The Windshield

     Conceptually, this is what we want (pardon my shaky hands)
 

     First we need a pattern that identifies the shape and the angles of curves to be done.

     Overall width is 22.6" and tapers to 15" down at the lower front forks. The top curves back toward the rider with 11" of height with a 3" bend. There is a 1" flat section then the lower sections curves back 2 to 2.5" toward the bottom. The sides curve as well. To mount the windshield, we will use threaded rod 1/4" bent to suit mounting to 1" conduit claps at the handlebars and the fork struts. The windshield provides wind deflection, easier movement at higher speeds, and stops both rain, snow, and bugs from splattering all over you as you ride.
1) Molding acrylic plastic is not hard to do, and the material is readily available.  This one has a slight compound curve (bend in two directions) but most windshields are just a simple curve.

2) This type of windshield would probably work for most any bike. It is mounted with four struts of 1/4" all-thread, bolted through the plastic. It should hold steady at up to 75 MPH, with no vibration or movement.

3) For the plastic part of the windshield I use clear acrylic, .125" thick.  A 24" x 36" piece was large enough. It is sold in home improvement stores for replacing glass in windows.

4) These are the materials that are used for the mounting hardware.  This will vary from bike to bike, depending on what is available to attach it to.  I will attach to the forks and the handlebars. Consumables which you will need:
Tools Required:
5)The layout for the windshield is based on measurements taken from the bike.  Generally you want to be looking over the top of the windshield.  Other than that, just make it like you want it.
     My layout was made by measuring and drafted by hand onto construction paper. Then I transferred it to cardboard and adjusted till it looked right.
     I then recreated it using Gimp (GNU Image Manipulation Program [freely downloadable])
       I could have taken the Gimp file to Rileys reproduction or Staples to have a full size print made, but lacking transportation this was not an option.
     Cut out the pattern and align it on the plastic.  Trace the outline with a permanent marker. Cut just outside the line with your saw.  Use a course file, working lengthwise along the edge, to cut down to the line and smooth out any inconsistencies.  Use a fine file to remove the course file marks, then sand with progressively finer sandpaper on a sanding block, to make a smooth edge.  Use a hard sanding block for this, or you will tend to round off the edge.
     I do not recommend using a flame to polish the edge of the windshield.  This is quick and makes a nice edge, but the plastic will craze and crack if it ever comes into contact with a solvent.  Acrylic adhesive and alcohol are two common solvents which can cause crazing.  Check YouTube for videos showing this effect.

     When the plastic is heated it will be flexible like a thick, heavy sheet of rubber.  We need to lay this hot plastic in a form to hold it in shape until it cools.

Heating the Plastic

6) There are two ways to proceed now. If you have an oven large enough to do the job of heating you can heat the Plastic and lift it to a form for molding it, or you can construct a form out of wood and heat the plastic with a hair dryer or heat gun with the plastic laying on the form. So lets talk about the form first, then we can heat and mold it to the form.

     Two or three things have to happen with our form. Firstly, we need our cross ways curve (side to side), and then we need the upper and lower length ways curve. Using corrugated cardboard larger than the Plastic stock and laying flat on the work surface we prepare to fix standoffs. Down the left and right sides we want a 3" curve up.
     Using a piece of heavy corrugated cardboard for a mold base.  A table top or plywood would work as well.  My windshield was to have a rise at the edges of about 3", so start by making two 3" tall struts out of corrugated cardboard, doubled over for strength.  These were taped down to the base, parallel to each other, and a couple inches further apart than the width of the windshield. 
     A piece of card stock is then laid across these two struts, and taped down to the board in the center and to the struts at the edges.  This defines the major crosswise curve of the windshield.

     You could stop at this point and have a functional mold with a simple curve.  I wanted the bottom of the windshield to curve back, so add two pieces of card stock, tight to the mold surface on one edge, and 2" above the surface at the corners. 
     It is most important that the mold be symmetrical.  If one side is higher than the other the curve will be off, and it will look odd on the bike.

     When a satisfactory curve has been achieved the mold is lined with two layers of felt cloth.  This prevents the hot plastic from picking up the pattern of the tape and seams in the mold.  To ensure that the plastic is correctly positioned the paper pattern is laid on the felt in the mold, and the outline is traced onto the felt with a marker.

Oven Method

     Place the piece of sheet metal in the oven on a single rack at about the center of the oven.  The oven used is gas fired.  Preheat the oven to about 325 F degrees.  Remove the protective paper or plastic film from your windshield plastic, and wipe it down carefully.  You do not want bits of plastic stuck to the surface.
     Make sure your mold is ready, and you can easily move the hot plastic from the oven to the mold.  Wear long sleeves and long oven gloves to protect your hands from the hot plastic.  Be very careful.  You can easily burn yourself.
     Place the plastic flat in the center of the sheet metal in the oven, close it up, and wait about 20 minutes.  You should NOT smell plastic.  If you do, it is getting too hot.
     When the time is up, open the oven and lift the plastic gently off the sheet metal and lay it directly in the mold with a minimum of handling.  Slide the plastic around in the mold to align with the outline of the windshield, and leave it to cool for about 30 minutes.  If all goes well, you have a molded windshield!

Hair Dryer Method

     For this to work, You need to take care to place the plastic in line with your pattern drawn on the felt. Using the high heat setting of the hair dryer and a 2 to 3 inch distance, move the hairdryer nozzle back and forth over a larger area and avoid staying in one place too long. It is slow as in very slow to do the shaping this way. In time the plastic will begin to bend to the form. Warning it will still retain heat and get hot even in this slow form method. Where the oven method can take upwards of 30 minutes to cool, The Hair dryer method can cool in under 12 minutes.

Windshield Mounts

     The mounts for your windshield are probably going to different from mine.  Using #4 electrical conduit clamps on the fork tubes to attach to the bike.  Before installing these cut pieces of rubber from an inner tube and glued them to the inside of the clamps where they touch the forks.  This provides better grip, reduces the possibility of scratches on the tubes, and allows for some movement.

     Locate the holes to allow for a straight line from the bend to the clamp.  Drill very carefully.  The stepped drill bit will make a clean hole without risk of cracking the plastic.  Otherwise drill successively larger holes to minimize chipping.
     The struts run from the holes in the ends of the clamps to grommets installed in drilled holes in the windshield.  It can take a great deal of trial and error to determine where the holes needed to be, and how to bend the all-thread rod.  The idea is to orient the bend in the rod so that it penetrates the windshield perpendicular to the surface of the plastic at that point.
     The strut assembly consists of a bent piece of all-thread, with a nut on each side of the hole in the clamp, a nut after the bend, where the rod penetrates the grommet in the windshield, and an acorn nut on the outside of the windshield.  Put a washer on both sides of the grommet to keep the nuts from pulling through.
     All-thread rod bends fairly easily using a vice.  If you thread a nut onto the rod down to the point where you want the bend, and put another nut right at the end of the rod, you can clamp both nuts in the vice.  This lets you clamp the rod without ruining the threads.  If you put a piece of tubing over the other end of the rod, down to the point of the bend, you can get a clean bend without curving the rest of the rod.
     When everything was fitted correctly take the struts out one at a time and slide heat-shrink tubing over them.  A lit match pulls the plastic tight, and covers the threads.  This looks better, and it keeps the plating from rubbing off.  It also protects any cables (throttle, brake, wiring, and speedometer cables) that might touch the strut.