Civic44

I have an 88 Civic hatch and I bought an extra hatch-trunk so that I can make a lightweight one (legal in one series I want to run). Here are a few questions:
- what thickness lexan should I use (minimum weight, or course)?
- should I remove the glass from the hatch right away, or are there some measurements to be taken first?
- should I remove the glass myself and if so, how? Heatgun? Solvent?
- should there be some big holes in the lexan as I've often seen (I'm assuming it lets the air that comes in through the open driver-side window exit) and where should they be?
- I'm assuming you screw the lexan to the hatch. What type of screws? I guess one would drill all the holes in the lexan for the screws, then maybe duct tape the window in place and re-dril the holes into the hatch?
- every how many inches do you need a screw?
- how do you prevent the lexan from cracking near the screws?
- what is the minimum distance from the edge that the screw holes should go?
- approximately how much should I be saving weight-wise, assuming I also remove any unnecessary metal in the hatch as well?
- also, how do I remove the logo and Civic writing so I can properly repaint the hatch? Heat gun? Are the badges glued on or do they go through holes in the sheet metal?

I can't think of anything else right now. As you can tell, I haven't started the job and find it intimidating...

bbqman

Dude, why didn't you ask me? Rainman's been doing these for years.

Let me know.

NegativeLift

if you dont find help here try the drag racing forum

martini

Any thickness. Get a general measurement of your hatch glass, so you know how much you are going to need, of course.

I would remove the glass from the hatch. You'll need to figure out how yourself. Perhaps a auto glass place will help you out and remove it for you. After that, I like to take some crate paper, lay it over the glass, and cut out a pattern. Then take that patten, and trace it on the lexan, then I use a reciprocating hand saw to cut it up. it has to be clamped down good and tight in the area you are cutting, or else it will flap around, and your cut will be jagged. Then I sand down all the endges so they look nice (power belt sander...this can also be used for fine fitting).

I have never seen and big holes in the lexan (unless you're talking about the door windows).

Don't screw the lexan in, it will crack if you do that. You are going to want to rivet. You a tiny drill bit, put the window in place, then use the same drill bit to drill into your hatch On two adjacent holes (somewhere at the top works best). step up to a bigger bit, and do the same on the same two holes until you can fit your rivet in (use aluminum, stainless steel is a bitch to drill out if you make a mistake, or ever need to replace the lexan). One you can fit your rivet in, punch it in, and work your way around until they are all riveted in. I would expect to put a rivet every 4-6 inches or so. If you want, you can find weather stripping putty at auto body shops that you can sandwhich inbetween your hatch and the lexan for a good waterproof seal.

Can't say how much weight you'll save, because I don't know.

but don't forget to do your painting and everything on the lexan. if you need more help, go to the drag racing forum.

owen_the_soyboy

1/8" thick

DB2-R81

Screws and rivets are for drag racers read this and do it right!

This information was supplied by Kurt Weiss, SCCA Competition Board member
and an engineer with GE Plastics, makers of LEXAN, in response to a query.

Posted from the SCCA Production Car Racing

----------------------------------------------------
LEXAN!! Alright. It's a great material, and great sheet.

I can't start any discussion about LEXAN resins without giving some background
on the material. LEXAN Sheet and resins are made from Polycarbonate. It's
tough stuff. No doubt you've seen pictures of lug nuts and wheels bouncing
off of NASCAR windshields. What LEXAN does best is take impact. As strong
as it is there are some things that it doesn't like. It can probably be
summarized by long term application of stress. Hoop stress (around a bolt)
is evil. Tensile stress is evil. Stress concentrators like sharp corners are
evil. There are many chemicals which can attack LEXAN resins, and they will
all accelerate failure in the presence of stress. The absolute worst thing
that you could ever conceive of doing to a LEXAN sheet would be to stretch it
over a windshield frame, and hold it in with rivets. The stretching isn't so
bad in itself since you're distributing stresses over a broad area, but the
rivets will create a very high hoop stress in a very small area, and tie the
windshield down so hard that it won't be able to expand and contract with
temperature. In that situation, if the windshield didn't crack from sitting
still in the garage, it will most assuredly crack after some temperature
excursions or heaven forbid after being cleaned with a harsh chemical. You'd
be cursing me out before your third race.... Did I mention that the stuff isn't
cheap.

