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Model Forum / General / Rockets / January 2006vacumm bagging, another approach?
someone tell me if my theory is wrong, but with vac bagging you only get a total of 14psi force onthe parts you are attempting to bag. whay not sink it into a pool with tons of water? rather than suck the air out, you squeeze it out. not a perfect solution, but with the addition of a weak vacuum pump, you would be guearanteed a perfect setup. a bit too late(early?) to be thinking, but since i am up and got the newsreader to finally work..... > someone tell me if my theory is wrong, but with vac bagging you only get a > total of 14psi force onthe parts you are attempting to bag. > > whay not sink it into a pool with tons of water? rather than suck the air > out, you squeeze it out. To get one atmosphere of pressure you have to go down 33 feet. A backyard pool with a depth of 6 feet gives less than 3psi. 12 feet gives about 5.5psi. It might add a little extra squeeze, but not much. >> someone tell me if my theory is wrong, but with vac bagging you only >> get a total of 14psi force onthe parts you are attempting to bag. [quoted text clipped - 7 lines] > > It might add a little extra squeeze, but not much. Lemme guesss.... you scuba? Ted Novak TRA#5512 IEAS#75 >> To get one atmosphere of pressure you have to go down 33 feet. A >> backyard pool with a depth of 6 feet gives less than 3psi. 12 feet [quoted text clipped - 3 lines] > > Lemme guesss.... you scuba? Yup. Recertified after 20+ years and planning a trip to the Florida Keys with my son's Boy Scout troop. There's no such thing as too many hobbies, is there? ;-) >>> To get one atmosphere of pressure you have to go down 33 feet. A >>> backyard pool with a depth of 6 feet gives less than 3psi. 12 feet [quoted text clipped - 7 lines] > Keys with my son's Boy Scout troop. There's no such thing as too many > hobbies, is there? ;-) I certified in '82 on Maui. Haven't dived, or gone back since '85 but my sis still scubas when she goes down to FL. When people ask me about the scuba experience I just tell them it's damn near religious. Something about swimming with sharks and not getting eaten :) Ted Novak TRA#5512 IEAS#75 > When people ask me about the scuba experience I just tell them it's damn > near religious. Something about swimming with sharks and not getting > eaten :) I didn't know you were a lawyer.  SignatureBob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<< Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf www.encompasserve.org/~kaplow_r/ www.nira-rocketry.org www.nar.org Homeland Security Administration: The Gestapo of the 21st Century >>When people ask me about the scuba experience I just tell them it's damn >>near religious. Something about swimming with sharks and not getting >>eaten :) > > I didn't know you were a lawyer. No but I do work for them. Just started a new gig at a firm today :) Ted Novak TRA#5512 IEAS#75 >>> When people ask me about the scuba experience I just tell them it's >>> damn near religious. Something about swimming with sharks and not [quoted text clipped - 7 lines] > TRA#5512 > IEAS#75 Do You keep the spear gun handy? >>>> When people ask me about the scuba experience I just tell them it's >>>> damn near religious. Something about swimming with sharks and not [quoted text clipped - 9 lines] > > Do You keep the spear gun handy? Well, I could hold the *data* for ransom.... Ted Novak TRA#5512 IEAS#75 > No but I do work for them. Just started a new gig at a firm today :) I could use one about now too. Been out for just over 2 months. My computer and my job went to florida, and I didn't even get a t-shirt :-( SignatureBob Kaplow NAR # 18L >>> To reply, there's no internet on Mars (yet)! <<< Kaplow Klips & Baffle: http://nira-rocketry.org/Document/MayJun00.pdf www.encompasserve.org/~kaplow_r/ www.nira-rocketry.org www.nar.org Homeland Security Administration: The Gestapo of the 21st Century >>No but I do work for them. Just started a new gig at a firm today :) > > I could use one about now too. Been out for just over 2 months. My computer > and my job went to florida, and I didn't even get a t-shirt :-( I hear ya brutha. I've spent about 12 months total unemployed since 9/11. Sucks when your single and have high mortgage. Needless to say this took a big toll on rocket stuff, but there's more important things in life. The only reason I've been able to fly the last 4 1/2 years is because I stocked up big time on motors and kits years ago. About 3 weeks ago I started my first build since 9/11. Granted they're modrocs but what the hell, I'm building rockets. I'm giving myself 2 more years in IT then it's on to something else. No clue what it'll be but I'm going to make certain it's great. I'm getting too old for this IT sh.t. Ted Novak TRA#5512 IEAS#75 > I'm giving myself 2 more years in IT then it's on to something else. No > clue what it'll be but I'm going to make certain it's great. I'm > getting too old for this IT sh.t. Decades ago I thought IT was the ticket. I was a hot-shot Systems Programmer (remember those) with a goal of becoming a Data Center manager by 30. It was a fun job for someone right out of college. Luckily I made a couple of job changes that landed me in development and then design, first in software and now hardware. IT is basically a support role, which makes