One Idea that I've come up with, at least for a prototype, is to use vacuum
forming plastic.  This method is used by hobbyists all the time to make plastic
one of a kind, or even limited production parts.

The equipment for doing this is relatively simple.  A table top with small holes
all over it (hickory, or even aluminum), mounted on a air tight box.  Plugged
into it is a regular vacuum cleaner.  You'd make a positive out of hickory wood
(or something that won't melt easily), but make it a bit smaller than you want
the finished part to be (depends on thickness of the plastic your using).  I.E,
if your using 1/16" plastic, make your mold piece 1/16" smaller in all
dimentions.

You'd heat up the plastic either in an oven (it needs to be clamped in a frame),
or with an overhead heating element (over the table, with the plastic directly
under it).  You have your smaller wooden proto on the table top, place the semi
molten plastic sheet on top of it, and turn of the vacuum.  The plastic forms
around your smaller proto.

For a keypad, you'd also have to make a "cookie cutter" of sorts out of a thin
band of metal, to cut your molded keycaps out of the sheet.  Make the cutter a
bit bigger than each keycap, to leave a lip bigger than the hole the key is
mounted in.  Also, you'd leave a "sprig" of plastic attached to the bottom edge
and side of each keycap which connects to the other keycap "sprigs" with a
another wider sprig or bar of plastic sheet.  The "sprig" and bar of plastic
still attached to each keycap, is glued or melted to the inside of your plastic
case, and the sprigs act like springs of sorts (I've seen this done on regular
commercial electronics).  You'd only need to make the sprigs in the cutter, so
they would have to part of the mold pieces.

Now you can either use tactile switches underneath each keycap, or I've even
found where I can get individual silicone/carbon button switches (but only in
round or square).

                            /\
O     O    O    O    |
 |___|___|___|    \/

(ASCII layout of keycaps and sprigs)
( use fixedsys font to correct if needed)
   ________
_|                  |_
|__________|=======(sprig)

(ASCII side profile of each key cap)

Although the outside surface won't be "exact" (like mold injected plastic or
silicone), it should be pretty darned close to what you want.

Let me know what you think of this method...




-----Original Message-----
From: Vit <piclist2001@hotmail.com>
To: Bob <op1cwk@flashmail.com>
Date: Sunday, April 07, 2002 3:06 PM
Subject: Re: [OT]: Keypad or Keycaps


>
>> Have been looking for a good source for tactile keycaps, or an inexpensive
>way
>> to make a silicone keypad that could interface to tactiles/domes/etc...
>My
>> keypad would consist of two "arrow" shaped keys for up/down control, and
>four
>> oval or round memory preset keys laid out as follows (ASCII drawing
>below).
>>
>>                     /\
>> o  o  o  o
>>                     \/
>
>
>Bob, I think a lot of people (including myself) would appreciate any
>information that you can share about this topic.  My partner and I will be
>looking for something very similar in a few months, as soon as we get our
>final prototype working.
>
>So, if you find any good sources, *please, let us all know!  :)
>
>Vitaliy
>

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