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4'X4' Formers?

 
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vrogy
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Joined: 31 Jul 2007
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Location: in Sunny Florida!

PostPosted: Mon Aug 15, 2011 10:57 pm    Post subject: 4'X4' Formers? Reply with quote

Are there any 4' square formers out there? I looked back through several forum pages, didn't see any.

I've got a bunch of really big MDF molds- stuff that won't even fit on a 2'X4' platen. Also, it's much faster to form a whole half-sheet of parts at a time!

Would that size necessitate custom electrical service? What special considerations may apply there?
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spektr
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PostPosted: Tue Aug 16, 2011 10:07 am    Post subject: Reply with quote

When you get to sizes like this, the little things start mattering a lot. Heating is simple to do , its not hard. Sheet clamping , movement and tool interfaces matter much more. I doubt seriously if theres 1 machine in the country with a 4 x 4 foot platen. Platens are inefficient for larger machines. If you really need something this big, answer a few questions.
What plastic will you form, how many will you need to form a day, how many different tools will you be loading into it. Do you want to do electric or gas ovens. Will you be using PLC controllers. Will you be needing plug assist or overhead tools. Are you zoned for this? Just a few things to consider.....

Scott.
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vrogy
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PostPosted: Mon Oct 17, 2011 6:23 am    Post subject: Reply with quote

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spektr
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PostPosted: Mon Oct 17, 2011 9:38 am    Post subject: Reply with quote

Cool, nice to have a large machine. I bet you could use under half the material if you rotate the tool 45 degrees, build spacers and use vac-snapback overhead tools.. It would also kill the webbing....
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vrogy
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PostPosted: Mon Oct 17, 2011 9:53 am    Post subject: Reply with quote

Yeah, this is a rough first pull. It works, though.

I'd be interested to know what kind of locally-sourced materials would work to build high-temp air seals for the oven-frame sealed edge. Maybe fiberglass insulation bound with thin-gauge wire to strips of hardiboard? Also if something as simple as a high-wattage hair dryer could produce enough pressure to billow the plastic up.
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jdougn
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PostPosted: Mon Oct 17, 2011 11:14 am    Post subject: Reply with quote

Wow! That is huge but looks like you're off to a good start!!

What type of plastic? What type of project?

Don't know the configuration of your vac former so this idea may not work. But one thought is to invert the plastic & mold. Mold on top with hot plastic sagged down below the mold. You'd have to have a lot of up pressure on the plastic carrier or travel the mold itself.

How close is the edge of the plastic carrier to the edge of the platen? If you can increase that distance the hotter plastic should seal against the platen better, especially if there are no vent holes within at least an inch of the edge of the platen. Side thought: aluminum HVAC tape seems to work well and handle the heat on the platen. I use it plug unwanted holes on platens dedicated to particular molds.

I've tried a bunch of different approaches to getting a good seal between 3/16" Black ABS plastic and the platen. Can't find any that work well long-term. Some types of weather stripping helped and a wooden half round with a silicone overlay did okay...sometimes. None worked like I wanted. Seems like the best seal is a very smooth platen edge meeting hot plastic with plenty of initial pressure to form the plastic over the platen edge. My plastic carrier frame is painted flat black to help it absorb heat and help keep the edge of the plastic hotter.

Other than that, a 10cfm vac pump for the 2'x4' ProtoForm design vac former that I run helps compensate for edge leakage. Wish I had more cfm at times. The platen base always tests tight with no leakage so all the leakage must come through under the hot plastic via the relatively short distance from the edge of the platen and the first vacuum holes.
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Awesomeness



Joined: 17 Oct 2011
Posts: 3

PostPosted: Thu Oct 27, 2011 6:24 pm    Post subject: Reply with quote

jdougn wrote:
What type of plastic? What type of project?

Don't know the configuration of your vac former so this idea may not work. But one thought is to invert the plastic & mold. Mold on top with hot plastic sagged down below the mold. You'd have to have a lot of up pressure on the plastic carrier or travel the mold itself.

How close is the edge of the plastic carrier to the edge of the platen? If you can increase that distance the hotter plastic should seal against the platen better, especially if there are no vent holes within at least an inch of the edge of the platen. Side thought: aluminum HVAC tape seems to work well and handle the heat on the platen. I use it plug unwanted holes on platens dedicated to particular molds.

I've tried a bunch of different approaches to getting a good seal between 3/16" Black ABS plastic and the platen. Can't find any that work well long-term. Some types of weather stripping helped and a wooden half round with a silicone overlay did okay...sometimes. None worked like I wanted. Seems like the best seal is a very smooth platen edge meeting hot plastic with plenty of initial pressure to form the plastic over the platen edge. My plastic carrier frame is painted flat black to help it absorb heat and help keep the edge of the plastic hotter.

