Heat bending polycarbonate for a windscreen

[dlaing]

I am not sure which Givi you have, but I think the bends are too complex and you may need vacuum forming

Or maybe you have a different fairing

[Guest ratchethack]

I am not sure which Givi you have, but I think the bends are too complex and you may need vacuum forming ...Or maybe you have a different fairing

No-a Givi, it's-a Stucchi!

 

Dave, the Stucchi windscreen has a simple, conical shape with small reverse curves at the edges. It's not a compound curve like the Givi.

 

The smarter I think I might be getting about this (thanks to all the expertise of this here Forum! ), the better acrylic sounds, which might be a whole lot less trouble. Acrylic would at least eliminate the need for drying for 8 hrs. at 250F.

 

Come to think of it, if I went with 1/16" LEXAN instead of 1/8", I could probably get away with no heat forming at all, & just flex it to shape, and Bob's y'er Uncle!

 

So many complications. . . .So THIS is why these things are so hard to come by. . . . . .

[Guest ratchethack]

You gotta make the little molecules move about a bit. They are lazy when cold. The slip roll gives the added impetus. A bit overbent will allow for relaxation and normalization during the next few thermal cycles.

Gary, I might've missed something here. At first I thought you were suggesting cold forming with a slip roller. But now you mention thermal cycles. Are you suggesting heating it first? Heating between successive passes thru the slip roller? I'm a little confused.

[dlaing]

No-a Givi, it's-a Stucchi!

 

Dave, the Stucchi windscreen has a simple, conical shape with small reverse curves at the edges. It's not a compound curve like the Givi.

 

The smarter I think I might be getting about this (thanks to all the expertise of this here Forum! ), the better acrylic sounds, which might be a whole lot less trouble. Acrylic would at least eliminate the need for drying for 8 hrs. at 250F.

 

Come to think of it, if I went with 1/16" LEXAN instead of 1/8", I could probably get away with no heat forming at all, & just flex it to shape, and Bob's y'er Uncle!

 

So many complications. . . .So THIS is why these things are so hard to come by. . . . . .

I always thought the Stucchi fairings were made by Givi. Obviously they are different

Yah, I would just find some some premium brand acrylic thin enough to bend.

If it is a tad too thick, a head gun, a crude form of roughly the right circumference, like maybe a large bucket or tire or sheet metal bent to desired shape, and some patience will bend it right.

[mike wilson]

Don't forget to back off your drill bit's cutting edge before drilling the holes for fixing. Nowt more infuriating than a drill grabbing the workpiece. Well, there is - but it's still pretty annoying at the time.

[g.forrest]

HOT air gun allways does it for me. then its just the mold.

[Guest ratchethack]

Don't forget to back off your drill bit's cutting edge before drilling the holes for fixing. Nowt more infuriating than a drill grabbing the workpiece. Well, there is - but it's still pretty annoying at the time.

Good point, Mike. Learned this one the hard way long ago.

 

2 options to be well tested on scrap first so's to avoid grabbing the work & creeping cracks later:

 

1. Melting holes with a bit of rod heated with soldering iron.

 

2. Drill holes with sharp bit, carefully & s-l-o-w-l-y feeding the bit at low speed, followed by heat-polish & chamfer with very light pass of soldering iron.

 

[Guest ratchethack]

Eh? Enlighten me, por favor? I thought a properly ground bit was a sharp bit??

 

I use a "Drill Doctor" bit grinder.

[Guest ratchethack]

Hmm, thanks, Gary, but I've got a general-purpose home shop and hadn't done much specialized polycarbonate work at all (until now), hence my original question. I reckon I'll hafta make do with the Drill MD bit and just be extra slow & careful not to let 'er "take off" on me as I feed in the bit.

 

Thanks f'er the education.

[Guest Gary Cheek]

Yep, Understood. You may want to take a whetstone and just put a small flat on the face of the drill so the drill is not quite as "sharp".Actually you are trying for a negative rake of a degree or two. The clearace angle can be up to 15 degrees and still work fine with some negative rake. You dont really need fancy tools. The simplest often work best. This will help prevent hogging or grabbing. I didn't mean to sound flip but a "sharp" drill with reliefs and point angles used for general purpose can be a bit grabby. Could spoil a nice part too.

