Introduction: Variable Insulating Cup - Convection Cup

If you like this instructable, check out my other 3D printed creations on my other instructables or on my website.

It has been said before that the simplest inventions are usually the best, such a the lightbulb, and the cup... and I am here today to re-design the latter, the cup, and talk you through the process the whole way from concept to design (then to reality if you own a 3D printer) for all abilities of CAD (computer aided design) modelling skills (designed using AutoDesk's free CAD software 'AutoDesk 123D Design')...

First let's start with an impressive statistic: over 100 million people drink coffee EVERY morning in America alone, that means even more drink any hot beverages including tea and hot chocolate at least once a week, this introduces the need for a cup that's suitable for all the problems of drinking hot drinks.

First Problem:
Let me introduce the first problem with cups (including mugs), they cause hot drinks to cool down rather quickly as they are not very insulating, this makes the need for an invention for something to keep hot drinks hotter for longer necessary so hot drinks can be enjoyed over a longer time without going cold... Yes, I know, that has already been invented, it's called a vacuum flask which is sold under many names such as the Thermos® Flask. This quite ingenious invention solves this problem by taking into account all three ways of heat loss from the drink: conduction, convection and radiation by having the drink surrounded by a silvered container separated by a vacuum, the vacuum prevents conduction and convection and the reflective surface of the silvered container prevents heat loss via radiation.

Second Problem:
The second problem that arises when having hot drinks is essentially the opposite of the first, many hot drinks such as coffee are required to be made with boiling water and this introduces the problem that boiling water is too hot to drink and it can take a long time for a drink to cool down to a suitable drinkable temperature before we can drink it resulting in the inpatient of us and those of us on a tight schedule burning our tongues and throats. This problem is ironically worse when we attempt to solve the first problem of hot drinks cooling too quickly by using a product such as a vacuum flask which slows down the rate of cooling of the hot drink, this means more time is needed before a boiling hot drink reaches a suitable drinking temperature and can be drunk. So what can be done to solve both problems?...

Coming up with a solution:
When I realised these two problems, I realised it would be almost impossible to create a cup to solve both as the required features are opposite, a cup that first cools the boiling hot drink to a drinkable temperature but then keeps it hot for as long as possible so it can be enjoyed for longer.
So to summarise, the cup must quickly lose heat from the drink but then prevent this happening once it has reached a drinkable temperature...

So here is my solution...

Step 1: The Solution

The Solution: Variable Insulating Cup
My idea is to change the insulating properties of a cup while it is in use by taking advantage of two of the three methods of heat loss, conduction and convection, by allowing the user to switch between two selectable modes that affect the insulating characteristics of the cup depending on their need...

High Insulating Mode:
To first solve the first problem of drinks cooling down too quickly, I have prevented heat loss through conduction and convection by designing a unique double walled cup design (which is very well suited towards being 3D printed), similar to that of a vacuum flask however instead of a vacuum, the cup traps 5mm of air in between the inside surface of the cup and the outside surface acting as a very effective insulator. Air is one of the best insulators and it is used as the main insulator in nearly all types of insulation by utilising trapping air such as wool and styrofoam. Did you know that many indoor ski slopes are kept cool by being insulated in a very similar manner to my double walled cup design by having a layer of air between the internal walls and the external walls keeping the the ski slope cold.

Low Insulating (heat loss) Mode:
To solve the second problem of drinks staying too hot for too long when they are first made, I utilise the methods of heat transfer by both conduction and convection to draw heat away from the cup as quick as possible. By simply rotating the ring at the top, this opens vents at the top of the outer layer of the cup allowing air to circulate through the vents at the bottom and the open vents at the top circulating air in the cavity in-between the inner and outer walls of the cup. Due to the hot drink heating up the air in the cavity between the two walls, this causes this air to be less dense and lighter that the surrounding ambient air making a convection current by causing this air to rise up and out through the top vents from between the cup's walls due to its lower density and causes cold air to be drawn in through the bottom vents and this cold air is then heated up by the drink and the cycle starts again which ultimately draws heat away from the drink efficiently.

Next is to test this concept in the real world to find out if it would work as expected and to what extent it would work...

Step 2: Concept Testing

To test the effectiveness of the concept, a few months ago I decided to designed a simple proof of concept design for this idea using 'AutoDesk Inventor' and got the chance to get it 3D printed by Instructables a couple of months ago thanks to a promotion at the time.

