Welcome back to my DIY Vacuum Form Machine Build tutorial series where we are going to fabricate a heat box for the heating elements we sourced from an old thrift store toaster oven. If you don’t have any heating elements yet, I suggest you either buy them or get them for less by tearing down appliances like a toaster oven or space heater. In the previous tutorial, I showed you exactly how to pull heating elements from a toaster oven I bought for $10. If you’re thinking about building your own homemade vacuum forming machine, it’s best to start with the heating elements because that will determine a great deal of your design. In my previous tutorial (Part 1) on how to source heating elements to use for your homemade vacuformer, I give you a variety of options from buying them online to finding them inside appliances.

In this Part 2 of my DIY Vacuum Forming Machine Build, I’ll take you through exactly how I designed and fabricated a heat box based on my toaster oven heating elements using inexpensive tools and no welding.

In this DIY Vacuum Forming Machine Tutorial:

What is a vacuum form machine heat box?

The process of vacuum forming involves heating a sheet of plastic until it becomes malleable, and then shaping it over a mold using a vacuum to suck the air out and force the plastic to conform to the shape of the mold.

The heat box in a vacuum forming machine is the component responsible for heating the plastic sheet. This can be an enclosed space where the plastic is placed, or it can be a heater unit that directs heat towards the plastic. It’s crucial for the heat to be evenly distributed across the plastic sheet for uniform shaping, which is why the design and effectiveness of the heat box is a critical aspect when building your own vacuum forming machine.

Heat Box Design Options

The heat box for your homemade vacuum forming machine doesn’t have to be complicated. The most important design element is that it heats the plastic sheet evenly without burning it. Here are a few heat box design options that other DIY vacuum form machine builders have used from simple chambers to more elaborate welded-together units. My plan was to come up with something compact that didn’t require any welding.

Space Heater in a Box Vacuum Former

If you don’t want to get into any wiring or electrical work, this is by far the easiest method for heating your plastic. All you have to do is get a basic space heater and build a wooden box for it to sit in. Be sure to cover the inside of your wooden box with reflective tape or aluminum foil so the wood doesn’t absorb the heat. By placing the space heater so that the heating elements face up, the heat will naturally rise. Then you can rest the frame holding the plastic sheet on top of the box and let it heat up from underneath.

Here’s an example of a tall wooden box with no bottom. Youtuber, James Bruton, lined his heat box with aluminum foil on the inside and placed it right over the space heater to enclose it. You’ll have to experiment a bit with the height of the box. Too tall and your plastic sheet will take forever to heat. Too short and your plastic sheet could melt or burn.

Although this is the easiest option for making a heat box for your DIY vacuum form machine, I didn’t go this route. The main reason for my decision is that I work out of a small space and that’s a big box that’ll take up valuable real estate.

Flip Book Vacuum Former

In this design, the heat box and vacuum box sit side-by-side and the frame that holds your plastic sheet is attached between the two sources. This way the frame can flip from one source to another like turning a page of a book.

Here are two examples of homemade vacuum form machines that use the side-by-side design. The plastic sheet is placed in a metal frame and sits directly above the heat box. Once the plastic is ready, you then flip it over to the vacuum side for forming.

This is a great compact design that you can store on a shelf when it’s not being used. The only drawback is that you have to pay attention during the heating process because the plastic is sitting directly above the heating elements. As the plastic heats up, it will start sagging down TOWARDS the heat source. The closer it gets the faster it heats up to the point that it will begin melting or even burn up if it comes into contact with one of your heating elements.

Here’s what happened to Doug Costlow’s plastic sheet during the first test of his DIY vacuum forming machine. Luckily no damage was done and he was able to clean the plastic off the heating elements. No matter what design you choose to build your vacuum former with, it takes a little practice before you know when the plastic is ready to form.

Stacked Vacuum Former

This is by far the most popular design for both professional and home-made vacuum form machines. In this layout, the heat box sits above the vacuum box and you move your plastic sheet frame from the heat source above down to the vacuum box where it gets formed.

This design has several advantages, the main one being that as the plastic heats up, it will sag downwards, AWAY from the heating elements.

