1938 WILLYS HOOD ORNAMENT, THE MAKING OF THE
PLASTIC INSERT
ACRYLIC PLASTIC GUIDANCE/HANDY HINTS FROM TOM
CARVER
Here are three posts from Tom Carver who reviews all the do's and
don'ts of working with Acrylic....Tom is owner and builder of
'31Plymouth with BB Chevy and presently building a Deuce Pickup from
scratch...a build from scratch hot rodder.....mgb
I got my hood ornament back last night finally....looks
great.....better than it probably ever did new...so this
morningthe a , I stopped into Ridout Plastics and bought
myself a big piece of Acrylic, clear, about 12 inches square
and a 1 1/4 thick....will need a fine tooth blade for my
table saw to cut it and then I can probably shape with my
grinding wheel or the die grinder till I get it close to
shape and then one is suppose to use very fine sand paper to
finish it off and bring it back to the glass finish...guess
there is a polishing compound as well....but I will leave
it....I have enough I can have a couple go's if I mess it
up...cost 20 bucks ....I bought the whole chunk as if they
cut me a little sliver it was going to be 10 bucks....mgb
Pretty neat Mike. That's a huge slab of acrylic. Yeah, a
carbide tipped blade with a lot of teeth should do a good job.
When you start cutting, it may get warm and tend to get the
acrylic sticky, so keep pushing through at a steady rate so the
blade won't get stuck to the acrylic. Acrylic will shatter into
big jagged hunks if you're too violent with cutting or drilling.
A band saw would be better if you need to cut out odd shapes --
in case you know somebody with one. If you use a belt sander or
a disc sander, keep moving around. If you hold the acrylic in
one spot on the same area of sandpaper too long, it'll overheat
and start to melt and then it'll melt all over the sandpaper and
either tear all the sand off the paper or completely gum up the
paper. If you keep it moving all the time it'll be okay though.
If you need to remove a lot of acrylic to start shaping it,
you'll probably want to start out with some really coarse 32 or
50 grit -- otherwise you'll take all day. You say you
might use your "grinding wheel"? A grinding wheel like you
use to sharpen tools would just melt the acrylic and smear it
around and make a mess of the grinding wheel. Coarse
sandpaper would work a lot better. You want something with
an open grit, so that lots of air can get in there to help keep
it cool.
Oh yeah, I should warn you that acrylic can catch on fire
with an invisible clear flame. It burns pretty easily.
You don't know it's on fire until you see it melting and boiling
at the surface because the flame is almost perfectly clear.
When it burns it smells kind of like apples. I've never
had it catch on fire using a sander, but I've had it catch on
fire while doing "flame polishing".
Sorry if I sound like a shop teacher. I'm used to
warning all the students here at work about everything to keep
them from destroying the lab.
Tom
--
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][ ][:
[] Tom Carver []:.
][ Ginzton Labs Microstructures Facility ][:..
[] Stanford University []:...
][ =========================================== ][:...
Thanks Tom....as you can tell, I know nothing about
this....getting at my table saw is going to be a
pain....they had suggested I use a drimmel tool for some of
the shaping or a die grinder with a fine grinding tip.....I
will stay away from my grinder now....and I don't want a
fire either...may have to look around for a band saw to
borrow..mgb
yeah, you want something that kind of scoops away the material,
rather than rubbing it off. Nice sharp carbide blades or sharp
coarse sandpaper moving fast. As long as you keep it cool, it
sands or cuts away easy. It's just when you use something dull
that just rubs on it and gets it hot, that you run into
problems. If you could cut the basic shape out on a bandsaw and
use a belt sander or disc sander to shape it, that would
probably be the best bet. Or for stuff like that, sometimes a
right angle die grinder with little 3" coarse sanding disks
works great. I did all the sanding of epoxy resin and
fiberglass when I made those fiberglass mouldings that run along
the bottom of my Plymouth under the doors using one of those 3"
sanders with 3-M "rol-lok" 32 or 50 grit sanding disks. They
cut real nice. That's how I sanded the high spots off the epoxy
on my roof insert too in between layers. In the shop here at
work we have a big 6" belt sander with about 50 grit paper on it
-- it works good for stuff like sanding plastic unless somebody
got the grit all dull by sanding glass or titanium or
something. If the paper's dull, it just melts the plastic and
makes a mess.