I set about testing the effectiveness of this concept by setting up the cup on a kitchen top with first the vents closed and filling it with 60C water and recording the temperature every 30 seconds for 30 minutes (60 readings in total for each scenario) using a time lapse application on my iPad and later I then put this data into Microsoft Excel and then converted it into a graph using the same program which graphically plotted the heat loss that could then be easily compared. I then repeated this with the vents open and then once more with the vents open until the drink reached 50C and then the vents closed for the rest of the time lapse simulating normal use.
Here are my results (a graph of these results is within the pictures above):

With the vents open: the drink cools down 33% quicker than with the vents closed.
With the vents closed: the drink stays hotter for 50% longer than with the vents open.
With the vents open and then closed when the drink had reached 50C: the drink started cooling down quickly and then once the vents were closed the rate of cooling slowed dramatically.

IT WORKS!!! Just as expected, this system allows you to quickly cool a hot drink to a drinkable temperature and then keep it warm for as long as possible.

All that is left is to design a more stylish and ergonomic design around this now proven concept...

Step 3: Designing - Cup

At the top of all the following design steps, there is a video showing the exact steps I took which are then explained as text below each video. Make sure to watch the video in HD as it helps with the clarity of the numbers I type in.

All that is left is to design a more stylish and ergonomic design around this now proven concept, and to do this, I am going to use AutoDesk's free 3D CAD modelling software 'AutoDesk 123D Design' and for these purposes I am going to design this for 3D printing on a 'MakerBot Replicator 2' (using PLA which is a non toxic biodegradable plastic derived from corn starch) or any other 3D printer/3D printing technique by taking advantage of many of 3D printing's unique attributes (I'm not new to the world of 3D printing!).

First download and open 'AutoDesk 123D Design' available at this download link if you don't already have it and click on 'Start a New Project' (if this dialogue appears, if it doesn't, click on the 123D logo and click on the 'New' button). Make sure in the bottom right of the window it shows 'Units:mm' as this instructable uses millimeters as the units in all the dimensions, if this is not the case, hover over whatever unit is being displayed, and then select 'mm' from the drop down box.

During this step, I am going to use a very powerful tool in the 123D software called 'Revolve' which allows very complex organic shapes to be created from a simple 2D sketch, this can create a lot more ergonomic and organic shapes that the simple 'Extrude' features.

To start with, by using the 'Spline' and 'Polyline' tools under the 'Sketch' category at the top by clicking on the respective tool in the 'Sketch' category and then clicking on the grid to start a sketch, I drew out an ergonomic profile of the outer face of a basic cup shape. After using a tool, tap the enter key or click on the small green tick that appears to confirm the drawn line and exit the sketch. After selecting a new tool, I always made sure to select (click on) one of the previously drawn lines to make sure I was adding to the existing sketch which helps later when performing functions on this sketch (such as the 'Revolve' function I use later). After exiting the sketch, the lines and splines can still be modified by clicking and dragging respective points in the sketch, this is useful throughout this tutorial.

I then added some dimensions by clicking on one of the lines I have drawn followed by hovering over the gear symbol that appears and then clicking on the 'Edit Dimension' button, I then added dimensions to appropriately size the profile by clicking on two points or lines to add a dimension between then clicking to confirm and then double clicking on the created dimension to edit it, I made the height of the cup 11mm shorter than the proposed final height of the cup (for space to add an indentation for the 10mmx1mm thick rotating 'vent covering collar' later allowing the user to select the insulating characteristics of the cup), some dimensions can also be added while drawing with certain tools such as the 'Polyline' tool by simply typing in the desired dimension while drawing a line, view the video above to see the other dimensions I used at this point.

Using the 'Offset' tool under the 'Sketch' category at the top, I clicked on the profile and created three copies inside the original at distances 1mm, 6mm and 7mm away which are for the other three faces of the two walls making each wall 1mm thick (which I think is suitable for fused filament 3D printing) and creating a 5mm thick air gap between them, it is in this gap that air will either circulate to cool down the drink or insulate the cup to keep the drink warm depending on the user's preference.

