How to roll-yer-own windshield

Well, do you have an oven big enough to hold a piece of plastic that
big, plus the mold? I've done some plastic forming for model airplanes
and usually home ovens have hot spots and cold spots that make them
unusable unless you're lucky.

You might want to try industrial heat guns after strapping the plastic
down to a former. Use a lot of patience and time and keep the nozzle(s)
moving.

To make a former, you can take a sheet of aluminum or heavy cardboard
and use straps to make a partial barrel shape. Use different length
straps for a more complex shape.

If the shield doesn't cover the line of sight, you might want to try
something else more workable, like heavy cardboard, for the experiments.
That's assuming you have a quiet back road to test on.

You can put a rib former in the back of a piece of cardboard to make it
stiffer.

Note that Givi makes lots of nice windshields, as well as hard luggage.
I've also used Slip Streamer windshields too. There's National Cycle too.

Note also that if you cut a rectangular or triangular slot low down in
the shield it can change the aerodynamics significantly, and kill
buffeting by filling in the vacuum pocket that causes the reverse flow.

This guy has some weird ideas, but they're worth looking at:
<http://www.calsci.com/motorcycleinfo/Products.html>
<http://www.calsci.com/motorcycleinfo/VStromprod.html>
<http://www.calsci.com/motorcycleinfo/index.html>

He talks about a method of estimating windshield height, and also about
his theory about vents.

He might make you one, as a one-off. No telling. You can ask.

I did have "fun" finding a windshield for my DL-650. I'm 6'2" and I
wanted something I could ride from Orlando to DC.

The stock piece-of-shit is worse than useless. Over 45mph it was like
someone was grabbing the chinbar of my helmet and yanking it around as
hard as they could. I couldn't stand that for more than 10-20 minutes.

Taking it off, I had the same experience you did. I have a naked SV-650
but it has sport seating so you're leaned into the wind and it's not so
bad. The DL is sit-up, so you need strong arms w/o a fairing.

I finally got the 27" tall screen from Cee Baileys' whose original line
of business is making replacement windshields for small airplanes.

<http://www.ceebaileys.com/suzuki/vstromws3.html>

It's a quality piece of work, and it was even packed really well. It
doesn't look like they have anything for a 900F though.

Anyway, it's about 2" above the line of sight, and it leaves me in a
nice bubble. One problem I noticed recently is that a tank bag causes a
little turbulence.

You probably don't want to hack on your factory shield, get an
aftermarket one, and hack on that. I usually try to leave stock parts as
stock as possible in case it all goes tits-up and I want to go back to
stock.

Good luck.

-gc

 

I need advice on how to make a motorcycle windshield, starting with a piece
of sheet acrylic. I have an existing windshield to use as a guide. The
baking, marking, cutting and drilling should be easy enough. I think the
hard part will be making a forming mold that I can use to shape the plexi
sheet, preferably without destroying the existing shield in the process.
Any experts in the house to help get me started?

Backstory: Since my wife got her Concours and started making grand touring
plans, I've felt like I need to play a little catch-up with my elderly UJM.
Among other things I bought and installed a Rifle sport fairing. The first
windshield I ordered (the shortest) produced unacceptable turbulence around
my head. I swapped that for the tallest shield, and while much improved
(e.g. I can actually ride at speed for more than 20 minutes) I still get a
lot of wind buffeting behind the shield. The top of the shield is right in
the middle of my sight line, which I find very distracting.

The new fairing meets my goal of relieving wind pressure so that I don't
have to hang onto the bars for dear life at 75+ MPH, but the effect on the
overall quality of the ride is a net negative at this point. However,
between removing the short shield and installing the tall one, I spent a few
days riding behind the fairing with no windshield, and that wasn't a bad
ride at all. But that looks dorky, and didn't do much to relieve wind
pressure.

The idea now is to fabricate my own cheap windshields to experiment with,
and try to find the right size for a very short windshield that will relieve
the wind pressure on my chest without creating any head buffeting. I don't
especially want to attack my factory shield with a saber saw until I have a
very clear idea of where I want to go with it.

-Scott

 

Use the same thickness plexiglass as the original windshield so the
bend radius of your home built shield will be exactly the same and it
will bolt right up.

