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Vacuum Forming, Movie Prop, Sci-fi and GIjOE Forum
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TK 109
Guru
Joined: 11 May 2007
Posts: 712
Location: Galena, Ohio
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 Posted: Thu Oct 11, 2007 5:47 pm Post subject: |
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OH YEAH!!
that's what its all about! (picking up ladies  )
i like that armor, you did well.
you are wise to not put it up for sale, as it would be SOOO popular you might get sued by lucasfilms the first day you put it up for sale... (that'd be bad..)
point, you do VERY NICE WORK!!
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-Alex
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drcrash
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Joined: 04 Sep 2006
Posts: 705
Location: Austin, Texas
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| Posted: Fri Oct 12, 2007 7:51 am Post subject: |
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Nice work!
| clonesix wrote: | | I had a full test of the machine this past weekend and it performed very well. A full 2X2 sheet of 0.125" HIPS was ready to go in 3 minutes, and none of the molds broke when I pulled the vacuum. |
Interesting data point. Could you tell us more about your oven... like how many coils, and the ohms across the coils? Also, do you know the actual voltage of the power you're using?
I'd be good to have that information for reference in designing over-and-under ovens. (3 minutes sounds about right for 1/8" plastic, so knowing how to replicate the watts per square foot would be good.)
BTW, in your picture, it looks like your oven is running reasonably hot (nice orange glow), so I'm wondering if you strung it tighter than the oven calculator says to. (If not, that's interesting.)
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20 gallons of reserve goes in one pull, but recharges before you can heat the next piece.
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How many CFM is your pump? (It looks reasonable-sized.) I would think that if you're getting a decent seal and your platen bottom is sealed, you'd never really run out of vacuum---after the initial pull-down, the vacuum level would go up somewhat, and stabilize at something reasonably high. (Slowly if you don't shut off the tank 2-stage style, or quickly if you do.)
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Paul (a.k.a. Dr. Crash)
Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com |
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clonesix
Novice
Joined: 19 Jan 2007
Posts: 63
Location: california
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| Posted: Sat Oct 13, 2007 11:17 pm Post subject: |
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| drcrash wrote: | Nice work!
| clonesix wrote: | | I had a full test of the machine this past weekend and it performed very well. A full 2X2 sheet of 0.125" HIPS was ready to go in 3 minutes, and none of the molds broke when I pulled the vacuum. |
Interesting data point. Could you tell us more about your oven... like how many coils, and the ohms across the coils? Also, do you know the actual voltage of the power you're using? |
I built the oven to the specs in the Thurton James book. I can't say exactly what the length of wire is, but I have 15.5 ohms per circuit, on 220V.
| drcrash wrote: |
I'd be good to have that information for reference in designing over-and-under ovens. (3 minutes sounds about right for 1/8" plastic, so knowing how to replicate the watts per square foot would be good.)
BTW, in your picture, it looks like your oven is running reasonably hot (nice orange glow), so I'm wondering if you strung it tighter than the oven calculator says to. (If not, that's interesting.) |
Don't know
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20 gallons of reserve goes in one pull, but recharges before you can heat the next piece.
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| drcrash wrote: |
How many CFM is your pump? (It looks reasonable-sized.) I would think that if you're getting a decent seal and your platen bottom is sealed, you'd never really run out of vacuum---after the initial pull-down, the vacuum level would go up somewhat, and stabilize at something reasonably high. (Slowly if you don't shut off the tank 2-stage style, or quickly if you do.) |
7 cfm Gast.
I have been getting good pulls, but I am losing a few to bad seal. I have toggle clamps on the front and back, but I feel that I may need to put one on the sides too. Someone also suggested that the platen holes are drilled too far from the edge. I don't know if drillng hole closer to the edge woul create a better seal or not. |
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drcrash
Guru
Joined: 04 Sep 2006
Posts: 705
Location: Austin, Texas
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| Posted: Sun Oct 14, 2007 3:26 pm Post subject: |
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| clonesix wrote: |
I built the oven to the specs in the Thurton James book. I can't say exactly what the length of wire is, but I have 15.5 ohms per circuit, on 220V.
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Could you clarify that? 220 volts divided by 15.5 ohms gives 14.19 amps, and muliplied by the 220 volts, that gives 3123 watts. So one 15.5 ohm segment would give roughly the right heat for a 2 x 2 foot oven. (But it would be blazing.)
Maybe I'm misunderstanding something.
The TJ book doesn't give explicit plans for a 220 oven. If you run the oven wired for 110 on 220, you'll get twice the current and four times the heat... but maybe you're using consecutive pairs of 110V segments (a la the TJ layout) as 220V segments, so that you have two segments rather than four? (Maybe that's what you mean by "two circuits"?)
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Paul (a.k.a. Dr. Crash)
Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com |
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drcrash
Guru
Joined: 04 Sep 2006
Posts: 705
Location: Austin, Texas
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| Posted: Sun Oct 14, 2007 3:40 pm Post subject: |
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| clonesix wrote: |
I have been getting good pulls, but I am losing a few to bad seal. I have toggle clamps on the front and back, but I feel that I may need to put one on the sides too. Someone also suggested that the platen holes are drilled too far from the edge. I don't know if drillng hole closer to the edge woul create a better seal or not. |
I wouldn't think so. I would think that having holes too close to the edges would be more likely to be a problem.
It looks like your platen is (or was) just melamine-covered particle board or something, cut straight, with no rounded smooth edges or gasket to make a good seal. I'd expect that to be more likely to cause problems. If you have a very sharp edge, the plastic can't bend to a tight enough radius to conform to it.
The usual thing is a rounded, very smooth edge. (Doug Walsh recommends a fairly large radius, like 1/4", I think. Mine are 1/8" or 3/16", and that seems to be working great for me, but I have only been forming thin plastic lately. I used three coats of finishing epoxy, sanding in between, to harden MDF and leave a smooth surface for the plastic to form onto.)
Are the edges of your plastic pulling away from your frames, or starting to? If not, I wouldn't think more clamps would help---your problem is not with the frames, but with getting the plastic to make a seal around the edge of the platen.
If the plastic is not making a good seal around the edges of the platen, you are likely relying on the plastic sucking down to the top surface of the platen near the edges. Drilling holes closer to the edges might interfere with that and make things worse, not better. If your platen surface is textured, not smooth, that could interfere, too.
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Paul (a.k.a. Dr. Crash)
Tired of buying cheap plastic crap? Now you can make your own! www.VacuumFormerPlans.com |
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knightshade
Expert
Joined: 19 Jun 2005
Posts: 123
Location: Rochester NY
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| Posted: Sun Oct 14, 2007 4:40 pm Post subject: |
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| clonesix wrote: |  |
I've seen this type of over/under design a few times, along with a lever to raise/lower the plastic holding frame.
Overall - I'm liking the design.
Two basic advantages that I'm seeing are:
1.) ease of one man operation
2.) Space Saving (so far as floor space is concerned)
The down side is that I'm guessing that one has to have more advanced construction skills to put it together.
Any tips for someone considering to rework their table? |
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