I then added the space for the vent covering collar at the top by adding a further 11mm height to the cup as a 10mm high indented section (by 1.1mm to hold the 1mm thick collar (producing a 0.1mm clearance when the collar is installed allowing it to be rotated easily)) to hold the collar later by using the 'Polyline' tool to draw this section as shown in the video above. As I am designing this for 3D printing, I also added a 20 degree angled line under the overhang produced by the indentation for the collar getting rid of the need to have support material printed below it in the insulation cavity as this would affect the cups functions.

Using the 'Polyine' tool again I closed off each pair of lines at both ends so they would become solid shapes that can be converted to 3D.

When the walls are ready to be converted to 3D, they will have a reddish hue to them, if this doesn't occur that means that the lines making up each wall are not all joined so are not continuous which I found to be the fault of the 'Offset' function as when the lines were offset, they were also split apart, to fix this, simply delete the horizontal lines that were offset during the 'Offset' operation, and then simply re-draw them back in the same place making sure each end attaches to the other corresponding lines, the walls should now have a reddish hue to them if they didn't before.

Then using the 'Rectangle' tool, I added ribs of 2mmx5mm in the air gap at the bottom of the cup to support the base of the inner wall of the cup so it can be 3D printed while still trapping air to insulate and prevent heat loss through the bottom of the cup.

Now I revolved the drawing using the 'Revolve' tool under the 'Construct' category at the top, I selected the two walls of the cup and the ribs at the bottom of the cup, I then selected the 'Axis' button and then selected the vertical line of the far left rib to act as the axis of rotation. Then I typed in '360' so the profile would revolve a full 360 degrees and then tapped the enter button to confirm.

The basic 3D shape is now completed and all that now needs to be added is a handle, the vents and the vent covering collar...

Step 4: Designing - Handle

Now I am going to use a another of 123D's powerful tools called 'Sweep' to create the handle of the cup. This tool also allows you a lot of freedom of creating practical organic and ergonomic shapes (however it does not give you as much freedom as the 'loft' tool which allows you to create very complex organic shapes however this tool is not required to be used in this instructable).

In this demonstration, I am going to show you how to create a simple handle however by simply changing the shape of the path you create you can create some quite funky handle designs very easily (an example is shown in the pictures at the top of this step).

First, using the 'Ellipse' tool under the 'Sketch' category, I clicked on an empty part of the grid to start a new sketch and drew an oval with radius 10mm in the x-axis and with radius 5mm in the y-axis about a quarter of the way up the cup with the centre point touching the outside of the cup.

Then I selected the 'Spline' tool under the 'Sketch' category and clicked on an empty part of the grid (to make sure I had started a new independent sketch to the last) and drew a simple cup handle shape starting at the centre of the oval I had drawn before and drawing out the shape of a handle before ending the spline at the wall of the cup near the top.

After exiting the sketch (by clicking on the tick or tapping the enter key), I selected the oval and hovered over the 'gear' symbol and then clicked on the 'Move' button and rotated the oval 90 degrees around the y-axis by grabbing and dragging the corresponding handle making the oval (roughly) tangent to the cup.

Next I clicked on the 'Sweep' tool under the 'Construct' category and selected the oval as the 'Profile' and then clicked the 'Path' button and then selected the handle shaped spline to act as the path for the sweep, before confirming using the enter key I made sure the sweep function was set to create a 'New Solid' in the button to the right of the 'Path' button.

The handle and the cup are not yet connected together so to connect them together I first clicked on the handle and clicked on the 'Move' button that appears towards the bottom of the screen and then moved the handle towards the cup until the edges of the handle are inside the cup by grabbing and dragging the 'handle' with an arrow in the correct axis of intended movement.

Now we have the problem that part of the handle is now inside the insulation cavity, to solve this, I selected the 'Revolve' tool again under the 'Construct' category and I selected the insulation cavity area of the sketch that was used to create the initial cup shape as the 'Profile', and again selected the 'Axis' button and then selected the vertical line on the far left of this sketch however this time I clicked on the button next to the 'Axis' button and selected for the 'Revolve' tool to 'Cut' so it would remove all the material that is in this cavity (parts of the handle).

Next I combined the two solids by using the 'Combine' tool and selecting both the cup and the handle by clicking on them individually and then confirmed the function using the enter key, these two solids that were created individually and acted independently have now been combined into one solid and so will behave as one solid, this makes further steps easier.

