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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#41
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Vacuum chamber ideas
On Fri, 22 Oct 2010 22:17:12 -0700, "Califbill"
wrote: Just build a reinforced metal top with a small window or two in it. You do not need to see what is happening except for grins. Could grind a lens on the end of a plastic slug to see all over the cavity. Im still wondering how the OP is going to close the bags of food when the vacuum has been achieved if he cant reach inside. "DoN. Nichols" wrote in message ... On 2010-10-21, RS at work wrote: DoN. Nichols wrote: Yes, it does. But ... [ ... my post snipped ... ] DoN, I appreciate your criticism. I find that the process of designing something even more satisfying than building the thing it self. I have set an arbitrary goal of $200 for building this project, which may or may not be doable; nothing is cast in stone yet. O.K. For the top of the chamber I was originally thinking about some 1? Lexan, then I priced the stuff, not cheap. :-) I then asked myself how strong does it have to be? And, is there something else that can do the job cheaper? Tempered glass is pretty strong stuff. I have seen a 200# person stand on the glass of a pinball machine. And that is only 1/4? thick. I think that the centers of some of the bumpers are support columns distributed over the top, so I'm not sure what this proves without knowing precisely where the weight was applied, and where the support columns were relative to that. In checking a bit, I noted that one glass company shows a guy jumping up and down on a sheet of 3/8 supported on wood blocks about 5 feet apart. That is somewhat more meaningful. I also noted that people build big aquariums out of glass and acrylic glued together and supporting holding tons of water. We don't know what other support members may be present hidden from view. While I am not sure, I suspect that a clear span of 14? X 16? X 3/8 or 1/2 might support the 3,300 lbs of pressure and still give an acceptable safety factor. I have a call into the glass company to check with the engineers that know. O.K. They will certainly err on the conservative side. Assuming I will get a satisfactory reply to the glass inquiry, the plastic sidewall I described admittedly sounds like a failure waiting to happen, but here is my thinking. Assume that you have a nice thick chunk of 6? pipe sealed on one end, and on the open end you have a sheet of Plexiglas and a rubber gasket. If a vacuum were drawn out of the pipe would a 1/4 sheet of acrylic have the ability to resist fracture if you got near a full vacuum? I think it would, as it is about 300 lbs. evenly applied over about 19 square inches. Hmm ... I don't know the ID of your "6?" (which I presume to be 6 inch) pipe, so calculating from the OD, I come up with 28.27 square inches, or 145.6 pounds total force. Now if you can accept that proposition, think about a 1/4? sheet of Plexiglas that is 6 ? by 4? and has a 1/4? X 1/2 bonded to each one of the 4? ends and between and along the 6 inch sides you have two 3/8 thick sides that are 1 inch high and are tee shaped with the top of the tee being 1/2? high 6 1/2? wide and the bottom being 5 1/2? wide and bonded to the ends with the tabs sticking out. Again -- I don't trust the bonded principle. There are a lot of things which can go wrong in the bonding. And -- if you are going to try solvent bonding over a large area -- expect the solvent to be trapped in the center areas, weakening them. And -- add to that the fact that acryllic tends to form cracks from exposure to oil (from the machine tool which fabricated the parts, unless you worked with totally clean new tools dipped in acetone to wash off the oil before cutting. Also -- all clamping surfaces will similarly need to be cleaned of oil totally. What you would have would be a Plexiglas box with 1/2? sidewalls and 4 tabs that are 3/8? X 1/2? X 1/2?. Until I see evidence to the contrary, I am reluctant to consider two layers of Plexiglas bonded together to be any stronger than the thicker of the two individual layers. If you were then to suspend this box on the tabs between two rails and loaded the box with 360 lbs., would it hold? I think it would. This looks a lot smaller than what you originally wanted in volume. Now if I haven?t lost you yet, the top and bottom of the chamber are going to be exerting a total force against the sidewalls of about 6,720 lbs. This will be supported by about 15 square inches of Plexiglas that is 6 inches high. Would a block of Plexiglas 3 3/4 inches square and 6 inches high support 6,720 lbs.? Maybe -- but consider that the walls are undergong lateral force which could weaken them. Consider a pipe 20' tall supporting a load something like 80% of the calculated safe load. Then apply 20% of that force sideways to the center of the pipe. What would happen? As far as the glue joints go, the glue joints should be stronger than the plastic itself. This -- I don't trust. Especially with the surface area being solvent glued together. How long would it take the solvent to dry in the center of the glued surface? If my thinking is off here I would like to know where. The regular RCMer?s tend to be a bunch that is pretty damn smart, which is why I tossed the concept out there. Well ... I tend to be rather conservative when it comes to vacuum containers. And for the tempered glass -- what happens with that if a scratch is applied to the surface -- especially on the center of the inside, so it becomes a stress riser. The cost between Plexiglas and Lexan is not much, so I might opt to go that route, also I might increase the number of side support ribs to spread out the load a bit more to increase the safety factor, it kind of depends on the yield I can get from a stock sheet of plastic. I would feel more comfortable with Lexan. It is not as brittle as Plexiglas. (Have you ever used the scribe and bend method of cutting Plexiglas?) Thanks again for your criticism. You're welcome. Best of luck, DoN. I am the Sword of my Family and the Shield of my Nation. If sent, I will crush everything you have built, burn everything you love, and kill every one of you. (Hebrew quote) |