I've painted a pretty grim picture, haven't I? Well there are things that we
can do to make it last. Most importantly is don't use anything other than
really gentle cleaners on it. Straight window cleaner is alright as long as
you don't soak the windshield with it, and then let it pool around the
attachment points. You'd be asking for it. Best thing to use is soap and
water. Use lots of water. LEXAN sheet, even the mar resistant grades will
scratch, so the more water you use the less chance you have of grinding in dirt.

Second thing is, and this one is just as important, mount it correctly. We
have worked with Five Star (stock car bodies and windshields) for years. They
used to have all sorts of problems and complaints until we convinced them that
the best way to mount the windshield was to allow it to float. Float may be a
bad word, but you don't want to tie the thing down with fasteners. My buddy in
the sheet department helped develop what the NASCAR guys use to hold in their
windshields. They put the windshield in a rubber track, and then just hold it
to the frame with the 6 or eight windshield clips. No screws or bolts go
through the windshield. As soon as you put a screw in the windshield you are
going to want to tighten it, and as soon as you tighten it you will create
localized stresses, and the game will be over.

If I can't convince you not to put fasteners in the thing, keep in mind that
the LEXAN does have to grow and contract with temperature. Coefficient of
Thermal Expansion (CTE) is 5X10-5"/"degree F. In other words, if you see a 50
degree temperature excursion you're going to see .0025" growth for every inch
of plastic. Doesn't sound like much, but if your windshield is 50 inches long,
it means that you're going to have .125" of growth every time you park the car
in the sun, or .125" of contraction when the car sits in your cold garage
(Florida, okay maybe not) over the winter. Long and the short of this is, if
you are going to use a 1/4" bolt, you will need a MINIMUM of a 3/8" hole to
allow for CTE. Don't overtighten the bolt, and use BIG!!! washers. You're
best off not putting the bolt in.

As for the forming of the sheet, MR grades of LEXAN sheet use a Silicone hard
coat. Works great for scratch resistance, but doesn't like it when the sheet
goes up to forming temperatures. That growth we talked about above cracks and
distorts the hard coat. The FMR grades of LEXAN sheet use a modified melamine
instead. Not quite as great in scratch resistance, but it can take the up to
315F. That's enough to use a drape forming process. It's not enough for
vacuum forming! According to my buddy in Sheet, for one off windshields they
take felt and cover a glass windshield, then they heat the LEXAN up to 310 to
315F. It's taken out of the oven and draped over the felt covered windshield.
Because the LEXAN is still quite stiff at that temperature, a second felt
covered glass windshield is used to sandwich the LEXAN. Sounds scary to me.
Not for the faint of heart.

So in most cases:

- Use clips
- Try not to use bolts
- You should probably use the FMR sheet, but since you aren't going to be
heating the sheet, and there isn't much crown to the windshield you could
probably get away with MR.
- Cold forming is okay, but leave drape forming to the experts.
- Use gentle cleaners.

Long answer, but hope that it helps.

Regards, Kurt A. Weiss
Manager, Manufacturing Services
GE Plastics

essex

Is there a difference between Lexan & Plexiglass? Or is plexiglass just a generic term as Lexan seems to be a GE product?

They sell plexiglass at homedepot is this the same stuff?

Civic44

Wow, thanks for the detailed responses. I can't wait to start on this project! I'll post pics when it's done (it will be a while).

JeffS

No, they are different materials.

slammed_93_hatch

plexiglass is harder then ****. its the **** that they use in some speaker boxes

EMod Civic

I used really thin lexan on my car, like 1/16". Like the detailed post above said, you absolutely don't want to rivit it on. On my rear quarter windows, I did drill a few 1/4" holes at the front of the window to run a screw through. The screw was not tight to the lexan, but was just there to hold the window from blowing out. I mainly used silicon caulk to glue the lexan in. On the hatch, I glued it and ran two aluminum straps from top to bottom to keep it from blowing out. Cutting big holes to let air out will definately reduce the risk of the window blowing out, but they don't keep the rain out. One cool touch I did was to paint the black border around the edges of the lexan so they looked just like the factory windows. To do this, just use a razor to carefully cut the paper backing off around the edges of the windows, just like the originals. Then remove the paper from the edges, leaving it in the center. Then spray paint the edges black (on the inside). It's just like you used to do when painting lexan RC car bodies. It looks great, is simple to do, and seemed to hold up fine.

-Chris