Lastly, I selected the cup by clicking on it and then clicked on the 'Move' button near the bottom of the screen and re-orientated it by rotating the cup 90 degrees around the x-axis and moving the cup 50mm upwards so the cup is sitting on the grid upright, this step will also make the next steps a lot easier.

Next is to add the vents followed by the collar...

Step 5: Designing - Upper Vents

In this step, I created the vents around the top side of the cup that can be covered or left open using the collar I designed after to either insulate or increase heat loss from the drink.

Creating the vents was quite a simple and quick step as it takes advantage of the 'Pattern' functions of 123D design which saves a lot of time and makes the vents equally spaces out and neat.

To start with I selected the 'Box' tool from the 'Primitives' category at the top and changed its dimensions to 5x5x5mm before placing it on the grid, this box is going to be used later to subtract material from the cup to make vents between the insulation cavity in the cup and the outside air.

Next, I clicked on the 'Snap' tool and selected a face of the cube followed by the outer face of the indentation around the top of the cup made to hold the collar, this tool very neatly places the cube in the middle of this indentation against the outer face which saves a lot of time compared to manually moving the cube to exactly the same location.

By using the 'Snap' tool, this also groups the two bodies together so they can no longer act as separate objects so can no longer be manipulated separately (which helps most of the time), however to fix this, all you need to do is click on the cup, and select 'Ungroup' under the 'Grouping' category at the top, they will now act independently as separate bodies.

Next, I clicked on the cube and clicked on the 'Move' button that appears towards the bottom of the screen, then using the corresponding handle with an arrow in the axis of intended movement, I moved the cube 1.1mm (this value can also be entered into the text field as '-1.1' if this is easier) into the cup's outer wall before confirming the movement with the enter key.

Now I clicked on the 'Combine' tool I used earlier and clicked on the cup (as the 'Target Solid') followed by the cube (as the 'Source Solid') and then selected for the tool to 'Subtract' (the 'Source Solid' from the 'Target Solid') by clicking on the button next to the 'Source Solid' button and select 'Subtract', I then confirmed again using the enter button which created one of my vents.

I then used (clicked on) the 'Circular Pattern' tool under the 'Pattern' category at the top and selected (clicked on) the four faces of the vent produced by the 'Subtract' function I used, then I clicked on the 'Axis' button and clicked on any of the circles at the top of the cup to act as the axis of rotation, finally I typed in the number '20' as the number of occurrences this pattern will produce around the selected axis and then confirmed the operation using the enter key.

Next is to add the vents at the bottom of the cup allowing a convection current to be produced when needed to increase heat loss from the cup...

Step 6: Designing - Lower Vents

Creating the bottom vents was very similar to creating the top vents...

To make the shape of the lower vents more interesting than the upper vents, I started off by creating a torus by clicking on the 'Torus' tool under the 'Primitives' category at the top and changed the dimensions of the torus so it's 'Major Radius' was 10mm and it's 'Minor Radius' was 5mm. I placed this torus on the grid (by clicking) just in front of the front of the cup.

Next I clicked on the torus and clicked on the 'Move' button that appears near the bottom of the screen and moved the torus using the corresponding handle with an arrow along the axis of proposed movement and moved it into the cup about 5mm.

I then subtracted the torus away from cup to create a vent and copied this four times around the base of the cup with the same techniques used in the previous step (any changed text is in [square brackets]):

"Now I clicked on the 'Combine' tool I used earlier and clicked on the cup (as the 'Target Solid') followed by the [Torus] (as the 'Source Solid') and then selected for the tool to 'Subtract' (the 'Source Solid' from the 'Target Solid') by clicking on the button next to the 'Source Solid' button and select 'Subtract', I then confirmed again using the enter button which created one of my vents.

I then used (clicked on) the 'Circular Pattern' tool under the 'Pattern' category at the top and selected (clicked on) [the face] of the vent produced by the 'Subtract' function I used, then I clicked on the 'Axis' button and clicked on any of the circles at the top of the cup to act as the axis of rotation, finally I typed in the number ['4'] as the number of occurrences this pattern will produce around the selected axis and then confirmed the operation using the enter key."

Are you still with me??? Good... Lastly is the creation of the collar that can be rotated to either block or open the vents around the top of the cup...

Step 7: Designing - Collar

Here is the final step, making the collar...

This is the collar that after printing can be placed on the top of the cup in the indentation and it can be turned to either block off the upper vents (to make the cup high insulating) or to open these vents and allow convection currents to draw heat away from the cup's contents (low insulating mode).

