Vacuforming Questions

cavx said:

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I am also thinking about ditching the bottom layer of the two part frame. I use screws to attach the frame and plastic anyway, so looking at the results am thinking if I even need a 2nd layer. Doing this will bring the plastic closer to the platen.

Boy...I don't know. I would worry that the plastic would sag down and tear from the screws or create havoc with your seal. I have always use both a top and bottom frame around the plastic.

Let us know if it works...but if I was a bettin' man....!


I am really interested if the lid adjustment works. If so, I am thinking of going to your design. My oven has hot spots.

tictoc said:

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Boy...I don't know. I would worry that the plastic would sag down and tear from the screws or create havoc with your seal. I have always use both a top and bottom frame around the plastic.

I don't think the the holes would tear as the plastic doesn't heat right up to the edges when sandwiched between the two frame halves. If there was direct heat right to the edged, the frames would get charred.

tictoc said:

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Let us know if it works...but if I was a bettin' man....!


I am really interested if the lid adjustment works. If so, I am thinking of going to your design. My oven has hot spots.

I will do.

Today I got to see a real Vac Form in action. Very cool. This unit had what looks like a stove or oven element on a rolling bed about 4" above the clamp for the plastic.

The unit's platen was about 150mm lower than the plastic and raised up into the hot plastic.

The heat time was essentially waiting for the elements to glow red, then it was moved over the plastic.

Whilst the plastic was heating, the operator used compressed air from under the plastic to bulge the surface and "pre-stretch" the plastic as it got hot. He explained that this could make a perfect dome if you had a round hole cut into a sheet of MDF. Right away I thought a cheap way to get a dome for an R2 build

Like in all the videos I have seen, the plastic rippled, went tight, then sagged. The compressed air helped lift the centre without cooling the plastic. Heating time was about 2 minute on this rig.

I really liked the way the heater was downward radiating over the plastic. If the plastic melts, the molten material will not land on the element and start a fire.

Here are the results of the professional Vac Form.



I need to rework my bucks as the suction from the Vac Pump they use pulled the plastic around the undercuts and as a result, the large Heel Cup pull tore which compromised the seal and why the black parts shown are not pulled all the way to their bases. Also I had to split the plastic to get the black Ankle Buckle out.

So I have a bit of work to do here so I can get better pulls should I use this machine again.

3d-builder said:

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Your plastic is not touching down on the platen......I think i spoke with you about this before. Maybe the plastic makes good vacuum just sitting on it as a sheet minus the framework . But from what I can see in the picture your equator of your frame work where the plastic sits between is higher than the platen. It sure looks that way to me........ Also i don't see any dimples in the plastic another reason i am saying the plastic is not touching the platen.

The reason the plastic is not touching all the way around is simply because it is not hot enough to be stretched. Where it is hot enough, it worked a treat.

You won't see the dimples in the photos because I have shrunk them too much and that detail is lost. They are there, trust me.

And no ......no way 1.5mm styrene should take 45 min to heat......thats insane! You got to get the heat to 350 deg if it took you 45 min to heat 1.5mm YOUR NO WHERE CLOSE to 350deg or you just have the plastic sitting up way to high on the box you made.

I'd say too high and one reason why I want to rework the heat box.

Link below to where to me it seems your frame work's equator
is way above the surface of the platen.
http://www.therpf.com/attachments/f9...665d1339931728

http://www.therpf.com/attachments/f1...217d1341823037

So link 1 shows the two halves of the frames where each half is 16mm MDF. The plastic is 16mm off the platen at this time. This is in part why I want to one half of the frame. I used screws anyway to attach the frame halves with the plastic sandwiched between.

2nd link is of the plastic being re-heated. So this in not on the platen at all. I ended up heating this sheet of plastic 3 times.

So what I have to do is:

1. Rework the heater to get more heat. I need below 4 min.
2. Lower the plastic in the frame if the plastic still does not pull down enough all the way.

I was looking at your parts on the right in this link it looks to be a knee pad? Sorry if that's not what it is.........you should fill the entire bottom of this buck with something maybe a clay. Because whats happening is the plastic has nothing to follow down to the platen. So you are having this big air pocket between the part and the platen when it's formed. As you can see even the industrial machine has a problem......but would work great if it was filled. Understanding how the vacuum forming is effected from the parts design will help you when you go on to make more parts.


One more thing you might want to try and I am only saying this because the parts don't look that big is build a smaller machine, that's frame work willl fit in your oven? Form the parts on a smaller rig so you get the hang of it, although you might have bigger parts for your project.....never hurts to have a few forming tables around .......i have like 4! LOL

You spoke about only using half the frame work which will
lower you to the platen .......which is essentially what I was getting at.
You can staple the plastic but at 1.5 mm you will need a heavy duty stapler like a construction one. I tried that once it was a royal pain
in the ass popping out all the staples though.....between pulls!

