RE: Elastomer for buttons

From: Smith Derek-EDS014 (
Date: Tue Jun 29 1999 - 22:19:37 EEST


Ok, I'm finally going through my old RP mail, and this may be way out of
date, but here goes anyway.

We often use the RTV silicones for this type of application. Many of
Motorola's products have keypads and other tactile buttons which are
elastomeric. While we will create an aluminum mold for making many of these
prototypes at a "fairly" rapid rate (1 every 10 minutes or so with
accelerated curing via temperature), usually the engineer in Product
Development only requires 3 or 4 to evaluate a concept.

The perfect solution for this situation is to use the Actua - oops, I mean
ThermoJet - to make a wax tool. We usually just mix the RTV, degas it,
selectively place it onto the mold halves, degas some more, then close up
the mold. Alignment features are printed into the two halves, and small
vents allow the excess RTV to "squeeze" out prior to cure. A substantial
weight (such as a steel mold insert blank) is perfect for pushing the two
halves together without crushing the wax inserts. The weight is left on the
assembled mold, and left for the following day, allowing the RTV to cure at
room temperature (hence, Room Temperature Vulcanized).

In the morning, a hammer or heat gun is used to break or melt away the
"Investment Mold", resulting in very nice, detailed elastomeric parts. We
actually run one of our Actua's exclusively for this application, the demand
for which is actually larger than the need for concept models.

I've presented this application in the past at Georgia Tech and a couple of
other venues. We have been doing this since day one of the Beta program, and
have no current plans to stop. It works substantially better than an SLA
mold as there is no cleaning necessary. We don't even use mold release. We
have since developed the ability to do undercuts, and have taken this
concept further, but I think your question has been answered, so I'll stop




E. Derek Smith
Technology Scout
3DP Program Manager

Communications Enterprise (P2TC)
8000 West Sunrise Blvd., Room 4J9
Ft. Lauderdale, Florida 33322

954-723-4790 (Phone)
954-723-4934 (Fax)

> -----Original Message-----
> From: Ian Gibson []
> Sent: Tuesday, May 18, 1999 8:43 PM
> To:
> Subject: Elastomer for buttons
> Hi rp-ml
> Has anyone used any of the elastomeric materials to fabricate
> soft-feel
> buttons for electronic appliances (calculators, computer
> games, etc.)? Does
> it work? I have an application where I need to make some
> buttons that are
> unusual shapes and want to know the best way to do it.
> IG
> Dr. Ian Gibson
> Associate Professor
> Department of Mechanical Engineering
> The University of Hong Kong
> tel: (852) 28597901
> fax: (852) 28585415
> Still crazy after all these years - Paul Simon
> For more information about the rp-ml, see

For more information about the rp-ml, see

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