FEELER: Hardtop Lexan back window
 

1st off I didn't know if I should start this in this section or like the general section cause at the moment there is NO GROUP BUY YET. This is just a feeler to see if there is enough interest to me to try and see if I could start a group buy. AGAIN, THIS NOT A GROUP BUY YET.

Ok so I bought a hardtop off of a local guy for $150. The catch is that the back window is shattered. So after calling around to a couple places about getting a glass window replaced I’m not willing to spend roughly $400-500$ on it. I’ve decided I’m going to put a Lexan window in place of the glass.

The benefits of a Lexan window are that it’s much lighter, and much safer than glass. ¼” thick Lexan can stop a brick being throw at it and have it just bounce off. And ½” thick Lexan can stop a .38 from a short barrel revolver. Also Lexan doesn’t shatter.

YouTube - Lexan Vs. 3m
In the video you’ll see a guy hitting a Lexan window with a sledgehammer for 5minutes and all it does is dent. It’s comparing the Lexan window to 3m’s safety film.

So I’m going to be calling around to several places Monday to see if anyone would make me a window for my top and usually making multiple items of something custom can drop the price. So I’m seeing if there’s interest in it for me to even ask wherever I decide to have them make me one.

As for installing the window the regular window replacement man can do it for you for around 80$ and they will come to your house.

Feel free to discuss amongst yourselves and I’ll keep everything updated on here with what’s going on.

You have to figure out scratch resistance on the lexan too. Does it come with a coating? A Lot of the drag racers here that use it for a couple years have to replace it to use the window it gets so opaque. Everything digs in, but on the back glass maybe it would be ok?

It's actually really easy to build your own Lexan rear window. There's no need to make it complicated or expensive.

Targa Miata

Keith, I saw that but its not really a write up on how to do it. they were just showing they did it and gave 3 general postings with 3 very general pictures on how they did it. EDIT: also in their posts they said if you dont have a band saw, jigsaw, or reciprocating saw you can have a plastic shop cut it for you.

But you're right it shouldn't be very expensive, and it could possibly be cheaper to get several of them professionally made. Also who knows maybe the company would become a legitimate supplier of the window, and that would be great for the community to have another option. This would also help lower the price that most miata places charge for the glass window because there is now an alternative to it.

To clarify in the OP the 80$ mentioned was not a price for the window shipped or anything like that. It was a speculation on how much a professional auto window repair shop may charge to just install the Lexan window once you have it. I have to wait till monday till the places that i'm going to call are open.

"They" is me. I wrote that. What else do you need?

1. make template
2. cut out Lexan
3. rivet it on

Knowledge of how to trace shapes, cut plastic and install rivets is assumed. If you can't manage #2, then simply take an accurate template to a plastic shop and say "make me this".

Total cost depends on the price of polycarbonate (the generic name for Lexan) in your area, but it'll be in the $50 range. Possibly more if you want it cut to your template. Add in $3.99 for a box of rivets and there's your cost.

If you want a window that a glass shop can install for you, you'll have to have it bent to shape instead of using the rivets to hold it in shape. By that point, I suspect that you're not going to want to pay for it anymore if you're not doing the work yourself.

I've done a number of Lexan windows on cars. It's really quite simple, there's no reason to try to make it difficult.

i want one

keith, if its so easy and cheap why don't "you" (FM) sell them? seems pretty obvious that if its cheap and easy to do and there is a demand for it, why wouldn't you sell it? gotta be a reason right?

and urban-i'll keep you updated with whats going on.

Shipping on the piece of polycarbonate that size will be more than the cost of the material itself.

Im planning on making one for my car, If I found an affordable precut one Id buy it.

i doubt that it would cost over 50$ to ship it. even if it did, its not like we can go order a precut one elsewhere. not everyone wants to DIY everything.

Sultz4- exactly why i started this thread.

I used to know someone like you who drove a miata, we threw rocks at him. :giggle:

I wouldn't want to get out kindergarten scissors and and trace out a piece of polycarb taking an exhorbatant amount of time, and possibly ruining the sheet I'm working with. I'd brather have something professionally cut and maybe heated up to the glass transition and formed to some degree to make it able to be installed by a professional. Time and materials are whats going to cost you to do it yourself. You could spend 8 hours getting this thing right ontop of what you spent and are risking on materials, or you could work 8 hours and make enough to have a water jet cut two of them perfect.

