Thanks a lot, Frank. I didn't realize it would be so hard to glass over the
hardboard. I thought about making a mold but it seemed like a waste or effort
if I only wanted one part. Your idea of a single use mold made from the
hardboard structure is a great one. I think building a box strong enough to
press the glass into without breaking might be hard, but I'll give it a shot.
- Doug
-Original Message-
From: rctankcombat@googlegroups.com [mailto:rctankcombat@googlegroups.com] On
Behalf Of Frank Pittelli
Sent: Saturday, March 21, 2015 10:43 AM
To: rctankcombat@googlegroups.com
Subject: Re: [TANKS] fiberglass question
Warning: If you glass the outside of the hardboard it will require a lot of
time to yield a nice, smooth finished surface. First of all, multi-faceted
surfaces need to be laid up in multiple passes, because it is hard to cover an
outside corner without creating bubbles (surface tension is your enemy when
laying up fiberglass). With your turret, minimally 3 lay ups would be
required. Second, after the lay ups, you'll need to sand/fill multiple times
to get a smooth, metal-like, surface.
Personally, I would use the hard-board to make a one-time negative mold and
then lay up the fiberglass inside the mold form to make an all-fiberglass part.
The result will be lighter, will provide more interior room, will be
completely waterproof and will require less sanding on the finished surface.
Basically, just make your hard-board box so that the interior surface of the
form is the desired exterior measurement of the turret.
Hard-board is great for molds, because it is easy to work with and has a nice
smooth finish. For flat sections, place reinforcing ribs on the outside as
needed so that you can press on those sections when laying up the glass without
them flexing. Tack nail or glue them in place.
After the box is built, coat the inside with a couple coats of sanding sealer,
with a very light sanding in-between each coat. Then, rub on a couple coats of
paste wax to seal it completely. Finally, spray two light coats of PVA on the
surface, allowing it to dry in between coats.
PVA forms a water-soluble film that makes it easier to release the part from
the mold. Your turret is simple enough that you might not need PVA, but it
never hurts to use it.
For lay up, I always use a layer of mat against the mold, because it yields
the best outer surface (no cloth pattern). Then, another layer of mat to build
up the thickness and finally a layer of cloth to keep things neat on the inside
and add more strength. That's plenty strong for our purposes, especially given
the structure of the turret. If you think flexing will be a problem on a flat
section (like the top), use carbon fiber cloth in those areas to stiffen them.
After the part has cured to touch, slowly pry it away from the mold, a little
section at a time and it will eventually pop out. Wash off the PVA residue
with water, trim the edges and you should have a perfect turret. You can then
cut whatever holes are needed.
If you've never done a mold before, make a smaller version and learn on that.
It's not as complicated as it sounds. And, once you've mastered molding, your
3D printer will become the perfect mold-making tool.
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