Here are a few examples of home-made vacuum formers with heat boxes that sit above the vacuum box. Some are made almost entirely out of wood while others incorporate metal heat boxes and look polished enough as if they came from an ecommerce store. For added convenience you can integrate your vacuum form machine as part of a wooden rolling cart so you can store plastic sheets as well as the vacuum source. You can also build one as a desktop machine and then store it on a shelf when you’re done if you don’t have the floor space.

This stacked design is what I chose for my DIY vacuum forming machine and because I’m short on floor space, mine will be a table-top unit. While doing my research I found that most designs involve welding which gives you a much more professional look but I know many of you starting out may not have one …yet! So I built mine using good ol’ fashioned nut and bolt technology with common tools you all most likely have.

Calculating the Heat Box Dimensions

The shape and size of your heat box will largely depend on the heating elements you plan to use. They can be pulled out of certain appliances pretty easily or you can purchase them online. I recommend electric smoker heating elements because they already come with a power cord you can plug into the wall as well as mounting hardware you can modify for your design. I harvested mine from an old toaster oven and they are connected in pairs by a metal rod on one side. Each end of the heating elements has a ceramic insulator.

Your heating element(s) may look different or have another style insulator on the ends. Excluding the “wing nut” portion of the insulator, my heating elements are 11.75″ long. I measured the length in this way because the wing nuts will sit outside the heat box. Each pair is 4.5″ apart so I plan to mount the pairs side by side, maintaining that 4.5″ distance.

We’ll get into the actual wiring strategy in a later tutorial but for now we have enough information to come up with the dimensions for our heat box. The easiest dimension to start with is the width or depth of the heat box since that’s determined by the length of the heating elements. In my case, that dimension will be 11.75″. Then each pair of heating elements is connected at 4.5″ apart by a solid metal rod. By laying the two pairs side by side with 4.5″ of space between each heating element I had to decide how much room to leave on either side of the outer heating elements. At the most I figured this value could be no more than 4.5″ or there would be too much room for the heat to dissipate. I went a little less, at 3.25″.

Why not 4.5″? That probably would have been fine too. Other than the width of your heating elements, there’s no mathematical rule for coming up with the other dimensions. Expect to do some experimenting, testing, and making adjustments along the way. If you leave too much room on either end, your plastic won’t heat up as much at the outer edges. So 4.5″ or below is probably best and it so happens that with 3.25″ on either end gives me an even 20″ in length.

The last dimension I need is the height of the heat box. If I make it too tall, then the heat will rise and hang out at the top. If it’s too short then the heat may be too intense when deflected down towards the plastic sheet. Again there’s no hard and fast rule here. I decided to try a height of 5″.

Final Heat Box Dimensions: 11.75″ W x 20″ L x 5″ H

Heat Box Materials

The two most common materials I’ve seen people use to build their heat boxes is wood, metal or a combination of both. Each has their pros and cons and your comfort level may lean you towards one or the other.

Wood

Wood is perhaps the easier option for most DIY vacuum form machine builders. Although we automatically think …hmmm …wood + heat = fire …I’ve seen quite a few heat boxes built solely out of wood that operate just fine. I myself was a bit hesitant to do go this route because knowing me, I’d always be focused on the fire aspect rather than my project. If you’re still intent on using wood because of its easy availability and workability, you should take some precautions to mitigate the risk of fire.

• Explore Heat Barriers: Lining the interior of your wooden box with a heat-resistant material is a crucial step. Heat-resistant or refractory materials like firebrick, ceramic tiles, or high-temperature insulation materials such as mineral wool or ceramic fiber blankets can serve as a heat barrier and protect the wood from direct heat.
• Use Fire Retardants: Fire retardant paint or sprays can be applied to the interior and exterior of the box to provide a degree of protection against accidental ignition.
• Provide Adequate Ventilation: Even with precautions, a wooden heat box can get hot. Adequate ventilation will help to dissipate the heat and prevent overheating.
• Control Temperature: Use a temperature controller to monitor the temperature within the box. This helps prevent the temperature from getting too high and causing a fire hazard. If you sourced your heating elements from a toaster oven, you can use the thermostat to set the temperature. Many electric smoker heating elements also have a thermostat control knob.
• Distance From Heat Source: The heating elements shouldn’t come in direct contact with the wooden parts. Make sure only the ceramic insulator touches the wood and that the heating elements aren’t positioned too close to the top of your heat box.
• Deflect Heat Downwards: Wood tends to absorb the heat coming from the heating elements so it helps to cover the inside of your heat box with heat reflective tape or a heat shield with an aluminized surface. This also helps direct the heat down towards the plastic sheet.
• Regular Inspection: Regularly check the box for signs of charring or other damage. If you notice any issues, discontinue use and repair or replace the damaged part.
• Safety Equipment: Always keep a fire extinguisher nearby when operating your vacuum forming machine.

