Curved Windscreen Glass

[migwell]

Bit late but just so some know, I was asked to pick up a screen for a countach from Pilkington Glass on the Isle of sheppey in Kent a few years back and the guy showed me round, the bucks they use are wood and if you pay to have one offs done then you own the tooling and buck so if others later ask for a screen they have to get it through you, not through pilkington. The process was flat glass laid over the buck run through a conveyor oven and so the glass sinks into the buck and so obtains its shape, then polishing etc is done, cost I can imagine arent cheap as alot of work is involved

[skwdenyer]

530dTPhil said:

Customers supplying CAD data for low volume screen manufacture are few and far between. Over the past three years we have probably produced half a dozen glasses from CAD files. What we normally receive is a wooden buck of the intended shape which is then used to produce bending and checking fixtures for the glass.

CAD data is the best way to go and produces very good results right from the beginning. For the likes of Farbio and Noble with the technology to do it this wasn't a problem, but when someone is rebuilding a one off vehicle or trying to go into very low volume production, it can be a cost too far.

We have had good success with cutting screens down for other applications as long as we have something to aim for. The rear screen for the Talbot Lago Teardrop recreation in http://www.pistonheads.co.uk/gassing/topic.asp?h=0... is something that we supplied and fitted. This was cut from a car windscreen and was millimetre perfect to the aluminium buck supplied.

If you can supply a pattern of what you require, we can usually come up with something very close cut from another glass.

Edited by 530dTPhil on Monday 16th March 07:22

Thank you for the interesting information. However, I hope you don't mind, but it didn't quite answer my questions! Could I have another go?

I know I'm none-too-brief sometimes, so here are the bullet points:

• do you have CAD files for existing windscreens which could be used by a designer, or do they exist somewhere available?
• what are the (approximate, ball-park, order-of-magnitude) costs of cutting-down an existing windscreen?

Thanks!

[530dTPhil]

skwdenyer said:

Thank you for the interesting information. However, I hope you don't mind, but it didn't quite answer my questions! Could I have another go?

I know I'm none-too-brief sometimes, so here are the bullet points:

• do you have CAD files for existing windscreens which could be used by a designer, or do they exist somewhere available?
• what are the (approximate, ball-park, order-of-magnitude) costs of cutting-down an existing windscreen?

Thanks!

We only hold CAD files for the projects that we have handled. The glass manufacturers will hold information for the windscreens that they produce but I am sure would be contractually bound not to disclose this to a third party if it had been supplied by their customer. There isn't a library of CAD data that you could tap into to find what you want, which I think is what you are really looking for.

Cutting down an existing windscreen is a farily inexpensive process, normally a couple of hours labour for cutting and polishing plus the cost of any glasses used in the process.

We would be happy to help or offer practical advice if needed.

[minor5]

You could try http://www.rioglass.com/

we used to buy our laminated single curvature aprox 2mts sq windsreens from them at £28 each

[mrmaggit]

Having seen Phils' lads at work at the BBWF a couple of years ago, if any of you need windscreens fitting, these are the guys to use.

Sorry if this looks like a blatant plug (which it is) but I know talented people when I see them.

And no, I don't get paid by them.

[skwdenyer]

530dTPhil said:

skwdenyer said:

Thank you for the interesting information. However, I hope you don't mind, but it didn't quite answer my questions! Could I have another go?

I know I'm none-too-brief sometimes, so here are the bullet points:

• do you have CAD files for existing windscreens which could be used by a designer, or do they exist somewhere available?
• what are the (approximate, ball-park, order-of-magnitude) costs of cutting-down an existing windscreen?

Thanks!

We only hold CAD files for the projects that we have handled. The glass manufacturers will hold information for the windscreens that they produce but I am sure would be contractually bound not to disclose this to a third party if it had been supplied by their customer. There isn't a library of CAD data that you could tap into to find what you want, which I think is what you are really looking for.

Cutting down an existing windscreen is a farily inexpensive process, normally a couple of hours labour for cutting and polishing plus the cost of any glasses used in the process.

