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Make A Polycarbonate Motorcycle Sidecar Windscreen

12 Sep

source: http://sidecar.home.insightbb.com/windshield.html


Sidecar Windshield How-to

This page explains the steps I took to make a polycarbonate plastic windshield for my 1984 California Sidecar Co. Friendship I.

STEPS
1. Remove and trace the old windshield on paper
2. Measure the tracing size and order the new plastic (mine was 27″ x 41″)
3. Trace the old windshield onto the new plastic.
4. Cut and trim the new piece
5. Drill, bend and pre mount the new windshield
6. Mark the bottom edge of the new windshield on the sidecar body
7. Apply a new foam seal (if a new one is desired)
8. Mount the windshield
9. Install the snaps for the soft-top
TRACE THE PATTERN
I took the snaps off the old plastic and laid it down on large piece of paper. As I slowly rocked the old shield from side-to-side I drew its outline. This gave me a flat pattern to measure so I would know how large a piece of plastic to order.
paper pattern
MATERIALS
I paid $75 for a piece of 3/16″ (aprox. 7mm) thick polycarbonate plastic. I recommend using 1/8″ thick material. I’ve had problems with tiny cracks that have appeared on the outer radius of the shield. Bending the plastic to this radius without heat has proven to be too much stress. The local plastic shop sold me HYZOD a LEXAN equivalent made by Sheffield, a subsidiary of the Bayer (aspirin) Co. I also bought a roll of 3M foam tape that is normally used to make a seal between a pick-up truck topper and the sides of the bed.

test fit
CUT
To cut the plastic I traced the pattern of the shield directly onto the protective sheet covering the new plastic. I extended the pattern lines about 1/4″ all the way around prior to cutting to have a little room for error. I cut the shape with a fine toothed, saber saw and used a table top, electric disc sander to finish the edges. The plastic was a dream to work with.

DRILL
I simply drilled the holes with the plastic on top of a piece of wood.

MOUNTING
Pre mount the shield and trace the bottom edge onto the sidecar body with a pencil or china marker. Remove the shield and apply the foam seal with the bottom edge along this line.

Because the plastic wants to stay flat, three or four hands would be useful. I used a strong nylon twine and tied a bowstring between the second snap holes. This helped hold the plastic in a curve that allowed me to bolt the shield in place. I was worried about the string breaking. The plastic had a lot of tension on it and it would have really hurt (maybe injured) me if the string had broken.

“bow string”
DON’T OVER TIGHTEN!
Ideally the screw heads would just touch the plastic and stop. The problem is tension must be applied to pull the plastic down to the foam seal. This is not ideal. The stress on the holes causes stress cracks in the material. Drill the mounting screw holes large enough to allow for some movement.
LESSONS LEARNED
– Regular polycarbonate plastic is very soft. It scratches extremely easily. It may be worth the extra cost to buy the polycarb with the hardness coating. Like they use on cycle windshields. The fellow that sold me the plastic said it was about twice the cost (i.e. $150 US in 2001).

– The trailing edge of the plastic is developing tiny cracks. I’m not sure why but my guess is the radius of the bed is a little too much for the plastic.
I was warned NOT to heat the plastic to make the bend because it would expand in uncontrollable directions. I would be tempted to try heat because of these tiny cracks.
trailing edge cracks

– The mounting holes are cracking on the inboard side of the sidecar only! I have no idea why they would develop cracks only on one side. Perhaps making the mounting holes a little larger and adding washers or rubber grommets would ease the stress on the material around these holes.
mounting hole cracks

A more experienced windshield maker may have the answer to some of these problems.
Someone mentioned that he would like to make your windshield taller. Perhaps you could make the trailing edge longer. You would have to figure out where to drill the holes and make a new soft top, but it should work.

extended pattern

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6 Comments

Posted by on September 12, 2007 in Fabrication, Polycarbonate, Recreation

 

6 responses to “Make A Polycarbonate Motorcycle Sidecar Windscreen

  1. Andrew Lawry

    November 10, 2007 at 6:53 am

    Hi
    I made a windscreen for my BMW R80 from Polycarbonate or acrilic, I can’t remember which it was about 18 years ago. I bent it by hand holing it in front of an electic heater trying to evenly warm up the center from top to bottom evenly. I was stressing it with fingers and thumb, suddenly it “went” so I backed away from the heater while holding it as i wanted, it cooled, and stayed with the perfect curve! I was very pleased, it lasted for years. I still have the same R80, I managed to buy a factory screen and mount. i gave the home made one away. I recommend bending.
    Good luck, Andrew (New Zealand)

     
  2. Matthew

    May 27, 2008 at 12:37 am

    The windshield is probably developing the cracks not from from being bent into shape, but from flexing in the wind (and from the engine/road vibration). This is why it is cracking along the edge, rather than down the middle. The material may be soft enough to bend into shape, but too hard to flex comfortably with the wind. Even if you can’t see it (or if it is hardly noticeable) the edge of the windshield is vibrating back and forth very quickly – hundreds or thousands of times a second, like a string on a guitar.

    A a guitar string vibrates along its whole length. At the same time it also vibrates into parts of the whole length 1/2, 1/3, 1/4…etc. (like a standing wave in a rope). You can’t see it doing this, but it is. Eventually guitar string wears out or breaks. The same thing happens with the windshield.

    The problem is that the plastic is too hard (i.e. not flexible enough), hence the stress fractures where it bends repeatedly. It cracks at the screw holes because the vibration is transferred there, but it can’t flex freely because it is immobilized by the screw heads. The holes are also the weakest part of the windshield.

    Being in a pre-stressed condition (being bent) just makes things worse.

    If you make the windshield thicker, this will reduce the vibration, and add strength. This might fix the problem.

    A thinner windshield would flex more easily, so this might work, but since the material is prone to stress fractures anyway, they might come back eventually. On the other hand, having more vibration could just make things worse.

    You might try finding a softer (more flexible) plastic.

    Adding rubber grommets/padding at the screw holes might help there.

    You have a cool website. I was looking into building a fish tank.

    Hope that helps,

    Matthew

     
  3. darsara

    June 3, 2008 at 1:55 pm

    dear my friend

    i am intrest on your prodacts pls send to my your catalogue

    best regards

    darsara

     
  4. Ron DeYoung

    August 23, 2008 at 5:47 pm

    Great information on cutting acrylic windshields. I have a Honda 1983 Goldwing with a Vetter fairing that has a w/s like that, 1/4″ thick. Problem: it’s actually about 2″ too tall…my line of sight hits the top edge 90% of the time. I’d like to shorten it. I was thinking of removing it, putting layers of heavy duty masking tape over it, and cutting per the instructions here. Any experience or suggestions? Thanks.

     
  5. terry jones

    September 29, 2008 at 7:08 pm

    ron de young.

    I trimmed my windscreen in place with a high speed dremmel and a cutoff wheel. took about 2 minutes and i finished sanded with 450 grit paper. looks like factory and I didn’t even take it off the bike

     
  6. Andrew O

    April 13, 2009 at 2:45 pm

    I have a Ural which came with a sidecar windshield. To be truthful we don’t use it that often. I found that it creates kind of a “wind tunnel” effect between the sidecar windshield and bike windshield, which can make it uncomfortable on your face if you are wearing anything but a full face helmet.

    It also knocks my bike off balance. I tried angling the bike windshield and this helped a bit with the balance issue.

    Anyone know how to properly set one up to avoid these problems, or if it is actually possible?

    An interesting story about my Ural adventures can be found at: http://loveubecause.com/2009/04/13/loveubecause-you-are-my-motorbike/

    Enjoy!

     

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