49 to 52 Chevy chop: taper windshield sides?

I'm preparing to chop my 50 Chevy this winter (my first chop). I plan to get the windshield cut down to size first, and make the metal fit the gl*** during the chop based on sage advice I've gathered here over the last dozen years.

I'll be using a 50 Olds one piece windscreen. I know the A-pillar angle will tilt in a little when the roof comes down, so should I have my gl*** guy taper the sides of the gl*** too when he's cutting it down? I could probably measure it out and calculate the new post angle, but I haven't read much about this from those who have lived it.

Experienced gl*** guys and Chevy roof choppers, what do you think? Should the gl*** sides be altered, or is the change in A-pillar angle not enough to worry about, and the rubber around the gl*** will accommodate the slight change?

I appreciate your advice. I may be over thinking this, but I'm trying to anticipate as many of the small problems as I can to make this go well.

Cheers.




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Do the metalwork first. Gl*** last.

 

I did metal work first on my 49 Fleetline.

 

Ok, so maybe the "gl*** first" advice is more suited to wrap around windscreens?

Thanks for the advice so far. Keep it coming guys, anybody disagree?


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I never heard of doing the gl*** first on any chop.

 

One such example: posts 8&9 in this thread;
http://www.jalopyjournal.com/forum/index.php?threads/Question-for-top-choppers.788561/

And I swear I've read it several other times from other members who I trust over the years, but can't find any other examples to save my life at the moment.

I dunno, the idea of "shape the flexible metal to fit the rigid gl***" seemed reasonable to me. Just because it's not done that way all the time doesn't mean it's invalid. But if I'm off base with this idea, tell me. I'm just looking for informed opinions to help make up for my own inexperience. So far, you guys are changing my mind, and I'm grateful for the input.




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Cut the gl*** first. Do you know how many projects go unfinished or use plexigl*** because they cant get the gl*** cut to fit.

 

See, now that's what I'm talking about. It seems to make sense, but HOW should I get the gl*** cut? Just reduce the vertical size by the amount I need, or do I need to reshape the sides too? I guess that's my real question.




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Greetings! From all the top-chop information I've acquired over the years, the answer is yes, if you "tilt" the posts, you will also have to trim the sides of the windshield. Best of luck with your project

 

That's what I figured, thanks for the input.

If anybody has done this (BEFORE cutting the roof) and has some tips on how to measure and determine the new A-pillar angle, I'm all ears.

I figure I could calculate it with a protractor, a level and some trigonometry, but if there is a real world tested method, lay it on me.

Great advice guys, I appreciate it.


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Hi Jeff ... Have just had the gl*** cut for my 49 Caddy....I did a 4 1/2" chop... I have used a 70s VW Kombie screen..this would be the same curve required probally for you car....the Caddy is a split screen so the VW screen had to cut in half and the 2 screens cut....the shape of the VW screen and top edge is the same as the Caddy screen so I only had to get the bottom of the VW screen cut off ...about 8" right across...got this done at my local gl*** cutter for $50.. new VW screen $125 so for $175 I have my 2 new screens.....I would do the chop first and then get your gl*** cut....Then once you have finished your metal work buy a new rubber windscreen seal...cut it to suit the chop..make a 3 ply template to fit the opening for the gl*** cutter..this is what I always do when doing a top chop.....

 

I've done quite a few chop, mostly 50's stuff, not the easy 30's cars. I usually cut the top, then do the gl***. Unless you know that the shape you are making as you cut the top of the gl*** off, will be differetn from what it was originally.
On a mildly curved 50-54 Chevy,that's not the case. Even my wraparound gl*** 55 Olds, didn't need reshaping of the metal up top, just spread the roof a bit to meet up with the A pillars. 58 and up cars you'd be doing some reshaping.
That said, I am not a huge fan of angling the windshields back on most cars. Changes too mauch stuff you have to correct later. ANd on 50's cars, it doesn't necessarilly look better.
My advice, standard issue stuff: cut the top, do NOT change the A pillats, either inward, or back. Spread the roof to fit, and then when you cut the gl***, it will pop right in, as long as you don't do a rediculous chop on it.

