Vacuforming Questions

[SChristides]

bit like this

Creating the original Stormtrooper - YouTube


Just had a thought. Wouldn't having a heater enclosed in a box expose it to more heat than it would be made for and possibly melt things, like the cord? Or do you reckon the box will have enough clearance to give enough airflow to prevent that problem? I'm guess length of usage will determine the heater failing also (I don't intending on putting it through hours of usage at a time)

 

[cavx]

Thanks for that link. Very cool

My heater is elevated and the power cord runs below the heating unit and it out of the box with plenty of free air around that. Only the reflective hollow and heat bars are inside the flume on my design.

 

[cavx]

I did my first few runs today. Suction seems good as I did get the dimples of the holes of the Platen on go 3. However I need to work on the heating unit as I don't think a 1.5mm piece of HIPS should really take 45min to get hot enough. I think I need to move the heating unit closer to the plastic.

The beauty is that even though I made a few stuff ups today, I was able to simply reheat the plastic and go again. It flattened out perfectly and pulled much better with more time on the heat.

Heat time 1: 8min
Heat time 2: 30min
Heat time 3: 45min and I think I could have left it on for another 5 min and it would still be OK.

No it is not a penis or other phallic symbol. I shall call this piece the "MAG in Carbinite"

Not happy with the result, it went back over the heater and after a few minutes, it began to return to its beginning.

And after about 30 mins, flat again for round 2.

I ended up redoing this it again and I think I need more height under my bucks. So I have rigged them up on a block of wood and will pull them again later on tonight.

 

[cavx]

So yeah, a redesign on the heat box is now a must. I decided that I would have another go tonight, but the ambient air temp cooled the plastic before I could get any real suction happening. Again I had left it heat up for 45mins, and the result was pretty poor.

So I decided to do something a little different by constructing a frame over the platen and suspending the heating element there. This proved that I need to get the plastic closer to the heat as the material was soft in 2 to 3 minutes. The challenge is that it also is much easier to burn the plastic and I did this on one section, so that is now a throw away.

I did raise the bucks but it didn't matter too much as the plastic cooled too fast even with the garage door closed. So I have pull 3 which is better than 1 and 2, but still far from perfect.

It is actually easier to see the detail from the inside.

Maybe there is not enough suction here either as the detail is there on the higher parts, but it is not there at the base and both parts were slightly raised off the platen for this pull.

 

[tictoc]

Are you sure you have a good seal when the platen goes onto the vacuum box?

You might try lining the vacuum form table top with some rubber (closed cell) weatherstripping. The weatherstripping should line up exactly with your frame and create a tight seal. It wears out but this might be your problem.

Also, when you heat your plastic sheet, try to put a foil or flashing lined lid over it. This will help keep the top of the plastic from cooling. Also, in the beginning, you might want to flip your plastic to help heat both sides.

 

[cavx]

Are you sure you have a good seal when the platen goes onto the vacuum box?

Not sure if I am understanding your question here, but my Platen and Vacuum Box are one sealed unit. The holes in the Platen are the top panel of the Vacuum Box and I made sure to seal the whole thing when I assembled it. I've run a few vacuum tests and I can not pull up the sheet that I am testing with once the seal is made.

You might try lining the vacuum form table top with some rubber (closed cell) weatherstripping. The weatherstripping should line up exactly with your frame and create a tight seal. It wears out but this might be your problem.

I did that yesterday. I used door rubber seals that have a sticky adhesive on one side. I then re-ran my vac tests and was convinced the seal was good.

Also, when you heat your plastic sheet, try to put a foil or flashing lined lid over it. This will help keep the top of the plastic from cooling. Also, in the beginning, you might want to flip your plastic to help heat both sides.

That makes sense as I do think so much heat is lost off the top surface. I still think redesigning the heat box so that the heating elements (and I think I will need more than one for this) is maybe 4" off the plastic. It is quite a distance off now and I just don't think that my strip heater is as hot as the "patio heater" Jame of XRobots used.

What I noticed last night is that my heaters "low mode" only used one strip heat bar, so maybe a pair of these (they cost about $15.00, so not expensive to add a 2nd heater) on low side by side might give a wider heated area.

I also have some big draw slides, so might even make the heat unit inverted and slide away like many professional units do.

Last pull was cold before I had reached 50% of the Buck height, so it would not matter if I was using a Vacuum Pump for suction, the plastic would not be able to be formed as it simply was not hot enough.

Having a quick look in in regards to a comment made earlier on, I am thinking of adding a boarder out from the base of the platen/vacuum box and making new frames. This way the platen goes up and into the hot plastic as the frame is pulled down.

So far this project has cost just $100 and it almost works, so I don't mind if I need to spend more to perfect it.

 

[tictoc]

Sorry for the confusion...I do mean the box and platen. I actually used some silicone to seal the inside of my vacuum box .....but it sounds like you are already on top of the troubleshooting.