You're going to use gravity to "drape mold" the hot plastic, so you'll
need to make a male mold of plaster of paris that you can cover with a
thin layer of cotton flannel to keep the plastic from sticking to the
plaster.

Use plenty of wide masking tape or duct tape or whatever tape you have
to protect the front of the windshield while working with it.

You will need to make side dams to contain the wet plaster of paris
while it dries. They may be made of
several cardbord segments to follow the windshield's edge, and bent so
you can attach one side to the front of the windshield with tape, and
the other side will be vertical to hold the wet plaster.

Attach the cardboad segments all the way around the edge of the
windshield, and then use duct tape all the way around the segments to
hold them together. The surfaces of the cardboard that will be
toward the inside of this female mold will need to be waxed.

You will also need to heavily wax the rear side of your existing
windshield, then lay it flat on a table and block it with pieces of
wood so it doesn't rock.

Buy a 100 pound bag of plaster of paris. That will save going back to
the store for more, if your first mold crumbles upon removal from the
back of your stock windshield.

And, don't be stingy with the thickness of the plaster of paris mold.
Three or four inches might be about right for the height of the edge
dams, so the male mold will be stable.

Fill up this homebrewed female mold with the wet plaster of paris and
let it set up.

Then you can turn the female mold over and untape the cardbord
segments and pull them away from the edges of the plaster.

Carefully warm the windshield to melt the wax so you can pick it up
and the resulting male mold will be left behind. Warm sunlight might
be adequate for melting the wax.

You will need a large oven to evenly heat your acrylic sheet to
between 250 and 320 degrees F.

You can use a heat gun, heat lamp, blow torch, hibachi, barbecue
grill, or whatever to heat your plastic, but nothing works as well as
oven heating for
even temperature throughout the sheet.

Most people don't have an oven big enough to contain the plastic sheet
and the mold. We had
a huge insulated metal box at the engineering lab and it sat on a
table covered with an asbestos sheet and heat from a gas burner was
directed into the box from below.

We could heat parts up to 1000 degrees F for environmental testing.

It would be nice if you had a huge metal box like that. You could try
using a large cardboard box that a refrigerator came in.

Lined with aluminum foil, it probably wouldn't catch on fire because
the ignition temperature of paper is 415 degrees F (thank you, Ray
Bradbury) and corrugated cardboard is also mixed with clay to make it
smooth and shiny.

Let the plastic cool to at least 175 before trying to remove it from
the mold.

Trimming the resulting bent plexiglass to shape is as easy as sawing
and sanding and breaking the sharp edges with a file.

It's tempting to just put the shaped windshield up against the fairing
and match drill the mounting holes, but you will be very disappointed
if you get a crack radiating from even one hole in your laboriously
built windshield.

I recommend using the fairing for a pattern to mark the hole location
and then work with the windshield
separately and very carefully.

When I built a large 3' X 3' plexiglass chamber for the process lab at
Hughes, I used alcohol to lubricate the drill.

 

Wyncha take the short windshield and gradually build the
height until you find something comfortable ? Seems like
if it's not in your line of sight, you could use almost anything
to do this. Possibly some of that corrugated plastic that
they use for signs taped and/or clamped in place.

An alternative might be some kind of adjustable wing
deflector on top of the short windshield. That's one on
my long list of stuff I gotta try as soon as I get a round
tuit. A wing deflector sounds easier to build and work
with instead of trying to fabricate a whole windshield.

 

Mmm. Is a convection oven any help? Mine's got the little fan in the back
that we almost never use. Hopefully it's big enough since I'm aiming to
experiment with smaller windshields under 15" tall. If not, I'll figure out
something else.

I like that. I'll need to get a heat gun for another upcoming project
anyway.

That's a good idea. The shield shape is a simple curve (cylindrical or
maybe conical) that should be easily reproducible with some sheet metal.

Thanks, Gene.

-Scott

 

I have some from usplastic.com and they work quite well. Worth the dough.

Use alcohol to lube the drill and keep the plastic from melting and
sticking.

-gc

 

Hmm. How about plaster-impregnated gauze? Seven or eight layers ought to
be fairly sturdy. Maybe brush some epoxy over that to stiffen it up.

For the molding itself, I've read that parchment paper makes a serviceable
release agent.

