comes in from the side and shears it off. The blanks are then rolled down an inclined channel lined with thread chaser plates on each side which spin the shank and roll the thread form onto it. I saw this years ago in Birmingham when I was in the automotive industry and was quite amazed by it, although I have to say that it takes second place to the even more amazing automatic spring formers. Don't know whether you could replicate this at home though, short of turning a blank and then sparking the hex form in, or using a tiny cutter and a dividing head to set the hex shape up. HTH

Peter

mangled snipped-for-privacy@yahoo.comsaid

Bar is fed into an 'up-setting' m/c which forms the head and socket and then cut to length.

Blanks are hopper fed to a thread rolling machine.

JG

thread

formers.

David,

Tony Phillips showed me a very interesting device for forming hexagonal (or indeed square) blind holes in the SM&EE workshop at the recent Midlands exhibition at the Fosse.

Held in the tailstock it consisted of a chuck free running on a thrust race which was itself on a dovetail to adjust offset and mounted at a slight angle to the axis of the tailstock so it pointed 'crossing the axis'. In the chuck was a cutter whose cross section was hexagonal, but tapering rearwards to give relief.

I didn't actually see it cutting, but as I understand it the work is held in the headstock, drilled with a hole the a/f of the hexagon and the tailstock device brought up and feed applied using the tailstock feed wheel. The work rotates the free running chuck 'walking' the cutter round the hole and cutting with a shaping action.

I made a mental note to get more details from Tony when he next comes to Marshall House.

AWEM

Do a search for wobble broach.

-- Regards,

John Stevenson Nottingham, England.

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hex/philips/cheese

thread

tailstock

John,

Many thanks for that - excellent description here:

Thanks all for the interesting replies. ISTM that spark erosion maybe the easy way to do it at home for small quantities anyway.

David

David,

That is the way I'd do it as I have a spark eroder but beware it will set up stress risers due to minute cracking at the roots so the bolt head won't be as strong as if it were 'cold headed'. The 'wobbly broach' method has me intrigued, and certainly I'd like to try it !

AWEM

David, there are three articles from 'Model Engineer' magazine, written by Martin Cleeve, that deal with this issue.

Issues 02/Feb/56:200-202; 09/Feb/56:241-243; 16/Feb/56:271-273.

They are available online via one of the many Yahoo groups and the tireless efforts of J W Early (unfortunately I can't remember which one).

I could email them to you if you wish (cut toenails to reply).

I have no spark eroder, and have done a special this way: make a hex punch or broach (from a bit of Allen key) and tap that into a round hole, preferably using a staking tool to hold things in alignment. You might need to drill or chisel out the chips from time to time.

BTW, I often work the other way round, using a caphead as a handy source of high tensile material.

I made a one-off stainless steel cap head screw from a piece of rod by heating it as hot as I could in a butane flame and ramming a suitable sized alan key into it a few times, making sure to remove the alan key before the metal cooled enough to grip it! Then I threaded the rod with a die - and it works!

Dave