What does this mean , on my Lexan?

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The instructions written in graphics only, no words, on the backing sheet imply that I must make the hole through my Lexan sheet 3mm bigger than the screw I'm putting through the hole.
Is that possible?
Why? Maybe the reason doesn't apply to my situation.
The graphic shows a screw with arrows pointed at the threaded part from both sides, and to the left of that a circle with a diagonal slash through it.
Immediately to the right of that, it has
Circlle/with/slash + 3 mm and then a drill bit with arrows pointing from both sides, towards the bit. So the second part is Circle +3 mm Bit.
Does that mean what I think it does?
Thanks
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On Wednesday, November 5, 2014 12:05:08 PM UTC-6, micky wrote:

Are you going to drill any holes in it...or are you on another anal retentive binge for more responses?
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In

GD.......didn't you win enough last nite : ) You SOBs ain't never happy..............but watchin bammy dancin and the look of disgust on his face right now brings a big grin on my face<BEG>
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It's in the first paragraph, that I'm supposed to drill the hole 3mm bigger than the screw.

The graphic showed a screw so I used the word screw, but it's really going to be a pop rivet There will be under the head of the rivet a flat washer, then the lexan, then a part of a piece of vinyl**, then another washer, and then the compressed end of the pop rivet.
I would think the metal washer between the vinyl and the squished end would keep the rivet expansion from reaching further up (above the washer) to the rivet tube where it goes through the Lexan. But maybe I should make the hole bigger by 1mm, 2mm, the full 3?
**that goes around three sides of the Lexan***. This vinyl was originally fused to the rear window of my convertible. The window broke while I was lowering the top. In large part because it was the first year Toyota made a convertible and the window was too big for the space it was intended to go it. (It had already ripped off a plastic groove behind the back seat meant to hold the boot cover, that it used to catch on and eventually ripped off. . A 2001 car I've looked at in a used car lot also has its groove ripped off.
***The fourth side, the top, will require a different setup, because the tension on the fabric makes pulling it back to the orignal position impossible. It came apart there two years ago, and I patched it with a little extra fabric from an old vinyl top and some VHB adhesive tape, but maybe that was starting to loosen and that allowed the window to break, which was strange since the glass had gotten beyond, lower than, where that plastic groove had been, and there was nothing to catch on below that.

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So it does mean I should make the hole larger than the screw, or pop rivet??

Gratitude.
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On Wednesday, November 5, 2014 12:05:08 PM UTC-6, micky wrote:
...next you will be saying this convertible spends the Winter outside! Good God!
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| The instructions written in graphics only, no words, on the backing | sheet imply that I must make the hole through my Lexan sheet 3mm bigger | than the screw I'm putting through the hole. | | Is that possible? | | Why? Maybe the reason doesn't apply to my situation.
It applies. Holes in plastic should always be bigger because the expansion/contraction can make the sheet buckle otherwise. By drilling larger holes you allow the sheet some space. I usually use small washers so that I can make bigger holes. Finish washers will also work if it needs to look nice.
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On 11/5/14, 5:48 PM, Mayayana wrote:

sure washers are used.
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On 11/5/2014 7:55 PM, J Burns wrote:

3mm larger than the screw allows 1.5mm in each direction. Coefficient of Thermal Expansion, 10E-4/°F.
Found this Thermal expansion due to its approximately 5 times greater rate of expansion compared to glass we recommend allowances be made both in the framing or screwing down. The rate is about 2.1 mm at 3 m per 10°C.
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wrote:

change etc without putting stress on the hole. It is generally necessary unless, possibly, you are bolting to lexan of the same composition and thickness.
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wrote:

It was built as a coupe on the Toyota assembly line, and converted to a soft-top by American Sun Roof Corporation for Toyota. (The car was built in Cambridge Ontario and the conversion was done by ASC in Kitchener Ontario)
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micky posted for all of us...

It means exactly what you you think it means; it has to be 3mm larger. It may be because of expansion / contraction or stress from drilling. Are you using this for a window in a car top or do I have a memory fart?
--
Tekkie

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That's right. I started this months ago, but got interrupted by the right front and rear wheel damage, etc, the washer changing in the bathtub that required getting new stems, and a bunch of other things.
My answer to Clare, when I write it, should say why this has taken so long.

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micky;3304935 Wrote: >

I agree with both Mayayana and Clare Snyder here. Plastics have the largest coefficient of thermal expansion. The lowest coefficient is with ceramic materials like brick, glass, concrete, mortar at 5 to 12 parts per million per degree Celsius. Then metals at from about 12 to 40 parts per million per degree C. And finally plastics, which for PVC is about 200 ppm/deg. C. if memory serves.
But, you should keep in mind that the 3 mm is for the largest dimension of the sheet of plastic. (4'X8'?) If you're only using 1/4 of a sheet, you may only need 1/4 of that 3 mm to allow for thermal expansion and contraction. But, since you're using rivets which won't allow for any sliding of the plastic as it expands or contracts, you need to allow some way for the plastic to move or it will buckle when it expands. You may want to use nylon screws and nuts instead of rivets. Most places that specialize in fasteners will be able to order nylon screws, nuts and washers for you. That way you can fasten the plastic down, but still have some slippage of the plastic between the nylon washers to allow for thermal expansion and contraction.
--
nestork


