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
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?
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
| 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.
3mm larger than the screw allows 1.5mm in each direction.
Coefficient of Thermal Expansion, 10E-4/°F.
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.
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
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?
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
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.
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).
funny that the manufacturer would specify 3mm without mentioning size or
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.
Nylon screws and washers sound good to me. I used them on Plexiglas
windshields. It didn't occur to me to drill oversize holes.
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
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.
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
On Wed, 05 Nov 2014 19:45:20 -0500, firstname.lastname@example.org 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
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
I've been waiting 40 years to see if I could do a better job than I did
the first time.
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
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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