it ripe for outsourcing. Plus technology changes so rapidly its hard to keep your skills honed on tomorrows technology while keeping yesterday's running. I think corporate IT is a dead-end, but personal services has a huge future. If "professionals" have a hard time understanding today's technology, how can "normal" people cope? I regularly field questions from relatives on what seems like trivial problems to me. If you can stand to work with ignorant (not stupid) people and help them use technology (e.g. setting up a digital camera, monthly/quarterly software maintanance) there is a growing market opportunity. >>When people ask me about the scuba experience I just tell them it's damn >>near religious. Something about swimming with sharks and not getting >>eaten :) > > I didn't know you were a lawyer. He didn't say He *was* a shark. >>>When people ask me about the scuba experience I just tell them it's damn >>>near religious. Something about swimming with sharks and not getting [quoted text clipped - 3 lines] > > He didn't say He *was* a shark. Remora? >> someone tell me if my theory is wrong, but with vac bagging you only get >> a total of 14psi force onthe parts you are attempting to bag. [quoted text clipped - 7 lines] > > It might add a little extra squeeze, but not much. would i be correct then to say that dropping down to 33 feet will be the equivalent of pulling full vacuum then? ok, so a pool wont do it......but the laze at one of our launch sites would do. wazee lake, 355 feet. wonder what kind of rube goldberg device i'd have to build for that? >>>someone tell me if my theory is wrong, but with vac bagging you only get >>>a total of 14psi force onthe parts you are attempting to bag. [quoted text clipped - 14 lines] > do. wazee lake, 355 feet. wonder what kind of rube goldberg device i'd have > to build for that? Why not just use heat shrink tape, aerosleeve glass and a heat gun? Ted Novak TRA#5512 IEAS#75 > ater Schuld wrote: > > someone tell me if my theory is wrong, but with vac bagging you only get [quoted text clipped - 10 lines] > > It might add a little extra squeeze, but not much. Why not put it into a bucket of wet concrete???? The extra density of the concrete should work wonders. Besides, when the concrete cures your part is sure to never come appart!!! KT >someone tell me if my theory is wrong, but with vac bagging you only get a >total of 14psi force onthe parts you are attempting to bag. [quoted text clipped - 7 lines] >a bit too late(early?) to be thinking, but since i am up and got the >newsreader to finally work..... The pool should work if you don't crush the tubes. Why? More pressure is not better. In fact, you can overdo it and end up with a structure that doesnt have enough resin just using a good vacuum pump. > someone tell me if my theory is wrong, but with vac bagging you only get a > total of 14psi force onthe parts you are attempting to bag. [quoted text clipped - 7 lines] > a bit too late(early?) to be thinking, but since i am up and got the > newsreader to finally work..... i was hpoing someone would bring that up. wonder how you could counteract that.......maybe an excess resin to meet the volume of the excess resivoir. need to have a floatign check valve then. rube goldberg indeed. note: planning on something big, so buying a vacuum pump may be prohibitive, renting non-realistic. maybe using a gas engine driven by an electric motor. hmmmm > Why? More pressure is not better. In fact, you can overdo it and end up > with a structure that doesnt have enough resin just using a good vacuum [quoted text clipped - 12 lines] >> a bit too late(early?) to be thinking, but since i am up and got the >> newsreader to finally work..... I've done 5.5" tubes using a Foodsaver vacuum sealer. I've also had very good luck with release + breather only (no vacuum). The benefit of vacuum is that it removes more resin which means it saves weight. There is no benefit in the strength of the composite. I did a quick estimate once on how much weight I could save on a large rocket (say 25lbs dry) using vacuum (2:1 fabric:resin) vs not (1:1). IIRC, less than a pound (assuming 3 wraps of 5oz cloth). Made me wonder why I even bother. On smaller/lighter rockets the weight savings may be worth the effort. I think sinking a large tube, in a waterproof bag, 33 feet under water just to save a few ounces of resin weight is, well, silly. But hey, this is a hobby right ;-) > i was hpoing someone would bring that up. wonder how you could counteract > that.......maybe an excess resin to meet the volume of the excess resivoir. [quoted text clipped - 6 lines] > > maybe using a gas engine driven by an electric motor. hmmmm There is an optimum ratio of fabric to resin which is 60:40 (fabric to resin) for most of the stuff we are likely to use. This is pretty dry looking. If you get too much resin on the part, it can clog the breather, ooze down the vacuum line, and into the pump. I've never gotten farther than into the first few inches of vacuum line, but I tend to use a long line now to ensure that it never makes it to the pump. Larry > I've done 5.5" tubes using a Foodsaver vacuum sealer. > [quoted text clipped - 22 lines] > > > > maybe using a gas engine driven by an electric motor. hmmmm >i was hpoing someone would bring that up. wonder how you could counteract >that.......maybe an excess resin to meet