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Riveted windscreens


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#1 Charlieman

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Posted 16 March 2020 - 01:20

They look very sexy. What are the components and how are they put together? What are the options for a flexible screen, managing vibration characteristics for screen and fasteners? Alternatives for an open roof car?



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#2 AJB

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Posted 18 March 2020 - 06:55

Can you give us an example?

#3 Charlieman

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Posted 20 March 2020 - 01:13

I was thinking of cars like the Maserati 150S in this fine photo from cooper997:

 

https://forums.autos...urne/?p=9031219

 

I asked questions about the components and materials, so I'll describe it as a mouldable plastic screen fixed to the body by shiny fasteners.



#4 Odseybod

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Posted 20 March 2020 - 10:06

A pity the bloke who owned the mooring where my boat lives is no longer with us, as he could have answered the question in detail. As well as boaty things, he had a sideline of making perspex windscreens for all sorts of vehicles ancient and modern (together with another line in recreating vinyl roofs for Dolly Sprints, Capris, Silver Shadows, etc). Very enterprising.  He said one of the most complicated (and expensive) screens he was commissioned to do was also one of the smallest, for a Williams F1 car (memory says an FW07, but probably wrong). An unexplored art-form.



#5 Bonde

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Posted 21 March 2020 - 00:34

Charlieman,

 

You can actually rivet acrylic ('Plexiglas' or 'Perspex') with soft blind or soft solid aluminium rivets (use washers under the upset head), or use nice shiny button-head screws and Nyloc nuts. It's a good idea to back-up the drill on the backside of the work with a sacrificial wooden block to prevent cracking the acrylic when the drill bit pops through. With polycarbonate ('Lexan') it's easier - it doesn't crack as readily as acrylic.

 

(I don't know if the above was of any use to you... :well: )



#6 Wirra

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Posted 21 March 2020 - 03:55

If you want them to be removable use what are variously called;

Blind nuts

Sex nuts and bolts, or

Binding post  - as in the brass fasteners use in large document folder.

https://apexfastener...teners/sex-bolt

 

I used them to attach grips to the sliding Perspex windows on my car.

Window-slide-grips-1s.jpg


Edited by Wirra, 21 March 2020 - 04:04.


#7 AJB

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Posted 21 March 2020 - 08:46

A few years ago I was chatting to the owner of a historic racer with a moulded screen. The manufacturer had a sideline in moulding plastic card slots for ATMs. Unfortunately, he wasn't making them for the banks, and wasn't going to be making any more windscreens for 3 years.

#8 brucemoxon

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Posted 21 March 2020 - 10:25

Also, I've heard to drill perspex, your bit must be blunt - otherwise it's more likely to crack.

 

No idea if this helps.

 

 

 

BRM



#9 10kDA

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Posted 21 March 2020 - 14:31

Rivets introduce too many fussy problems if you have to repair or replace the screen or whatever it's mounted to. It's better to use screws and nuts right from the start. The "frame" if you want to call it that, meaning the opaque part of the vehicle to which the transparency is mounted, can be whatever the body structure is made of, or something else entirely - aluminum sheet, laid-up fiberglass, whatever. Lexan (polycarbonate) is easy to work with if the shape is a simple flat-wrapped curve. However lexan is sensitive to hydrocarbons and it can degrade in the presence of most of the motorsports liquids prone to leak or splash. Plexiglass (perspex) is an acrylic with good workable properties, a high degreee of resilience and durability, and is cheaper. Plexiglass is easy to heat-form and free-form blow (or vacuum-form) into a desired shape. Lexan can be blown but its workable temperature range is very narrow, going from pliable to blistered within a small window. Unless you want to buy, build, and maintain a tightly controlled and calibrated oven, it's probably not worth the trouble making something from lexan when it can be made of plexiglass. But you never know what a designer may randomly call out. Plexiglass begins to get flexy around 250F and depending on thickness will become completely formable around 275F and the working temp can go up to 350F or so as I recall. If you blow a bubble shape in plexiglass and you don't like it for whatever rewason, you can release the air pressure and maintain the temp and the plexiglass will return to sheet form with only slight distortion - so it's possible to salvage something from a mistake. I never tried that with lexan but I doubt with all my heart and soul it would work. Plexiglass is best drilled with a shallow or no angle to the drill point, or you can just heat a pin, bolt, or wire coat hanger with a propane torch and poke it through, usually creating a slight ridge at the edge of the hole that greatly increases resistance to cracking. A helpful trick is to make the hole in the plexiglass large enough so a small piece of flexible plastic tubing with i.d. about the size of the screw diameter and long enough to slightly extend beyond the max thickness of plexi & frame will cause the tubing to expand enough to contact the inside edge of the holes in the plexiglass as the screws are tightened - therefore, shock mounting. When drilling or otherwise working with plexiglass, keep some acetone on hand to flow into any cracks. It's as if the crack never happened, but you will have to buff any resulting surface irregularity if you're after perfection. There's more to it than this, of course, but it's not a mystery. All this stuff is how I've worked with plexiglass on homebuilt aircraft and gliders for 50 years or so, and on the windscreens of my race bikes. It was well-established before I picked it up. I believe these practices have carried over to race cars as well.


Edited by 10kDA, 21 March 2020 - 16:11.


#10 Bloggsworth

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Posted 21 March 2020 - 19:18

You need a "slow" drill for acrylic or the material climbs up the drill which leads to cracking.

 

DSLP.jpg



#11 Charlieman

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Posted 26 March 2020 - 13:48

Thanks all for the info. It was just a casual query about a small but potentially expensive part of racing cars...

 

I recall a mate's brother making replacement perspex side screens for his car. He cut out the first screen and it was time to drill a hole, followed by the ominous click when the sheet cracked. For the second attempt, he bought bigger sheets and drilled the holes first.