Fabricating a windscreen - Failure! (picture thread)

[bodypainter]

I hate to fail, but I did this time although it may not have been all my fault.

Anyway, I want a windscreen for my SLK. By all accounts, it reduces wind turbulence in the cabin but the mesh version that came with the car isn't that desirable (and was missing from my car when I bought it). So I shopped the internet and found what I thought was a very nice design for sale. Trouble is they want $300 for what amounts to $50 worth of stuff. I don't mind a business making a profit but I thought, hell - I *know* how to work acrylic so I'll just build my own.

So, off I go to Home Depot for a piece of acrylic. This was probably my first and only mistake. Home Depot quit carrying Plexiglas several years ago and replaced it with some generic acrylic sheeting but I was in too big a hurry to drive the extra miles to a plastics wholesaler for the good stuff.

First I cut out a cardboard template of the shape I wanted - a modified version of what is for sale.

I got the piece cut without problems.

I spent a freaking hour peeling the cheap shit plastic cover off the cheap acrylic sheet and was ready to do my bends.

I got the bends done and was test fitting it in the car, making sure it would clear as the top went up and down and POP, it snapped in my hands.

I'll tell y'all what, I have been working with acrylic for a decade. Anyone who's seen my aquariums knows I know how to cut, shape, bend, and bond acrylic. This should NOT have happened. I believe the acrylic sheet had a flaw when I bought it. That's about six hours of labor down the shitter.

Oh well, live and learn. I'll be off today to get some more stock and try, try again. Hopefully I'll be able to post some pictures titled "SUCCESS" with the completed windscreen installed and my wife and I can go for a cruise without her having to tie her hair back.

This is what the finished screen looks like. The next one will be the same only minus the broken drivers side wing.


/poorpoorpitifulme

[rockogre]

Bummer. Do it yourself doesn't always work but, like you, I usuallly try. And I can't count the times that I was too lazy to drive that extra mile and ended up driving 10 extra miles to get it right.

Hope the next one works for ya.

[Scorps]

I don't really see where that would go on that make of car?


hope to see some pictures!

[merkerguitars]

Man thats a bummer. But atleast it's not really your fault, it was you had crappy materials. It should look nice when your done.

[Destrox]

I'm having trouble picturing what this would be on a car, anyone mind spelling it out for me?

[steveincolumbus]

here are some exaples of ones in place for all of you wondering what the hell it is

http://www.slk32.com/pages/windscreens/windscreens.html

[bodypainter]

Here is where I am at with my 2nd try at this (this picture from about 15 minutes ago). It's just resting in place but will mount only about 1/4 inch higher.



Obviously not done. I haven't drilled the mounting holes or flamed the edges and of course it's covered with my hand prints and acrylic shavings but I'm getting there. I now know it clears the top so that's a relief.

Gotta take a break - may finish today, may not.

[bodypainter]

Not 100% done, but close enough to install it and take it for a spin. That's enough for today!

Oh wait, after it gets dark I want to take it out for a bit also. The reason I bent the center piece back was to keep dash light reflections off the screen and I want to see how that works.

[End User]

Might be a dumb question, but I can't see how having the windshield behind the occupants helps to reduce wind turbulence. Does someone have a scientific explanation?
Unfortunately, I've never been in a convertible before, so dont know how all this works....

[Peryn]

Basically, you form a low pressure zone inside the cabin. Wind flows over the top of the passenger compartment, and in from the back/trunk area. Depending on the car, you will sometimes see people driving down the freeway with their hair blowing forward instead of back. Seems kinda odd, but thats how i understand it works. Very similar to the back of a pickup truck bed. When someone has a bed full of dirt or something, and its blowing off, ever notice how it usually blows forward, into the back window, and then out the sides? Same idea....air swirls in from behind to fill the low pressure area.



From http://auto.howstuffworks.com/convertible1.htm

One of these details is the small, glass shield located behind the headrests. Have you ever seen people driving a convertible with their hair blowing forward? This happens because the fast-moving air coming off the top of the windshield encounters the slow-moving air inside the cabin. Some of the fast-moving air is decelerated by the slow-moving air. As it slows down, it becomes turbulent, and vortexes form. These vortexes of turbulent air are like little horizontal tornadoes. They spin in such a way as to blow air forward into the cockpit. This can be uncomfortable for the occupants, and can increase the aerodynamic drag. The glass shield behind the headrests blocks this air, making the cabin quieter and more comfortable, as well as improving the aerodynamics.

Rarely use the windscreen in my brothers RX-7, but it really does make quite a difference as far as noise and comfort is concerned, and probably helps mileage with the top down some too.

[thadon]

pretty cool do it your self job, I hope this one lasts a long time for you

[Scorps]

Oh now I see how that works!


Good Job!

[twilightfoix]

gratz man. glad you got it done. perseverance always pays off in the end

[bodypainter]

I removed the 2nd version from the car yesterday and I'm not putting it back. I made a couple mistakes with this one but the bottom line is that it isn't strong enough.

I made the center piece too big all around. Too tall, too wide. I made the side pieces too flimsy - they chatter in the wind at speed and either need to be attached to the roll bars or extend down to the studs like the WSA versions do.

My original goal was to engineer a full width screen that didn't cost seat travel and was in some way uniquely my own. I paid attention to existing designs but thought I could re-engineer to my specs and still have a useable item. After all, it's just for me and doesn't have to stand up to the expectations and/or abuse of strangers as a commercial product would.

So I'm not quite there yet. I do believe I'll build a 3rd version and a 4th would not surprise me. It has nothing to do with money (even though I think the WSA screens are overpriced) and everything to do with making a screen that is the best in some significant way. I'll keep this group informed because I'm also a big mouth showoff. Later!

[mastertakana]

thats cool. at first i thought you should just buy one. but, i am very impressed with your diy ethic.good luck.

[WarWagon]

I'm impressed that you were able to get acrylic that thick to even bend that much. I've done enough where I could see polycarb or lexan obviously, but I always have acrylic crack like crazy.

[bodypainter]

WarWagon - bending acrylic is easy, you just need heat.



In this picture I'm working on an aquarium but you can see what I'm doing. I've clamped the piece over the edge of my bench and am using a propane torch to heat both above and below where I want the bend (right where it goes over the edge). Heat evenly and slowly - if you get it too hot the plexi will bubble. About 30 passes with the torch and that piece will start to droop. Support it while you get it even softer and then you can bend it as far as you want. I make a left to right pass, pick the torch up and move it back to the left for another pass. If you go back and forth (without picking up) you'll heat the ends more than the middle.

After you remove it from the clamps you'll have a minute or two to put it in exactly the shape you want. Give it a try!

[WarWagon]

Ah, ok, I was under the impression that the screen was bent without the use of heat, and simply held in place with tension.