Method of making a helmet
A method of making a helmet comprises the steps of cutting a plurality of substantially rectangular, preferably square, blanks from a sheet of resin-impregnated fabric, making curved cuts ( 1 ) in each blank to form a crown portion ( 5 ) and lobe portions ( 3 ) therefrom, arranging a stack of said sheets into a helmet preform such that the lobe portions of any blank partially overlap adjacent lobe portions of the same blank, and molding the helmet from the preform.
1. A method of making a helmet comprising the steps of cutting a plurality of substantially rectangular blanks from a sheet of fabric, making curved cuts in each blank to form a crown portion and lobe portions therefrom, arranging a stack of said sheets into a helmet preform by pushing the stack of blanks into a substantially hemispherical cavity so as to cause the lobe portions of each blank to partially overlap adjacent lobe portions of the same blank, and molding the helmet from the preform.
2. A method according to claim 1 , wherein the sheet of fabric has previously been impregnated with resin.
3. A method according to claim 2 , wherein the resin is phenolic resin.
4. A method according to claim 3 , wherein the rectangular blanks are substantially square.
5. A method according to claim 4 , wherein the step of making cuts comprises forming only one cut extending inwardly from each side of each blank, thus forming only four lobe portions from the blank.
6. A method according to claim 1 , wherein the rectangular blanks are substantially square.
7. A method according to claim 1 , wherein the step of making cuts comprises forming only one cut extending inwardly from each side of each blank, thus forming only four lobe portions from the blank.
8. A method according to claim 1 , wherein the cuts start at a position on each side of the blank which divides the side into two fractions of between 0.3/0.7 and 0.45/0.55.
9. A method according to claim 8 , wherein each cut then follows an arc of a circle towards the other side of the blank to which the cut is already closest.
10. A method according to claim 9 , wherein the cuts do not extend further than any perpendicular bisector of any side of the blank.
11. A method according to claim 10 , wherein each cut terminates at the first perpendicular bisector reached.
12. A method according to claim 1 , wherein the centers of the blanks in the stack are aligned and there is an angular offset between adjacent blanks.
13. A method according to claim 1 , wherein the blanks are of more than one size.
14. A method according to claim 1 , wherein the blanks have a thickness between 0.3 and 1 mm.
15. A method according to claim 1 , wherein the molding step involves the application of heat as well as pressure.
16. A method according to claim 1 , wherein the molded helmet is trimmed in order to form a helmet with a rim that lies substantially in one plane.
17. A helmet formed from a stack of fibrous blanks impregnated with resin, each blank comprising a trimmed rectangle and each blank having four curved cuts extending inwardly, one from each side of the rectangle.