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

Date: Thu, 19 Dec 2002 12:56:34 -0800
To: Mike Brattland <mgbrattland@gerlecreek.com>
From: Tom Carver <carver@fastloki.stanford.edu>
Subject: Re: Ornament

 

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
--
 o%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%o
][                                                 ][:
[]                  Tom Carver                     []:.
][      Ginzton Labs Microstructures Facility      ][:..
[]             Stanford University                 []:...
][   ===========================================   ][:...
[]            carver@ee.stanford.edu               []:...

Date: Thu, 19 Dec 2002 16:08:58 -0800
To: Mike Brattland <mgbrattland@gerlecreek.com>
From: Tom Carver <carver@fastloki.stanford.edu>
Subject: Re: Ornament

 

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
--

Date: Tue, 14 Jan 2003 12:30:07 -0800
To: Mike Brattland <mgbrattland@gerlecreek.com>
From: Tom Carver <carver@fastloki.stanford.edu>
Subject: Re: 37-38 Willys Hood Ornament Top Piece
X-MIME-Autoconverted: from quoted-printable to 8bit by localhost.localdomain id h0EKjxf10106

 

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.
 o%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%o
][                                                 ][:
[]                  Tom Carver                     []:.
][      Ginzton Labs Microstructures Facility      ][:..
[]             Stanford University                 []:...
][   ===========================================   ][:...
[]            carver@ee.stanford.edu               []:...