I wanted a slightly decorated one, something just slightly different from the ones I'd seen. I might use this for a body painting at some stage, but made it to fit me for a change.
Check out this awesome instructable on a card helmet as well:
One of the very best I've seen using card as the basis, fantastic work. Had I found this earlier I might have used his dome template instead of constructing one from scratch. Grrr
Step 1: Getting started
The basis for all my helmets is a card dome made to fit the wearer. This is reinforced with resin and then coated with car body filler and sanded smooth. It takes quite a bit of effort doing it this way, but it is cheap.
For tools and materials see my other 'ible on making an armour mask. Same basic principles and using the same set of materials and tools.
In this case however, the dome needs to be a smooth shell. I started with some old cut up cereal boxes for the basic card. I measured my head from just above the eyebrow, over the tops of my ears to get the correct dimension for the base. Mine came out to 23 inches. I cut two strips 12 1/4" inches long and 3/4" wide. This gave me a 3/4 inch overlap on each for gluing. The advantage of doing it this way is that the glue tabs will tend to create a slight oval rather than a circle which is exactly what we want for a helmet. Your head ain't round.
Once glued together, I cut some strips 3/4" wide to start to build the dome. By varying the length of the first strip you can vary the shape of the dome. How 'pointed' it is etc.
This dome must be smooth, so I joined the first strip to the circle we made using masking tape. The ends of the strip actually rest on the top of the circle. This is fiddly to do but will pay dividends later.
Note: As each stage dries, keep test fitting to make sure that it is still the correct size AND SHAPE for your head. You should be able to get a finger between your head and the inside of the circle.
Next cut the first two side strips. It is important that these are exactly the same length. These will form the first two side supports for the dome. If you measure and position the strips carefully, then you will get a concentric dome. If however, like me, you want to alter the shape of your dome, then by moving them relative to the circle you can force the first support strip to change it's shape. I wanted a softer curve at the front and a steeper one at the back. I set my second supports off centre (towards the rear) by about 4mm. This forces the crest of the dome towards the rear of the helmet. Join the two support strips with masking tape, again butting the ends of the card.
Next I cut 4 more strips of cereal box, and using the 'by eye' method (that means an educated guess), I joined each strip to the base circle then bent them in to the correct general shape. Holding them against the crown I marked them, and then cut them with a scalpel so that they were a good butting fit with the crown. I joined them with masking tape.
Now it gets really fiddly. I switched to a much thinner card, 160gsm printer card in fact. I cut three sheets of card into 3/4" strips and offered one up to the frame of the dome I had made. Again using the 'by eye' method I calculated the correct length to reach from the circle to the crown. Working on alternate sides of the circle I started adding in strips, only securing them with masking tape at the base. I then glued the top sections into the inside of the crown trying to bend them to follow the contours of the frame.
Once they had all dried I started adding in the final sets of strips buy gluing them onto the back sides of the strips already in place. Once the glue had set I used little strips of masking tape to fully secure the bases and the crowns of each one.
After two days of work, including all the drying times, I had a dome that was already pretty smooth and the correct shape. This will require far less filler later.
I did a test fit, then finally gave each and every joint line a fillet of glue using my finger. I then let it dry overnight.