Good luck!

3d-builder said:

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I was looking at your parts on the right in this link it looks to be a knee pad? Sorry if that's not what it is.........you should fill the entire bottom of this buck with something maybe a clay. Because whats happening is the plastic has nothing to follow down to the platen. So you are having this big air pocket between the part and the platen when it's formed. As you can see even the industrial machine has a problem......but would work great if it was filled. Understanding how the vacuum forming is effected from the parts design will help you when you go on to make more parts.

Absolutely this is all a huge learning curve. The parts are for scratch build MAG shoe where the big white part is the Heel Cup and smaller black parts (that will be white on the actual project) are versions of the Ankle Buckle. The reason I turned to Vac Forming is that it is relatively cheap and allows me to duplicate the part many times over. When I first looked into making these parts, they were going to be cast, but time and money did not allow.

Watching the way the plastic wrapped around the parts the other day was neat, but somewhat expected. I honestly thought the plastic would just pull down vertical over a cavity.

One more thing you might want to try and I am only saying this because the parts don't look that big is build a smaller machine, that's frame work willl fit in your oven? Form the parts on a smaller rig so you get the hang of it, although you might have bigger parts for your project.....never hurts to have a few forming tables around .......i have like 4! LOL

Not sure if this fits in my oven. Not sure if the wife would allow me to stick this in HER oven either.

My first "tester" was a small unit made from large diameter PVC pipe. Basically I used two end caps which were glued in and drilled a heap of 3mm holes in one end, then a 32mm hole in the side. Wrapped tape around the end of the VAX hose. Made a small frame and off I went. Not perfect, but good enough to encourage me to make this larger MDF version.

You spoke about only using half the frame work which will
lower you to the platen .......which is essentially what I was getting at.
You can staple the plastic but at 1.5 mm you will need a heavy duty stapler like a construction one. I tried that once it was a royal pain
in the ass popping out all the staples though.....between pulls!

I have flat heat 16mm Robinson screws here that I intend to use. The rubber seal that I have placed around the platen is about 4mm high and these screw heads are less than 3mm. Drill with a square drive bit and away I go. I do have one of the industrial staplers and your right, you need pliers to get the staples out.

Good luck!

Thank you. This site is soooo cool because people are willing to share their knowledge and I am learning something everyday I post here.

No problem......

Not sure if this would be an option for you, as I have an electric stove
in my house.But the largest part i ever formed the frame work for the
plastic was not going to fit in my oven. I placed the frame work up on
the cook top and let it roll, put all the burners on high.....

3d-builder said:

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No problem......

Not sure if this would be an option for you, as I have an electric stove
in my house.But the largest part i ever formed the frame work for the
plastic was not going to fit in my oven. I placed the frame work up on
the cook top and let it roll, put all the burners on high.....

Out of curiosity how big is that frame you put on top of the stove?

3d-builder said:

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Not sure if this would be an option for you

My wife just saw this and said not an option

I think I need to raid my box of draw slides to make my frame raise and fall with the heater above the whole rig.

SChristides said:

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Out of curiosity how big is that frame you put on top of the stove?

Man I am not sure i don't have the forming table any more .......
but it was big! LOL

cavx said:

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My wife just saw this and said not an option

I think I need to raid my box of draw slides to make my frame raise and fall with the heater above the whole rig.

Yea i could understand that.......it's not a big deal though really,
although I know she wouldn't understand! LOL It's not like the plastic
warms and just melts to the stove! LOL It's such a slow gradual process
i actually poke it with my finger at it's max .......never had a problem!

3d-builder said:

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Yea i could understand that.......it's not a big deal though really,
although I know she wouldn't understand! LOL It's not like the plastic
warms and just melts to the stove! LOL It's such a slow gradual process
i actually poke it with my finger at it's max .......never had a problem!

My wife is actually very understanding to all of my projects and even encouraging with some. We watched LOVE NEVER DIES on Blu last night and she asked if a PHANTOM OF THE OPERA is possible. I said it could possibly be made from 3mm white acrylic and even though you can buy those cheap and nasty ones from toy stores, I think a 2 or 3mm thick version would be nice prop to have. The mask in this sequel is actually quite different from the one used in the 25th Anniversary show. It has IMO a better shape and if I do one, would have to be this newer shape.

I have been given a "heads up" by a an engineer I use for machine work where he said I really need an oven element with a thermostat to control the temperature.

Do I even need the thermostat? The way I see this is it gets turned on to max anyway, heats the plastic and is shut down for the pull. I should actually think that is some ways, having the heater above ( at 10" still quite warm, not on) might actually be of assistance to the Vac Forming process when not using a vacuum pump for suction. The cool down time will be slightly longer, but hopefully I would get a better pull from keeping the plastic warm slightly longer.

Thoughts?

3d - Builder, whilst looking at your amazing Y-Wing build, I noticed you have what appears to be one of these.