Remember, even with these precautions, a wooden heat box poses a higher fire risk than a box made from more heat-resistant materials.

Metal

Metal is arguably the best material to use for building your heat box. But many people shy away from it because they automatically think it means you have to weld and use specialized metal working tools. That largely depends on the type of metal you choose but you can build a no-weld beginner-friendly heat box with aluminum. It’s easy to cut, drill and bend so there’s no welding required.

I decided to build my heat box entirely out of aluminum parts that you can easily find at your local home improvement store. And to hold everything together, I’m using a combination of bolts, nuts and screws.

How to Build a Heat Box for your DIY Vacuum Former

Now that I had my dimensions and decided on my materials, it’s time to start putting everything together. My strategy was to use a roll of aluminum roof flashing to build the sides of the heat box and secure the rectangular shape with aluminum c-channel bolted together. Let’s go through the vacuum form heat box construction process step-by-step.

Cut the Roof Flashing to Size

My roll of aluminum roof flashing was 14″ tall by 10′ long. Rather than cut individual panels for each side of the box, I decided to cut one long length with a 5″ height and create bends where the corners of the heat box should be. I felt that one wrap-around piece would be stronger than connecting multiple panels together and involve far less hardware. The total length required to make the heat box is 63.5″ (20″ + 11.75″ + 20″ + 11.75″). It’s a good idea to add another inch or two to the length so you have extra material to fold over. I added another inch for a total of 64.5″.

Roof flashing is very easy to cut with a pair of tin snips. The hardest part is trying to keep it from sliding off the table as you cut so it may be easier to do it on the floor.

Make Bends for the Corners of your Heat Box

After cutting out my piece of roof flashing, I was left with a long floppy strip I now have to bend according to our measurements to turn it into a rectangular box. Starting at one of the ends, measure out each panel in order along the strip and mark them with a Sharpie or piece of chalk.

You don’t need any special metalworking tools for bending something as flexible as roof flashing, just one or two wood blocks works great. Another option is to use a sharp edge of a table to make bends in your metal. I lined up a piece of 1 x 4 whiteboard on top of my strip at the first mark and clamped it down. Then I took the free end of the strip and bent it upwards. You can get a sharper bend if you use another block of wood on the back side and sandwich the strip as hard as you can. Repeat the process at each of your marks.

At the end, your metal strip should resemble an open-ended rectangle.

Our DIY vacuum form heat box is a bit floppy at this point but we’re going to be adding supports to the sides soon. But while the strip is still flexible, now is a good time to drill out the holes for the heating elements.

Drill Holes for Heating Elements

On the 20″ sides of our heat box, we need to mark the locations for the four heating elements we harvested from a thrift store toaster oven. According to our diagram, the first hole needs to be 3.25″ from the bend or corner. Then the next hole will be 4.5″ from that. You’ll have another hole 4.5″ from the previous one. And finally, the fourth hole should be 4.5″ from the previous hole and 3.25″ from the corner. Hopefully, if you measured and bent everything correctly, these measurements should be right or very close. Each hole must also be 2.25″ from the edge.

The ceramic end caps of our heating elements have a wing nut shape that we have to cut out. Luckily, I saved the retaining plates that were holding the heating elements in place inside the toaster oven so we can use them as a template. Never throw anything out when disassembling electronics or appliances because you’ll often be able to modify or adapt certain pieces to your new build. I love it when my hoarding gets rewarded!

After trying a few methods like tin snips and large drill bits, I found that using a step bit was the easiest way to drill out the center portion and gave me the cleanest edges. A large regular drill bit works great too but you’ll have some barbs to clean up either with a rotary tool or metal file. To cut out the wings, I used a rotary tool with a diamond bit but a carbide bit would do the job too.

