In many developing countries, students who suffer from loss of limbs are unable to run around with their friends, as they can't afford a suitable prosthetic limb. This impacts their physical health as they can't exercise like a child should, and their mental health, because they can't play with their friends. To fix this, they need a prosthetic limb, but a basic model of a prosthetic leg can cost over $5000AU, which many people would struggle to afford. This is directly in comparison with a 3D-printer, that costs only several hundred dollars. I think there is an obvious solution...

Something to note is that I have changed my toolbar to suit what I do, so if there is a tool that I use and I show it to be on my toolbar, but it isn't on yours, select the dropdown under the place I have show this icon to be on my account, and you should find it with the name the same as what I have called it, and possibly the same icon as I have shown. And all the times I say (press A) for example, means that this is the shortcut to get the function I am using, and you should hit that key on your keyboard.

Also, by the end of this instructables, the steps aren't broken into coherent steps, as much as slightly more manageable chunks.

(Grade 11 at Calvin Christian School, Australia)

Supplies

3D printer, I used a FlashForge Adventurer, because it was that or the Anet A8, and the Anet doesn't print nearly as nice as the Adventurer
Fusion 360
A model in need of a new foot. I used my brother, who actually has 2 fully functioning feet, but he was the only person I had, and his feet are smaller than mine. If your model is missing a foot, use the other one, but remember to use the right side on the left and vice versa, cause feet don't have an axis of symmetry.
Grid paper (if you plan on tracing your models foot)
I guess a 3D scanner would be useful, but I didn't use one.

Step 1: Employ Your Model

If you have a 3D scanner, skip up to step 7, where you'll have to open the model on Fusion 360, and then keep following along.

Get your model and trace their foot on some grid paper (the one they do have. If they don't have any, get their shoe size and scale a picture of a foot off google to fit it)

Find some rough dimensions on how high their arch is, and take as many key points as suits your fancy. I measured how high his foot was roughly every 20mm, but that's just me.

Step 2: The First Sketch

You're going to have to repeat this step a couple of times, how many times depends on how rough you are ok with the model looking, but you'll want at least 3, I did 8 in the end, but 5 is a good number.

Open up Fusion 360. On the toolbar, select the 'new component' icon (image 1), and press enter (on your keyboard). You can change the name of the component if you want, but I couldn't be bothered to.

Click Create Sketch on the top bar (image 2), and for the plane, select the Z-X plane at the origin. Using the dimensions you took in step 1, draw a cross section of the foot (image 3), right through the centre using the line tool (press L). I added orange construction lines (press X) every 20mm because I this was where I measured the height of my brothers foot, but this isn't strictly necessary. I also added in a spot where the toe would bend, because I thought I might add another detail, but I didn't, so you can just keep the base of the foot flat, or add the toe for realism if you want another challenge.

If you have straight lines with ugly angles you can fillet these by selecting two connecting lines (hold shift) and filleting them with the button on the toolbar (image 4). You can change how much the fillet is set at, or just let Fusion do what it wants, it will make a smooth curve either way. I had all my fillets at 40mm. To fillet the next corner, just select two connecting lines again (holding the shift key) and they will have the same fillet as the previous one. If you don't want this, press the enter key before selecting the two lines, and press fillet on the toolbar. When your happy with it, select the big green tick on the top right corner to finish your sketch. (image 5)

Step 3: All the Other Sketches

To make the next sketch, first you have to make an offset plane by selecting the 'construct' dropdown, and clicking 'offset' (image 6). Select the origin plane or the sketch you just completed as the starting plane, then type the distance you want it to be. The size of the foot will determine how far away you put the offset, I measured it out to the far right side of my brothers foot. Then select the 'sketch' icon, this time selecting the plane you just created, and draw the cross section of the right side of the foot, same as how you did the cross section in the middle. A useful tool here, if there are lines that are the same in the middle section as this side, is the project tool (press P). This brings a line on a different plane onto the plane you are working on, so you can use it in that sketch, or use it as a reference point you can snap to.

