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geekhack Projects => Making Stuff Together! => Topic started by: Thimplum on Fri, 21 June 2013, 15:52:31

Title: Double shot manufacturing question
Post by: Thimplum on Fri, 21 June 2013, 15:52:31

Hi,
   I've been reading a lot about keycap manufacturing, and I'm not quite sure about the method for making double shot keys such as O, D, and Q. My understanding is that the top of the cap is molded with a hole in it, to match the shape of the character, and then another piece is molded to fit that hole. But, lets say that you molded an "O". Wouldn't the middle of the O fall out before the other piece was inserted? It would be the same with D, Q, A, B and many other letters.


        Thanks in advance!

Title: Re: Double shot manufacturing question
Post by: CPTBadAss on Fri, 21 June 2013, 15:56:54

There is a mold that has 2 parts. That first part is the legend/letter, and the second part has the rest of the cap. The injection molder shoots the first part with plastic, which will only fill part of the mold and then the second part is filled immediately after with plastic. The legend or letter isn't moved, it's all contained within the singular mold.

Look up injection molding on YouTube. Otherwise I can find pictures of the process at SP and if you really want, take pictures from my textbooks.

Title: Re: Double shot manufacturing question
Post by: Thimplum on Fri, 21 June 2013, 16:46:56

Ah... thanks! I feel so dumb now...  :-[

Title: Re: Double shot manufacturing question
Post by: Thimplum on Sat, 22 June 2013, 09:41:34

Actually, could you post said pictures of the process from "SP"(whatever that is)? Thanks.

Title: Re: Double shot manufacturing question
Post by: CPTBadAss on Sat, 22 June 2013, 09:56:50

SP = Signature Plastics. Where many keycap sets come from. Klaxon, R4 Dolch, and Raindrop are all examples that came from that company.

Pictures:
http://geekhack.org/index.php?topic=34521.msg703103#msg703103
http://geekhack.org/index.php?topic=34521.msg704016#msg704016
http://geekhack.org/index.php?topic=34521.msg704303#msg704303

Video of Injection Molding:
http://geekhack.org/index.php?topic=34521.msg704343#msg704343

Title: Re: Double shot manufacturing question
Post by: BLJ Consulting on Sat, 22 June 2013, 10:33:26

The plastics industry is terrible with nomenclature but FWIW the keycap process is better described as overmolding since there are 2 completely separate molds.  One mold makes the 1st shot (letter) and the 2nd overmolds the body.  Sometimes called plastic insert molded.

Doubleshot generally refers to the process where 1/2 half of the mold is shared between 2 cavities with different geometry.  The 1st shot never comes off 1/2 the mold until both shots are completed.

Double shot, overmold, multishot, 2 shot, insert molding are all commonly used terms that have slight differences but are frequently used interchangeability.

Title: Re: Double shot manufacturing question
Post by: CPTBadAss on Sat, 22 June 2013, 10:46:37

So there is a transfer of the first shot/insert out of the first mold to the second mold? Or are the two molds on top or intertwined together? I just assumed that since the typical nomenclature was doubleshot, that it was in one mold like you described BLJ. Guess that's what I get for assuming.

Title: Re: Double shot manufacturing question
Post by: SpAmRaY on Sat, 22 June 2013, 10:47:36

So the small square plastic part containing the legend in the video, the 'first shot pieces', I don't guess they are good for anything are they? I've got a few from a crap bag! ;)

At least now I know what they are.

Title: Re: Double shot manufacturing question
Post by: CPTBadAss on Sat, 22 June 2013, 10:55:55

Quote from: ray4jc on Sat, 22 June 2013, 10:47:36

So the small square plastic part containing the legend in the video, the 'first shot pieces', I don't guess they are good for anything are they?

They're probably just test pieces to show how their process works. Good for keyboard science and general knowledge :D