the volume of the excess resivoir. [quoted text clipped - 23 lines] >>> a bit too late(early?) to be thinking, but since i am up and got the >>> newsreader to finally work..... You're starting to sound like you are serious about this. If you are you should do your homework before you jump in. 8-) You dont need a big pump to do a big project, unless we're talking about something on the scale of a boat hull. Assuming we're talking about rockets, any vacuum pump will do. It doesnt take much CFM to do vacuum bagging. In fact, I often use a vacuum cleaner to get most of the air out of the bag first, then switch to the vacuum pump. If you've got a compressor you can use one of those venturi vacuum generators. > i was hpoing someone would bring that up. wonder how you could counteract > that.......maybe an excess resin to meet the volume of the excess resivoir. [quoted text clipped - 23 lines] > >> a bit too late(early?) to be thinking, but since i am up and got the > >> newsreader to finally work..... > You dont need a big pump to do a big project, unless we're talking about > something on the scale of a boat hull. yes i am > Assuming we're talking about rockets, any vacuum pump will do. It doesnt > take much CFM to do vacuum bagging. In fact, I often use a vacuum cleaner > to get most of the air out of the bag first, then switch to the vacuum > pump. i've heard that aricraft builders don't even use the vacuum pump in this method. but you do need to use a vacuum that uses and extra fan to cool the motor as most use the vacuum impeller for double duty > If you've got a compressor you can use one of those venturi vacuum > generators. [quoted text clipped - 32 lines] >> >> a bit too late(early?) to be thinking, but since i am up and got the >> >> newsreader to finally work..... I use a surplus medical vacuum pump rated for continuous duty to do glider wings and rocket parts. If you can get a good enough seal on your bag, it should work to hold a vacuum on something as big as a boat hull. You'd have to use something like a shop vac to remove most of the air and then seal off that opening. The bag can be a sheet of polyethlene folded over like a taco and sealed with Moretite caulk. That's the grey stuff that comes on a roll and looks like a sticky modeling clay. I found a box at Home Depot years ago and am still using it. You warm a strip by rolling it in your hands, put it between the two layers of poly you want to seal, and use a wall paper roller (a little wood wheel about an inch wide and maybe 2 inches in diameter on a handle) to press everything firmly together. Just work around the envelope a little at a time and make sure not to puncture it. I honestly don't know if you can get a good enough seal on something that big since I've spent a fair amount of time chasing leaks in a rocket sized bag. The most common leaks are where the vacuum pump line hooks in and anywhere you get a crease or wrinkle in the poly. For a job this size, you should put a trap in the line to capture excess resin so it does not go into the pump. A thick jar with fittings in the lid to allow the line from the pump to come in one and another line to continue on to the bag should work. I know from experience that a plastic gasoline can is not strong enough. :-( > in and anywhere you get a crease or wrinkle in the poly. For a job > this size, you should put a trap in the line to capture excess resin so > it does not go into the pump. A thick jar with fittings in the lid to > allow the line from the pump to come in one and another line to > continue on to the bag should work. I know from experience that a > plastic gasoline can is not strong enough. :-( I wonder if a 5 gal bucket could stand up to the vacuum>? >> in and anywhere you get a crease or wrinkle in the poly. For a job >>this size, you should put a trap in the line to capture excess resin so [quoted text clipped - 4 lines] > > I wonder if a 5 gal bucket could stand up to the vacuum>? Unlikely. >>> in and anywhere you get a crease or wrinkle in the poly. For a job >>>this size, you should put a trap in the line to capture excess resin so >>>it does not go into the pump. A thick jar with fittings in the lid to >>>allow the line from the pump to come in one and another line to >>>continue on to the bag should work. I know from experience that a >>>plastic gasoline can is not strong enough. :-( >> I wonder if a 5 gal bucket could stand up to the vacuum>? >Unlikely. I know from experience that a 55 gal. steel drum will not withstand a strong vacuum. >I know from experience that a 55 gal. steel drum will not withstand a >strong vacuum. > > Will it stand up to a light dusting??? David Erbas-White >> I know from experience that a 55 gal. steel drum will not withstand a >> strong vacuum. [quoted text clipped - 4 lines] > > David Erbas-White Well I think the Henderson incident proved that it can't. Ted Novak TRA#5512 IEAS#75 >>> I know from experience that a 55 gal. steel drum will not withstand a >>> strong vacuum. [quoted text clipped - 10 lines] > TRA#5512 > IEAS#75 Ah yes, The Florence Henderson incident, I just hope something like that never happens again. >>I know from experience that a 55 gal. steel drum will not withstand a >>strong vacuum. [quoted text clipped - 4 lines] > >David Erbas-White About 20", IIRC, YMMV, Etc. |
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