Other than that, a 10cfm vac pump for the 2'x4' ProtoForm design vac former that I run helps compensate for edge leakage. Wish I had more cfm at times. The platen base always tests tight with no leakage so all the leakage must come through under the hot plastic via the relatively short distance from the edge of the platen and the first vacuum holes.


I'm the one in the picture above (finally got my account activated, yah!).

We're using 1/16" ABS in that picture.

At 4'x4' (oven is about 6'x6', with the insulation), the whole thing is just too massive to do the inverted cool-guy oven thing currently.

I found some silicone weatherstipping that I was thinking about trying. What about your previous weatherstripping tests did you not like?

We're using a two-stage, ShopVac & venturi-pump+30gal tank, vacuum setup. Once you open the tank, there is too much open volume for a vacuum pump to keep up, I would think.

Is the thicker plastic harder or easier to seal?

Sorry for all the questions. This is my first vacuformer (and of course I figured it was a good idea to jump straight in the deep end, and build a giant one, haha).

Guido
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PARATECH1
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PostPosted: Thu Oct 27, 2011 7:44 pm    Post subject: Reply with quote

Thats a big sheet of plastic! What were you making a mold of? Any chance of you putting up photos of your machine.

When I finish building my shop I hope to either attempt to build or buy a vacuumformer big enough to mold car hoods. I have seen pretty good deals at times on E-Bay.
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PARATECH1
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PostPosted: Thu Oct 27, 2011 7:49 pm    Post subject: Reply with quote

What type of power or amperage does your machine use? Most of the really big vacuumformers use 3 stage power.
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Awesomeness



Joined: 17 Oct 2011
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PostPosted: Thu Oct 27, 2011 8:29 pm    Post subject: Reply with quote

The mold is a shoulder bell for a full-size space armor suit.

I'll get some pictures of the vacuformer, at some point. It's pretty ghetto, compared to the fancy ProFormers and whatnot that people are building on here. It's all wrapped in unfaced fiberglass insulation and chicken wire, because I was having trouble getting it to heat up. (A 4'x4' oven has 8x the surface area, and heat loss, of a 2'x2' oven.) The oven is about 6'x6', and sits on the floor. The platen is 4'x4'x1', and sits on the table of my CNC router, next to the oven.

It runs on 220V power, sort of. 220V outlets actually have two separate 110V circuits, which you can connect together to get 220V. My vacuformer runs two sets of coils, each off one of the 110V circuits. The real advantage of the 220V circuit is amperage. It's a 50A connection (to each of the 110V sides individually, or 50A @ 220V). The former actually only draws about 35-40A though.
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jdougn
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PostPosted: Sat Oct 29, 2011 1:25 pm    Post subject: Reply with quote

Awesomeness wrote:
I'm the one in the picture above (finally got my account activated, yah!).

We're using 1/16" ABS in that picture.

At 4'x4' (oven is about 6'x6', with the insulation), the whole thing is just too massive to do the inverted cool-guy oven thing currently.

I found some silicone weatherstripping that I was thinking about trying. What about your previous weatherstripping tests did you not like?

We're using a two-stage, Shop-Vac & venturi-pump+30gal tank, vacuum setup. Once you open the tank, there is too much open volume for a vacuum pump to keep up, I would think.

Is the thicker plastic harder or easier to seal?

Sorry for all the questions. This is my first vacuformer (and of course I figured it was a good idea to jump straight in the deep end, and build a giant one, haha).

Guido


Hey Guido, is that space armor for real world use or stage? Regardless, it looks like a very cool project!

Weatherstripping: The stuff I liked best was the EPDM "D" shaped weatherstrip. The hollow "D" really sealed well since the EPDM is not porous but it eventually breaks down from the heat. Some of the foam weatherstrip is very porous and lets air move straight through edgewise. Any that I've found has a couple of various problems. Most often the adhesive gives way first. If you get past that with epoxy or super glue then the weatherstrip itself eventually breaks away from the adhesive. I've got to imagine there's a lot of force and heat being applied to weatherstrip being used like this. There's probably a commercial product available to handle the heat & pressure but I've not found it.

Vac System: In most applications we talk about on here a shop vac really doesn't help. However, your project is way past what most of us are doing! It works for you so it's good to go! The shop vac doesn't pull very much total vacuum but in your case it probably does help. I know my 30 gallon tank gets "polluted" (drops from 27+in-Hg to less than 18 in-Hg) beyond use with certain 2'x4' pulls that I do. But with isolating the polluted tank and switching over to the 10 cfm vac pump the plastic still forms fine.