As for the heat...hmmm. I love your design. It seems sound. The larger top would seem to allow it to heat more uniformly and eliminate hot spots. But you might just need more heat if the box is too tall.

My "oven" is just a rectangular box with a removable lid and no bottom. It is about 26 inches tall. It is lined with flashing just like yours. I use two little electric grills as heaters. They are 1500 watts each and just sit on the concrete floor of my garage. It takes my oven about 10 minutes to heat up nicely (with the lid on) before I start trying to form with plastic. I always use a lid over my frame and plastic when I am forming. It takes about 3 minutes for the .080 styrene to soften and sag before I can place it on the vacuum table.

 

[cavx]

Sorry for the confusion...I do mean the box and platen. I actually used some silicone to seal the inside of my vacuum box .....but it sounds like you are already on top of the troubleshooting.

Thank you. Because I made the Platen/Vac Box out of 16mm MDF, I used "Aquadere" [white wood glue] and made sure I had a good bead of it on the insides as I squashed the joins down. No different to how I would (and have) made speaker enclosures. Rather than just drill a hole for the VAX to attach, I went and bought the proper plastic part and glued that in as well.

As for the heat...hmmm. I love your design. It seems sound. The larger top would seem to allow it to heat more uniformly and eliminate hot spots. But you might just need more heat if the box is too tall.

That makes sense. I am thinking I need to reduce the height and open the angle up a bit to keep the same area at the top. Yeah, it is definitely a heat issue, but this heating box was made with the single heater only. Adding a 2nd unit will require a redesign.

My "oven" is just a rectangular box with a removable lid and no bottom. It is about 26 inches tall. It is lined with flashing just like yours. I use two little electric grills as heaters. They are 1500 watts each and just sit on the concrete floor of my garage. It takes my oven about 10 minutes to heat up nicely (with the lid on) before I start trying to form with plastic. I always use a lid over my frame and plastic when I am forming. It takes about 3 minutes for the .080 styrene to soften and sag before I can place it on the vacuum table.

My heater is 1600W on high mode. The lid is the key too I think because I am just losing heat right out the top off the surface of the plastic. What worries me though is melting, and having hot plastic drip into the heating elements and starting a fire. This is why I think I want to build the box with the heater on the top that is either slid out of flipped. A sliding design requires more space, but is safer than one that flips.

I don't really know what heating time mine heater requires. I simply started when the elements were both glowing at a stable red.

 

[tictoc]

My heater is 1600W on high mode. The lid is the key too I think because I am just losing heat right out the top off the surface of the plastic. What worries me though is melting, and having hot plastic drip into the heating elements and starting a fire. This is why I think I want to build the box with the heater on the top that is either slid out of flipped. A sliding design requires more space, but is safer than one that flips.

I don't really know what heating time mine heater requires. I simply started when the elements were both glowing at a stable red.

Even when you cook food in your oven you should allow the oven to preheat and give it at least 10-15 minutes to sit after it reaches temperature.

I have never had a fire (knock on wood) but that is why I put the heaters on the concrete floor. If there is a problem, the whole kitten caboodle will get shoved to the driveway.

It sounds like you are properly paranoid about fire so I don't think it will happen if you always watch your plastic. Make a log about your heating times and how long it takes the oven to heat up and stick to that.

Try a flashing lined lid before you rip things apart and let us know how it went.

 

[cavx]

Even when you cook food in your oven you should allow the oven to preheat and give it at least 10-15 minutes to sit after it reaches temperature.

I have never had a fire (knock on wood) but that is why I put the heaters on the concrete floor. If there is a problem, the whole kitten caboodle will get shoved to the driveway.

It sounds like you are properly paranoid about fire

Not paranoid, but concerned about the real possibility.

Try a flashing lined lid before you rip things apart and let us know how it went.

I will make a lid in the next days and report back.

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.

 

[tictoc]

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....! :lol


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

 

[cavx]

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.

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


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 :love

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.

 

[cavx]

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]

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........:facepalm Also i don't see any dimples in the plastic another reason i am saying the plastic is not touching the platen.
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.

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/my-bttf-inspired-bag-vac-form-1.jpg-98665d1339931728

http://www.therpf.com/attachments/f11/vacuforming-questions-vac-form-2.jpg-102217d1341823037

 

[cavx]

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........:facepalm 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/my-bttf-inspired-bag-vac-form-1.jpg-98665d1339931728

http://www.therpf.com/attachments/f11/vacuforming-questions-vac-form-2.jpg-102217d1341823037

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.

 

[3d-builder]

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! thumbsdown

Good luck!

 

[cavx]

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! thumbsdown

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.

 

[3d-builder]

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.....:lol

 

[SChristides]

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.....:lol

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

 

[cavx]

Not sure if this would be an option for you

:lol My wife just saw this and said not an option :lol

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.