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Manufacturing Screw Head with Negative Draft

P

PHScrew

Plastic
Joined
Jan 27, 2014
Location
Minnesota
Hi All - I'm an Inventor with no manufacturing background. I invented a stripless screw and bit design. The screw head has a negative draft. I've been told by Swiss manufacturers that my screw is too small to be machined. I'm looking into 3D metal printing and MIM. Can someone tell a newbie the best way to manufacture a screw with a negative draft in the screw cavity? Thanks!
 
Can you post a drawing of your screw? I suspect your #1 issue is you are speaking with the wrong shops. First off unless this is a specialty medical bone screw that you are charging a few $100 on you are not going to metal print it. Next issue is despite the name being "screw" machine shop believe it or not very few screws are made at them. Rather it is a term for high volume machining of small parts. A swiss screw machine is a special type of screw machine that most often usually isn't making screws unless you are talking something very special.

Since you say you have no manufacturing experience you would probably do well to watch some youtube videos on fastener manufacturing. Simply put most all of your mass produced fasteners are formed not machined. So depending on size they would either cold form, or if really big hot form your head. With out seeing what you are trying to do it likely is doable, but I bet you are speaking with the wrong people. Here's a tour of a manufacturer you may want to speak with. https://www.youtube.com/watch?v=ZOsnteNWJ_c
 
Out of curiosity, what is the advantage of the negative draft? I can imagine some sliding cores for injection moulding or some kind of broaching action to add the draft to a formed head.
 
The advantage is that the negative draft pulls the bit I designed into the head of the screw so it won't cam-out or strip. You also don't need any axial force (pushing on the driver) to keep the bit engaged with the screw so basically its a screw that won't strip and you don't need to push on it when screwing it in. I just finished patenting the idea.

What are sliding cores and broaching action? Do you think MIM is the way to go? Any idea what that will cost me?

Here's another question. I want the bit to be magnetic - how do I get that made?

Thanks wil gilmore!
 
Armedsask - the Robertson is a good one but it will strip and you have to push on it to get it in. Same with the Torx and all the others.
 
Oh I see, the cavity is in-sloped, or "negative draft".

Alright, that will be a right royal PITA to make in volume. Maybe some double-upsetting process where the head is pushed back down on itself after initial shaping.

Regards.

Mike
 
Mike - you got it - the cavity is in-sloped and trying to find a way to produce it has been a real PITA for sure. By double upsetting, do you mean cold heading it then pounding it in again to make the in-slope? Know anyone I could talk to about double upsetting?

Thanks!
 
I think that 'double upsetting' sounds genius. If a guy could come up with an attachment for a standard coldheading machine, all of a sudden this would be pretty viable...
 
Hi Red James - I should clarify - my design is "patent pending" not patented yet. Pozidriv does not have a negative draft cavity and will cam out. Mine won't - and I'll guarantee it once I get them on the market. You'll see a lot of designs say "won't strip" or "strip free" but they will all strip under the right conditions.
 
According to the Wikipedia article, the Pozidriv has vertical flanks, not canted out towards the base of the head, so not the same action.
 
Parkerbender- do you know any coldheading shops that might take this on? If I could cold head them, I'd be in business.
 
I'm not advocating Pozidrive, just saying they have been around for years. And yes, the cavity is straight sided while the driver has the anti-cam angle.

Just curious PHScrew, how are your screws removed?
 
The screws are removed with the same bit and function as they are driven - also without stripping. One of the benefits is that you can drive them without stripping but you can also remove them without stripping. It will help with recycling and reclamation. Another benefit, according to the Solidworks models is that there is no material loss on the screw or the bit and minimal stress so I think I can guarantee the bit for life. Now if I can just find a coldhead shop that will make it work.

I appreciate the help here guys. If I can get this up and running, I'll post a coupon for the website and send you a free batch of screws and a bit.
 
Pozidriv is a piece of shit. People always confuse it with phillips and as a result screws and drivers go to hell in no time.

Use torx...it worx.
Or any variety of square and hex.
 
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