We would be happy to help or offer practical advice if needed.

Thanks again. One last question, if I may: are there any "gotchas" in bonding-in a windscreen which was originally designed for an unbonded application? And can the black-out "coating" (unsure what it is; sorry) that on production cars usually covers the bonding be applied to an existing 'screen, or is it in the laminate layer?

[Davi]

skwdenyer said:

And can the black-out "coating" (unsure what it is; sorry) that on production cars usually covers the bonding be applied to an existing 'screen, or is it in the laminate layer?

I can answer that one - yes it can be applied to existing

[Glassman]

The "blackout" is an obscuration film/coating designed to provide the bonding agent with UV protection. In most cases it is a ceramic frit applied at the factory, but a suitable black 'adhesion promoter' (or glass primer) will work just as well.

[530dTPhil]

Glassman said:

The "blackout" is an obscuration film/coating designed to provide the bonding agent with UV protection. In most cases it is a ceramic frit applied at the factory, but a suitable black 'adhesion promoter' (or glass primer) will work just as well.

What he said.

The preparation, priming and bonding process has to be done properly or the screen may leak, fall out or, at worst, compromise the safety of the vehicle. It's not just a bit of black paint and a tube of silicone, so get it done properly by a professional.

[skwdenyer]

530dTPhil said:

Glassman said:

The "blackout" is an obscuration film/coating designed to provide the bonding agent with UV protection. In most cases it is a ceramic frit applied at the factory, but a suitable black 'adhesion promoter' (or glass primer) will work just as well.

What he said.

The preparation, priming and bonding process has to be done properly or the screen may leak, fall out or, at worst, compromise the safety of the vehicle. It's not just a bit of black paint and a tube of silicone, so get it done properly by a professional.

Thanks. I wouldn't be looking at this as a DIY proposition I have done structural glazing for buildings; designed, specified, and installed, so I know something about priming, preparation, and selection of (in my case one of Dow Corning's) specialist "goo". But clearly the automotive load cases, and especially the dynamic loads, are very different!

At this stage, I'm looking for design info, not a DIY recipe

Re my first question; is there any practical difference between a bonded-in screen and a "rubbered" screen? I appreciate that latter will have larger corner radii than might be ideal for a bonded-in screen (aesthetically, at least), but other than that is there any difference, or can a "rubbered" screen be used in a bonded application?

[530dTPhil]

skwdenyer said:

Re my first question; is there any practical difference between a bonded-in screen and a "rubbered" screen?

In short, no there is no difference. It's just a piece of laminated glass cut polished and bent to a particular shape.

skwdenyer said:

I appreciate that latter will have larger corner radii than might be ideal for a bonded-in screen (aesthetically, at least), but other than that is there any difference, or can a "rubbered" screen be used in a bonded application?

Direct glazing (bonding) was introduced to improve structural strength, reduce weight and allow robots to install the glass on the production line. You can therefore use a piece of glass intended to be rubber glazed in a direct glazed application with appropriate preparation of the glass.

[skwdenyer]

530dTPhil said:

skwdenyer said:

Re my first question; is there any practical difference between a bonded-in screen and a "rubbered" screen?

In short, no there is no difference. It's just a piece of laminated glass cut polished and bent to a particular shape.

skwdenyer said:

I appreciate that latter will have larger corner radii than might be ideal for a bonded-in screen (aesthetically, at least), but other than that is there any difference, or can a "rubbered" screen be used in a bonded application?

Direct glazing (bonding) was introduced to improve structural strength, reduce weight and allow robots to install the glass on the production line. You can therefore use a piece of glass intended to be rubber glazed in a direct glazed application with appropriate preparation of the glass.

Thank you. What I was alluding to, but should have said!, was whether there was a different spec for the glass (thickness, inter-laminar adhesion strength, edge treatment) for the different applications. Clearly, from your reply, there isn't, which makes life a little easier!