Do the same for the left side, and you can leave it at that, or, if you want it to look a bit smoother as the finished model, create a cross section in between the right side, and the middle, and the left side and the middle.

Step 4: Don't Forget to Save It!!

Don't forget to save it! Click on the floppy disk (save) icon on the top left (image 8) and rename your model to something appropriate, like 'Foot Model' (image 9), and save it to a suitable location, or just let it save where it saves, because that's where everything saves and if it's not there I won't know where it is.... This is my favourite strategy.

Step 5: Have a Short Break

Staring at a screen for hours on end isn't particularly healthy, so go outside for a while, take a 10 minute stroll through nature, or around your block, or down your hallway if you can't get outside, and find something interesting; a feather, a flower; a shiny rock; a button; whatever takes your fancy.

. . .

How was your walk? What did you find? Are you feeling refreshed? Well then, let's continue!

The next step was rather difficult for me, so I think you need to be prepared for extreme annoyance and hatred of all things technology.

Step 6: Make It 3D

This is the bit where you can make it look like a foot, yay!

***PLEASE NOTE (because I often forget): When you start up Fusion 360 after a break always make sure you work on the appropriate component. On the left side there is a list of words: browser, document settings, named views, etc. At the bottom there should be the component you created when you opened Fusion 360, I left mine as the stock standard 'Component1' name, but you might have changed it. Hover your cursor over this name and a dot should appear to the right of it (image 1). When you hover over the dot the words 'activate component' should appear. Click the dot. You have just activated the component!

The tool used here is called a loft (image 2), and to use it, you select 2 sketches and it does some magic and makes it a 3D shape. When I did it it didn't always look quite how I wanted it to, with triangles in all the wrong places. Luckily you can fix that without too much difficulty, but sometimes it is very difficult, and you need to deselect the shapes and start again.

So, you click on the loft button, then select two sketches. It will (should) immediately fill in solid, and you'll notice that there are large-ish dots all over it (image 3). These will likely be in different places on your model, and you have to figure out what they are doing! Each dot joins to another dot on the other plane with a dotted line, and you can move them around until you are satisfied with where they are.

When I did it, it ended up looking like image 4 at the back, which is not what I was after, so I moved around the dots, being careful not to cross the lines over because otherwise it doesn't work. My finished loft is shown in images 5 & 6. This is the sort of look I aimed for with each of my lofts, but you can do it differently.

Once you are happy, select OK in the box on the right (image 7), and repeat this process for all of the sketches.

Step 7: Make 3 Copies

Once you have a lovely looking foot (image 1) you are ready to split your model into 3 parts that can be slide together with a dove-tail like joint. This is partly because most 3D printers aren't big enough to print an entire foot, but also so that if one print fails you don't have to reprint the whole thing, or if it breaks you can replace the broken part. Also ease of print, because I for one do not enjoy cleaning supports off a print, and I'm sure you would appreciate any effort made so it can be printed without supports.

Okay. First you're gonna have to make 3 copies of your model. On the left hand side there should be a whole lot of labels (I don't know what this bit is called) but you're gonna want to right click on the component you made at the start (that you should still be working in!) and select copy (image 2).

Activate the main model, same as how you activated the separate component way back in step 4, and right click somewhere below your component, anywhere will do, and click 'paste new'. It will paste an exact copy of what you've already made, don't click 'paste' (instead of paste new) because any changes you made to one would also happen to the other, and we don't want that. Once you have pasted it, press enter, because we want it to be over the top of the other one. Do this again so you have 3 copies of your model.

These three versions of your foot are going to become the heel, toe and middle of the foot respectively. You can rename them as such by double clicking on the names of them and typing in the new name.

Step 8: Sketch Plane for the Heel

Activate the component labelled as heel and hide all the other components by clicking the eye on the left of the names. Create an offset plane (shown in step 2). It doesn't matter how far away the plane is, so long as it is not overlapping the model, because that will make it a lot simpler later on. Create a sketch on this new plane. You have do decide how long the heel will be, I went straight down from where I put the ankle which I found to be easiest.

