In this
guide we will cover the basics of vacuum bagging parts. Now
that you have learned the skills from the earlier how-to's, you are
ready to tackle something more elaborate. Vacuum bagging not
only allows you to make very light weight parts, but also removes the
need for a negative mold.
Because no one likes the the fiberglass parts on ebay, and you want
something more unique than just a cheap part wrapped in graphite, you
have decided to make your own parts. But where do you start?
Vacuum bagging equipment is somewhat specialized, and
expensive. Thats what makes this how-to unique.
Instead of using specific equipment, I have in the shop, I
will do this how-to assuming you have nothing to work with.
For only $50 dollars I will show you how to build a basic
vacuum bagging system with common parts. All you have to
supply is the resin and fiber. While some elements of this
how-to are not the best professional practices, it will get the job
done. Keep in mind that this guide is intended for the
hobbyist on a budget and requires no hard to obtain parts.
The core of any system is of course the pump and the bag. The
vacuum pump can be sourced off ebay or any auto store. The
same pumps used to suck the oil out of dipsticks will also work for our
task here. These pumps will draw decent vacuum with enough
flow for small to medium vacuum projects. With shipping/tax
you can usually get these for ~ $24. If you are only going to
do a few small parts, you can run the pump directly to the bag.
However, if you want the pump to have a longer service life, or you opt
for a more expensive pump and wish to protect it, you will
need a resin/VOC trap. VOCs, or volatile organic compounds
are a byproduct of the resin curing. Pumping them through any motor is
not a good idea. This is why you need to construct a
scrubber.
The core of your scrubber will be a paint or cashew can. I
find the shorter cashew cans resist imploding better, but any metal can
with a metal lid will work. If you have it, you can even use
PVC pipe. The first thing to do is reinforce the lid so you
can add vacuum ports. Cut a 2" section off your piece of
aluminum stock. Then coat the back of the piece with epoxy.
Before it can dry bolt it in place with 4 small bolts as show
below. A dab of epoxy on each bolt will assure there are no
leaks.
Allow the
epoxy to cure at least 8 hours. With the epoxy cured you can
now drill 2 holes and chase them with a 1/8 NPT tap. Now
install the two fittings. Pipe-dope will make sure there are
no leaks, but you can also use the same epoxy you used in the earlier
step. Take a 16" piece of copper pipe and drill several very
small holes in the last 10" of it. Then crimp the bottom end
shut and bend it into a coil as shown below. You do not need
to worry about the smoothness of the bends as long as you don't kink it
shut.
Now put
the copper coil into the can and fill the can ~2/3 with charcoal
pellets. You can find charcoal at any aquarium store for a
few dollars. Now connect a short section of rubber hose
between the copper coil and and the barb as shown below. I
used safety wire to hold it in place but you can also use zipties.
With everything connected you can now close up the can.
Before
going into any detail lets cover the basics on what we have done and
what we will do. So far we have created a VOC scrubber to
help
protect our pump. In the next steps we will connect the pump
to the scrubber, and finally our scrubber to the bag with the mold and
materials inside.
You do
not have to use glass or steel stock for the base of your bag, but it
makes it easier. If you are not using a rigid
bottom just make sure you add enough pleats so your bag does not bunch
around the mold.
Traditionally
a PVA bag would be used. But since you cannot buy PVA just
anywhere, we are using polyethylene. Glad ForceFlex trash bags are 100%
polyethylene and are available pretty much anywhere. Using
duct or flash tape, tape the the bag down to 3 sides of your base.
Leave one side open so you can add the molds and material
later. Now is a good time to cut a small hole in the bag and
insert the vacuum hose from the scrubber. Tape the hose in
place and insure there are no leaks. If everything is
correct, you should be able to fold the bag shut and turn on the bump.
Within a few seconds the bag should empty. If the
bag does not empty you have a leak that needs to be tracked down and
corrected.
Now coat
your mold with mold release. If you do not have mold release,
lay a piece of polyethylene across the mold as shown below.
Now add 1
layer of your mat with enough extra to stick out at least 1/4" from the
mold. Completely wet out the first layer with whatever resin
you decided to use. Because you have several additional steps
to
complete still, I suggest potting your resin for at least 10 minutes.
Now lay one more layer of mat onto the wet resin.
To make
removal easier I suggest laying another piece of polyethylene over the
wet mat. Before doing this though, poke 2-3 holes per inch in
the polyethylene to allow resin to be pulled through.
The final layer is a layer of polyester fill. Aquarium stores
also sell this for a dollar or two. This layer assure, that
all the details of the mold are preserved, and that excess resin is
wicked away.
The mold and material are now ready to go in the bag. Make
sure you do not knock the mat and resin off the mold onto the top of
the
bag.
Because
we are not using the vacuum bag specific connectors, the
bag will want to suck to the hose end and stop the pump from drawing
down
the entire bag. The easy fix for this is fold a sponge or a
wad of paper towels over the hose end. The pump will have no
problem drawing through the sponge which will act as a resin trap to
catch any excess resin.
Above you
can see the bottom of the bag taped shut and the pump on. You
should leave the pump on at least long enough to allow the resin to
set. During this time check from time to time for leaks.
Should you locate any, tape will usually seal them up.
Once the
resin is set you can turn off the pump and cut open the bag.
If everything went as planned, all the layers should peel
apart easily.
Above is
the part removed from the mold and trimmed up. You can see in
the pictures that there is excess resin around the two ends.
This can be removed in a few seconds with sanding.
Most parts will need some touch up sanding after coming out
of the mold which will leave them with a semi-gloss look.
Should you desire a high gloss finish, it can be achieved
with a single coat of acrylic clear.
|
