I seen on the orbitron somewhat of the process of the making of a bubble top, but nothing that answered any questions. So how do those guys do it?? 1shot
I've heard one way is to make a airtight box with the same diameter hole as you want your bubble cut in the top. Put a heat lamp in it with a flat piece of Plexiglas bolted over the hole clamped with a ring, When the Plexiglas gets soft put compressed air in the box to expand the bubble. Or a big mold and a giant oven
I had Gene Winfield explain it a few years ago,,, someone has the napkin with pictures,,, basically attach your plexiglass to a ring at the top of a box like structure,,, put it in the oven,,, it will melt and form the half globe shape if the ring is round,,, more of a teardrop shape if it isn't,,, he's offered to help at his shop,,, of course that was a lifetime ago,,, and I don't need anything with bubbles anymore,,,, xoxox hootch
I had Gene Winfield explain it a few years ago,,, someone has the napkin with pictures,,, basically attach your plexiglass to a ring at the top of a box like structure,,, put it in the oven,,, it will melt and form the half globe shape if the ring is round,,, more of a teardrop shape if it isn't,,, he's offered to help at his shop,,, of course that was a lifetime ago,,, and I don't need anything with bubbles anymore,,,, xoxox hootch
Vacuum forming is your friend. This link will give you an idea on the "small" side. http://www.modelairplanenews.com/ME...5F&tier=4&id=BF9769BE6DF74E0CA8B0EA8FFBA3FF88 You can also reverse the process and blow the top using a "female" buck instead. There was a HAMBer who, years and years ago, built a box mold, pressurized the box with a air compressor and blew out tail light lenses. Basically the process was this: 1) Build a metal, airtight box. 2) Weld in a airline bung into the side of the box 3) Slice off the box top. 4) Cut your design into the top face of the box 5) Lay a piece a lexan or plastic of choice between box bottom and box top (note you will want to fashion some type of nut and bolt array to attach the top section back to the bottom section and keep it air tight) 6) Attach air compressor and start to apply air pressure 7) Use heat gun or heat lamps to slowly melt the plastic The combination of heat and air pressure will form your bubble. Just lots of practice, and failures!
Lost Angel, I saw that site a long time ago and bookmarked it, but then that old computer crashed. Thanks for the link. I saved it again. I plan to try this some day soon and, if it works, do a tech article on it. I think the biggest scare is losing all that money if a bubble blows out. Plastic isn't cheap enough to waste too many pieces.
I read in one of the various books I have lying around that you want to start with at least 1/4" for a car top. Preferably 3/8" or better. When the bubble stretches out during the process, the middle gets pretty thin, or so I've read. I may be wrong, though. I was wrong once before
I've actually talked at length to Starbird about this very concept. As well as a few airplane makers. A few tips on them... Sean's idea on using a vacuum form is really good if your doing complex parts that don't need to be clear, but for a bubble top that you will need to see through the distortion you get in this process is going to make the car un-driveable. Starbird explained that you can't have anything touching the surface that you plan to see out of, this is because of distortion. And the other thing is you have to be able to heat the Plexiglass uniformly so that when you inject the compressed air into the mold you get an even expansion of the plexi. If it is not evenly heated the plexi will stretch more in some places and less in others giving you varied thicknesses in the top, and thus distortion, think of it like the convex shape of a magnifying glass. It would make it pretty hard to see out of when things are wizzing past you at highway speeds changing shape through the window, I'm getting sick just thinking about it. Plus if it acted like a magnifying glass, just think about the sun beaming through on a sunny day at noon, you would be like an ant under a magnifying glass, you'd probably fry! Pretty awesome though, I plan on building a bubble top in the near future, but I'll probably have Starbirds supplier make it for me.
Some of us crawled out from under a rock somewhere and others have been living in a bubble. Some of us have done both.
There was a tech piece on here somewhere that showed how to make tail lights using basically the same procedure but on a smaller scale. Really interesting.
1 shot, I don't know what size you need but another avenue is using a dome skylight from a major building center. That's what I was planning. Stoled that idea off of here from someone that did that. I'm not positive who it was now.
i was looking at the oven built out Celotex tuff-R. would a propane heater like the the one in the picture work? maybe mount 3 heaters on the bottom so it will heat evenly. i have heaters like that one thats why i'm asking.
I tried that home made oven myself and it did not work, couldnt get the heat even enough. I ended up taking my mold to a plastics fabricator. Masterglas in Farmington Mn. they have a big convection oven. The mold and acrylic were bolted together placed on a cart and wheeled into the oven, when the temp of the acrylic reached 360 degrees the cart was rolled out and air applied. I did this twice, when I restored the Road agent and when I built the futurian.
Just a couple more tips if you are going to build a mold. the ring that you are going to blow through has to have a pretty large radius sanded into the bottom edge, this makes it easier for the acrylic to start forming. also I used 1/8 inch thick high temp silicone rubber sheet to make a gasket around the outside edge, it goes between the plastic and the solid piece of plywood with the air fitting in it. without a gasket you wont be able to build enough pressure. also as mentioned before free blowing is the only way to get a distortion free bubbletop, any sort of female mold the the plastic touches will cause distortion
Moriarity, i'm glad you let us kno before i went and tried making my own. you saved me some money. great advise from someone who has done them. thank you sir!
I would say Moriarity should know-I heard Roth used a mold and borrowed a buddy's pizza oven ,but always wondered and kinda figured with him it could be true.
One thing I learned working with plexiglass is that there is a definate heat range that you will have to stay in. too cold you get cracks, too hot you get bubbles in the plactic it self.. Some thing to keep in mind...
look up "Plastic Fabricators" in Tulsa Ok.......... no big mystery or secret.....they do all of the bubbles for Darryl Starbird and they'll tell you what they need from you to make your bubble
btt .the custom rodder article (how to make a bubble top) from years back is basically repeated in this months issue of Car c(k)ulture deluxe.... a pretty nice article for that mag, was written by starbirds grandson.
this is great...planning a bubble top at the moment...have been looking at them big, round, plexiglass, hanging chairs from the 70s. Evil bay had them for around $400
Cool video of a small scale blown bubble... <object width="560" height="340"><param name="movie" value="http://www.youtube.com/v/BiCxrvXTS4Y&hl=en&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/BiCxrvXTS4Y&hl=en&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="560" height="340"></embed></object>
I read once that one of the early customizers (Roth?) had a bubble done by a company that made the bubble covers for bowling alleys. A recent trip to the playground with the kids revealed a modular play structure with plexi bubbles. Hmmm....
i work on packaging machines and compressed air and heat is how the "pouches" are formed for the product. temp. is a very critical factor.
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