However, the next question: is there a standard thickness for 'screens? I know that, from time to time, the likes of Porsche fit "thinner glass" to "lightweight" editions, but how does 'screen thickness vary (if at all)? With my engineer's hat on, I'd say that the more pronounced the curvature of the glass the thinner the glass can be (subject, of course, to specifics of impact resistance to foreign objects), but has the industry just standardised on a single thickness? Or is that one of the questions I'd be asked if I ordered a 'screen?

Thanks again for all of the helpful replies so far!

[530dTPhil]

There is no standard thickness. Clearly it's a balance between weight and fit for purpose. The BMW Mini has one of the thinnest screens around at under 5mm; 2mm glass, .76 PVB interlayer and 2mm glass. At the other end of the scale, many commercials are 7.8 mm thick to provide the necessary strength across the large area of glass so that there is no cracking when the cab flexes.
For most normal applications somewhere between 5 and 6mm is fine but occasionally the manufacturer may recommend something slightly different based on shape or if the customer requests a thickness and specification for which they are not licensed to produce for road use. This can be solar reflective, heated, heavy tints etc.
For example, we supplied a one piece, full size, double curvature, heavily tinted 7.1mm laminated glass roof for an L322 Range Rover. A licence application was necessary to allow the vehcile to be used legally with the roof on UK roads.

[skwdenyer]

530dTPhil said:

There is no standard thickness. Clearly it's a balance between weight and fit for purpose. The BMW Mini has one of the thinnest screens around at under 5mm; 2mm glass, .76 PVB interlayer and 2mm glass. At the other end of the scale, many commercials are 7.8 mm thick to provide the necessary strength across the large area of glass so that there is no cracking when the cab flexes.
For most normal applications somewhere between 5 and 6mm is fine but occasionally the manufacturer may recommend something slightly different based on shape or if the customer requests a thickness and specification for which they are not licensed to produce for road use. This can be solar reflective, heated, heavy tints etc.
For example, we supplied a one piece, full size, double curvature, heavily tinted 7.1mm laminated glass roof for an L322 Range Rover. A licence application was necessary to allow the vehcile to be used legally with the roof on UK roads.

Thank you again; all very interesting stuff. If I have this right, the license that you hold allowing you to (presumably) E-mark your glass is specific to the range of sizes that you've demonstrated that you can produce in an appropriate manner?

Out of interest, how much did that R-R roof weigh? Doesn't sound like it would have done the CofG much good But a fabulous thing to drive under, I'm sure!

[denisb]

Was going to recommend somewhere else, but Phil seems to know what he is on about!

Phil, bad luck, you are now on my favourites, expect a weird request sometime soon.

[530dTPhil]

It's the manufacturing plant that has the licence from BSI to E mark specific thicknesses and combinations of glass. Additional licences can be obtained for other combinations but there is a cost.

We didn't actually weigh the roof but lifting in to place took five people and was a little worrying to say the least! It was produced from CAD data and was a millimetre perfect fit on the vehicle.

[Joe T]

Just like to thank Phil and the guys for the job they have just done on the Costin windscreen, on time and to price quoted.
All from scratch taken from a blank we supplied, and for car we want to display at Detling so little or no margin for error.

Well Done

Crude video of glass here
http://www.youtube.com/watch?v=LezC7Bpmglg&fea...

Cheers

Joe T

[530dTPhil]

Thanks for the vote of confidence.

Just for the record, we don't fit them with tank tape! This was Joe's work to ensure that top part of the frame was bonded to the car in the correct position.

[lkcl]

hi phil,

i'm a software engineer, so i know when's good and when's not good to use computers i saw your post about accepting CAD/CAM files and went "oh dear, a reason to learn how to use mm3d (misfit modelling 3d)" and find some conversion software etc. etc.

so can i ask you: what do you need, to make a windshield? really. tell me, and i can look it up. do you need fileformats in dxf, or stl? i use free software, and it turns out that there's quite a lot of that around.

thanks in advance,

l.

[530dTPhil]

Normal file format is .dxf or .IGS. Most factories will accept either format.