Cutting curved glass (for a chopped top)

I have been asked by many on here about how i cut curved glass with a sand blaster ,so i thought i would try and save those who are insterested sum $$ if they choose to do it them selves and cut their own windshield .Im affraid i dont have any pics to back this up ,but i do have a witness (my freind and Hamber Scrape) to me cutting the windshield for my 54 chevy car after we chopped it .Its been atleast 5 or 6 years ago ,but my method worked for me the first time .

Okay first off forget what you have been told about cutting windshields by everyone else and how you need a glass cutter ,denatured alky ,etc .There is an easier way to do it ...

Measure the amount of glass to be cut off from the pieces you cut off the windshield posts ,plus the thickness of the blade you used to cut the posts times 2 .Now measure from the top off the windshield down and mark a STRAIGHT line across the glass where you need to cut it but DO NOT mark the corners ,go Straight across the glass ( i will tell you why shortly).The reason i say measure from the top down is because chances are the bottom of the opening is unaltered (or atleast not as much as the top part) after the posts mods from the chop ,so leave that alone and just screw with the top part.After you have determined and drawn a line Straight Across the windshield where you need to cut it mask all the glass below the line on both sides off with several layers of Duct Tape to protect it from the sand.

Now we start on the tricky part ,the cutting.Understand that glass is stupid and is gunna take the path of least resistance every time when it breaks.What you are gunna try and do is control the break of the glass with common sence ,a steady hand ,and patience.Okay you have the glass taped off completely where you dont want it cut and Straight across the windshield on both sides.Find yourself an old tire to lay the glass on and an old blanket or something folded up on top of the tire .Make sure that the part your cutting off is supported as well .Now with about 50-60 psi of air through the blaster and "Sugar Type " blasting sand your ready the cut.Dont use regular blasting sand cuz it has small rocks in it .Try and stay off the tape .What i mean is use the tape edge as a guide ,but dont ride on it.The sand will go through the tape and mess up the glass if you stay directly on it too long.

Make sure you cut from the interior side of the glass .You will see why in a minute .Start on one side of the glass and go back and forth evenly on the taped off line and i mean evenly (as if you were spraying paint on a panel with a paint gun) .Stop often and make sure the glass is not getting too hot.If you cant lay your hand on it from the heat ,its too hot and your about to mess up so take your sweet ass time and go slow.It wont take long and you will start to see the laminate as you cut through the inside piece of glass.This is a good time to grab a beer and let the glass cool off .After it feels cool start again and just let the sand eat the laminate as it goes.Remember keep it even and steady side to side.If you do it right pretty soon you will start to see a dotted line as your getting through the last piece ,keep it steady back and forth .What you are after here is controling the break and this is why i said to cut from the inside out .This way the glass falls away from its self as it breaks and not into its self ,which could cause it to crack .If you keep it even you will see a crack start to run in the dotted line you made and the top portion will just fall off.Do not try and help it break with your hands or anything else.It will run when its ready on its own and just seperate from the other piece.

The hard part is done .Now take the piece you just cut off and use it as a templet to mark the curves on the top corners of the shortened windshield .Peel back the tape on the corners ,retape the curves and cut them the same way as you did the main cut ,taking you sweet ass time .Resist the temptation to get cocky at this point because if you get it too hot cutting the curves it will crack.It will be even easier to build up heat cutting the corners because your working in a small area of the glass ,so take it easy ...

Okay ,its now cut to the size and shape you need.At this point your gunna have sum slightly jaged edges where the "Run" accured in the "Trench".No problem ,use a DA sander with a medium grit and clean the edges up gently and i mean GENTLY.

Pull off the duct tape and your done .BTW , i had an auto glass guy with 50 years exp. tell me it was impossible to cut curved laminated glass with just a sand blaster ,i proved him wrong ...

 

Interesting

 

Great post.....thanks........

Ray

 

Good tech and description of the process!

 

Slick...............thanks.

 

great post my dad & I chopped a 67 eldarodo in the early 80's after letting a glass shop bust 4 windshields ,he sat in the back yard @ 3 nights after work and cut the last windshield the junkyard had, glass guy was surprised when we showed up to have it installed ,told him do not break this one!!! side note my winter project is a chopped 50 caddy that needs a windshield & no junkyard with 5 windshields to get it right ,wish me luck!!

 

i use blasting stencil....you can stand on it for as long as you want and sand will not eat it..makes nice 90* cuts .....sign shops and tomb stone mfg.