 

The boring stuff: When I first started out in the trades it was in HEAVY press repair. One night a rush job required drilling a 1-1/4" hole through both sides of a 18 inch Dia. 16 inch long bronze bushing. A combination of piss poor radial drill setup and a green kid not reducing the radial relief caused the bushing to tear loose. I retreated only to have the now flying bushing take out my knee and a huge chunk of the drill in my forearm. Seeing your knee-cap come thru the skin anf standing up on edge can generate a lot of interest in drill sharpening and radial drill set-ups!

 

Not that you would hurt yourself but it may spoil the job.

[Guest ratchethack]

Now this is the kinda stuff that makes this Forum wot it is. Where else am I gonna get this?!

 

Thankfully, most o' my moto mechanical stuff is so small in terms of mass and force that it's not too life-threatening.

 

Thanks again Gary, f'er the tech knowledge and the heads-up life-experience info.

 

Y'got my full attention with that kneecap thing. . . .

 

Fortunately (or not), I'm merely a perpetual Journeyman Shade-Tree Mechanic with nothing but seat-o'-the pants training from watching other aspiring Shade-Tree Mechanics do stuff the wrong way. If I'd been given any professional knowledge of machine tools, I'd likely have removed substantially larger parts of me anatomy than I already have. Most of the self-instigated bio material losses I've sustained have been small enough to be well distributed about the shop (floor, ceiling, walls, etc.) All joints still work, though I've been sewed up many times, and various surgeons have put back together several sets o' mangled & shattered phalanges over the years. Only one o' my fingers doesn't look quite right, the one that I managed to disintegrate into bone fragments too small to pin back together. Piddly stuff, really.

 

Speaking of self-induced mayhem, Ever use a come-along to preload & install new garage door springs? That's on the list f'er tomorrow. . . .

[Steve G.]

The business I'm in entails cutting, shaping, and edge polishing and drilling acrylic and polycabonate quite often. You are correct, the two are quite different, and working the two needs different techniques. Polycarbonate [ trade product like Lexan etc] is easiest to work with, mainly because it is very highly resistant to cracking, either by cutting with table saw or jig saw, or drilling holes. Acrylic is a joke mostly, and could be dangerous on a bike in light of it's ease of cracking into jagged things much like glass. Unfortunately, forming either poly or acrylic into a shape or curve is the trickiest of all things you can do with it, mainly because, unless you have a dedicated form to do production line forming, you will have a tricky time bending this stuff without introducing optical imperfections. These will be caused by a heat gun being placed too long in one place, or you will put an indentation into the surface of the sheet when pressing it down. Very mild shapes obiously are easier, with less chance of imperfections.

Sanding the edges to a nice polish will most certainly entail the use of a wet sander, found at any glass shop. Water needs to be used for that nice polish, as the low melting point of both means that it's easy to start the stuff 'melting' to itself while sanding dry, where it then 'folds over' on itself, causing lumps. Water keeps things cool.

Cutting it with a jig saw, use any thing you have if you are planning on polishing the edges. A metal jig blade will actually melt through the stuff, and it often seals itself up to a degree after the blade goes through. I use a big old wood blade, no melting then.

Drilling? no problem at all with poly. Acrylic is a joke, very risky chance of cracking as the drill falls through the bottom of the sheet. Melting through? I guess that would reduce the risk of acrylic cracks, but it's not needed on poly, just put the drill through it.

Ciao, Steve

[Guest ratchethack]

Another apparently very well-qualified perspective. Much appreciated, Steve.

 

Thanks.

[dlaing]

Keep in mind that there is more than one type of acrylic.

And there is more than one type of polycarbonate.

This PDF gives info on some variations of Acrylite PLUS

http://www.cyro.com/Internet/SiteContent.n...pdf?OpenElement

This chart shows some variations of polycarbonate

I think you will find the UV resistance essential.

Of course if you are picking scraps out of a bin, you might not get to select the optimal plastic.

[Guest Gary Cheek]

Edge polishing with acrylics entails sanding and more often than not we would "flame polish " with a torch. With polycarbonate, when bandsawed the edges were ususaly filed , sanded and for the best finishes a rag or brush weeted with methylene chloride would solventpolish the edge. Being careful not to get any on the surface.

General Motors Parts Fab was a very early consumer of the then new plastic materials. They worked with manufacturers and actually helped develop many of the techniques being used today.

We use even more plastic now in the concept cars than ever.

 

 

This is one of the GM concept cars using a Lexan power retracted top. The top was fabricated at GM Parts Fab in 1959. Big parts form just like little parts. Of course a bigger oven , in this case the oven is about the size of a 1 1/2 car garage. This car is great fun to work on! It can be quite challenging at times.