Topic: Trimming windscreen

[bwaller]

Has anyone got first hand advice on trimming a windscreen? It is a full bubble on a race fairing & I'm using only the upper part of the fairing. In this case the bubble is a little top heavy and should be reduced in size. It's very thin and I surely don't want to ruin it.

[nomad]

No experience cutting a windscreen, but... perhaps this will work for you (TEST IT FIRST).

I've cut lexan (at least I think it was) before and when I got all the trimming done, I hit the edge with a fine sandpaper to give it a fairly clean edge.  After that, I barely hit the freshly sanded edge with a low heat flame from a propane torch.  I just barely swiped it with the flame.  It "melted" the sanded part back to a nice clear edge.

Like I said though... test this on the trimmed off piece if you decide to do it.  I don't think all clear plastics react the same.

*Disclaimer... "Individual results may vary." 

[Jerry Rxman Griffin aka MuthaF'er]

Put protective tape around the cut line on both sides. What do you plan on cutting with?

[bwaller]

That's why I'm asking, not sure what would be best. I thought about a small cut-off wheel in a dremel. It's really thin so I think that might be better than a fine blade in a bandsaw. It would be hard to manipulate in a bandsaw.

I'm all ears if someone has a better idea.

[domer]

depending on what its made of, i think a cut-off wheel might cause more grief than its worth. have to spin too fast to cut, in turn generating too much heat and melting as it cuts... id try a fine tooth blade in a jig-saw. 

[scottly]

If I recall correctly, I used a fine toothed blade in a coping saw. Domer is correct that any type of high speed cutting tends to melt the plastic. I was cutting some 5/16" plexi with a sawzall a while back, and the plastic kept fusing back together behind the blade.

[bwaller]

I like the coping saw idea, now do I still have a coping saw. 

[N.S.Dave]

I've trimmed a couple of bubbles, though both were fairly new, and the plastic wasn't brittle. The previous posters made some good comments. A rotary tool does usually spin too fast and generates too much heat. The bandsaw is indeed difficult to manage a screen on (tried it, difficult to support with all those curves). I ended up using a fine blade in a variable speed jigsaw, some tape to prevent scratches, and at least 4 hands. The piece needs lots of support so vibration doesn't lead to cracking.
I've also cut thin plastic with good quality Aviation snips, they work well if the material isn't brittle. Remember, same as with cutting sheet metal, don't cut the full 'stroke' of the snips or you might end up with a crack when the points come together.

[nomad]

If it's really thin, I wonder if it could simply be scored a few times to get cleanly through it?

[Tom in Newcastle......Ontario]

GL1000.windscreen it was a bit thicker,maybe 1/4-3/16,used soft discs on my grinder to lower the cracked shield(edge crack)

rotation of the grinder was along the screen not cross wise,the screen I was doing was basically flat and had no real radius's

Try it on a piece of scrap first,the grinder does melt the plastic but keep it moving a bit  then use a snap off type blade to cut the melt off,you can also just drag the blade along ,it kind of scrapes the plastic,

My not work for your situation but did in mine

Yeah sounds " Ham Fisted"but it did work with some care