 

Yes the stencil is better than duct tape ,but not neccasary .I was broke at the time i did this and was doing good to buy the sand .Besides the rubber gasket will hide the edge of the glass once installed ,but i got the edge pretty sqaure anyway with the DA sander afterwards .If i did one today i would use the stencil though ...

 

Electrical tape will tolerate more blasting than duct tape.

 

Thanks!!

 

Good to know.

 

Had a member pm me about a few things i left out ,so i thought i would add them .As best i remember i kept the blaster tip about 8 or 10 inches from the glass .If you choose to use the tape stop often and make sure your not going through it .The tape will work but you must use several layers near the cut line.I think i put something like 5 or 6 layers on mine and didnt have any trouble .As far as the stencil goes ,it whats pros use to stencil / ingrave tomb stones .I suppose you could get it from a place that sells tombstones .Also wear a face shield when you do this as your gunna get sand in places on you that you didnt think was possilbe ...

 

i havn't tried this but a friend suggested to bury the windshield in sand for support....just leave the waste exposed for the long cut...i guess if it was a $$$ w/s it would be worth it...

 

Nice post Shocker. I cut a w/s for my '56 Caddy convert several years ago after a glass shop assured me they'd cut it without cracking it! Made a nice template to build the posts around though!

I had a siphon feed blaster and a 5hp compresser with a 30 gallon tank, which worked well 'cause I had to stop often to let the compresser keep up, then stop to let it cool down, then let it catch up, then let it cool down... No worries cutting too much and heating the glass!

 

Hey Man, Thanks for the info ,nice tech post !

 

I dont think that method would work.Its a neat idea but IMO the trick is to keep the glass out of a bind until it has a thin spot to let go the length of the piece .I deliberately made the glass crack as it got thin in the "trench" i made with the blaster,i just made it crack where i wanted it to.I think alot of people mess up because they dont sandblast it evenly .If its cut through in sum spots and still halfway attached in others when it starts to "Run", its gunna crack where it wants and probably where you dont want ...

 

Don't mean to step on any toes, but this is what I did:

http://www.jalopyjournal.com/forum/showthread.php?t=296834&highlight=sandblast+windshield

 

No offence taking .Glad to see that i wasnt the only one with the gutts to cut a windshield their self.Funny thing is i had a junk windshield from a 54 to practice on but i didnt.I practiced on the good one i had .I looked into getting someone to cut the windshield for me first and the guy told me it would be $300 and no gaurantee on how many it would take to get a good one .I figured that could get pricey quick ,so i tried it myself ...

 

Glad to help when i can Dennis.Sorry i missed you guys at PNP ,but i had to work.See you at the Thaw ...

 

Actually I wore out my enthusiasm cutting my practice windshield that I ended up using that one. I have a spare one that is better, so once I build the confidence again I will cut that one. Ass you know its nerve wrecking thinking that every pass will be the last one.

And yes the no guarantee sold me on cutting it myself, all i could imagine was giving someone $250 bux and getting back a broken windshield, hell i thought might as well break it my self and keep the $250 to find another one

The worse thing about it was that it did break but not from cutting, from the install, i "leaned" into it too much because I was getting impatient and ""crack"", fuk it, its on the car now and it aint gonna come off.

 

You are right the tape is not necessary, but in the long run it will make things alot easier, this is the tape I used, it was well worth the $$

http://www.tptools.com/Product.aspx?display_id=362

 

Agreed the stencil would make it lots easier and one less thing to have to worry about .If i ever cut another windshield i will be using it ...

 

This place is just a wealth of information. Great thread.

 

excellent! How long does it take about to cut one? I've heard a whole day

 

also how much material did you use?

 

To keep from getting the cut HOT and cracking the glass I have rented a commercial (WATER ) sand blaster for cutting ceramic,worked great.The water and sand is messy but I didn't have to worry about heat cracking it. I have also chopped curved windshields with a Roto Zip using a ceramic bit .Water is a must to keep the heat down.I build a wooden buck that fits snug to the inside of glass ,duct tape it to the glass for support.Practice on a old windshield first and go slow.It takes about 45 minutes to cut.It takes longer to get set up than the cut takes.

 

Also you need to support the part you are cutting off so it won't flex and crack your glass when you get to the end of your cut.

 

It seems like it took about 2 hrs to cut ,and i used about 80 lbs of sand to cut it ...

 

I know you can "water jet cut" flat car glass really easily. I bet the same could be done with curved glass, somehow?

 

I tried having a late model Caprice windshield cut down by water jet, and about 10 seconds into the cut, it cracked. Maybe the guy operating the water jet didn't know what he was doing? Stu