Step 9: Change the Heel Into a Part by Itself

Project (press P) the top right corner, or the top line and the right line (on the heel), whatever you have, into the new sketch and press enter. This corner will be the main point for a rectangle you will create (press R). Click on the point you just projected and then click another point on the bottom fight side. It doesn't matter where you put this point, so long as you cover the entire heel (image 2). Use the line tool (press L) to create 2 dovetail joints. The dimensions of these doesn't matter yet, as they will be defined very soon (image 3). Select the 'equal' tool (image 4) and click on all the diagonal lines of your dovetails so they are each the same length as the others. You will have to create 3 pairs. You also need to make the end lines equal length, as shown by the colours in image 5, with each colour representing one pair of equal length lines. Using construction lines (press X), create a rectangle (press R) from one corner of the top diagonal line of the dovetail to the other corner (image 6), and using the dimension tool (press D), change the dimensions of the rectangle to a scale of 1:6, this being the ratio used by woodworkers in their dovetails. Select the top line of the rectangle and type in your desired value, then select the side line of the rectangle *not the entire dovetail, just the small rectangle* and put in the desired value for that. I put it as 2 mm up and 12 across (image 7). Because you made all the different ones be equal just before it should change them all to suit.

Using the Project tool (press P), project the bottom of the foot into the sketch. Select the break tool (image 8) and create a break on the vertical line next to the heel on the inside of each of the dovetails (image 9). You will also need to create a break over the line you just projected. The centre lines of the dovetails can then be deleted (image 10). Next up, select the equal tool (image 4), and make the lines paired in image 11 equal. Finish sketch.

Using the extrude tool (Press E), select the sketch you have just made and drag it into the foot model. It should turn red to show that it is cutting, not joining (image 12). When you have dragged it all the way past the other side of the model hit the enter key, and you have completed the heel.

Step 10: Toe Sketch Plane

Activate the toe component, and make it visible, and the heel invisible, and create a new sketch, exactly how you did it in step 8.

Step 11: The Toe

Here you have to more or less repeat step 9, except reversed, and over the toe.

Find where you want to have the toe start, I chose a spot about 1/3 of the way from the toe, perhaps a bit less. A smaller toe will make for a bigger centre section, which is very desirable, but you still want some solid bits for the toe.

Draw a rectangle over the other part of the foot (the bit that's not the toe), and repeat step 9, with a one change. This changes is that instead of making the rectangle to determine the dovetails dimensions at 2mm high and 12mm long, make them be 1mm high and 6mm long.

Step 12: The Middle

*Most of my screenshots for this part are with the 3D shape of the foot hidden. This is not necessary, its just so I can see what is going on. If you wish to do this too, click the arrow at the side of the name for the middle component (far left), and a whole lot of words should drop down from it. Click the eye icon beside the word 'Bodies'. The body should be hidden*

Activate the middle component, without hiding all the other components. Create a sketch the same way you have done for the heel and toe. Project (Press P) the dovetail joints that you made in the heel and the toe into this sketch (image 1). Select all the lines (image 2) and press X to make them construction lines. Select one side (image 3) and, using the offset tool (Press O), create an offset to allow the joints to slide together with enough room. I made an offset of 0.5mm to the inside, but that depends on the precision of your 3D-printer, that is, if you have a super cheap 3D-printer, you might have to create a larger offset, or if your 3D-printer is very good quality, you might be able to get away with a smaller offset.

Repeat this on the other side, making sure your offset is to the centre of the foot.

Turn it into a closed shape using the line tool (Press L) (image 4) and draw a rectangle (Press R) that encases the entire model (image 5). Finish the sketch.

If you made the body of the middle component hidden at the start, now is the time to bring it back by repeating the steps you took then.

There should be 2 separate shapes in the sketch you just made, one inside the other (image 6). Select the outside shape, shown as pink in image 6, and extrude that over the middle component, letting it turn red to show that it is cutting, and bringing it over the entire width (image 7).

Step 13: Checkpoint

You should now have 3 components of a foot: a heel; a toe; and a middle bit. I have shown these in the image above as being yellow, green, and purple, respectively.

