Slithering Snakes!! What happened?

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mywoodshopca

mywoodshopca

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Charlottetown, PEI Canada, Derby Kansas and Canyon
Where oh where did I go wrong?

Snake skin is dry, had it in the shop for awhile now, its been glued to the tubes at least a month or two.

Cast tonight and not sure what happened after that.

Put into pressure pot - cast at about 17lbs so I wouldnt force alumilite into the tubes.

Blanks was tacky when taken out of the pot. At that time I only had one "blowout" bubble on one end where a little air must have snuck out from the tube. After they were fully dry, I saw all these bubbles.

It was under pressure at least 20 + minutes

Alumilite Crystal Clear


Thanks Jason
 

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Jason, I gave up using Crystal Clear for skins, it seems to be a waste of time, try using water clear for it.

If you are going to try it agin, leave it under pressure for a couple of hours.
 
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I had a scorpion fart once in PR. instead of bubbles, you get a nasty crack... that smells funny:eek:
 
I know bruce119 made some snakeskin blanks with Alumilite. He sold them here and I bought a few from him. There weren't any bubbles in those, so maybe shoot him a PM. I don't think Crystal Clear was available then, so it's likely he used Water Clear.
 
I'm not an alumilite user but I've been known to cast a few snake skin blanks using polyester resin. I no longer use pressure. I can't comment on how much pressure is needed for alumilite, but I can comment on the suggestion that pressure reduces the bubble size. I once thought so myself. The purpose of pressure when casting is to help prevent bubbles, not to reduce the size of the bubbles. Pressure helps to keep whatever air is in the resin in solution and not let it escape. Consider carbonated drinks such as soft drinks. Carbon dioxide is dissolved in the soda and the pressure inside the airspace of the drink keeps the carbonation in the solution. Once the cap is removed the carbon dioxide starts to release and the fizz and bubbles form. When I was still using pressure to cast PR I cast at 20psi which worked just as well as higher pressures. Good luck with your casting. Alumilite is an excellent product (so I've been told) but PR may be the better choice for snake skins of other embedded casting.
Do a good turn daily!
Don


mywoodshopca said:
I was thinking that at first too though but whats the max I could do though without forcing the alumilite into the tube?
Thanks!
Click to expand...
 
I guess how much pressure you use is somewhat dependent on how you are plugging your tubes. My thought, when I finally get around to casting blanks with the tubes, would be to turn wooden plugs that taper (picture the types of rubber plugs you used on test tubes in science class). The increase in pressure should press on the plug but not press it in completely or allow leaks.

Also..... the pressure DOES indeed crush the air bubbles. It is basic physics and can be demonstrated in many ways. I amaze kids when I inflate a seemingly empty balloon in my vacuum chamber. By simply removing the air pressure from around the outside of the balloon the little bit of air trapped inside of it can expand enough to inflate it. The exact opposite would happen if I put an inflated balloon under pressure...... it would shrink. Put it under enough pressure and it would end up totally uninflated.

The soda example given above is actually an example of this very same principle. The carbonation actually pressurizes the inside of the bottle enough to neutralize the bubbles. Open it and suddenly the pressure changes and the bubbles can once again expand.
 
buzz7164 said:
Open it and suddenly the pressure changes and the bubbles can once again expand.
Click to expand...

I think the analogy is confusing two different issues.

There's two kinds of bubbles to worry about.. the ones that are already
there, and the ones formed by the resin out-gassing.

Warming the resin will lower the viscosity and allow any existing bubbles
to easily rise to the surface.

Pressure will keep new bubbles from forming while the resin cures.

The example of the soft drink bottle does not show that "the bubbles
can once again expand" .. it shows that the pressure is stopping new
bubbles from forming.

If it were simply keeping the bubbles small enough to be invisible, then
once you open the bottle the bubbles would instantly appear, rise to the
surface, pop and be gone. But that isn't what's happening.
(plus, if you used enough pressure to make those bubbles invisible,
your soft drinks would have to come in a steel bottle)

Open the bottle and watch closely. Pick a spot in the bottle and keep your
eyes there. You can watch new bubbles forming, over and over. They
form, rise, pop and they're gone. Then another one forms right in the same
place. These are not 'previously invisible' bubbles that have been crushed
to invisibility by the small amount of pressure in the bottle. These are new
bubbles forming all the time. This is what the pressure holds in check, and
why a lot of pressure isn't needed.

As for the pressure crushing the existing bubbles till you can't see them,
I still can't get my mind around that one. Boyle's law says that when you
double the pressure, you halve the volume. It would take a helluva lot of
pressure to make those bubbles invisible to the eye.. I'm more than
half blind and I can still see them. Much easier to let those bubbles rise to
the top by warming the resin first. Putting the resin under 20 or 30 lbs
of pressure to stop any out-gassing would be icing on the cake..
 
First of all we are not talking about large air bubbles to begin with. I degas my alumilite under vacuum before mixing and then cast under pressure. The larger air bubbles will rise to the surface but the tiny ones don't have enough buoyancy to rise through the viscous resin. Alumilite sets up too quickly to try to use vibration or to simply wait it out and heating the resin will only serve to speed up the setting process.

Atmospheric pressure at sea level is a bit under 15 psi. So if we cast at 30 psi our tiny bubbles are now only half their original size (according to Boyle's Law). 60 psi and they are a quarter their original size and 80 psi (which I cast at) will create bubbles that are just slightly smaller than one fifth of their original size. Remember, these bubbles were pretty tiny to begin with and are now virtually invisible to the naked eye.
 
buzz7164 said:
Snip

Atmospheric pressure at sea level is a bit under 15 psi. So if we cast at 30 psi our tiny bubbles are now only half their original size (according to Boyle's Law). 60 psi and they are a quarter their original size and 80 psi (which I cast at) will create bubbles that are just slightly smaller than one fifth of their original size. Remember, these bubbles were pretty tiny to begin with and are now virtually invisible to the naked eye.
Click to expand...

Boyle's law states that double the pressure, half the volume. Volume and "size" are not the same thing.
 
buzz7164 said:
Okay...... they are now roughly one fifth of their original "volume". Still considerably smaller than before.

Sheeesh!
Click to expand...

My point is that replacing the word Volume with Size is inaccurate.

example:
an air bubble at sea level that has a volume of 6mm^3 has a radius of 1.12725mm

at 5 atmospheres the volume is 1.2mm^3 but it's radius is .65922mm
----------------------------------------------------------------------------------------------
Linearly the "size" of the bubble at 5atm is a bit over half of it's original "size" even though it has 1/5th the volume.


Of course I am rusty at the math, and I think mm^3 are also called centiliters
Boyle's Law is p1V1=p2V2
Volume of a sphere is V=4/3*pi*r^3
 
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Jason, while they argue the laws of physics, try a few things that may actually help you. First, make sure the scales are removed before casting, second, rub a little alumilite onto the skin with your finger or a stick to get it into all the little nooks, third, plug the tube with a dowel or rubber plugs, fourth, leave it under a higher pressure overnight.
 
wolftat said:
Jason, while they argue the laws of physics, try a few things that may actually help you. First, make sure the scales are removed before casting, second, rub a little alumilite onto the skin with your finger or a stick to get it into all the little nooks, third, plug the tube with a dowel or rubber plugs, fourth, leave it under a higher pressure overnight.
Click to expand...


Thanks lol

Will give it a try :)

Would putting a good coat of CA over it help before doing the alumilite? I imagine it would need to sit a day to degas?
 
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