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GameboyRMH
GameboyRMH UltimaDork
6/1/13 6:27 a.m.

Anyone done this? I've been thinking of trying this to make ABS quarter panels & hood skin for my 'rolla. I think the only difficulty with the hood would be the sheer size of the thing, but the quarter panels have some slight compound curvature to them.

cwh
cwh PowerDork
6/1/13 8:10 a.m.

Honestly, I think you would be better off doing fibreglass.

jere
jere Reader
6/2/13 2:58 p.m.

How are you planning to evenly heat the plastic? Without knowing that I would be looking at some kind of easy DIY in your garage composite too

bearmtnmartin
bearmtnmartin HalfDork
6/2/13 3:20 p.m.

I buy a lot of rotomoded plastic tanks. I asked my supplier for a different shape and it took him 2 years to build the mold and work the bugs out.

Knurled
Knurled UltraDork
6/2/13 3:23 p.m.

Somewhere in the back room in the ol' noggin, an idea keeps popping up for making fenders out of old bedsheets and 3M spray adhesive...

fanfoy
fanfoy Reader
6/2/13 4:38 p.m.

Are you talking of thermoforming?

If that's the case, I know there are a few DIY kits out there, but it usually is for small parts.

Like Jere said, when you go with large parts, the hardest part is heating a large sheet and holding it while it is soft.

GameboyRMH
GameboyRMH UltimaDork
6/2/13 5:52 p.m.

Yep thermoforming. The video shows vacuum molding, drape molding is basically the same thing but just using gravity and mechanical forming instead of sucking the material onto the mold. I've seen it done for simple shapes. Big parts can be preheated in an oven, for doing something as large as the hood...I dunno, a metal sheet to spread heat and a campfire?

fanfoy
fanfoy Reader
6/2/13 6:33 p.m.

Well depending on the shape, vacuum is mostly there to make sure you don't have air trapped between the mold and the plastic you want to form. Drilling tiny holes in your mold might do the trick.

As for contact heating, when I used to work in the PVC industry, we used to avoid it because it was very easy to overheat one side while the other side wasn't hot enough. So you would end up with a burned side and the other side with cracks because it was soft enough.

If the plastic sheet is thin enough, I'd give a shot. If you have a spare hood, I would try to put the plastic sheet over the hood and heat up the underside of the hood as evenly as possible. Maybe use some radiant heat lamps to warm up the other side. This is all very experimental, and I honestly don't know if you'd get good results. There is a nice table of target temperatures on this site.

Good luck and keep us posted if you try.

Kenny_McCormic
Kenny_McCormic PowerDork
6/2/13 7:56 p.m.
Knurled wrote: Somewhere in the back room in the ol' noggin, an idea keeps popping up for making fenders out of old bedsheets and 3M spray adhesive...

You want to make a Trabant?

Wally
Wally MegaDork
6/2/13 8:06 p.m.

Do you know anyone with a pizza oven?

MrJoshua
MrJoshua PowerDork
6/2/13 8:50 p.m.

I read up on this (Vac forming) a LOT a few years ago. I had fantasies of a challenge car with something like an RC car body on it. For big things you make a 4 post canopy bed with toaster wire up top and your vac platform on the bottom.The plastic is attached to a wood frame that rides up and down on the posts. Keep the plastic and wood frame at the top near the heat until it starts to droop then lower it onto your part and start the vacuum. The problems I saw were cost, strength, and heat resistance.

GameboyRMH
GameboyRMH UltimaDork
6/3/13 11:00 a.m.

Had a wacky idea for doing the hood just now...what if I cut some material a little bigger than the hood, lay the material on the car's hood (not worried about ruining paint), then use a heat gun to work the panel into the same shape as the car's hood. There's slight curvature along the length of the hood, 2 creases along the length of the hood, 2 bumps near the back and a turndown near the nose, that's it. This is how I saw someone make a go-kart fairing on a wooden form, but on a larger scale and with more than just 2 folds.

93EXCivic
93EXCivic MegaDork
6/3/13 11:14 a.m.
cwh wrote: Honestly, I think you would be better off doing fibreglass.

This. Fiberglass seems way easier. I have tried to do the thremoforming with a pretty decent sized oven and it sucked. Composites are way easier.

MadScientistMatt
MadScientistMatt UberDork
6/3/13 11:28 a.m.

I don't like the idea of an ABS hood for a car that's actually driven. Combine a lot of aerodynamic pressure with engine heat, and it's likely to deform at speed. Fiberglass would be a lot better.