Plastic: IMX, 1/16" ABS will seal better than 1/4" ABS. I think the thinner plastic may heat more thoroughly at the edge making it more pliable and easier to seal. Plus, thicker plastic takes more down pressure simply because it is thicker and more resistant to changing shape.

Keep posting up!

hth, DougN
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Awesomeness



Joined: 17 Oct 2011
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PostPosted: Sat Oct 29, 2011 4:58 pm    Post subject: Reply with quote

jdougn wrote:
Hey Guido, is that space armor for real world use or stage? Regardless, it looks like a very cool project!


Umm? I'm not sure either of those. I'm not making it for a performance of "Space Marine the Musical", nor do I plan to wear it to work. Shocked It's just a costume, to wear at a convention or Halloween party, so which would that be?

jdougn wrote:
Weatherstripping: The stuff I liked best was the EPDM "D" shaped weatherstrip. The hollow "D" really sealed well since...


I was considering using this...
http://duckbrand.com/Products/weatherization/window-door-seals/silicone-weatherstrip-seals.aspx

Silicone (heat resistant) - CHECK
D-shaped - CHECK
Non-porous - CHECK

Maybe in addition to the adhesive, I could staple-gun it to the platen (in between the two rows of it - it's two D's wide)?

jdougn wrote:
Vac System: In most applications we talk about on here a shop vac really doesn't help. However, your project is way past what most of us are doing!


The big problem is volume. The platen 46" square platen has a 3/4" air gap between the top hole-drilled layer and the solid back. That's roughly 1587 in^3, or 6.87 gallons! The high-vacuum tank I have (the only one I could find) is 30 gallons, plus a 1.5"Diam.x20'L suction hose, which adds 1.8 gallons more. I live near Denver, literally the "Mile High City", so we can only pull about 24"Hg max vacuum here.

At the very least, simple theory would suggest a 4'x4' platen needs 4x the vacuum tank volume of a 2'x2' machine, or 2x that of a 2'x4' one. Combined with the fact that I pull 20% less vacuum that people at less altitude-challenged locations, I would need even more.

All that is just describing the platen, which is 2x by 2x larger in surface area, but the "tented" area under a piece of hot plastic stretched over a mold is 8x larger in volume, because it's 3D (e.g. 2x longer, 2x wider, 2x taller).

The ShopVac is almost a necessity, unless I had a 150 gallon vacuum tank. (And yes, I've been keeping my eye out for a cheap, larger tank.) It very quickly evacuates a lot of the air, and gets enough vacuum built up to seal the plastic sheet to the platen some. (Anyone who has tried to get a flat tire to reseat with just the low airflow of an air compressor, has had a similar experience, in reverse.)

There is still some leakage somewhere - maybe the edges of the platen. I'm working on that. It could also be that the plastic just didn't seal well to the platen - I'm working on that too. I'm getting better at playing with the insulation on the top cover of the oven, to heat the plastic more evenly (especially at the edges).

jdougn wrote:

Plastic: IMX, 1/16" ABS will seal better than 1/4" ABS.


Good to know, thanks. I'm still very green to all this.
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jdougn
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PostPosted: Sat Oct 29, 2011 7:55 pm    Post subject: Reply with quote

It would be interesting if it were real space armor but even making something that compelx for parties & stuff is cool.

The Duck brand weatherstriping is EPDM and should work fine. The two D's are designed to easily rip apart. If you try staples plan on using alot since vac forming puts a lot of sideways pressure on the weatherstriping.

The multi-stage system you are using is probably a really good match for your situation. Interesting thoughts on tank size that make sense. Hope you didn't think I was knocking your system.

For the tank, you've probably already thought of this but it shouldn't be too hard to plumb in additional tanks instead of going to one big tank. I liked the flat tire analogy.

What materials is the platen made out of? I've tried both silicone caulk smeared all over the outside of the platen and fiberglass resin "painted" on the platen. Both worked fine. I use a highly modified platen and each mold is attached to a dedicated base that locks into the platen. No chance of the mold getting picked up by the plastic since the mold is fastened to the base. Makes production work much faster, more predictable, and mold changes are still really quick.

My platen base is air tight but there are minor leaks all around the edge where the hot plastic meets the platen base. The weatherstriping will help a lot with the plastic to platen leaks. I hadn't thought of using staples but that may keep the weatherstriping in place. I use aluminum HVAC tape around the edge of the platen base since it provides a much smoother surface for the plastic to seal against than the wood platen base.

You're doing really well for just getting started and obviously have a pretty decent background in this general type of work. I'm looking forward to seeing how your project works out.
dn
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