50AE Posted August 8, 2011 Posted August 8, 2011 (edited) This thread will be related with vacuum hemispheres discussion and making. I must say I am very happy with this technology. Making molds is a piece of cake, forming the hemis is fast and pleasant and the cleanup is easy. The mold: I use to do them with a fiberglass impregnated polyester resin, generally used as a body kit. It's not as strong as fiberglass and epoxy, but it works good. A spherical shape is also needed on which the mold will be formed. A rubber ball for kids is a good start, if you can find the right size. Remember that the wet hemispheres shrink when they dry, so a slightly large mold must be done. I do 94mm ID on 4" and 118mm for 5".Furthermore, remember to coat the ball with something a separator, I found out that vegetable oil works well.The holes should be tiny, I drill them with a 3mm bit.Then PVC pipe segments are used to adapt the mold to the vacuum pipe. http://img543.imageshack.us/img543/5568/picture00211.th.jpg http://img52.imageshack.us/img52/4035/21757020378607632164110.th.jpg http://img37.imageshack.us/img37/3941/25255721838341486190710.th.jpg These are old photos and I don't recommend the way the mold on the middle pic is fixed. The edges of the mold should be on top of the housing, not inside of it like on the image. I experienced some problems with the edges breaking. The vacuum Most vacuum cleaners that are water compatible will work, I'm working with a 1.5kW vac, it works very well for the 5", perhaps it will do for the 7" as well. Choice of paper and preparing the mulch The best paper to use is recycled kraft. It is cheap and it gets soft when wet. While only newspapers work too, they tend to form too fragile hemis, which deform very easily when wet. A mix of kraft and newspaper would work well, but I don't like the printed paper, because it tends to blacken my blender in a very nasty, uncleanable way.I use the dirty kraft sheets from my working surfaces, I like to be green. The blades of the blader tend to blunt very fast, so they should be sharpened from time to time.Of course, glue has to be added to the mulch. The best one is wheat paste, as it is cheap, avaible and gives a quite good resistance to the wet hemi. I use to eyeball the glue, I prepare wheat paste from about 50g of wheat flour and I add them to 10L of mulch.Water ratio to paper is not critical, I add until I feel the mulch is not thick and lets my hand swim freely. http://img812.imageshack.us/img812/2929/picture354y.th.jpg The process This is where the fun comes in. You have to turn on the vacuum and dive the mold into the mulch for a few seconds. The more it stays inside, the more paper it will pick up and the thicker hemi will be. You will have to practice a bit to get the feel. When taking off the mold, the paper will will be rough. A balloon or a rubber ball has to be pushed to smoothen the surface. During this, don't stop the vac, let it run to keep the hemi glued to the mold. After smoothing, hang the mold very closely to your table to drop the hemi onto it. Then stop the vac or remove the pipe off. Sometimes the hemi won't fall itself, so you will have to blow into the mold. http://img14.imageshack.us/img14/4091/picture345e.th.jpg http://img155.imageshack.us/img155/6710/picture347f.th.jpg http://img834.imageshack.us/img834/5458/picture348v.th.jpg http://img28.imageshack.us/img28/1365/picture349.th.jpg http://img846.imageshack.us/img846/5508/picture351v.th.jpg http://img215.imageshack.us/img215/3492/picture352z.th.jpg http://img23.imageshack.us/img23/584/picture353d.th.jpg The hemis They are fragile when wet, so they must be carefuly let for drying. Afterwards they become quite hard when dry. The edges are cut using scissors. They must be coated with a laquer or parrafin to make them waterproof, because they will get fragile with the pasting. http://img849.imageshack.us/img849/1481/picture355a.th.jpg http://img820.imageshack.us/img820/3573/picture357r.th.jpg 100% newspaper 4" hemis: http://img812.imageshack.us/img812/8972/vacuum43.th.jpg Conclusion It's a great, fun and fast way. When you get the feel, you can do a hemi per minute. If you make a mistake, you can always throw the bad hemi into the mulch. The most boring part is the paper blending process.These hemis are much weaker than the classic rye straw/paper commercial ones and the breaks are better, because the equator is less significant. A 5" shell with vacuum formed hemispheres: http://img814.imageshack.us/img814/1046/picture194o.th.jpg P.S. I am a Firebreather now Edited August 8, 2011 by 50AE
50AE Posted August 8, 2011 Author Posted August 8, 2011 The idea is not mine, it is taken from a member of passfire. It isn't very old though. One should try to commercialize it and start selling hemis in bulk for cheap They are quite light as well.