Drilling out all the wing nut shaped holes was probably the most tedious part of the heat box build but it was also the best way of holding the heating elements in place without having to fabricate some kind of bracket for them. In the end my holes on both 20″ sides seemed to line up pretty well.

I highly recommend test-fitting your heating elements at this point. In order to temporarily hold my metal strip into its rectangular shape, I used a piece of masking tape so I could have both hands free to maneuver each heating element. This is when I quickly discovered that the wing nut portion of the ceramic cap went in easily but it got stuck at the larger diameter round cuff just behind the wing nut.

On one of the 20″ sides, I had to enlarge the center round part of my holes so the entire ceramic cap could slide through. As for the other side, I only had to refine a few areas here and there because only the wing nut portion goes through that side. The larger diameter cuff stays inside the heat box.

After enlarging all the center holes of one 20″ side, I took one last opportunity to test fit the ceramic end caps of the heating elements.

Reinforce the Heat Box with Aluminum C-channel

Our heat box’s rectangular form is still a bit too floppy so we need to add more structure to help maintain its shape. I cut pieces of 3/4″ aluminum c-channel using a rotary tool and cut off wheel to match the dimensions of the heat box and even mitered the corners by hand. They’re not exact but it will be enough to firm up our heat box structure.

I drilled four holes all the way through the longer pieces that attach to the 20″ sides and three holes to the pieces that attach to the 11.75″ sides of the heat box. Unlike steel, aluminum is really easy to drill through so it’s a great metal for those of you just starting out with fabrication.

Next, I marked the location of the holes from the aluminum c-channel to the bottom of the heat box. With the heat box still in a flexible state, it’s easy to drill out all the holes along the strip of roof flashing.

If you also end up using 3/4″ aluminum c-channel for the heat box portion of your homemade vacuum forming machine, then 1 1/4″ bolts with matching nuts is a good size for fasteners. You can always go longer if that’s what you have lying around but I prefer to use the smallest length that’s appropriate for the job so you don’t get all these protruding studs.

It’s a good idea to hand-tighten the bolts for now so it’s easier to make adjustments later on. Once all the aluminum c-channel bars are attached along the bottom of the heat box, you’ll notice it feels a lot more stable now. There will still be a little wiggle but once it gets attached to the vacuum box, it won’t be going anywhere.

Cover the Top to Deflect the Heat Downwards

We all know that heat rises so I needed to devise some kind of roof for my heat box to deflect the heat down towards the plastic sheet below it. Using the same technique as with the aluminum c-channel strips along the bottom, I created a rectangular border at the top using L-shaped aluminum angle stock and attached the pieces using small bolts and nuts. You can cut these easily with a rotary tool and cut-off wheel and you don’t have to miter the ends like I did.

This not only gave the top of the heat box more structure, it also provided an area to attach my roof. I measured out and cut a piece of roof flashing from the same roll I used to create the walls of my heat box and laid it on top of the angle bar border.

Just a few small bolts is all you need to secure the roof. Try and get your roof as flat as possible as you bolt it down around the edges so you don’t end up with humps where heat could escape.

I drilled one hole at a time through both the aluminum sheet and angle bar simultaneously and attached bolts and nuts one by one so I could make adjustments and flatten any humps along the way. Using a center hole punch tool is helpful for drilling accurate holes because it prevents your drill bit from sliding around when it first starts up.

Final Heating Element Test Fit

Your heat box is complete! But before you start celebrating, let’s do one last test fit for our heating elements. They should be easy to install and sit rather snug in the openings we drilled out. Make any final adjustments to the holes until the fitment is right and tighten down all the nuts and bolts.

And that wraps up my comprehensive guide on how to build a heat box for your DIY vacuum forming machine with simple tools and no welding. With careful planning, safety precautions, and the right materials, you’re now ready to fabricate your own heat box. Depending on the size and shape of the heating elements you use and how many you incorporate, your design may look different than mine. I would love to see what you come up with!

But the journey doesn’t end here! With the heat box complete, we’ll be using its dimensions to design the vacuum box for our DIY vacuum form machine next.

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