 

In my experience, you'll be doing both.
Get the chop about where you want it, cut gl***, m***age roof line to match gl***, trim gl*** to fit, fine tune

 

I cut the roof first on them all. 50 Chevy is pretty straight forward. The gl*** cutter who doesn't break the gl*** is where the fun begins

 

I'm going to cut gl*** first on my 54.. Once the gl*** is cut you can make patterns and make metal fit.. Easier to cut, bend, shrink, stretch and weld metal than it is to bend shrink or stretch gl*** and forget trying to weld gl***!! Just my 2cents


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You need to do both. First cut the top but just tack weld it, get everything lookin' like you want then have the windshield cut. On the early Chevys the A posts will lean in some but do not lean them back or the windshield will not fit. Its alot easier to move the top around if its not welded solid. I have done several this way and it is definitely the easiest way to get the best possible fit on the windshield.

 

Thanks guys.

Just to be clear, I wont lay the windshield back at all. I only meant changing the side-to-side angle of the A-pillars.

You know the drill: the roof comes down and forward, relief cuts in the 4 corners of the frame, the top "stubs" of the A pillars get pushed out a hair, the bottoms get pushed in a hair, and they all line up nice and straight again.


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Hi Jeff ..... Have found a 50 Chevy that was on HAMB earlier this year shows chop and how to cut you gl***
http://www.jalopyjournal.com/forum/...aminated-gl***-the-cheap-and-easy-way.865394/
http://www.jalopyjournal.com/forum/threads/morgans-51-chev-sedan-build-up-australia.634268/page-13

Here are a couple of pics of my chop and gl***..this is a 49 Caddy would be very much the same just a little wider

 

I did gl*** last on mine. I cut my own gl*** using a router and a diamond bit for cutting tile. It works. There are some you tube videos on it.
http://www.jalopyjournal.com/forum/threads/52-chevy-chop.496354/

 

You know the drill: the roof comes down and forward, relief cuts in the 4 corners of the frame, the top "stubs" of the A pillars get pushed out a hair, the bottoms get pushed in a hair, and they all line up nice and straight again.


That works with 30's stuff, but when you get to the 50's, as I said, things change!
It's pretty easy to measure how much "tumblehome" or narrowing of the roof as it goes up, you car has. Or, more importantly, how much difference there will be in the width, when you remove however many inches you are planning to chop it.
I HIGHLY recommend doing this, as the lower you go, the more width difference you have to contend with \, and it can become a huge amount for work. Sometimes just a difference of one inch can change it from a "not too bad" job, to a tremendous amount of work.
IIRC, when I chopped my Olds, I only took out 2 1/4 in. The top of the windshield had to be spread about 3/4 in. I just made some cuts about a foot long on each side, just before the curvature became too much, and spread out each side 3/8" with a porta power to make up the difference.
Another inch and it would have been very difficult to get the gl*** to fit, and metalowrk would have been increased a lot!

 

There is more than one way to skin a cat

http://www.jalopyjournal.com/forum/threads/just-another-way-to-cut-down-a-windshield.278603/

 

TUMBLEHOME! Thank you! I was racking my brain to remember the actual word for this and was coming up empty.

So last night I decided to do some rough and dirty templating to see how it's all going to fall together. I layed a couple layers of masking tape over the top of the windshield and traced the stock window opening onto the tape.


Then I peeled it off and moved it down the gl*** by 3 1/2" to approximate the three vertical inch chop I'm planning. I used the center bar as a reference to make sure the tape was aligned correctly, and some dividers to check that the traced line was now 3 1/2" down from the top of the gl*** all the way across.


I added more tape to the top and bottom gaps and traced the window opening again. Now I've got a top line that represents the shape of the stock gl***, and the bottom line that shows the position of the windshield frame after the chop.


Taking a close look at the straight part of the A-pillar, I can see that the *ahem* tumblehome of the roof will result in
a misalignment of about 1/4" on the pillar (and, of course, the same on the p***enger side pillar too).


None of this is surprising, but the 1/4" is the number I was trying to guess at or calculate before. Now I know. I can correct for that with relief cuts in the top and bottom corners of the frame, and some tweaking of the pillar stubs. Of the dozen or so examples of 49-52 chops I've studied over the past year, all of them adjusted the pillar angles to correct for the misalignment, none of them spread the roof. All of them seemed to work out great and I don't remember finding any examples where the gl*** just wouldn't fit afterwards. I think the angles and shapes in play here are just not very severe with the mild/moderate chop I'm after. I can see getting into trouble if you hammer it way too much, but that's not my plan.