How's that motor spinning at 8500 rpm with 5000 g's on a 600 gram piston assembly? (couldn't resist)

bought my 60"x24"x.125" piece for $70. I'm honestly not sure if there's a huge demand for these. My miata is my race-only car, it rarely sees street miles. But if the original owner hadn't driven off with the hardtop unlatched and shattered the window, I wouldn't be looking to replace the glass. its perfectly clear, its solid, it seals, and it fits. Yes you save something like 5-6lbs, but unless you're after an all out race car (which even spec miata doesn't allow this) I really don't think its worth it.

The main problem in your method is that if you don't have an original rear window then you can't make an accurate template. You have the original window to start from. The OP bought a HT with a broken/missing rear window so he has nothing to start from. If there was a place that I/anyone could buy a paper template from on the cheap then the rest of you method could be followed very easily.

Unfortunately I don't know anyone willing to have their rear window removed in order to make said template...

Thats actually the part I'm worried about too, my current lexan window looks to be only 1/16" and its dipped in the middle a little bit, I'm worried it'll crack when I try to remove it, or crack when I try to flatten it. The dip in the middle will make a paper template slightly off too, we'll see what happens, I'm no good with taking pictures as I go so you guys are SOL.

If someone wants to send me a piece of paper to trace onto (roll it up and ship in a poster tube), I will trace the OEM window on my HT for you.

I just wonder how much under the lip of the rubber it goes? How good are your art skills?

the one needed would be the glass out of the hard top and traced all the way to the edges, does anyone have a hard top window out of the hard top?

not i, and probably not most of the people on here either

I think its going to have to be a best guess, and then check for proper fit. I have one here to measure, but the owner isn't going to letme rip out his back glass just to dimension it, and at half a grand to replace, I don't know if I'd blame him.

Yes! Someone get on this before I hack my own Lexan window. I just picked up a HT with a shattered window a few hours ago, was planning on making my own window and bolting it on, but I would definately be down to spend some extra cash for a molded lexan window, or even a flat window cut to the right dimensions because I know I will hack mine up..

im picking up a cf hardtop today so i need this!

You're making up numbers. 8 hours? Hardly. More like 2-3. If you're worried about ruining the sheet, then simply cut it oversize and trim it down. That's how I do it. Of course, if you're only allowed to use kindergarten scissors then it's possible this is a bit too advanced a project.

If there's this much demand for a pre-cut sheet, I'll see about making them available. Drilling holes and shaping the sheet will likely be left as an exercise to the installer, as you'll have to drill holes in your hardtop to install it anyhow.

The engine has survived the week-long Targa Newfoundland, more than a dozen track days for development and a number of dyno runs just fine. Next, it's going to Laguna Seca for a two-day track event. It has a nice wide torque spread so I don't have to spin it to 8500 all the time, but it's good to know I can. Thanks for asking!

that would be cool keith BUT wouldn't a pre-cut sheet be shaped already? otherwise we're back to square one again and just getting a piece of lexan. that needs to be cut and shaped.

Or are you gonna cut them slightly larger than the window and have us trim it down to proper size.

By shaping, I meant putting in the bends. You can do it with a heat gun, or you can let the rivets hold it in place. It's a lot easier to make and ship flat sheets.

If we're going to sell something, it'll be the correct size and will not require trimming. I'll have to see if I have a hardtop that hasn't been modified that I can use for testing first. I think the two Lexan tops here have some sections cut off.

Very anxious to see where this goes. I'm a couple of months out from needing a window.

I was actually just thinking the other day "Why doesn't FM sell lexan windows?" lol

Axis Power Racing sells their Lexan (I think, whatever window they put in their CF tops) for $300. It's flat and cut to shape. If FM can beat that, say $200-225 shipped, I'll buy it TODAY!

I would pay $200 in a heart beat. I figured it would cost me around $100 to make my own out of that scratch resistant stuff. If you do make one, please use that. I think its something like MR10?

so after calling around to local places today, no one in hte central NJ area wants to make them, their excuse is that to cut one to size would be ~500$, which is complete bullshit. I just went to Lowes and bought a giant piece for 75$.

Now if keith can come out with the precut ones within my 30day return policy i'll gladly buy theirs and return mine.

I do not set deadlines on product development. If we bring this to market - and it should be possible to do it within the quoted prices - it'll be available when it's available. So no promises on the 30-day window.

Its even worse, around here they only let me use calipers, I guess on one end they are sharp right? ;)

If the parts are able to curve, there is no reason they could not be shaped first and shipped flat. So long as you don't shunt excessively crosslinking in the heat up cycle there will be no more brittleness then when you started.