No problem. My kitchen oven is plenty large enough for the small shields I
want to make, and even has a convection fan. Is there a specific best
temperature to aim for? How much time does it need to bake? Let's assume
I'm using 3/16" acrylic.

Yep. A drill bit made especially for acrylics seems pretty cheap after that
happens once or twice.

Thanks,
-Scott

 

Whoa! Don't use alcohol on _acrylic_ plastic. At my workplace, we ruined
some very expensive tooling before learing that lesson. Whatever bits you
use, keep the speed down to avoid melting.

 

You could do that. You might even make a male plug out of scrap
cardbord mold by cutting about a hundred arcs and fastening them
together.

Some "plastic artists" make statuary out of thousands of pieces of
stacked cardboard and then burn the surface with a torch...

That sort of construction would also be good for making male plugs to
lay fiberglass over...

That's a useful exchange of information. You can buy cooking parchment
in a supermarket on the same aisle where the aluminum foil is
displayed.
Cooking parchment will survive exposure to the heat from a barbecue
grill long enough to steam fish and vegetables wrapped "en papillote".

The experts in the sport plane building community recommend from 250
to 320 degrees F. One writer described making a bubble canopy by
clamping a sheet of plexiglass between two plywood sheets and heating
it to 280 degrees by blowing hot air under the plastic. He recommends
tempering the plastic at 110 to 140 degrees for 8 hours after forming.

�How much time does it need to bake? �Let's assume

After about 10 minutes, the plastic should drape over the mold.

Interestingly, there is a rule for cold bending plexiglass. The
minimum radius of the bend must be 180 times the thickness of the
plastic.

So your minimum cold bending radius would be 33.75 inches.

However, if you are going to screw a piece of cold bent plexiglass to
a fairing made made of ABS, the softer ABS is not going to be happy
with a lot of preload, the plexiglass must actually be bent to the
same radius as the fairing.

 

Thanks! I'll keep that in mind.

-gc

 

I can't see the rest of this thread, for some reason they've all been
cancelled on this server 'cept this reply and the origonal post.

I've thought of this windscreen thing myself....

I've tried forming things from acrylic sheet heated in the oven. We were
trying to make domed covers for submerged lights in a basement once.

It forms like a sheet of rubber when heated, problem I've encountered is the
surface you stretch it over wrecks the optically nice surface. At one point
we made a male mold from wood, applied lots of layers of Varathane and wet
sanded, polished etc to optical clarity, it still wasn't good enough.

We tried clamping the outer edge on in a fixture and blowing the dome with
compressed air, which worked OK but it was to hard to get consistant
results.

If I could figure a way to not wreck the surface on the mold side, I think I
would try vacuum forming it. Old fridge compressors are supposed to make
good vacuum pumps, although I have never tried this. An old propane tank
would make for a good thing to store up enough vacuum. You'd clamp the cold
plexy in frame over the mold and apply radiant heat somehow to soften
it,then hit it with the vacuum.

The drilling holes thing, it's quite brittle and tends to crack all over the
place when you break thru. Things that seem to work... drill a small pilot
hole thru then drill 1/2 way thru from both sides. Or those brad point wood
drill bits work quite well, or you can grind the cutting edge of the drill
bit to about 90 deg so it scrapes its way thru.

Someone suggested Lexan to me once. But apparenty unless you bake for long
while to drive moisture out it'll get bubbles, and I don't think I want to
try go thru a Lexan windscreen if I run into something anyways.

P.

 

fwiw, my experience with acrylic, which is a sort of self educated
incompetence thing, or plastic in general, because I don't know the proper
methods of machining it ...

There is a problem when the feed is too slow, that's when the heat happens
and everything melts together into a glob.

I keep the air gun on it to get rid of the chips and keep things cool.

In my barn-shod way of doing things, I tend to attack it with a router. If
you don't stop or hesitate, everything seems to go fine....

P.

 

Me too. I thought isopropanol was safe for acrylic. Water will work,
though.

I believe alcohols are safe to use with polycarbonate, fwiw.

-Scott

 

Or it could be that propagation to your server sucks. USENET article
feeds can be iffy.

Drills designed for plastic have much different pilot and cutting angles
to prevent such problems. I found they're worth the money. You only need
a couple and they don't get dull.

Normal bits dig in and make microfractures that cause the cracking.

-gc