Bubble Blower or Q&D Vacu-Form

[Gil]

Hello All,

This is a quick and dirty way to blow plastic bubbles, well at least bumps and astrodomes and is easy enough that even the worst case of attention deficit disorder can form a bunch before wandering off to something else.

A cereal box card piece was cut to cover the opening of the shop vac hose. A 1.4 cm hole was cutout and Aleene's Tack It Over and Over was spread over the surface and let dry. The Tack It seals the plastic sheet to the surface and allows several dozen to be formed before loosing it's adhesive seal properties.

The heat sources used are a heat gun and a micro torch. A regular propane torch would work also but must be used judiciously as blow outs are easily accomplished with this style heat source. The heat gun used in the photo below doesn't provide an enourmous amount of heat so blow outs are hard to do but bubbles of lesser depth result.

A suitable piece of bubble pack is cutout and tacked down over the hole on the card. The shop vac turned on and the card with plastic is placed over the vac hose nozzel plastic side up. Apply the heat source to heat the plastic uniformly until it begins to sag inward forming the bubble. Keep heating till the depth of the bubble doesn't increase any longer. If the bubble blows out just grab another square of plastic and start over again.

Try experimenting with the shape of the hole. Gun blisters and other assundry bumps and things can be formed with this method.

That's it..., Quick & Dirty Bubble Blowing or is it Sucking?

Gil

[Leif Oh]

What a nice trick - appropriate technology at its best! - Leif

[Bowdenja]

Yeah very cool..er hot Gil

[cecil_severs]

Very cool (hot) idea indeed! I came up with a very different method a while back using clear contact paper and a clear glazing glue. Just to compile a couple of methods under the same thread, here's the link:

http://www.fiddlersgreen.net/AC/airc...c/blisters.htm

At the end of the that thread there's a mention of how to make clear parts using good ol Elmers as well.

Cecil

[charliec]

That's a nice idea.

I have a memory that the section of the 3D curve you'll generate from this rig is going to be a catenary rather than a parabola or spherical section.
( I might be wrong though - never was very good at Maths). For small diameters this probably won't be an issue but it might be noticeable at larger diameters.

[ For the people who haven't run into this - a catenary is the curve which describes the shape of a string hanging between two fixed end points. Good example is the shape of the cables on a suspension bridge like the Golden Gate bridge in San Fransisco. ]

Regards,

Charlie

[Gil]

Actually the idea comes from homebuilt aircraft and is basically how a "bubble canopy" is blown without spending a great fortune (in this case vacuum formed and building your own airplane still costs a simple fortune according to the wife)...., Charlie, caternary sounds right but at this scale it's hard to tell. I've been thinking that a hollowed out shape glued to the bottom of the card (a mold) would probably work for small sized canopies and the like. I'll try one of the GPM canopies to see if this is at all feasible...,

Gil

[Maurice]

There is a school of thought which maintains that a catenary is a home for religious felines.

See
http://www.sunsite.ubc.ca/LivingMath.../catenary.html
for it's definition and an amusing demo of how it can be geometrically generated by the rotation of a square.

It requires the application of a uniform field of force always perpendicular to the line between the points of suspension.

This is not the case in blow moulding where the applied force is the result of the pressure difference.
Even though the air is being evacuated in a single direction that pressure difference will always act perpendicular to the surface, so it's direction will be constantly varying at each point of the suface as the shape develops.

Maurice

[Bowdenja]

WOW!

Math Teachers all over the world are spinning in their graves. I guess they were right after all..... we would really need that stuff when we grow up!

You guys NEVER cease to amaze me!

[charliec]

I think I stand corrected....

O.k. Maurice - what's your prediction of the shape created? Assume uniform heating of the plastic - that's probably a safe approximation with the small
working diameters used compared to the heating source.

Regards,

Charlie

[Gil]

And now for the important stuff,

Anybody tried it yet?

The F4U canopy is too big for the vac hose. Have look around for a PVC expander fitting...,

More as it happens or occurs, whichever happens or occurs first...,

Gil

[Maurice]

Charlie

Sorry, wasn't seeking to correct anything, just to explain something I'm familiar with.
Basically it will try to form a spherical surface (just like any bubble) but there is distortion due to thinning as parts of the plastic move further away from their original position and are more easily stretched.

Cheers
Maurice