I'm not understanding why you can't make the parts to work with a stock style install. Get the right thickness, and a little reinforcement on the edges, and boom, call an installer and have him seal it. There is a definite reason engineers decided to install a window without rivets. Crack propagation, efficiency, seal, and all of those apply to polycarb as well as glass.

I'm sure you could build a replica of the stock glass. By the time you've done that, with the appropriate curve and paid someone to have it installed "stock style", you've gained nothing. I suspect the extra thickness of the polycarbonate will negate any weight advantage. 1/8" polycarbonate weighs almost exactly half of the weight of the 11 lb glass window. I'll check the thickness of stock glass at work if I can find the loose hardtop window. Meanwhile, the cost of having it installed on top of the higher production and shipping cost will eat up any savings over glass. So now you have a rear window that costs the same, weighs much the same and happens to be more scratch-prone than glass. I'm not seeing the advantage. As I mentioned, I'll confirm this if I can dig up the spare glass to see what fasteners are bonded to it, I seem to recall some studs glued on to the lower edge.

Bend it, then trying to force it to stay flat in shipping? It'll have to be shipped between two sheets of plywood screwed together to keep it from ripping through the packaging, and if it's more than 1/8" thick I don't think that's going to be possible. The hardtop glass has a fair bend to it. The windshield is much more gradual.

Polycarbonate is far more resistant to crack propagation than glass, and I've not seen any sign of problems in the various cars I've done. Seal - the top on my Targa car has seen some good rain, and hasn't leaked a drop. I used some exotic silicone sealant from Home Depot there. Efficiency...umm...I'm not sure exactly what that means. Do you mean aerodynamic efficiency?

I view this as a race modification. Lexan windows aren't even road legal in some states. If riveting it in means a lighter window, an easier installation and a lower overall cost, I call that good. I'm basing this on having actually done it a number of times, with cars that have seen the stresses of track use.

Ah, your too much of a pessimist. You can easily get around all the problems mentioned with a little ingenuity, and use a minimum thickness polycarb sheet while your at it. (.09375? .0625? let the HT do the structural work)

This also reduces shipping "forces" where flattening with cardboard would be reasonable.

Efficiency in the installation process, it costs a lot to design a machine to 3d interpolate over the top of a piece of glass and rivet it into place from the factory. It also takes a surprising long time for one person to rivet this into place in the drive way. Too much effort, holes, and then on top of that its not as sound as the other way.

A race modification or a cost effective replacement is a delicate balance. One implies expensive one implies cheap, in this case its both. Killer part. I view that 175-250 range shipped as reasonable for a pre-shaped water jet cut piece.

Oh jesus you guys go way over board and worry too much. I consider cutting and mounting a lexan window a fairly good skill to have, why let someone else do all the work. Buy a piece of lexan and go at it, you can do it!

I tore off my old pastic window today, it was pretty bad. the bottom edge has curled up exposing the bottom half of the hard top lip, and when I flattened the corners out to trace out the pattern on my lexan sheet, it cracked about every two inches. To give you a reference, it has been on there for at least the 7 years that I've owned the car, and opaque for about the last year. This is out of 1/16" plastic of unknown quality/brand. For this reason I suggest not using anything much thinner than 1/8".

I have a bunch of photos I could post, but they're all of the tear down, which would not be what you're doing. Are there any specific photos you guys want now that I have a hard top without a window, and any photos you want as I cut/mount the window?

Now some questions for Keith: I was considering using an electric sawzall to cut out my rough shape, probably with a metal blade since its more fine. Would this be advisable? I'm worried about it being too violent and tearing up the edge, and the feet/guide scratching up the edge as I follow my traced line. Also once I've cut out the rough shape, I'm worried it won't be precise enough to trim any excess off as needed, is there any warrant to my worries? I have available to me many wood and metal manual saws, and an angle grinder with various metal cutting wheels. But if you suggest only a band saw, jig saw or reciprocating saw, I'll gladly go see what I can pick up to use, I don't wanna screw up my sheet of lexan, but I'll gladly pick up another tool :)

Anyways, good luck with the pre-cut stuff guys, and thanks in advance Keith for your answers, you and your photos have been a huge help!

Use a regular jig saw with a metal blade. It cuts the lexan like butter and will give you WAY more control than a sawzall. Just buy the $30 cheapo at lowes. Its what I have, works perfectly.