Step 14: Disclaimer

With the middle component activated, you need to create the bend. This is done using an auxetic shape, and this is where you need to experiment with how thin you can 3D-print a sturdy shape.

I had to do heaps of test prints to get the right thickness, and even still I could probably change it more. The shape I used is a hexagonal auxetic shape, but there are many different types of auxetic shapes which you can find with a quick google search, and you would do well to experiment with those as well.

A good thickness is one that can bend a reasonable distance without snapping.

Step 15: Starting the Bend in the Middle

Create a polygon (image 1 & 2). It doesn't matter where you put it, as it will be moved to the right spot, but it is important that it has 6 sides, and a radius, which, in an ideal world, you would have tested to find what works, unless this is your test, in which case, we can make it 10mm.

Make one of the sides vertical by using the Horizontal/Vertical tool (image 3 & 4).

Create an offset (Press O) on the outside of the hexagon. The distance the offset goes is also something you will need to test for. Here I have made the offset 0.8mm.

Select both hexagons and copy them (Ctrl C). Deselect and paste them (Ctrl V). Drag the horizontal arrow until the shapes aren't overlapping (image 5) and press enter.

You'll need to zoom in a bit to do this. Using the line tool (Press L) draw a line on the left hexagon that goes from the inside bottom right corner, horizontally across to the outside line. It should snap to the horizonal if you are zoomed in enough. Select this line and make it a construction line (Press X).

Zooming back out, select the right hand hexagon and press M. Following image 6, chose point to point as the method of movement, then click on the right hexagon bottom left inside point, which will make it the origin point. Click the left hexagon at the point where the short line you just made intersects the outside shape. Press enter and the hexagons should align so they share one line on the side (image 7).

Delete the overlapping lines, selecting the ones that are longer (image 8).

Step 16: Continuing With the Hexagons

Select one of the vertical lines that you didn't delete and create an offset (Press O) to the inside of the rectangle, again this is something you might want to test to find what works best. I made an offset of 3.5mm. Repeat this on the other side (image 1).

Using the extend tool (image 2), extend the offset lines so they reach the very top and very bottom lines of the hexagon (image 3). Delete the vertical lines in the centre of these lines. Using the trim function (Press T), trim all the other lines in between the 2 lines you just created by clicking on the sections you don't want.

Create an offset of the vertical lines that is the width of the wall thickness to the inside of the hexagons, so I did 0.8mm (image 5, in green). Trim (Press T) the long bits that aren't needed (image 5, in yellow).

Repeat the previous 2 steps for the outside vertical lines of the hexagons (image 6)

Step 17: More Hexagons

Using the line tool (Press L) draw lines connecting the 2 vertically adjacent inner corners of the elongated hexagon (image 1, in yellow). Use the offset tool (Press O) to create an offset the same thickness as all the rest of the walls, in this case, 0.8mm (image 1, in green). Use the trim tool (Press T) to trim the parts of the hexagon where these overlap (image 1, in pink).

Press the X key so you are working with construction lines, then, following image 2, find the centre of the outside vertical lines (you can see that it is the centre because it shows a triangle, like what is circled in image 2). Draw a line connecting the hexagons from centre to centre. Draw a line down from the centre of this line. Draw a line from the bottom inside corner of the hexagon up to the centre line to find the point that would be where the normal hexagon would stop, following the same 30° from horizonal angle as the line.

Select all the parts, dragging from the top left to bottom right, and go Ctrl C, Ctrl V. Move them (image 3) so they are aligned with each other, then trim all the excess lines (image 4).

Do this a couple of times, probably once or twice is sufficient, but until you have enough hexagons to fill the height of the entire side profile of the middle section of the foot.

Step 18: Still More Hexagons

To make the pattern repeat going sideways, you need to add construction lines to make a point to follow.

Draw a construction line (Press X, then L) through the centre of one of the right side hexagons, going vertically. Then, using the mirror tool (image 1), create a mirror image of the vertical construction lines you made at the start of step 17. The mirror line will be the line you created at the start of this step (image 2).