To start with, I selected the 'Circle' tool under the 'Sketch' category at the top, I then clicked on the grid to select it as the plane for the sketch and clicked near (but not too near) the cup to select the centre of the circle and then typed in '80' to make the circle 80mm in diameter, I then tapped enter to lock the dimension and then clicked to finish drawing the circle, I then created another circle with the same technique with the centre being in the same spot as the existing circle's but this time made the diameter 78mm so this would create a collar section 1mm thick between the two circles.

Next I used the 'Extrude' tool under the 'Construct' category to create this collar in 3D, to do this I selected the 'Extrude' tool and clicked on the area between the two circles I created earlier, then I types in the text field '10' to set the extrusion height to 10mm making the collar 10mm tall.

From here onwards, the creation of the vents in the collar that match up with the upper vents on the cup is almost identical to step 5 where we created the upper vents (any changed text is in [square brackets]):

"To start with I selected the 'Box' tool from the 'Primitives' category at the top and changed it's dimensions to 5x5x5mm before placing it on the grid, this box is going to be used later to subtract material from the [collar] to make vents [that will either close or open the upper vents on the cup when placed in the indentation].

Next, I clicked on the 'Snap' tool and selected a face of the cube followed by the [outer face of the collar], this tool very neatly places the cube in the middle of [the collar] against the outer face which saves a lot of time compared to manually moving the cube to exactly the same location.

By using the 'Snap' tool, this also groups the two bodies together so they can no longer act as separate objects so can no longer be manipulated separately (which helps most of the time), however to fix this, all you need to do is click on the [collar], and select 'Ungroup' under the 'Grouping' category at the top, they will now act independently as separate bodies.

Next, I clicked on the cube and clicked on the 'Move' button that appears towards the bottom of the screen, then using the corresponding handle with an arrow in the axis of intended movement, I moved the cube [about 3mm] into the [collar's] outer wall before confirming the movement with the enter key.

Now I clicked on the 'Combine' tool I used earlier and clicked on the [collar] (as the 'Target Solid') followed by the cube (as the 'Source Solid') and then selected for the tool to 'Subtract' (the 'Source Solid' from the 'Target Solid') by clicking on the button next to the 'Source Solid' button and select 'Subtract', I then confirmed again using the enter button which created one of my vents.

I then used (clicked on) the 'Circular Pattern' tool under the 'Pattern' category at the top and selected (clicked on) the four faces of the vent produced by the 'Subtract' function I used, then I clicked on the 'Axis' button and clicked on any of the circles at the top of the [collar] to act as the axis of rotation, finally I typed in the number '20' as the number of occurrences this pattern will produce around the selected axis and then confirmed the operation using the enter key."

Now I could go further and fillet some edges however I feel the design will be more attractive and more easy to use without.

Last is to 3D print the design (if you want to)...

Step 8: Finished!!! Making - 3D Printing

The design laid out as it was in the last step is ready to be 3D printed by either using the '3D Print' button or by exporting the design as an .stl file (which can then be used by 3D printer software to be able to 3D print the design) by using the 'Export .STL' button, both these buttons (as well as other useful buttons such as save and open) are revealed when clicking on the '123D Design' logo, I have attempted to make the design as 3D printer friendly as possible by limiting overhangs and by designing with dimensions suitable for 3D printing.

If you don't have a 3D printer yourself (like myself) you can always upload the .stl file to a 3D printing service (such as Shapeways) and get it 3D printed by them.

Whatever method you choose if you choose to 3D print, it is YOUR responsibility to make sure the material you are using is safe to drink from if you intend to drink from the cup (if it is not, the cup will also be a very good educational demonstration of the effect of convection currents and heat loss).

You can also move the collar using the 'Move' button that appears at the bottom of the screen (that we have now used many times) when you click on the collar and position the collar on the cup itself to check out the function and fit.

Lastly, you can change the material appearance of the design by selecting the cup and/or the collar and clicking on the 'Material' button at the top, from here you can change the material and the colour, I found the 'Poly Clear' material under the 'Plastic' category allowed you to see the inner workings of the cup including the insulation cavity in the cup best as it made the material semi-transparent.

Finished!!!

Thanks for reading my instructable, feel free to check out my other 3D creations either on my other instructables or on my website.