I know this has nothing to do with robotics and I’m not sure if I am posting this topic in the right place? I’m not and I’m having a little trouble navigating this forum. Anyway, I am in the midst of building a vacuform machine. I still need to make some final decisions on size, but I have the most of it worked out. Problem is, I am not much of an electrician, I don’t really know enough out it to say I can competently wire something together correctly without step-by step instructions. I’m veering away from what the usual standard vacuum source is. Most people rely on a tank to pull all the air out to create the vacuum combined with the use of a vacuum pump. I need to consolidate my use of space and a tank will take up too much space. So, I am going to use (once I decide which to purchase) an industrial vacuum motor with a high CFPM capability. Something in the neighborhood of 130-150 CFPM (or higher). Wiring it… I’m hoping it isn’t too difficult? I need to be able to wire it to an on/off switch. A foot switch would be great, but I’m not sure I can do that? And of course, have it wired for a standard 11v-12v outlet for power. That’s the primary vacuum source with a vacuum pump as a secondary source to get as close to 29hg (optimum vacuum) as possible. The rest is kind of logistically challenging which I can hopefully work out net working with people I know. The real problem is designing and building the oven. I flat out am stumped doing that. I need the oven to have a wide range of adjustable temperatures ranging between 150 deg. F upward of 450 deg. F to be able to set and adjust forming temperatures for a range of different plastics. I’m also hoping that the oven can be used for duel use such as pre-drying harder to form plastics like acrylic and polycarbonate or curing certain resins. Anyway, what I really need help on is being able to make the right choice in purchasing the heating elements I need to be able to hopefully do these things and be able to wire all of this together, so it’s done right, and it works consistently. If there’s anyone willing to get me pointed in the right direction and get me on track, that would be extremely helpful and much appreciated.
I have a 11x17" hobby vacuum former, that used to be sold decades ago. The user was expected to use their home oven as the oven. So constructing a heater just for the vacuum forming may not be necessary if you are only occasionally doing it.
The next step up to a professional unit, that I saw, was simply a bank of heat lamps aimed down. The plastic was in a frame that was on a slide that went up to the heat lamps. No temperature control, as the user would gauge the readiness of the plastic, because it would first sag, and then start to shrink a bit, and reverse the sag a bit. Then it was ready. The other version I saw had the lamps aimed up in a box to the side of the vacuum table, and the frame was on a hinge between the two. The obvious advantage of the 1st version, is that melting plastic would never contact with the bulbs if the user let it get too hot.
Regarding drawing a vacuum. The hobby one I had, used a 2-stage vacuum system. A normal shop vac would be used for the 1st stage. Where it connected, there was a flap inside, that would close when the shop vac was no longer drawing any air through. The 2nd stage, was a simple bicycle pump, that had its valves reversed, so you pulled on the handle to draw vacuum. Is hose was connected to the vacuum chamber, and would have an effect once the main flap to the shop vac had closed.
I will add that if you want to get more creative, (and more work) is that when you connect vacuum fans in series, the pressure doubles, just like putting batteries in series. So, if you have two shop vacs, and one has a blower outlet, you can just connect them together. Depending on the thickness of the plastic, and the detail on the model, that may be sufficient. I’ve occasionally see shop vacs at thrift stores for cheap, because they didn’t have filters.
A variation on the idea, is to get just the top part of two shop vacs, and mount them in a box with holes on top and the bottom, to hold the vacuum fans. You could theoretically stack more fans, but since the heat is not being vented to the outside, each stage gets hotter air going over the motor. However, since you only operate the vacuums for less than a minute, that may not be a concern.
For a while I toyed with the idea of creating a “regenerative blower”, that works on a similar principle. However, each blower is connected to a shaft and there is only one motor. There are industrial versions of this. Though I have never seen a small one. I considered 3D printing, but was concerned it would not withstand the forces.
You could also consider the rechargeable air dusters that are fairly affordable now. Just connect in series. Though, you might consider taking the blowers out, and powering them from one source. But, depending on the size of your vacuum table, they may not have enough air flow.
I will add that a vacuum former is certainly a topic related to robotics. That’s how many robot outer bodies are made.
-Joe
That’s all noted and appreciated information. There are many ways to get close to a decent vacuum (at least for hobby purposes). Stacking consecutive (smaller vacuum motors together) will not to any great degree increase your vacuum pressure capabilities by that much. Doubling up on a motor that provides you 4-6hgAnd while a standard shop vav may suffice, you will be lucky if you squeeze 4hg-6hg will not give you 10hg-12hg vacuum from it. The key is to relieve as much of the trapped air out after you pull the hot sheet of plastic over your mold or forming buck. I’ve turned to industrial vacuum motors that will run off a standard 110v-120v power supply. No 2 phase or 220v hook- ups. The motors I am looking at can remove a remarkable amount of volume quickly. Some as high as 166 cfpm. However, even at that high of a CFPM, the actual inches in mercury lift is relatively low hovering between 8hg-10hg.That’s where the real vacuum ( the secondary kicks in). I have an old book about building a basic vacuum machine and a bicycle pump was one mentioned. However, for my particular interest, I want as high a vacuum I can achieve and I’m looking at a vacuum pump as that secondary source. I more or less have my vacuum sources worked out, but the real canundreum I am facing is the oven. I can’t use the oven in my kitchen. My forming surface will be at least 24" x 24". That won’t fit in my oven. Perhaps if I really put some effort into the molds they may be smaller, but my project is a good size. Plus there’s removing the plastic sheet from the kitchen to the garage. That will allow the plastic to cool down too much and it will never form properly. Most of my molds will be female/ negative molds, and there’s detail I want to be able to pick up. So, for my purposes and for the size of the molds I am estimating I will be casting, I really do need to build an actual oven.
I can’t say I am an expert, and it has been decades since I used vacuum forming. And in particular, the rise of very low cost microprocessors and high power electric control modules may have changed how the oven should be done.
But, the ones from my youth really were quite unsophisticated. And not really constructed like an oven, but more like an electric stove top. Some salvaged the heating wire from space heaters, and mounted them in insulated sheet metal boxes. They heated the plastic primarily through radiant heat, rather than convective heat. And they weren’t temperature controlled. Rather, the readiness of the plastic sheet was gauged by eye. But, obviously, this may create limits to the kinds of plastics.
I just thought about the idea of getting a pair of electric griddles. Though I have never tried that, and never even seen it suggested before. They would have some degree of temperature control. However, if you go with the approach, of putting the heat source above the plastic to be heated, then the design of the cook surface may not handle being upside down very well. I think the other orientation is likely to work very well. And the non-stick surface may be a major benefit if plastic were to melt onto the surface.
I see there are some commercial grade griddles, that would be large enough. But, they had stainless steel. Not so good for a radiant heat source.