Just curious about injection molding or casting

From: Richard Erlacher <edick_at_idcomm.com>
Date: Tue Aug 28 09:23:27 2001

Very small parts are difficult because it's hard to work with them under any
circumstances.

However, I've found that broken front-panel switches can be repaired either by
gluing the broken part with "super-glue" or by disassembling a complete switch
and replicating the broken part. As for matching the color, I've found that
making replacements for ALL the switches makes for a nice matching set, though
not original. That, of course, is a matter of aesthetics. Of course,
front-panel switches generally aren't what one would call "small" parts.

If you use the Silastic Moldmaking kits that are available, one problem that
comes up is augmenting the desired part in such a way that the resin can be
applied into the mold without injection hardware. A syringe will help some, but
the resin is generally quite thick, and requires a big one. I used a syringe I
got from my veterinarian to "squirt" horse-wormer into my dogs' mouths when I
had to worm the bunch of them, which was needed a couple of times a year. I've
had one of those for over 20 years and they allow themselves to be reused.

The difficulty with really small parts, or with parts that have thin barbs,
latches, etc, is that they're quite fragile and removing them from the mold can
be difficult to do without breaking them. Likewise, if you use plaster and
pot-metal (lost wax method) or anything of that sort. A two-part mold of any
sort brings with it the likelihood of a seam, that has to be removed with a
razor blade or XACTO knife, and that's seldom perfect. The seam can interfere
with proper operation, and certainly will present a cosmetic effect that you may
not like.

Building your own spare parts is not easy. For that reason, if you do it,
particularly if you turn out a really successful replica, let the rest of us
know about it, since that means that you have the tooling worked out and can
save us the effort of replicating your hard work. If you've done that, you
deserve appropriate compensation, well above the "normal" price of a part, for
making the otherwise impossible-to-replace part available once more.

Dick

----- Original Message -----
From: "Iggy Drougge" <optimus_at_canit.se>
To: "Jay West" <classiccmp_at_classiccmp.org>
Sent: Monday, August 27, 2001 9:28 AM
Subject: Re: Just curious about injection molding or casting


> Jay West skrev:
>
> I don't know why I'm even bothering to respond to an HTML person...
>
> >For small plastic parts, say - switches and actuators and the like - that get
> >broken or are missing from systems or peripherals. Is it within the realm of
> >the home hobbiest to forge duplicate parts? For example - a switch on a DEC
> >PC04 where you have 3 switches but are missing one. Can it easily be done to
> >make a casting of the part in some kind of clay, then work with dyes to get
> >the color right and pour in a plastic or resin and thus create another
> >identical switch?
>
> I haven't tried this, but there are certain plastic putties which are baked in
> an oven, quite popular amongst model enthusiasts. With the proper care in
> molding, perhaps this could be a replacement? It would be someting like
> Cernit, but I can't recall other brands. Model shops should be a good source
> in this kind of business. More professional modelers should know it all when
> it comes to casting and more advanced techniques as well.
>
> --
> En ligne avec Thor 2.6a.
>
> Keine Grenze verlockt mehr zum Schmuggeln als die Altersgrenze.
> --- Robert Musil
>
>
Received on Tue Aug 28 2001 - 09:23:27 BST

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