Keypad Project


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Thread: Keypad Project

  1. #1
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    Default Keypad Project

    Hi,

    This isn't related to creating molds, well... this project will need one, but that's not what I want to ask the question about. I've got a project going and I'm trying to create a backlit keypad like you would find on remotes. So the base layer of the buttons need to be transparent and then I I'll need to add a silkscreen and then make cutouts in the silkscreen the shape of letters and numbers.

    Problem is, there is next to no information on how to create something like this DIY. So decided to ask here. Hoping someone will have some info that I could use in this regard.

    Thanks.

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  2. #2
    Member john-100's Avatar
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    Default Re: Keypad Project

    I have not seen any DIY way to produce rubber dome switches like this :-

    Keypad Project-silicon-key-switches-jpg Keypad Project-rubber-dome-switch-jpg

    so I would look at tactile switches - possibly with intergral LED's
    Keypad Project-tl1240-series-illuminated-tact-switches-jpg

    to keep oil and dirt out of the switches cover the top with a thin clear silicon rubber sheet
    Keypad Project-silicone-sheet-superclear_large-jpg

    SuperClear Silicone Sheet | Silex Silicones Ltd

    a project I am interested to see other members solutions

    John



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    Member dharmic's Avatar
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    Default Re: Keypad Project

    Make a suitable mould, cold shoot it with translucent silicone. If you're not doing many you can even shoot it from a caulking gun in a big dollop in one half of the mould and squish it all together.

    Trim, etc.

    Overmould with black silicone for the lettering - if you can leave depressions in the clear where the black needs to go you can make the black reasonably thick and resilient.

    You can push down on tactile switches having the tops of the switches buried into the silicone cavities, use some intermediate piece in the silicone to spread the load and make keys feel a little more solid, or insert graphite slugs to push directly onto fingered pads on the PCB as they've done with the top left pic in john-100's photo.

    It's fiddly work to get right and the frame that sits between the keys is important too - it supports the keys from rocking side to side and keeps things in place. But it's doable with patience.



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    Default Re: Keypad Project

    Thanks Dharmic, what do you mean by overmold? So you have a smaller mold for the body and then a larger mold that is very marginally smaller to enable a thin top layer?

    I need more something closer to the blue keypad shown above, although I will need everything covered in black apart from the letters.

    I guess using graphite slugs is probably the best option since that's what the pros use. Must be a reason for it.



  5. #5
    Member john-100's Avatar
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    Default Re: Keypad Project

    Hi Atomic_Sheep

    I think you will find they print a graphite pad under the key so it can flex as its pushed down onto the PCB contacts
    to me the hardest part will be to get the part that acts as a spring to work correctly

    John


    PS
    https://deskthority.net/wiki/Rubber_dome



  6. #6
    Gold Member LeeWay's Avatar
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    Default Re: Keypad Project

    Lots of stuff is overmolded.
    I have a side project injection molding some knobs. They will include a flanged nut in the first mold for each knob. That molding retains the nut in the colored plastic. It could be transparent as well. It will have raised letters. Then these parts are mounted into a second mold. This molding will inject a rubberized layer around the knob except for the raised letters.
    The problem with this method is that you really need to make a bunch of them to make it cost effective. Thousands. You would be needing two molds for each button.
    If you could place all the buttons in a single mold, that would certainly help. Just inject the silicone in one cavity at a time. You would need a way to secure the buttons for the second injection, but it is very doable using silicone. Would probably take a day dry time before you open the molds.

    Lee


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    Member dharmic's Avatar
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    Default Re: Keypad Project

    Yep. I'm working on a project where I need to encapsulate an electronic PCB and enclose it with a battery in a housing for underwater stuff. Space requirements are really tight, so decided to cast the case in glass reinforced polyurethane around the PCB. Turns out that holding the piece you're trying to mould around in place properly is quite important

    Aluminum (I could have used corian etc) two part mould with a stainless insert for the battery cavity took days to design and machine, just for this one piece. I could, of course, keep making them but there's no need at present.

    Anyway: not cost effective for a one-off, but if it's a hobby and you're learning and enjoying time on the tool: who cares? If it's not a hobby then find a company that makes these things (there are a few around) and just pay them to make it happen.



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    Gold Member LeeWay's Avatar
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    Default Re: Keypad Project

    A lot of guys are even using a 3D printer to print molds especially for low pressure low volume parts. I think that may be an ideal mold making scenario for such parts. Low cost all around. Screw something up. No great loss.

    Lee


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    Member dharmic's Avatar
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    Default Re: Keypad Project

    I did exactly that for the first couple of goes with my project. The 3D printing has some issues though:
    - warping during printing due to the extreme temperature variations means straight lines often aren't;
    - Even down to a 0.1mm layer height your final product is going to have lines everywhere but flat surfaces;
    - Pretty hard to polish a print for a good surface finish;
    - Only good for one or two shots.

    Still, as is generally the case, 3D printing whilst limited for production is GREAT for prototyping.



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    Default Re: Keypad Project

    Quote Originally Posted by john-100 View Post
    Hi Atomic_Sheep

    I think you will find they print a graphite pad under the key so it can flex as its pushed down onto the PCB contacts
    to me the hardest part will be to get the part that acts as a spring to work correctly

    John


    PS
    https://deskthority.net/wiki/Rubber_dome
    Hmm... from what I've seen, the button is done like this:
    _
    / \

    So what ends up happening is as you press, the sides bow out and then spring back into shape once you release. But I see what you're saying, I was thinking of doing just straight edges
    _
    | |

    which I didn't think would be a problem, might not work.

    Quote Originally Posted by LeeWay View Post
    Lots of stuff is overmolded.
    I have a side project injection molding some knobs. They will include a flanged nut in the first mold for each knob. That molding retains the nut in the colored plastic. It could be transparent as well. It will have raised letters. Then these parts are mounted into a second mold. This molding will inject a rubberized layer around the knob except for the raised letters.
    The problem with this method is that you really need to make a bunch of them to make it cost effective. Thousands. You would be needing two molds for each button.
    If you could place all the buttons in a single mold, that would certainly help. Just inject the silicone in one cavity at a time. You would need a way to secure the buttons for the second injection, but it is very doable using silicone. Would probably take a day dry time before you open the molds.
    Didn't think about raising the letters, but this poses a new problem for me anyway since you can't exactly CNC a mold with perfectly square edges for lettering... hmm...



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    Default Re: Keypad Project

    Quote Originally Posted by dharmic View Post
    I did exactly that for the first couple of goes with my project. The 3D printing has some issues though:
    - warping during printing due to the extreme temperature variations means straight lines often aren't;
    - Even down to a 0.1mm layer height your final product is going to have lines everywhere but flat surfaces;
    - Pretty hard to polish a print for a good surface finish;
    - Only good for one or two shots.

    Still, as is generally the case, 3D printing whilst limited for production is GREAT for prototyping.
    The added bonus of 3D printing is that you can make better edges than the round edges that you get from CNC.

    I'll keep the temp prob in mind.

    Woops double posted.



  12. #12
    Member dharmic's Avatar
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    Default Re: Keypad Project

    If you need a zero radius internal, work out a way of making it external. Machine a plug, cast a female mould off it in epoxy and shoot your silicone in that



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