Cutting Plexiglass Windshields

I know I have read some where on this site about people who have trimed their windshields.  How hard is it to do this and what did you use?  I want to cut off one side of mine to match the side that is broken.

I've done the job with a saber saw as well as a coping saw you need a fairly fine blade operated fairly slowly to avoid heating the cut up enough to melt the material. I usually cover the plastic area with masking tape and mark the cut on that. The masking tape will prevent the saw's sole plate from scratching the material. Support the cut off piece so that it doesn't vibrate and break off.
Once the raw cut is made you'll need a file and fine sandpaper to finish the edge of the cut. It must be smooth with no nicks. The edges of the cut should be sanded to get a slightly round edge. Nicks are stress risers and can cause cracks to start. The finished edge should be mirror smooth, use wet/dry 400 grit to finish the edges. Go slow and gentle, it's not difficult. Acrylic plastic is easier to get a smooth cut but slow work on Polycarbonate will also work but don't use much pressure or blades speed.

I cut one with a saws-all.

As Paul suggested, sanding is the key. Do not try to use a sanding sponge, use a sanding block. The sanding block will allow you to shape. The sanding sponge.... not so much.

I tried to cut down my standard Givi screen once and it was just ok, for me. But that was my fault when I did this. I bought the right blade but I just didn't take my time. I left my screen on my bike and I should have put a tarp over the entire bike. I was surprised at how much 'plastic dust' came off as I was cutting. But it seems if you take the advice and go 'slowly' you should do ok.

One other consideration, do the cutting on a warm day or in a warm garage. These plastics are always more brittle in the cold. And don't skimp on the sanding, use a sanding block and keep at it with finer grades of sandpaper until you get an edge just as smooth as it originally was. Any nicks or sharp edges are 'stress raisers' where cracks start. It isn't rocket science, in fact it's easy, just go slow and careful and no one will ever know your windhshield was ever trimmed.

I have used the Dremel Trio tool to cut various plastics inc. w/screens and a helmet visor. It is essentially a router and therefore cuts rotationally rather than with a reciprocating action. This means you have none of the vibrations associated with jig-saws, especially on thinner materials. Care is needed in the orientation of the piece you are cutting as the cutting bit tends to "walk"to the left of the line of the cut.

I have a Dremel tool. I will check Home Depot tomorrow. Is the "Cutter" bit labeled for cutting plexiglass?

Be careful with a Dremel or other rotary cutter their high speed can overheat and melt the plastic. Sometimes a bit will grab in the material it's cutting so keep it slow and cool.

Use a fine reciprocating blade and go slowly. Put painters tape on both sides and put the cutting mark on the tape.

mike712, Just to be clear, the Dremel tool I refer to is the TRIO which looks like a jigsaw in one of its two configs. They have a cutter for plastics etc. I also have a 'standard' type Dremel and you can also buy a plastic bit for these. I have never tried cutting plastics with this one. The TRIO is more powerful and has a trigger speed control. What exavid and E.D. says is good practice.

ericclapham wrote:

mike712, Just to be clear, the Dremel tool I refer to is the TRIO which looks like a jigsaw in one of its two configs. They have a cutter for plastics etc. I also have a 'standard' type Dremel and you can also buy a plastic bit for these. I have never tried cutting plastics with this one. The TRIO is more powerful and has a trigger speed control. What exavid and E.D. says is good practice.

If you had a scrap piece (check with friends and maybe a repair shop) to practice on would be nice.

I am in no hurry to do this. Here is what i am thinking. I am going to try and find a scrap piece of plexiglass and use a dremel tool with the proper cutting tool. I think if I go really slow at the lowest speed I will be able to cut it with little damage. Any advice will be appreciated.

mike712 wrote:

I am in no hurry to do this.  Here is what i am thinking.  I am going to try and find a scrap piece of plexiglass and use a dremel tool with the proper cutting tool.  I think if I go really slow at the lowest speed I will be able to cut it with little damage.  Any advice will be appreciated.

If you feel the need to practice, tape off a line much higher than your target line and practice on your own windshield.

I cut mine with a sawz all. I had a spare shield so I wasn't worried about it, but my first cut was good and I didn't need to practice.

A drem tool will assist in rounding that sharp edge, but it can dig in too. Hard to dig in with a sanding block. It doesn't take very long to round that edge with a sanding block.