So, this is where I'm at right now. I'm going to do the gl*** after the chop, not before. Getting it done before would require me to guess ahead of time all the finished radii and angles of all four corners, and bet about a grand's worth of gl*** on my guess work. I'll be doing the chop work about 220 miles away from my gl*** guy, so just running it over for a couple tweaks and trims is not an option. We'll do the gl*** once the frame shape is locked in.

Once I get my stock gl*** out, I will make a fibergl*** copy of it to use as a dummy piece for test fitting and templating the final gl***. I don't mind to risk a few bucks worth of fibergl*** that I can remake if I cut it wrong the first time.

Thanks everyone who offered up some advice and opinions. This helped me answer some questions and improve my plan. My Alliance membership just paid for itself again.

 

That all sounds good, but I cut a '50 Chevy a few years ago about the same amount (3" at the pillars, about 2 3/4" vertical drop) and they had a trusted gl*** guy nearby so we cut the top first. They DID have to "adjust" the width of the windshield to make it all fit. And that was even after I did make relief cuts on both sides of the roof to spread out the tops of the posts a bit to ease alignment.
On my '53 I cut the entire roof skin off, made the frame fit the windshield I'd had cut first (for a measly 2" chop) and kept the windshield posts at the factory angle. This required adding about a 1/2 inch of metal to the center of the windshield surround at the top. The further down you go the bigger that gap is going to be.
So either you're going to have to have the top of the windshield narrowed to the same dimension it currently is (no math involved, the top of the roof stays the same so the new top of the windshield needs to be the same width as the current top of the windshield) OR you're going to have to widen the roof as you bring it down. Gl*** doesn't bend, and there's not enough slop in the fit to fudge 1/4" on each side. Sorry, but it's true.
Whether you but the car or the gl*** first is up to you (I've done both), but either way you need to take that width issue into account. With your gl*** guy so far away I'd have the gl*** cut first.

 

I agree with atomic. You don't know how much 1/2 in is, until you try to squeeze gl*** into something 1/2 in too small!
And don't do any cutting along the bottom of the A pillars! Again, you aren't changing the bottom of the gl***, so don't change where it fits!
This is how I did my Olds, way back in 83 or so. Easy to do, you don't need a porta power, even a small hydraulic jack, or screwjack will work. I cut back a bit over a foot to correct it 3/4". You should need a bit less, but it's only we lding, what's another few inches? Weld the posts, bring up the center flap, make some long triangular patches, and weld them in.

 

Sorry, I must not have been clear before. I understand that the new top edge of the cut-down gl*** will need to be narrowed to fit the top of the frame. I never intended to "fudge" a quarter inch of gl*** on each side. That would clearly never work. I think we're all saying the same thing here, but with different words.

Now that I've seen it with my dumb tape template, I can better visualize how the shape of the frame will change, and what needs to be done to the gl*** so it will fit the new frame. I think I'm good now.

Thanks everyone for the advice. Much appreciated.




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Yes, I just went back and re-read my earlier post, and I didn't really explain what I was thinking very well. Sorry for the confusion. I appreciate your guys' efforts to set me straight. It's all good information.

Cheers.




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Now I know why there are good chops and bad chops.....

 

Jeff, I'm glad we were all just saying the same thing with different words. For what it's worth, that tape trick you did was brilliant. I tried something similar with poster board but couldn't keep it aligned.
Post photos once you start cutting and welding!
And one last piece of advice if you can take any more: installing the gl*** isn't all that easy either. I got my windshield in "just good enough" myself, showed it to one gl*** "expert" who said you can't expect better fit on a chopped car (!), then took it to another shop who got it in perfectly in less than an hour.


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Always open to more advice, thanks!

I think I will leave the final gl*** install to the guy who is cutting it for me. He'll warranty the work too. He's done many of the chopped cars here in town and area.

Based on the good advice here, I've decided NOT to lean the A pillars in, and to spread the roof instead. I think that will also save a few headaches inside the doors by keeping the window frames in their stock angles too.

Now about those B pillars, should I split the roof far enough back to spread out the B pillars as needed too? I'm thinking this makes sense, but that's a long-*** weld down the low crown roof skin. Any more advice on that?

Thanks guys.




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Perhaps on a wrappeed windscrren I.d be tempted to split the roof. But on a standard screen like yours you will easily pull the pillars in or out. Same goes for B pillar.