Back Alley Bike Lamp?

December 14, 2010 7:58 AM

How can I make a clear plastic cast of a bicycle?

Assume that I have access to a bicycle graveyard of sorts. I would like to make a clear copy that could have various LEDs or whatever shoved into it to make a lamp. It would only need to support its own weight.

Is there a paint on / cut and peel off kind of a resin that would work? I would be most interested in a method that would allow the process to be done to a complete bicycle+components, but if going one part at a time is necessary then that's fine too.

I have a low budget, no experience, and the final project can look pretty ugly as long as it is recognizably a 'bike light'.

Any ideas?

posted by Acari to Grab Bag (12 answers total)

Instead of casting, I'd fabricate a frame from clear acrylic tubing and hang it with real components. Casting the whole thing, even in pieces, would require a lot of not-inexpensive material and be quite tricky.
posted by jon1270 at 8:13 AM on December 14, 2010 [1 favorite]

In my experience casting is tricky and expensive, I think you'd be much better off building the frame from clear plastic tubes. Maybe cast some of the smaller parts if you want them really accurate.
posted by ecurtz at 8:14 AM on December 14, 2010

I was going to suggest vacuum forming but I have no idea how practical that would be and I agree that clear plastic tubing sounds like the best method for creating the frame.
posted by EndsOfInvention at 8:19 AM on December 14, 2010

I think your best best is going to either either:

1. disassemble the bike and cast the pieces one by one, then reassemble the plastic bike
2. use clear plastic stock to build your own bike-shaped sculpture

Building a single mold that can cast an entire bike in one go will be impossible. Think of all those nooks and crannies.

Say you paint on the resin shell. There's no wayIt will be extremely difficult to get it off the bike [in order to fill it with clear plastic] without destroying it.

Say you encase the bike in a big block of silicone. How do you cut the block apart to get the bike out, while maintaining the silicone shell's condition such that you can put it back together and fill it with plastic?

Piece-by-piece molding is the way to go. This will be expensive, however. MAKE magazine has run a couple introductory molding articles by [metafilter's own] Adam Savage that would be good starting points.

Make Primer: Moldmaking by Adam Savage
Making a Hard-shell Mold
posted by chazlarson at 8:36 AM on December 14, 2010

Casting seems like a lot of work.
You could buy yourself a set of frame lugs and use clear plastic tubing instead of the usual steel/alu to build up a frame and then run your lights through that. Salvage an old set of wheels and you're done.
This saves you having to cut , mitre and glue the tubing to the correct angles, just slot it into the lugs.
You can even get 'practice' lugs which will be cheaper (scroll towards bottom of page).
posted by SyntacticSugar at 8:44 AM on December 14, 2010

Response by poster: I had initially discounted the idea of plastic tubes because I thought it would look really terrible even with carefully cut and glued tubing.

But with lugs, it could be beautiful! That is an excellent idea!

Any thoughts on the 'fork'? It won't have to rotate, but it should hold a [non-plastic] wheel.
posted by Acari at 10:04 AM on December 14, 2010

I'd imagine you could create a mold just for the fork and buy some resin to cast with... Can't think how you would build that up with rods, etc. I don't think a fork would be too hard to cast, really. You could probably create a mold for half of it and pour twice, since it is symmetrical. Try and find a plastics specialty shop like TAP (Bay Area), the guys there will have some ideas how to help you.

Also, do some small scale tests first. This stuff gets expensive fast. This thing will probably cost you at least $500 in materials by the time you're done, so you don't want to screw up or find out you can't pull it off after you've already sunk the cash.

Actually, on re-read, I think this project might be beyond a "low budget". Seriously. Plastic is expensive.
posted by annie o at 11:46 AM on December 14, 2010

Clear PVC pipe can be heated and bent just like white PVC. You could make the forks out of clear pipe. See this link to McMaster-Carr. Or, cut lengths of clear and replace all straight runs, basically socket clear pipe into the junction assemblies
Molding is a hard process, Learn it cause it's fun to do. But a complete bike would tax even a master prop maker. Good luck however you go.
posted by Pecantree at 7:19 PM on December 14, 2010

You'll need a fork crown for the forks, the ATB one looks suitable (most of the others look as though they'll take a profiled fork-leg). You could just slot the tubes right in, so that it ends up looking like this.
You probably wouldn't need the dropouts on the bottom to fix the wheel, just make the legs a little longer, drill a hole through them and bolt the axle in directly if it's not going to bear much of a load.
posted by SyntacticSugar at 4:42 AM on December 15, 2010

How clear? Wrap it in bling film/gladwrap, bind it up with laters of clear packing tape, slice open your tape-shell with an exactoknife and tape the seams back up. One translucent bikeshell.
posted by Iteki at 1:37 PM on December 16, 2010

Best answer: Examples of packing tape sculptures.
posted by Iteki at 10:19 AM on December 18, 2010

Response by poster: I love the range of expertise and advice I got out of this, but the packing tape sculptures are just about exactly the level of excellence I would actually try to accomplish [for a project that will be in line to die a thousand deaths every winter and be, by default, a theft target].

Maybe a coat of varnish or something to harden it up at the end, and we're in business!

Thanks, folks!
posted by Acari at 6:37 PM on December 18, 2010