Knurled
Knurled UltraDork
6/3/13 12:53 p.m.
Kenny_McCormic wrote:
Knurled wrote: Somewhere in the back room in the ol' noggin, an idea keeps popping up for making fenders out of old bedsheets and 3M spray adhesive...
You want to make a Trabant?

Well, yes. I mean, it worked for them, right?

spitfirebill
spitfirebill UberDork
6/3/13 1:06 p.m.

Didn't Aston Martin use thermoforming to make that huge, horrid car they made a couple of decades ago. Before that it is was a man, a hammer and a wooden buck.

yamaha
yamaha UberDork
6/3/13 1:09 p.m.

I'm thinking of making molds to fiberglass "bumper fillers" for the E21......the body lines without the massive bumpers suck.

Leafy
Leafy New Reader
6/3/13 1:21 p.m.

I was looking at make a fender and hood sized vacuform machine. I determined that my house does not have 3 phase 480v so I would not be able to make a large enough heater for 4x8 sheets of plastic. The vac table is the easy part, once you get over a 2x4 sized sheet the heater becomes almost impossible. I considered a using a forced hot air turbine propane heater but I determined that I did not want to do months worth of CFD to get the heat to distribute evenly in the oven box, and such a setup would make moving the sheet to the vac table very difficult.

And sheets of UV protected plastic in that size are over $150, and I would screw up at least 3 of them trying to make a set of fenders so $750 for a set of kevlar fenders that are professionally made all of a sudden became a good cheap idea.

GameboyRMH
GameboyRMH UltimaDork
6/3/13 1:43 p.m.

^Well that's a downer...between that and the engine heat problem for the hood I think I'll have to settle for fiberglass. The reason I didn't just go for fiberglass in the first place is because I was interested in the better durability of the ABS.

yamaha
yamaha UberDork
6/3/13 2:36 p.m.

In reply to GameboyRMH:

ABS wouldn't be very durable for a hood.....

Dbussey1
Dbussey1 New Reader
6/3/13 4:59 p.m.

Had some students try to vacuum form body panels for a Formula SAE car at the shop I used to supervise. They blew through a lot of material, and never got anything resembling a satisfactory part. It's tough to do on large parts, even with the proper tools.

You'd probably be much better off using fiberglass.

Warren v
Warren v Reader
6/3/13 5:15 p.m.
Dbussey1 wrote: Had some students try to vacuum form body panels for a Formula SAE car at the shop I used to supervise. They blew through a lot of material, and never got anything resembling a satisfactory part. It's tough to do on large parts, even with the proper tools. You'd probably be much better off using fiberglass.

What team Dbussey?

OP: Fiberglass. Thermoforming is out of your scope. It would only make sense if you want to make more than 2-3 dozen hoods.

For the sake of continuing the discussion on thermoforming, thermoforming is way easier than fiberglass if you plan and budget it out well. If you're building the table and oven yourself, you realistically need a minimum of $3k to do large panels (4'x4') right. The molds require a bit more work than fiberglass, as there is more heat management involved. It really needs to be a continuous material underneath the surface or else you get bubbles and whatnot. There are a few good resources and books out there, Formech makes a good primer on the actual process, this is a good guide for the newbs.

Thermoforming and vinyl for color is the modern way to make medium-volume lightweight panels. Heat reflective tapes and laser-cut 2D plastic backing braces eliminate heat and flex issues.

Dbussey1
Dbussey1 New Reader
6/3/13 9:17 p.m.

In reply to Warren v:

This would have been a team from Georgia Tech

MrJoshua
MrJoshua PowerDork
6/3/13 9:30 p.m.
Dbussey1 wrote: In reply to Warren v: This would have been a team from Georgia Tech

Well they always fail spectacularly the first year.

(They eventually win though, so that doesn't mean the original concept was a bad idea. )

Warren v
Warren v Reader
6/3/13 9:46 p.m.
Dbussey1 wrote: In reply to Warren v: This would have been a team from Georgia Tech

Heh, yeah, from what I saw it eventually ended up working out (I graduated May 2012, used to be on that team). I think their biggest problem was using foam as the the plugs instead of something a bit firmer. Vinyl covered a lot of the defects, and they were able to keep the car under 400#.

If you have tips about vacuforming large panels and some time in the next few weeks, I'd love to pick your brain about our plans for thermoformed bodywork production on the Exocet. Warren@Exomotive.com

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