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On 11/6/14, 1:34 AM, nestork wrote:

I hadn't thought about that. I looked it up. It's 70 ppm / C for Lexan. Glass-filled Lexan has a much lower coefficient (21 ppm/C). <http://boedeker.com/polyc_p.htm

funny that the manufacturer would specify 3mm without mentioning size or temperature range.
This page talks about Plexiglas, whose coefficient is a little bigger than Lexan, and which is affected by humidity. It says to avoid inflexible fasteners such as bolts, and adhesives should allow movement. <http://www.eplastics.com/Plastic/Plastics_Library/Coefficients-of-Thermal-Expansions-of-Plexiglass Nylon screws and washers sound good to me. I used them on Plexiglas windshields. It didn't occur to me to drill oversize holes.
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On Thu, 6 Nov 2014 07:34:50 +0100, nestork

Very good point.
But, since you're using rivets which won't allow for any

Well, it will only be attached to the rear "curtain" that used to hold the glass, to a 7/8" strip of vinyl that used to adhere to the glass, and the rest of the curtain is canvas, I think, or maybe vinyl but certainly bendable like cloth. .
Plus the lexan does bend a little. And indeed so does the glass from a factory window (Somehow they make glass that bends a bit, but straigtens out I'm sure when the top is lowered.) (Thursday I will see if I can get 1/8" instead of 3/16". I thought I needed 3/16" for the strength, but now I think it's stronger than it needs to be, if it fits.)

What would keep the plastic nuts from gradually falling off the screws?
And wouldnt' the diameter of the screws be bigger than the pop rivets, that IIRC are 1/8"? Diameter is important, because the original glass only overlapped the curtain by 7/8" If I make the new window taller than the old, it won't fit in the well, and I can't make it more than an inch wider because other things are in the way.
The backing sheet on the lexan also said holes had to be at least 2 cm. from the edge, which is over 3/4", which if I used exactly the same dimensions for the lexan as the glass was, would put the center of the hole in the vinyl just 1/8" from the edge of the vinyl. That won't work, so I made the lexan larger on the sides and the sides of the bottom (The bottom is curved down in the middle, but this still made it less able to fit inthe well, so I cut another 3/16" off the top of the plastic.
In other words, the farther from the edge of the plastic I put the holes, the closer it is to the edge of the vinyl. And vice versa. So it helps if the diameter of the pop rivets or plastic screws is small.

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wrote:

Ah, okay.

I was going to use washers anyhow, but didn't plan to make the holes bigger than necessary. I guess I have to do that.

Good idea, but in this case, they won't be visible. Of course that makes it harder to put them in on the sides, because I have to pull back the top. On t he bottom that's easy, and at the top an inch or two more of fabric will have to be added. I have two old black tops, and I used a piece of one two years ago. It's still attached by that VHB adhesive tape.
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On Wed, 05 Nov 2014 19:45:20 -0500, snipped-for-privacy@snyder.on.ca wrote:

This is a lesson I guess to always give loads of details in the first post, but I was only thinking, "What do the symbols mean?"
The lexan is free to move plenty, because it's only going to be riveted to the remains of the rear window curtain. after I carefully removed all the glass still fused with the black vinyl strip that runs around the glass.
But now I think the pop rivets will get bigger when squeezed, even a little bit below the metal washer, and I have to make the holes bigger to make room for that.
I remember now when I bought the pop riveter. I think it was 40 years ago, when I had put a vinyl rear window, then parked for 2 months in the summer facing north (with my rear window facing south) and it turned too cloudy to see through it. So I cut piece of plexiglass into a slightly tapered trapezoid, and pop riveted that the vinyl window. I must have cut the hole first. That worked pretty well except a corner of the plexiglass broke off after a year. That's why I wanted lexan this time.
I've been waiting 40 years to see if I could do a better job than I did the first time.
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On Wed, 05 Nov 2014 19:49:46 -0500, snipped-for-privacy@snyder.on.ca wrote:

Yes, I knew that.

And that. So was my '84 LeBaron, but I think by '88 they were built as convetibles. Certainly by '95.

That I didnt' know.

Or that. I guess it takes a Canadian to know all that Canadian stuff.
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wrote:

Thanks for all your help.
Unrelated to question of hole size, now I'm thinking I should have gotten 1/8" lexan instead of 3/16". It would be lighter, easier to attach, less weight on each hole (so the rivet or whatever wouldnt' rip out of the vinyl and I also wouldn't have to make as many attachment points), and since it's lexan, still very unlikely to break.
And it might flex more as the window is supposed to do when the top is up. (It's supposed to bend in the middle horizontally.)
I will make the holes bigger than I had planned, accordign to your advice in this thread.
Do you think 1/8" is strong enough to not break at the holes.
It's a good store, but they don't stock everything, and I've waited too long to order something,
So, they also make Lexan with an anti-UV finish, so it won't turn yellow. It only has to last 3 1/2 more years. Do you think the regular stuff will stay clear, not yellow, for most of 3.5 years even without the aniti-UV.
They also make Lexan with a mar-resistant finish since it lexan scratches more easily than acryllic**, though I don't know if one can get both at the same time.
**I had acryllic the first time and it broke at a corner, at a rivet, so I think I need the strength of lexan. OTOH, that was 40 years ago. Maybe they've improved acryllic's non-breaking since then.
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