It looks like these are cheap [on line] and I am sure my local camping store sells them. So the idea is to make a much lower profile version of my heat box that can fit over one of these. I'll make it with extended legs to allow access to the thermostat.

Today I re-worked my heating unit. I found a single element stove like pictured above (mine has a metal cover hot plate over the element that I think I need to remove) and I positioned the unit inside my heat flume where the hot plate is about 150mm away from the plastic.

Pros - much quicker heating times (about 4mins now)
Cons - only heats a circle of about 300mm out of the 600mm x 600mm sheet.
I think the thermostat needs to go because it reaches max operating temp pretty fast, but was not able to maintain the heat I needed.

So it well known that to get a good pull, you need to elevate the part. I used this block of wood and as you can see, either the plastic is still not hot enough or there is not enough suction. Maybe both. I will go with heat for right now as once again, I could not break the seal with the vacuum on.



This pull was actually pretty good, but I thought I could better it, so back over the heater it went.



I also replaced the wood with this short piece of plastic cut to the same length as the buck to hopefully get a better vertical pull on the ends.

I didn't glue it in place and it slipped during the 2nd pull giving a lopped sided part that awesome on one side

Back over the heater it went again, but I am not sure why, i could not get the heat back into the plastic.

So later on, I am going to take this little stove apart, remove the hot plate and maybe the thermostat as I noticed that kicked in a few times today and this means that the unit can only reach a certain temp and it them shuts down.

3d-builder said:

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3d-builder,

I swallowed hard and had a go at this stove top method today. WOW, now that is providing the heat I need

I also removed one half of the frame and screwed the plastic to the MDF and that worked really good as well.

I am still not getting 100% suction to the platen but think I can work around this with small mods to the bucks.

Today I ran out if HIPS so used a PVC. Interesting and a much nicer finish. HIPS whist it works just looks cheap compared to the finish on this. If I ever get this working to the point where I could make Stormtrooper Armor, I think this is the stuff I would want to use.

Was she home when you did it?

I have aluminum foil over the back for a reason,
there are electronics in the stove it has a digital
read out. With out the aluminum foil there......
And i mean there is a lot of foil......it would all
melt because the heat stays under there! You will
notice the knobs are off as well......because they
are plastic and they will melt!

3d-builder said:

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Was she home when you did it?

No shes at work and I am home looking after a sick kid, so did this once he fell asleep.

I have aluminum foil over the back for a reason,
there are electronics in the stove it has a digital
read out. With out the aluminum foil there......
And i mean there is a lot of foil......it would all
melt because the heat stays under there! You will
notice the knobs are off as well......because they
are plastic and they will melt!

I didn't box mine, just used 4 pieces of 200mm Pine and balanced the frame on top of that. Seemed to work OK.

I had another play with the quarts strip heater today and some plastic that folded when it slipped out of the frame on yesterdays stove top adventure. So today, I used the quarts strip heater, heated the plastic and was able to recover the sheet. I also learned something about just how much heat you can put into this stuff.

I had been told that you should be fumes coming off the plastic and it even at that point, it is not about to catch fire. So previously, I just was not allowing the plastic to get hot enough nor did my set up allow it.

I'm ditching the single element stove top I bought the other day (actually I should keep it for warming stuff) and will buy another one of these quartz strip heaters so I get a larger heated area. After today's play, I am also going to do a flip over heat arrangement so that the plastic is heated about 250mm over the platen, then flips up to just past 90 degrees whilst I do the pull.

I am working on making my frame raise up and down on 4 draw slides and the hinged heater will be above that. This will also ensure that my frame lines up with the platen each time to get the best seal.

And check this out for a tight pull.



Undercuts meant i had to physically cut the buck out and ideally this could have been made from thicker plastic, but I am getting there now

I was looking at the holes on your platen ......I would draw an X and mark the spot in each square cube and add a hole right in the middle of each one. Get a little more vacuum surface around the entire rig.

3d-builder said:

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Well that looks much better......what thickness did you use? I have never seen smoke or fumes when heating ......you might have it to close or to much heat...be careful with the PVC if your getting it to puff fumes.

Thanks. Sheet thickness is 1.5mm and I ended up with about 1.0mm after the pull on the 2 parts at the. That one at the bottom right got thin. The one on the left essentially didn't change its thickness, but didn't really pull down much either.

3d-builder said:

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I was looking at the holes on your platen ......I would draw an X and mark the spot in each square cube and add a hole right in the middle of each one. Get a little more vacuum surface around the entire rig.

Really? The spacing is about 3/4" as it is and there is 19 x 19 holes. What I did find helped was to reduce the amount of holes by blocking them with tape. I really should look into buying a Vacuum Pump for this I think.

Yea taping them off will centralize the vacuum around your part, but its nice to have more for different sized bucks......if its working good leave it alone! And if more holes would weaken the platen def leave it alone!!