Use the mirror tool again to create a reflection of the outside vertical line of the hexagon, using the line you just made as the mirror line.

Select all the lines, Ctrl C, Ctrl V, and move point to point, as shown in image 4, with image 5 being a close up of the origin point.

Trim all the excess, unneeded lines, then, using the line tool, fill in the gaps (image 6).

Step 19: Getting It in the Right Spot

Using either the extend tool (image 1) or the line tool (Press L), fill in the gap between the hexagons on the left side and draw a rectangle (Press R) so you have a point that lines up with the left side and the bottom (image 2)

Project (Press P) the bottom left corner into this sketch (image 3, the point is in red)

Select everything and move it (Press M) using the point to point part (image 4), so it lines up with the edge of the middle part and looks like image 5.

Project (Press P) the top and bottom corners on the right side of the middle section. If the top point isn't all the way at the top this doesn't matter too much, as these points are just being used for a basis to draw a line.

Draw a line (Press L) from the bottom point, crossing over the top point and going past the top of the hexagons (image 6) and delete all the lines on the wrong side. The trim function (Press T) can be used to trim any lines that cross over this vertical line.

Select the line, and make an offset (Press O) to the inside, the same thickness as what you have done everywhere else, in my case, this is 0.8mm. Go through the wall you have just made and trim (Press T) away any lines that cross it.

Project (Press P) the key points on the dovetail joints (image 7, green), then, using construction lines (Press X) trace them (image 7, yellow).

Selecting each dovetail in turn, create an offset that is not construction (Press X to turn it off) to the inside. The distance of the offset depends on how precise your 3D-printer is. I will do one that is 0.2mm. (image 8).

Using the trim (Press T) and line (Press L) tools, make the hexagon shape be one solid shape. It is a fully enclosed shape when it turns light blue. When done, it should look similar to image 9, with the yellow lines showing where you would have had to trim some lines, and the green showing where you would have had to add some. These are not the only places, but they are the main ones.

A tip: if you have completed a shape, but is hasn't turned blue, there must be a gap somewhere. To find the gap is rather tricky, but my best method is to use the line tool (Press L) and draw a line across the middle. If there is no gaps in part of it, that part will turn blue, but if there are gaps it will stay white. Keep drawing lines and narrowing down where the gap is until you find it and can fill it.

Draw a rectangle (Press R) over the entire shape.

Finish Sketch.

Step 20: Extrude

Extrude (Press E) the negative of the hexagons. That is, select everything but the hexagon lattice (image 1) and extrude it so it is past the solid bit of the foot.

Step 21: Optional, for Ease of Printing.

This step is not necessary, but means that you can print the middle section without supports.

Duplicate the middle section, the same as how you duplicated the whole model in step 7. With one of the middle sections activated, go through the sketches folder on the left side, and make the sketch that had the highest arch visible. Create a new sketch, using this sketch as the plane you are working on, and draw a rectangle that encases the entire side profile. Extrude this sketch so only one side of the middle remains.

Repeat (but cutting away the opposite side) for the other copy of the middle.

Step 22: Make a Hole to Stick a Leg To

Activate the heel component, and create a sketch on the top of it.

Find the centre of the top of the heel. I am unsure how important finding the centre is, or even if there's a better spot to put it that isn't in the centre, but I'll go with what looks like the centre, cause its hard to tell exactly.

Using the circle tool (Press C) click where you think the centre is, then drag out to the diameter of the connection you are using as a leg. I used a piece of 25mm post, so, with a slight gap in case of shrinkage, I'll make it 25.2mm.

Finish sketch.

Extrude the hole into the leg around 50mm. I haven't experimented with this, and a longer hole would have more surface area so the post won't slip out, but it might also make it harder to print.

Step 23: Print It!

I printed it at the normal setting that came on Ultimaker Cura, as I was never expecting it to be used. If you need it to be used, I would probably recommend a higher infill for strength.

You may have a bit of difficulty orienting the parts so you could print without support, but other than the middle part, any support that was needed shouldn't be to hard to remove.

Introduction: 3D Printed Prosthetic Foot