I think Keith and Travis are making it too difficult as well. I personally think the cutting and riveting are cake (I've done it on mine already). All I think is really needed is a paper/cardboard template that one can buy to trace onto their polycarbonate of choice. The most likely candidates to do this whole job are those picking up hardtops without existing rear windows. I've done the whole trim here and there to get it to fit, it doesn't end up too pretty and the fit isnt the best. If I had a template it would have fit perfectly.

I'm not making it difficult, I'm simply answering questions that are designed to be difficult. It's easy. I started off saying this, but it's become clear that not everyone wants the DIY route.

It wouldn't surprise me at all. Why not? Because I've done it. It doesn't take long. You're drilling polycarbonate and fiberglass, then popping in a rivet with a backing washer. There's no need to pre-bend the polycarbonate at all unless you're simply trying to make life difficult. Drilling a windshield frame made of high-strength steel, that takes a while and is no fun at all.

Now, back to some good questions.
I'd stay away from a sawzall. Great for cutting frame rails, not so good for shapes with bends. Polycarbonate is really easy stuff to cut, but it will melt so rotary tools can get messy. The jigsaw is pretty much perfect. I've used bandsaws as well. If you have an air compressor, then a little air saw does a great job. Once you've got one, you'll find how useful they are for doing light fabrication work like heatshields as well. Here are a couple of cheap options:
electric: Harbor Freight Tools - Quality Tools at the Lowest Prices
air: Harbor Freight Tools - Quality Tools at the Lowest Prices

The nice thing is that you can practice on the edges of your sheet to get an idea. By the way, it's really easy to trace and cut out a triangular vent window or two, and those slide right into the stock location without any difficult installation or bonding. Good way to lose a bit of weight and you can rivet in a NACA duct for a real race touch - see below. The clear vents are from Pegasus Racing and I think they're about $25. Use the top from a spray bottle to plug them, I've run this on a road car.
http://www.flyinmiata.com/projects/O...t/DSCN6367.jpg

I need to get off my ass and make those vent windows Ive always wanted to also

ok so a question now about weatherproofing and silicone. would it make more sense to silicone underneath the lexan then put rivets through it, and then again around the lip? adding an extra laying of protection?

Thats just it Keith, they are trying to make it difficult.

I'm glad you said what you said about the cheapo jigsaw, cause that's exactly what I did today, bought a $30 black and decker from home depot, I'm about to go out and start cutting, I'm excited to get this done, I haven't had a clear rear window in ages!

I'm definitely going to put in the triangle windows with NACA ducts, at least on the driver side, I've wanted some air in my helmeted face ever since I had to put the heater on full blast to keep from over heating at the track.

Disturbed, I think one bead of silicone under the lexan would be fine. The PO had a 1/2" bead of what seemed to be roofing tar (seriously, it was disgusting) under my old plastic window and it sealed fine. A small bead of silicone would do great.

I think people were talking about a molded window so that it could be installed without rivets (like stock), for a stock look. At this point I would be thrilled just to have a pre-cut flat sheet that I can bolt in. I agree, molded sheets would most likely bring the costs up high enough to negate the 5lb wieght savings of a Lexan window.

Well, after cutting out my window last night, I have to admit that a precut sheet would be a pretty sweet deal. Although I was working from a really crappy template. With a supposedly 'perfect' template, I would have no problems making a fairly accurate window, my new $30 jigsaw worked great.

An accurate template is really the product that I think needs to come out of this thread... if I haven't already mentioned that. Sounds like Curly echos that opinion.

With this forum, that "product" would sell one copy :) Sounds like a few people want a template, a few others want a pre-cut sheet. I'm waiting to get some quotes using a couple of different production methods so I have an idea of what the costs would be for the latter.

As for the silicone, I've only tried that once. A bead between the window and the flange caused enough of the silicone to ooze out that I was able to smooth it out with my finger around the edge.

I used the most expensive GE exterior silicone I could find at Lowes. It is really great stuff. Just watch out because it dries quickly (20-25min to dry film on the outside), but it will HELLA STICK to absolutely anything. You can't even scrape it off of the lexan. Its almost like an uber silicone sealant/glue.

@Keith - How about if you do provide a finished window for purchase, would it be fair to offer a template for free/cheap to those that do wish to DIY?

ya I agree, Id rather have a template most likely

Yes, with this forum it would be like a fender roller. One unlucky idiot would buy it then it would just be mailed around the country in a poster tube until its ruined and another unlucky idiot buys it and uses it once.

