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Author Topic: Button pad out of silicone or rubber  (Read 6536 times)
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Hello!

I'm trying to recreate the button pad here https://www.sparkfun.com/products/7835
I've already got mold made out of wood but I need to know what kind of product I should get to pour over it to make the rubber pad.
I don't own the product.

Anybody have any ideas?
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There are probably some artifical rubber formulations specifically for casting available through arts & crafts stores/catalogs.  Unfortunately I don't have any experience in that area, so I can't make any direct recommendations. 
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Liquid casting silicone (and appropriate release) would probably be best - let me dig in my bookmarks...

http://www.smooth-on.com/

They may have something you could use. What do you plan on using for the conductors on the pads? Or do you have a different solution for the switching?
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I'm not sure what to use for the conductors.  I don't understand what they mean when they say Part A and Part B.  Isn't it just one product?

EDIT: Also, If I had a RepRap, could I not just print a 3-d Plastic mold and then just pour it in there?
« Last Edit: August 14, 2012, 07:35:41 am by funkyguy4000 » Logged

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I'm not sure what to use for the conductors.  

Those black rings you see on the part from SparkFun are likely the conductors - generally they are carbon-impregnated rubber (not sure where or if you can easily buy that - but I bet some googling would turn up something). You mainly want something that isn't going to corrode or degrade over time. You might be able to make your own by following something like this:

http://www.instructables.com/id/Make-Conductive-Glue-and-Glue-a-Circuit/
http://www.inklesspress.com/conductive_glue.htm

I don't understand what they mean when they say Part A and Part B.  Isn't it just one product?

Some silicone molding compounds are two-part mixes; some must be measured by volume, some by weight (make sure you're clear on this when you purchase). Basically, one part is the liquid rubber and the other is the "curing compound" - similar to 2-part epoxy. Other silicones are single part compounds containing a volatile chemical that evaporates out as it cures (just like silicone glue/sealant - in fact, you might try that first; just brush it into your mold; though I don't know what you can use as a release agent, which you'll want no matter what compound you use).

EDIT: Also, If I had a RepRap, could I not just print a 3-d Plastic mold and then just pour it in there?

Yes, you could.
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Hmmm, I'll add this on to my list of motivation to make awesome apps for money so that I can buy a rep rap
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Those black rings you see on the part from SparkFun are likely the conductors - generally they are carbon-impregnated rubber (not sure where or if you can easily buy that - but I bet some googling would turn up something). You mainly want something that isn't going to corrode or degrade over time. You might be able to make your own by following something like this:

http://www.instructables.com/id/Make-Conductive-Glue-and-Glue-a-Circuit/
http://www.inklesspress.com/conductive_glue.htm

I would image that thin stainless steel washers with the proper inner and outer diameters would also work.  Perhaps not as well but they'd be eaiser to get than the carbon-rubber rings, and might be easier to work with in a confined space than the conductive glue.
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Oh thats true, although every time you press a button, you'd hear a "clink" noise and it would be a lot heavier, wouldn't it?
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Oh thats true, although every time you press a button, you'd hear a "clink" noise and it would be a lot heavier, wouldn't it?

Well it would make the button array measurably heavier, but I don't think enough to matter during use.  I think any noise would depend on a few things, like how far the washer actually moves, how much force is used, and how thick the silicone rubber around it is.

However, I think I might have found something even better...  How about flat copper washers only around 1 mm thick?
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Would I just glue them on?
GORILLA GLUE!
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Would I just glue them on?
GORILLA GLUE!


Probably, but you'd want to make sure whatever glue you use "plays nice" with the silicone rubber. 

Alternatively with something as light as the copper washers, you might just add them after the rubber has set a while but before the curing process is complete so the rubber sticks to one side of the washers.  I've never tried this though, so I can't guarentee good results.
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Yea, I'm just trying to get ideas.  I've never done this either.
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Yea, I'm just trying to get ideas.  I've never done this either.

It seems like making your own button pad is very possible, but you will have to experiment a little to work out the details of the process.  Please let us know how it goes.
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Will do smiley

I think what I'm going to do is just buy a buttonpad, and make a mold out of it and then just use that.
I'd bought some wood to try to custom make it myself....that didn't go well.
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The only problem with metal washers is that over time, they will eventually corrode. Stainless steel would be ok, but even it would have contact issues in the long term (which might be longer than you care about the project, though). If I were going to use metal, I think I would go for thin copper washers tinned with 60/40 solder; not as good as gold, of course...
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