There are plenty of magazine articles on how to chop a roof- we've even got one in this issue- yet probably the most important piece of the jigsaw in putting the car back on the road is never mentioned. Glass. Just how do you go about cutting that down? And if it's curved, as most post-'48 windshields are, what's the trick to cutting 'em without breaking 'em?
Though it's rarely mentioned, it's always a good idea to cut the glass and then chop the car to suit, as metal (or fiberglass!) can be moved around, whereas glass is going to be the same shape, just shorter, or in thousands of pieces! It should also be considered that only laminated glass can be cut; toughened glass cannot. If the car you want to chop has toughened glass, and you can't source laminated replacements, your only option (well, apart from the hideously expensive manufacture of a one-off piece) may be to try to use glass from another make or model that's similar in shape and modify the car to accept that.
When I chopped my '49 Chevy for instance, it was before I moved to the U.S., and while replacement glass is available here, it would have been exorbitantly expensive by the time it reached England, and that was if it was still in one piece, so I made a fiberglass template from the one bullet-holed half of the windshield I did have, and then went around to parking lots laying it over windshields! Believe it or not, a section of the windshield from a curved glass VW Bug was almost exactly the same shape, enabling me to make the two halves of the Chevy windshield from two VW versions. The only modification was to the top outside corners of the body aperture, where the glass curved inward slightly more than the original. It saved me a bunch of cash and I had brand-new glass.
Mike at The Glass House demonstrated...
Mike at The Glass House demonstrated how he chops curved windshields using this '51 Chevy glass. He made this neat little tool to mark the glass a consistent 3 inches down from the top edge.
Speaking of new glass, while photographing for this article at The Glass House, we asked proprietor Mike Cox whether old glass is perhaps more brittle than new glass. His opinion was that so long as it is in good condition, and the layers haven't started to separate, it should be no more brittle or harder to cut without breaking than new glass. Which is good news if your glass is in good condition and you want it cut down.
Flat laminated glass is relatively easy to cut, but curved glass is infinitely more tricky. We've seen it cut with varying degrees of success in the same manner as flat glass, by scribing it, breaking the glass, then heating and cutting the plastic laminate between the layers of glass, but the risk of breaking the glass when 'snapping' it along the scribelines is high because of the curve. Something to think about if your glass is rare or expensive. Mike prefers to sand the glass down to size on a large belt sander, and though this is time-consuming, the risk of breakage is minimal. On the '51 Chevy windshield half shown here, it took three hours to sand off 3 inches.
Cut It Yourself!
I was talking to Brad Masterson, who chopped the Chevy four-door on page 18 of this issue, about cutting down glass, and he told me that a friend of his had just cut his own '57 Chevy windshield using cheap diamond mini-cutting discs from his local discount tool supply house. If you're the do-it-yourself type and want to have a go at cutting your own glass, this could be the way to go. Not wanting to recommend something I hadn't tried myself, I grabbed a set of the aforementioned discs, and scrounged a piece of glass from a local supplier (The Glass Doctor in Temecula, California) and tried them for myself.
I really wanted to cut a windshield but didn't have one at hand, and couldn't scare up a cracked one in time (deadlines are like that!) so bearing in mind the only glass I could get at short notice was household plate glass and not automotive glass, the cutting discs worked very well. There was some chipping, but I'd put this down to the high speed of my nonadjustable cheapo electric mini-grinder, and it was nothing that couldn't be corrected when polishing or beveling the edge of the glass later. However, I would say this method would take as long as sanding the glass down, not to mention it'd be very nerve-racking, but it is an option. Oh, and if you go this route, take as many precautions as you can and then some. You don't want to be breathing fine glass dust, and there'll be a lot of it.
