Newsgroups: comp.robotics
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From: nahshon@vnet.ibm.com (Itai Nahshon)
Subject: Re: Homemade robot shells? How?
Sender: news@austin.ibm.com (News id)
Message-ID: <NAHSHON.95Jul2200703@rs3bt-01.haifa.ibm.com>
In-Reply-To: cmcmanis@Sun.COM's message of 1 Jul 1995 20:34:05 GMT
Date: Sun, 2 Jul 1995 17:07:03 GMT
References: <00992161.E81EB040@Msu.oscs.montana.edu> <3smcvq$6te@tabloid.amoco.com>
	<3ssuug$arl@handler.Eng.Sun.COM> <3t0rov$l0d@crcnis3.unl.edu>
	<3t4bft$50l@handler.Eng.Sun.COM>
Organization: IBM Israel Science and Technology, Haifa, Israel
Lines: 34

In article <3t4bft$50l@handler.Eng.Sun.COM> cmcmanis@Sun.COM (Chuck McManis) writes:

>the weave run in a different direction of stability. Once you've
>achieved the desired level of strength you start finishing it. That is
>done by painting on just resin and there is a special kind called "gel
>coat" that is typically white. Paint it on, let it dry, sand it smooth,
>repeat until you have the desired finish.

I guess chuck has used polyester resin. For finishing use "top-coat" and
not "gel-coat". If you want a clear (transparent) finish use "finishing
resin".
Top coat is gel-coat with added paraffin. "Finishing resin" is polyester
with added paraffin.

Polyesters do not cure properly in air. For the last coat paraffin is
added to the resin. The paraffin isolates the resin from the air and
lets the surface cure. Otherwise you get the external surface "sticky".

In general, gel-coat is used to finish inside molds and top coat to
finish or fix external surfaces.
For anything but the last layer do not use to-coat or finishing resin
because the parafin makes bad binding between layers.

Epoxy resins are superior to Polyester but they are both toxic and
more difficult to work with.

Look at the RC-flying-FAQ part2 for addresses of fiberglass and epoxy
resin supplies. Some of these places also carry ready made plates, rods
or tubes from composites that can be useful for robotics.


Itai Nahshon
Haifa, Israel