I have a 10" table saw, but I used a fine tooth 7-1/4" carbide
tipped blade to cut up acrylic and polycarbonate on it before.
Those smaller blades aren't too expensive at Home Depot. I
think the blade I used was meant for cutting paneling or thin
plywood. It worked fine for cutting plastic. I never cut any
1-1/4" thick stuff on it though. I cut some that thick on the
big "Do-All" bandsaw here at work though, and it was easy on
that one. Actually if it's that thick you don't need a real
fine blade on the band saw. I used the blade that has something
like 5 teeth per inch and it worked fine. That saw just has an
ordinary "bi-metal" type alloy steel blade.
Tom
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Pretty neat Mike. Both plastic parts came out really nice.
The router was a good idea on the second piece. I like your
write-up and the pictures on your website. Besides people
with Willys, probably some people wanting to make some other
sort of gizmos out of acrylic will stumble onto your website
and it'll help them out a lot.
If you can see down into the part from the top and you don't
like how the frosted part on the back side looks -- like in
the areas where you had to drill 1/4" and 5/16" (or whatever
it was) holes, there's a way you can make those look almost
polished. At Tap Plastics they sell some solvent cement for
gluing acrylic that has "methylene chloride" as the main
ingredient. You can paint over a rough machined surface
with that solvent cement, and it will melt the surface and
when it dries, it will look almost polished. They have two
kinds. One is a low viscosity that's good when you want to
make a quick bond like a T between two 1/4" acrylic sheets
that are machined to mate closely with each other, and the
other one is a thickened one that is made for laminating
larger slabs of acrylic to each other -- like if you wanted
to glue two large 1/2" slabs together to make a 1" slab.
The low viscosity one is very runny -- more runny than say
gasoline -- and it dries quickly so it doesn't have much
time to melt the plastic unless it's sandwiched between two
pieces, and if you put too much on, it tends to run all over
the place where you don't want it. You usually make the
bonds by "capillary action" where you just dab some at the
edge of the joint and it wicks in by capillary action. But
the thickened laminating type solvent cement stays liquid
for a while. It's about as thick as honey. You can use a
little paintbrush to paint that thicker one on and it will
melt the rough machined surface and when it dries, it'll
look like glass. Sometimes it'll wind up looking a little
milky. It depends on how rough it is and whether tiny air
bubbles get mixed in. When you bond something using those
solvent cements, and you do it right, you can see right
through the joint. Solvent cement actually welds the
plastic together by melting both sides into each other.
With the thick syrupy stuff, you have more time to squeeze
and try to work out the bubbles.
But actually, probably that machined satin finish on the
bottom side probably looks good. It probably helps it to
refract more light and make it sparkle more.
I just thought I'd let you know about that solvent cement
stuff just in case you might want to make the bottom look
clear.the they
I think somebody makes acrylic cement which is dyed
different colors so that people can make artistic things
where you look through a thick slab and see multiple layers
and colors at the bond joints. Or sometimes they'll
laminate different colors of acrylic together so that they
can make parts with colored stripes all through them.
Probably some acrylic lacquer or enamel would do the same
job if you just wanted to paint the bottom to make it
opaque. Maybe some black paint would make the bottom just
sort of disappear.
So how did you mount the acrylic piece to the chrome
ornament? Does it just snap in there, or is it screwed in,
or do you have to glue it in? Hey, if you have to glue it
in, Home Depot sells some stuff called something like "tub
and shower surround adhesive". It's like "liquid nails",
but it's designed to glue acrylic panels to the wall without
affecting the acrylic. Most adhesives will dissolve and
make a mess out of acrylic, or warp the acrylic, but that
stuff doesn't affect it. I used some before. It works
pretty well. It dries slowly into a soft stretchy white
rubber. It's moisture resistant. I think it's about $2 in a
12" caulking gun tube.
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][ ][:
[] Tom Carver []:.
][ Ginzton Labs Microstructures Facility ][:..
[] Stanford University []:...
][ =========================================== ][:...
[] carver@ee.stanford.edu []:...