But yes, you can't call yourself a DIY'er if you're unwilling to cut it out if you at least have a good template, I don't see the reason for a water-jet cut piece of art for a lexan window.

Water jet cutting is realistically less then 30 dollars a window. Is it worth 30 dollars to you?

Wow, this thread sure got carried away.

To me, a lexan window is, for the most part, for the DIY'er. Most people with hardtops aren't gonna go rip out the glass to save 5 pounds, especially if it's gonna cost them time and money. Only people you're targeting are people w/ busted glass looking for a cheaper fix and hardcore racers looking to shave every ounce they can. Your preformed lexan thing would be "cost of materials + cost of waterjetting+ R&D to get pattern for said cutting + extra shipping cost to ship curved piece". That's more than 30 bucks I'm afraid.

Yea, but people fail alot of times to see the hidden cost of DIY. You can buy an air jig, a piece of polycarb, a rivet gun, a box of rivets, high qaulity silicoln, punch holes in your hard top (basically 500 dollars because there is no retail value for a hardtop with rivet holes in it), a drill to drill the holes, drill bits to do it, a template, several hours of cutting to trim and fit, maybe a couple hours running to home depot or harbor freight for tools/parts. The possibility of cutting the polycarb wrong (another hundred), and having to start over, learning how to rivet, then making it look "right"

Other method... buy a piece of formed precut polycarb, it gets shipped to you, you call a guy who installs it. Total investment less then 350 I would think, cheaper then factory glass without the installation, lighter then factory glass, no damage to resale value of hardtop.

DIY has its place, but what is visibly off proabably shows up at about .01 inches. You telling me your going to be able to cut straight line (or even worse a curve) within a hundreth of an inch on a couple workhourses with a bowing piece of polycarb with atleast some of you at the helm of a jigsaw for the first time? There is reasonable, and then there is human limit.

I'd rather save the $30 and use it to buy a black and deck jigsaw that I can use for a few years. All I want is a template, period.

I don't give a fuck about a 1/100th of an inch. I just want close and flush fit.

Then thats another vote for template only.

Honestly Travis, its a great idea and I might've bought a pre-cut one if it was available for cheap at the time, but it wasn't. I already have rivets, drills, and now I have a jig saw I can use for future projects, some scrap lexan for the triangle windows, and some lexan cutting skills.

More power to you if you can get enough customers to make a decent profit from cutting a window. I guess I just hear more people leaning towards just using a template, and I'd worry that the market isn't there for you.

Well, I'll leave it alone, I was just trying to help out.

I'm sure you can find better things to do with your time that will cater to a larger crowd. Things that require more than a 30 dollar jig saw and a good idea.

Exactly what Pat said, its not that you don't deserve to make a great hardtop window, its that the window doesn't deserve your perfectionist style. This style could and should be applied elsewhere IMHO. Apparently traction bars are fairly important on some people's list for example.

Does anyone know how the stock rear window trim molding attaches? If I could just buy a new piece and make it work with a lexan rear, I wouldn't care about being off on my cuts because that would just hide it.

The only person talking about pre-bent Lexan is Travis.

If we start offering this, it'll be flat. There's no reason for it to be pre-bent. It would add expense for no benefit.

Based on my experience, it wouldn't be that hard to figure out the correct shape with a hardtop that has a busted window. It would require a bit of trial and error, but as long as you're smart enough to err on the side of cutting too little then you could do it. In the past, I've used the template to get in the ballpark and then done the final trimming on the top itself. The tolerances are legitimately within 0.5", not 0.01" if your cutting at home. If you're making a show Miata, then a polycarbonate rear window is a poor choice anyhow.

Ug, drilling the hardtop and window sucked! Its nerve racking as hell cause with any of the holes you could scrap your piece of polycarbonate. But I didn't do that, and have all 30ish holes drilled and bolted on (my rivet gun can't hold the 1/4" rivets I don't have, hence bolts).

I still have to mark some spots that I need to trim so it fully fits in the lip, un-bolt it, make the trims and deburr the holes, clean the lip, paint the lip, re-install and make any further trims, un-bolt it, lay down a bead of silicone, and bolt it up for the final time.

Yuk.

Oh and fiberglass splinters suck

Curly- got any pics of said job just to see what i can expect?

Yup I have some pictures, I'll make a separate thread as to try not to clutter this one any more.

enjoy

https://www.miataturbo.net/forum/t30104/

1/4" rivets would be overkill. 1/8" with a backing washer does the trick just fine.