Can the window glass be cut?

[Boy from Oz]

I want to trim about 50mm off the top of the door glass. I assume they are made of toughened glass. What technique can be used?

 

Are there alternative approaches to achieving the same outcome of smaller windows? Thanks.

[Sparky]

Short answer is yes, However, its not easy.

 

It involves lots of water and a grinder or a sand blaster...you cant really just "slice" a chunk of glass off you have to slowly remove material from the edge.... If you have a local HotRod or Kustom shop thats familiar with chopping tops they should be able to give you a quote.

 

Have spares handy

[CamH]

Sorry, but I've never heard of somebody doing this on an S30 before and I was wondering if you could explain to me why you want to have shorter windows.

[Sparky]

If you do something like this you might need to "adjust" the glass:

 

http://www.cardomain.com/id/chevyz240

[Tony D]

Most common method for cutting the laminated safety glass is to mask the window save for the 'cut line' with sheetmetal and heavy tape, then use a sandblaster to 'errode' it out with multiple passes. Masking both sides you alternate side to side and work to the plastic in the middle which should give way fairly easily.

 

If you have a good, precise nozzle, cutting will be fairly straightforward, with a slight hump in the middle, you then 'stone down' the end with a water flooded whetstone.

 

If you alter the sideglass so the upper profile remains unchanged, you can simply cut the bottom of the glass, and once your're through your done, as it's all hidden. Just reattach it to the guide and go from there.

 

For side glass, though, it's almost as easy to make your own polycarbonate windows and be done with it.

 

Windshields use the same procedure, but you won't have to finish it as it's all inside the rubber moulding anyway.

 

The finishing only comes if the part you cut will be on a roll-down portion, and like I said, though the templating is more complex, if you can do your chop without altering the door glass profile up top do that cutting where it won't be seen and your done without any finishing.

 

BTW, if you can get a pnuematic belt sander set up with some black emery strips you can do that finishing pretty quickly. Why pneumatic? Because your flooding it with water while polishing!

 

Hope that made it clearer.

 

Good Luck!

 

with the sandblaster and mask you 'can' cut it off all at once. You don't have to nibble away from the edge. For a 4" chop that would take forever! Even with agressive media!

[RB26powered74zcar]

You can not cut the glass on a Z car, except for the front windshield!!

[Boy from Oz]

I'm doing one of those 250 GTO conversions. I think the 50mm extra roof line really adds to the final appearance. I don't want to go to the sliding glass setup for security and functionality reasons. I guess I could make up a complete replacement (less the 50mm) out of perspex but I'm not sure how that would go for registration.

[Collectindust240Z]

I'm a glass guy. You absolutely CAN NOT cut the side windows or hatch glass. You can cut the windshield though. The windshield is laminated safety glass. The side windows are tempered glass. The glass is heat treated to strengthen it which changes it's molecular orientation. Therefore you cannot cut it. You can grind a little off of it, but rule of thumb is that you can only grind 1/2 the thickness of the glass. So that's about 3/32"... not much. If you don't believe me, you can try, but I guarantee that you will end up with a bunch of little cubes.

[Tony D]

If you do a 'straight chop' on the roof, all you need to do is alter the side channel and leave the glass partially rolled down anyway.

 

I have always made polycarbonate side windows as screwing with trying to cut glass (by whatever means) can be more trouble than it's worth. Maybe the 'little cubes' guy has it, but errosion of the glass done with a sandblaster is particularly gentle in the way it 'cuts', and I have never done it from only one side. I have always cut front and back with double masks.

 

I have broken more windows turning them over and dropping them than shattering them during the sandblasting process. Leaving vicegrips on the masks is not a particularly good idea, either.

 

Think 'spotblaster with rubber nozzle' for the 'cutting' implement.

[Careless]

I saw someone once cut a hole in some safety glass for a back-ho at my uncles repair shop.

 

What he did was use a special cutting tool to make a circular shaped cut, and slowly turned it into a rounded rectangle so as to not have to "chip" pieces off and create stress points.

 

He did that by using a rotary tool of some sort. and he did a damn good job too. I do remember him fastening something onto the window, though I believe it was soggy masonite, to allow it to conform to the contour of the window. It also had bricks taped to the edges to allow the weight of the brick to keep the soggy masonite held down, as well as duct tape wrapped around it too.

 

This was with the window "unbolted" from the unit, and surprisingly enough... one of the only back-hos i remember seeing with any rounded panes in his shop.

[CRAVED]

i remember seeing on a hot rod show from the US - will try to remember which one - where a window was cut down by scoring the glass, then covering the score with alcohol then lighting it, then section was then wiggled up and down until it parted from the main area of the glass..

 

cant tell what type of glass it was just thought it might jog someone memory

[RB26powered74zcar]

You can not cut the glass on a Z car, except for the front windshield!!

 

 

ONCE AGAIN.....

 

I've been in the glass business since 1974.

[Boy from Oz]

Thanks for all the responses. It seems pretty clear from the replies, and from other web research, that toughened/tempered glass cannot be cut to the degree I require. The good news for me is that acrylic and polycarbonate windows (not windscreens) can be used in pre-1994 vehicles in this country.

 

Can anyone advise (a) what is the difference between acrylic and polycarbonate and ( which is preferable?

 

One web comment states: Acrylic is more brittle and is harder than polycarbonate. As a result, Acrylic resists scratches better and needs to be handled more carefully when cutting and drilling. Polycarbonate is much more impact resistant (will absorb more kinetic energy before shattering). One of the results of this physical property is polycarbonate is less prone to cracking when being machined.

[Collectindust240Z]

And I've been a glazier since 1996. Oh, J. Soiluea, I was born in 1974!!! The safety glass you other guys saw being cut was laminated safety glass. Just two pieces of regular glass held together by a PVB inner layer. Yeah, I use denatured alcohol and fire to cut the inner layer. Really freaks out the customers! I would strongly recommend polycarbonate (lexan) over acrylic (plexiglass). Acrylic WILL shatter upon impact and you will never get a worse cut. The stuff could potentially kill you in an accident. Strong and sharp, not a good combination.

[Boy from Oz]

... Acrylic WILL shatter upon impact and you will never get a worse cut. The stuff could potentially kill you in an accident. Strong and sharp, not a good combination.

 

Thanks for the clearly important advice - polycarbonate is the way I will to go.

[CRAVED]

Thanks for all the responses. It seems pretty clear from the replies, and from other web research, that toughened/tempered glass cannot be cut to the degree I require. The good news for me is that acrylic and polycarbonate windows (not windscreens) can be used in pre-1994 vehicles in this country.

 

Now that is something i am shocked but pleased to hear... leaves so many options available.