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metaform3d
05-07-2008, 12:02 AM
I need to create an airtight seal that I can easily break and reform, and the seal also has to be somewhat forgiving to slop in the alignment of the parts. The approach that I have taken is not working and I was wondering if anyone had any other ideas.

What I have done is taken two flat sheets of acrylic with holes in the middle and try to line them up and form a seal. To do that I epoxied rings of hobby foam to both sides to act as gaskets, and mounted one of the plates on a servo so it could rotate into place. The problem is that even with generous amounts of petroleum jelly there is not good enough contact between the rings of foam to form a seal. If I press them together with my hands I can make it airtight, but trying to use the servo to do that just torques it more out of alignment.

One solution would be to find a different gasket material -- something that is thicker and softer than hobby foam so it could conform to misalignment between the plates, but still create an airtight seal. I don't know what that material would be or where I would find it.

Or perhaps there's another solution altogether. How can I bring two things together to form a seal but easily pull them apart again? TIA.

Eric
05-07-2008, 06:31 AM
This may not be much help, but when I come up with a challenage like that, it helps to think outside the hobby box. Go to Home Depot or similar place and talk with the plumbing pros and check out the weather stripping area. The plumbing pros might have the best advice.

Matt
05-07-2008, 10:54 AM
What about the rubber grip sheet (http://www.trossenrobotics.com/store/p/5300-Rubber-Grip-Sheet.aspx)? It is thick and will create a seal between plastic parts that aren't perfect. It's easy to cut also. You could stack layers if need be for really sloppy parts.

Sienna
05-08-2008, 12:01 PM
Can we ask what you are trying to make that you need a servo to close/open it?

I imagine for a motorized sealing system, you will need some form of alignment pins that prevent the edge from going over the screw, and maybe a worm shaft to raise / lower the sealing parts.

metaform3d
05-08-2008, 02:40 PM
It's part of my bartender bot: the iLush. I suppose I should post some pictures, but there still isn't that much to see yet. There's a set of six bottles set into a rotating rack like cartridges in a revolver. When the right one is in position the tap forms a seal which allows the siphon to suck the liquid up into the rest of the mechanism. Turns out my design for the tap doesn't work, at least using the materials I have. The rubber grip sheet looks like a good find -- I'm keeping that in mind.

Agreed about getting out of the hobby/craft mindset. I'm always on the lookout for elements from other engineering domains, especially stuff I can get at the hardware store. The iLush is cobbled together from random plumbing parts, hacked up bits of drip irrigation components, and medical gear, all bound up in a matrix of servos, motors and Phidgets.

Droid Works
05-08-2008, 02:46 PM
Just got to http://alumilite.com and buy a quick set kit and make one.

jrowe47
05-08-2008, 09:49 PM
Make sure that whatever material you use, you don't get something that can make people sick. Certain types of rubber can cause infertility in men, and can cause women to grow hair on their chests. Although, neither of those are necessarily bad things, as long as you keep the alchohol flowing. :P

Adrenalynn
05-08-2008, 11:05 PM
Make sure that whatever material you use, you don't get something that can make people sick. Certain types of rubber can cause infertility in men, and can cause women to grow hair on their chests. Although, neither of those are necessarily bad things, as long as you keep the alchohol flowing. :P

"Couple drinks and it straightens right out", huh? :p

metaform3d
05-09-2008, 03:11 AM
Yes, not killing people is pretty much implicit for a device like this. Everything is food-safe and indeed mostly medical quality.

I'm excited tonight. I've been calibrating the siphon and it's giving me almost perfectly linear outputs. Yay! I'm getting residue at the 2 ml level, but that just means the drinks have to be big. Who could have a problem with that? Unfortunately it takes about 90 seconds per oz, but... that's the cost of perfection.

Anyway, exciting to see the damn thing working for a change... Of course I've punted on the tap -- that will require some more thought for another day.