Plaster Turning

Freshly mixed plaster of Paris hardens within a few minutes and during that time it is possible to model it into regular shapes by pouring and turning. This is useful for producing cylindrical or spherical items without the use of a lathe.

Horizontal method

A horizontal spindle on which has been securely fastened some anchoring material (such as cloth or bandage) is laid in two vee-shaped stocks. A shaped metal profile is then fixed in a suitable position (angled so that wet plaster will run back from its edge) and the plaster is poured onto the spindle while it is slowly rotated. As the wet plaster builds up it is scraped away by the profile, producing a smooth and uniform item. This method is useful for making master items for the moulding or vacuum-forming processes.

Vertical method

Where large and heavy amounts of plaster are involved it is not so easy to use the rotating spindle method. An alternative is to perform the action vertically, with a rotating profile working around a static amount of plaster.

A vertically-mounted tube fitted firmly to a baseboard acts as a centre point. In this is placed a rod, to the top end of which is attached the profile. The plaster is poured onto the baseboard while the profile is slowly rotated, forming the obiect from the bottom upward.

In both these methods fluid plaster cleared away by the profile can be scooped up and re-poured over the article. Where very large amounts of plaster are being used it is necessary to stop the operation from time to time and mix fresh plaster. At this stage all dried swarf should be cleared away.

When large articles are being made the centre mass can be built up with pieces of expanded polystyrene or other coarse filler material, using the plaster only for the outer layer. With the vertical method female shapes can be turned if a strong supporting outer wall is made to acccommodate the plaster. Turning must be done carefully because the fluid material runs to the bottom and has to be scooped out as the work progresses.

PLASTER TURNING

1. Revolving spindle
A method of using liquid plaster to create a barrel shaped object. The object is revolved against a stationary profile.

2. Revolving profile
To form a large plaster bell, the profile is revolved while the object is held stationary.