allrocketspsl Posted August 8, 2011 Posted August 8, 2011 This thread will be related with vacuum hemispheres discussion and making. I must say I am very happy with this technology. Making molds is a piece of cake, forming the hemis is fast and pleasant and the cleanup is easy. The mold: I use to do them with a fiberglass impregnated polyester resin, generally used as a body kit. It's not as strong as fiberglass and epoxy, but it works good. A spherical shape is also needed on which the mold will be formed. A rubber ball for kids is a good start, if you can find the right size. Remember that the wet hemispheres shrink when they dry, so a slightly large mold must be done. I do 94mm ID on 4" and 118mm for 5".Furthermore, remember to coat the ball with something a separator, I found out that vegetable oil works well.The holes should be tiny, I drill them with a 3mm bit.Then PVC pipe segments are used to adapt the mold to the vacuum pipe. http://img543.imageshack.us/img543/5568/picture00211.th.jpg http://img52.imageshack.us/img52/4035/21757020378607632164110.th.jpg http://img37.imageshack.us/img37/3941/25255721838341486190710.th.jpg These are old photos and I don't recommend the way the mold on the middle pic is fixed. The edges of the mold should be on top of the housing, not inside of it like on the image. I experienced some problems with the edges breaking. The vacuum Most vacuum cleaners that are water compatible will work, I'm working with a 1.5kW vac, it works very well for the 5", perhaps it will do for the 7" as well. Choice of paper and preparing the mulch The best paper to use is recycled kraft. It is cheap and it gets soft when wet. While only newspapers work too, they tend to form too fragile hemis, which deform very easily when wet. A mix of kraft and newspaper would work well, but I don't like the printed paper, because it tends to blacken my blender in a very nasty, uncleanable way.I use the dirty kraft sheets from my working surfaces, I like to be green. The blades of the blader tend to blunt very fast, so they should be sharpened from time to time.Of course, glue has to be added to the mulch. The best one is wheat paste, as it is cheap, avaible and gives a quite good resistance to the wet hemi. I use to eyeball the glue, I prepare wheat paste from about 50g of wheat flour and I add them to 10L of mulch.Water ratio to paper is not critical, I add until I feel the mulch is not thick and lets my hand swim freely. http://img812.imageshack.us/img812/2929/picture354y.th.jpg The process This is where the fun comes in. You have to turn on the vacuum and dive the mold into the mulch for a few seconds. The more it stays inside, the more paper it will pick up and the thicker hemi will be. You will have to practice a bit to get the feel. When taking off the mold, the paper will will be rough. A balloon or a rubber ball has to be pushed to smoothen the surface. During this, don't stop the vac, let it run to keep the hemi glued to the mold. After smoothing, hang the mold very closely to your table to drop the hemi onto it. Then stop the vac or remove the pipe off. Sometimes the hemi won't fall itself, so you will have to blow into the mold. http://img14.imageshack.us/img14/4091/picture345e.th.jpg http://img155.imageshack.us/img155/6710/picture347f.th.jpg http://img834.imageshack.us/img834/5458/picture348v.th.jpg http://img28.imageshack.us/img28/1365/picture349.th.jpg http://img846.imageshack.us/img846/5508/picture351v.th.jpg http://img215.imageshack.us/img215/3492/picture352z.th.jpg http://img23.imageshack.us/img23/584/picture353d.th.jpg The hemis They are fragile when wet, so they must be carefuly let for drying. Afterwards they become quite hard when dry. The edges are cut using scissors. They must be coated with a laquer or parrafin to make them waterproof, because they will get fragile with the pasting. http://img849.imageshack.us/img849/1481/picture355a.th.jpg http://img820.imageshack.us/img820/3573/picture357r.th.jpg 100% newspaper 4" hemis: http://img812.imageshack.us/img812/8972/vacuum43.th.jpg Conclusion It's a great, fun and fast way. When you get the feel, you can do a hemi per minute. If you make a mistake, you can always throw the bad hemi into the mulch. The most boring part is the paper blending process.These hemis are much weaker than the classic rye straw/paper commercial ones and the breaks are better, because the equator is less significant. A 5" shell with vacuum formed hemispheres: http://img814.imageshack.us/img814/1046/picture194o.th.jpg P.S. I am a Firebreather now i use to use the cellouse fiber comes in a brick at stores like Michaels craft dries hard now using news paper for my mold just put up pyrobin positive and negative using wall paper paste harden,just tried polyurethane works good also and water soluable so i go back and forth
50AE Posted August 8, 2011 Author Posted August 8, 2011 I guess one comma is better than nothing Judging from the pic on pyrobin, your mold seems nice, but it's not vacuum. Are you saying you put paper mulch and press it? How do you take the hemi out?
Mumbles Posted August 8, 2011 Posted August 8, 2011 Another potential source for newspaper quality (kind of a misnomer ) paper is in the form of certain "green" insulations. They essentially use ground up and fluffed newspaper to make certain insulations. Additionally if one has ever moved they may be familiar with the off white packing paper sheets that is sometimes used to cover dishes and other more fragile things. This is simply unprinted news paper. Having moved several times in my life, this is what I use to cover my work area. Someone did try to commercialize this process, at least for their own personal commercial production. It was still cheaper to buy them from China though. It may be worth it for the larger sizes, but that brings with it it's own set of challenges. I was told that it's difficult to go much beyond 6". The larger shells tend to be too heavy when loading them, and tended to tear themselves apart. Even some low quality straw board hemispheres do that, but given how they're constructed, it's an easy fix. I've been interested in this method, and have worked on it a little bit, but it never really worked out extremely well for me. The hemispheres, even quite small tended to be too soft. I'm sure it was a technique thing on my end. A layer of masking tape works to waterproof the shells enough to paste for what it's worth.
allrocketspsl Posted August 9, 2011 Posted August 9, 2011 I guess one comma is better than nothing Judging from the pic on pyrobin, your mold seems nice, but it's not vacuum. Are you saying you put paper mulch and press it? How do you take the hemi out? news paper and wall paper paste,dries rock hard.over the positive saran wrap in the negative no need it pops out easily as the mold is porus(water putty).If your using just fiber try cellulose fiber it has a hardener in the fiber costing more but not much more craft stores sells bricks of it,for how your doing it would be perfect,just a thought!
DeepOvertone Posted August 9, 2011 Posted August 9, 2011 You can go to where they print newspapers and get rolls of the unprinted news paper. If they stop a production run before the roll runs out they usually don't put that roll back on the machine and they will sell the leftover roll for cheap. This is also a good work surface cover.
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