#42
Posted to rec.crafts.metalworking
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Vacuum chamber ideas
Gunner Asch on Sat, 23 Oct 2010 01:59:35 -0700
typed in rec.crafts.metalworking the following: On Fri, 22 Oct 2010 22:17:12 -0700, "Califbill" wrote: Just build a reinforced metal top with a small window or two in it. You do not need to see what is happening except for grins. Could grind a lens on the end of a plastic slug to see all over the cavity. Im still wondering how the OP is going to close the bags of food when the vacuum has been achieved if he cant reach inside. You know about the little man who turns off the light in the refrigerator? He has a cousin who owns a vacuum suit and is looking for work ... pyotr -- pyotr filipivich We will drink no whiskey before its nine. It's eight fifty eight. Close enough! |
#43
Posted to rec.crafts.metalworking
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Vacuum chamber ideas
"pyotr filipivich" wrote in message news Gunner Asch on Sat, 23 Oct 2010 01:59:35 -0700 typed in rec.crafts.metalworking the following: On Fri, 22 Oct 2010 22:17:12 -0700, "Califbill" wrote: Just build a reinforced metal top with a small window or two in it. You do not need to see what is happening except for grins. Could grind a lens on the end of a plastic slug to see all over the cavity. Im still wondering how the OP is going to close the bags of food when the vacuum has been achieved if he cant reach inside. You know about the little man who turns off the light in the refrigerator? He has a cousin who owns a vacuum suit and is looking for work ... pyotr Actually is easy. Just like a Tillia Food Saver. And every vacuum chamber one I have seen. You put the bag end on top of the sealer bar and neoprene / flexible gasket comes down against the bag and bar. the pressure is light and the air can be sucked out. Then when the heating bar is energized the gasket gives enough pressure to ensure a seal when the plastic is melted. And the little guy who controls the refrigerator light enjoys a moment of warmth from the heating bar. -- pyotr filipivich We will drink no whiskey before its nine. It's eight fifty eight. Close enough! |
#44
Posted to rec.crafts.metalworking
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Vacuum chamber ideas
On Sun, 24 Oct 2010 11:00:02 -0700, "Califbill"
wrote: "pyotr filipivich" wrote in message news Gunner Asch on Sat, 23 Oct 2010 01:59:35 -0700 typed in rec.crafts.metalworking the following: On Fri, 22 Oct 2010 22:17:12 -0700, "Califbill" wrote: Just build a reinforced metal top with a small window or two in it. You do not need to see what is happening except for grins. Could grind a lens on the end of a plastic slug to see all over the cavity. Im still wondering how the OP is going to close the bags of food when the vacuum has been achieved if he cant reach inside. You know about the little man who turns off the light in the refrigerator? He has a cousin who owns a vacuum suit and is looking for work ... pyotr Actually is easy. Just like a Tillia Food Saver. And every vacuum chamber one I have seen. You put the bag end on top of the sealer bar and neoprene / flexible gasket comes down against the bag and bar. the pressure is light and the air can be sucked out. Then when the heating bar is energized the gasket gives enough pressure to ensure a seal when the plastic is melted. And the little guy who controls the refrigerator light enjoys a moment of warmth from the heating bar. So they already have this nifty closing device ready to put in their various tubing and tanks? Gunner I am the Sword of my Family and the Shield of my Nation. If sent, I will crush everything you have built, burn everything you love, and kill every one of you. (Hebrew quote) |
#45
Posted to rec.crafts.metalworking
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Vacuum chamber ideas
"Gunner Asch" wrote in message
news On Sun, 24 Oct 2010 11:00:02 -0700, "Califbill" wrote: "pyotr filipivich" wrote in message news Gunner Asch on Sat, 23 Oct 2010 01:59:35 -0700 typed in rec.crafts.metalworking the following: On Fri, 22 Oct 2010 22:17:12 -0700, "Califbill" wrote: Just build a reinforced metal top with a small window or two in it. You do not need to see what is happening except for grins. Could grind a lens on the end of a plastic slug to see all over the cavity. Im still wondering how the OP is going to close the bags of food when the vacuum has been achieved if he cant reach inside. You know about the little man who turns off the light in the refrigerator? He has a cousin who owns a vacuum suit and is looking for work ... pyotr Actually is easy. Just like a Tillia Food Saver. And every vacuum chamber one I have seen. You put the bag end on top of the sealer bar and neoprene / flexible gasket comes down against the bag and bar. the pressure is light and the air can be sucked out. Then when the heating bar is energized the gasket gives enough pressure to ensure a seal when the plastic is melted. And the little guy who controls the refrigerator light enjoys a moment of warmth from the heating bar. So they already have this nifty closing device ready to put in their various tubing and tanks? Gunner Just get an old Food saver or build a gasket holder over the heater bar. http://www.abcoffice.com/mvs-31-views.htm Picture. Notice a silicon gasket at the top. |
#46
Posted to rec.crafts.metalworking
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Vacuum chamber ideas
Winston_Smith wrote:
On Wed, 13 Oct 2010 16:26:23 -0700 (PDT), RS at work wrote: Also if the stuff you are sealing is juicy it sucks the juice out of the bag and fouls the pump. The instructions say to freeze or partially freeze juicy foods before sealing. Over night does it. --- news://freenews.netfront.net/ - complaints: --- What it does is lower the boiling point and it "boils over". Can you say " Freeze dried ". :-) ...lew... |
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