 With the line to which the...  With the line to which the glass needed to be trimmed in place, masking tape was applied to prevent accidental damage to the glass (shown here on the bottom side of the glass). This vertical belt sander was used to literally sand away the unwanted section of glass. Using a 220-grit belt, it was a time-consuming process that eats the belts. Note the glass was upside down so Mike could see the mark he was working toward, plus it moved on the rollers easier this way, enabling Mike to work the glass from side to side. |  Once the marked line was reached,...  Once the marked line was reached, Mike removed some of the masking tape and beveled the edges of the glass as shown. This eliminated any rough edges or chips, which could later form weak points where a crack may start. |  The Glass House has hundreds...  The Glass House has hundreds of patterns for stock glass for old cars, housed in old roller cabinets. Here Mike is making a vent window for a '40 Ford using one of these patterns, though the same technique is used for cutting any flat glass, including glass for chopped cars that use flat glass. While we've seen curved glass cut down this way, we've also seen the many failed attempts before the successful final version! Using a glass-cutting tool, with WD-40 as lubricant, the desired shape was first scribed into the surface of the laminated glass. |
 Wide-jawed pliers were then...  Wide-jawed pliers were then used to apply pressure to the glass and break it along the scribeline, similar to cutting a ceramic tile. The trick here is not to tackle too much of a curve at once, but rather a series of straight lines. The edges will be sanded and polished later. |  Gently tapping the glass can...  Gently tapping the glass can help the process; here Mike tapped it from underneath. He then turned the glass over and scribed the other side exactly over the previous lines. |  After following the same steps...  After following the same steps as the first side, denatured alcohol was poured into the split in the glass and then lit on fire to melt the plastic membrane between the two layers of glass. |
 |  Then using the wide-jawed...  Then using the wide-jawed pliers to work the glass, a razor blade was used to cut through the softened plastic layer. |  The Glass House was going...  The Glass House was going to cut the glass for the windshield in my '46 roadster pickup, but before I could even think about cutting the glass, I needed patterns. Here's what a stock windshield rubber looked like when fitted to the chopped surround. Hmm, too big huh? |
 I used a new utility knife...  I used a new utility knife blade to cut the top sections from the center divider part of the rubber, then trimmed that section down to the required length. |  With a section removed from...  With a section removed from the divider between the two molded holes that mount the stainless trim, the small top piece was cut at an angle on each side and tape placed on the bodywork so I could cut the top sections at the same angle. |  Mocked together, it fits perfectly...  Mocked together, it fits perfectly once installed; you can see the three joints in the rubber which were glued together later. |
 With rubber that now fit the...  With rubber that now fit the surround, I could start making a pattern. Heavy paper was taped over the opening with the rubber in place and marked with a pencil. |  This pattern would fall through...  This pattern would fall through the opening though, as it needs to fit inside the rubber. Measuring the depth of the channel at the top, bottom, and outside showed a depth at just over 1/2 inch which meant an extra 1/2 inch needed to be added to these areas. The center bar portion of the channel was a little shallower. |  |
 If you look closely you can...  If you look closely you can see where the pattern fit in the rubber (the center divider had a shallower channel than the rest of the rubber). Mike is marking the slightly tinted glass for cutting. |  Here's how Mike supplied the...  Here's how Mike supplied the glass to me, taped to my patterns, perfectly sized, and with nice beveled edges. Perfect. |  If you've never fitted a windshield...  If you've never fitted a windshield to an older car before (not bonded or glued in) here's how it's done. The rubber is first fitted to the glass, which can be awkward when there are two pieces of glass! |
 Here's how Mike supplied the...  Here's how Mike supplied the glass to me, taped to my patterns, perfectly sized, and with nice beveled edges. Perfect. |  With the windshield laid on...  With the windshield laid on a flat surface, and a blanket to protect the glass, thick string (I actually use the guy rope from an old tent!) is fed into the channel, making sure to overlap the string in the center at the bottom of the windshield. |  With the glass and rubber...  With the glass and rubber laid in the opening, the string is carefully pulled through, enabling the rubber to wrap over the metal lip. Usually the glass is installed from the outside, pulling the string into the car, but the glass on the '46 installs from the inside, which made holding it fun. The garnish molding secures it in place. A second pair of hands is almost essential for this job, as you'll need someone to gently push the glass into place while you pull the string. Work across the bottom of the aperture, then up each side, then across the top, rather than attempting to pull the string from start to finish in one go. Although I didn't do it, many people find that coating the outside edge of the rubber with some dish soap will help it slide over the opening lip and prevent it from tearing. |