Method of 3D printing

1. A method of 3D printing an item, comprising the steps:

a) printing a first part of the item in three dimensions onto a substrate held by a holding means;

b) disengaging the first part of the item and the substrate from the holding means, reorientating the first part of the item, and then reengaging the first part of the item to the holding means with or without the substrate; and

c) printing a further part of the item in three dimensions on the first part of the item.

2. The method according to claim 1 , wherein the reorientating the first part of the item involves a change of 45°-180°.

3. The method according to claim 1 , wherein the reengaging the first part of the item with the holding means includes engaging the first part of the item with another substrate.

4. The method according to claim 1 , wherein the item is built up from print material sprayed from a spray head.

5. The method according to claim 4 , wherein the print material is cold sprayed.

6. The method according to claim 4 , wherein the printing is via a spray head, and wherein the spray head and/or the substrate is moved under the influence of a computerised controller to facilitate targeted placement of the print material as a cold spray as the item is built up, such movement being guided by recorded geometry parameters for the item.

7. The method according to claim 6 , wherein the geometry parameters notionally divide the item to be formed into distinct portions at least one of which is designated to be reoriented with respect to the holding means after the first part of the item is printed.

8. The method according to claim 1 , wherein:

a. the reorientating the first part of the item involves a change of 45°-180°;

b. the method is carried out without providing any support for the item as it forms, other than the substrate;

c. the item is built up from print material cold sprayed from a spray head;

d. the spray head and/or the substrate are moved under the influence of a computerised controller to facilitate targeted placement of the print material as the item is built up, such movement being guided by recorded geometry parameters for the item; and

e. the geometry parameters notionally divide the item to be formed into distinct portions at least one of which is designated to be reoriented after it is printed.

9. The method according to claim 1 , wherein disengaging the first part of the item from the substrate is by flexing or shock-loading the substrate in a jig and causing it to fracture along an interface with the first part of the item.

10. The method according to claim 3 , wherein one or both substrates is/are incorporated into the item.

11. The method according to claim 1 , wherein the print material comprises one or more of:

ferrous alloy;

powdered non-ferrous alloy; and

molten plastic filament.

12. A method of 3D printing an item, comprising the steps:

a) printing a first part of the item in three dimensions on a substrate held by a holding means;

b) disengaging the first part of the item and the substrate from the holding means, reorientating the first part of the item, and then reengaging the first part of the item to the holding means without the substrate; wherein the substrate is disengaged from the first part of the item by flexing or shock-loading the substrate in a jig and causing it to fracture along an interface with the first part of the item; and

c) printing a further part of the item in three dimensions on the first part of the item.