Making A Giant Egg

 

Completed egg shells

Completed fibreglass shells painted in shellac ready for finishing

The first step in making a giant egg is to make a giant egg – so a mould can be made.

Depending on the size of the egg you want to make will dictate how you go about making the egg form. Since the egg we needed to make was about 60cm tall it was decided to carve it from a block of polystyrene. Since the egg shape is symmetrical it is best to turn it on a lathe.

Preparing polystyrene block for turning

Preparing polystyrene block for turning

The polystyrene has to have plywood boards glued to both ends so a lathe faceplate and tailstock centre can be attached so it can be turned on the lathe.

The corners of the block are then cut off at 45 degrees to make turning a bit easier on the polystyrene. If this is not done it is likely large chunks will break off when the lathe chisel is applied to the turning block.

It is very, very messy turning polystyrene on a lathe so ensure the work area is covered with something to collect the shavings and clean up regularly as you work. This will minimise the polystyrene getting into every nook and cranny of your workshop.

Polystyrene mounted on the lathe ready for turning

Polystyrene mounted on the lathe ready for turning

Basic shape completed on the lathe

Basic shape completed on the lathe

Completed polystyrene egg

Completed polystyrene egg

The polystyrene is removed from the lathe and the two ends trimmed. Sandpaper is used to smooth both ends until their radius makes a smooth transition around the egg shape. It is important to get the shape exactly right with no obvious flat spots or sudden changes in the radius.

To support the egg while making the mould a box was built to put the egg form into so the middle flange can be made with plasticine. Once that has been done it is given a coat of PVA mould release in preparation for fibreglassing.

Ply box for making the top half of the mould.

Ply box for making the top half of the mould.

Flange finished around egg

Flange finished around egg and mould release applied

After the top half has been fibreglassed a timber support is fibreglassed on the mould so it sits horizontal when put on its side. The egg with the first half of the mould attached is removed from the support box and turned upside down to expose the underside of the egg form. This is cleaned up, PVA mould release applied and the second half is coated with fibreglass as described in previous mould making posts.

After polishing the inside of the mould halves with wax fibreglass casts are taken and trimmed to the flange line around the mould on both halves.

The two completed fibreglass mould halves

The two completed fibreglass mould halves

Fibreglass casts for egg ready for joining

Fibreglass casts for egg ready for joining

To ensure that both halves of the egg are joined together securely they need to be fibreglassed along the inside centre seam of the egg. To do this an access panel is cut in one half that is big enough to get your hand inside the egg shell. Blocks of wood are attached to the inside of the shell around where the access panel will be cut. This allows for easy re-installation of the panel section after the work has been done.

You can see the alignment blocks in the photo below with the access panel removed.

Cutting out an access panel in one half

Cutting out an access panel in one half

Access panel removed

Access panel removed so halves can be fibreglassed together

The two halves are taped together with mylar tape to keep them aligned. They are then fibreglassed on the inside along the centre seam. Once this has been done the access panel can be glued back into position and all gaps around the panel opening and the centre egg seam can be filled with polyester filler.

After sanding smooth the fibreglass is given a primer coat of de-waxed shellac.

Halves taped in position

Halves taped in position for fibreglassing from the inside

Access panel glued back in position

Access panel glued back in position and gaps filled and sanded

The completed eggs can be seen in this post.

Making a Giant Heart

Completed giant fibreglass heart

Completed giant 3D fibreglass heart

The making of a giant 3D heart for the recent Wayside Chapel winged heart project was a great exercise in how to sculpt large objects for armatures to make large fibreglass moulds. The heart had to be made as quickly and cheaply as possible so some shortcuts were made that had both positive and negative consequences.

Instead of making a two piece mould it was decided to make a perfectly symmetrical half mould so both front and rear sections could be cast from the same mould. This was achieved by first drawing half a heart on a piece of plywood. A second piece of plywood was fastened under the first and then both pieces were cut as one on a bandsaw. After sanding the the edges smooth the plywood *sandwich* was split and fastened together, side by side, making a perfectly symmetrical heart shape.

Heart outline in ply

A symmetrical outline of the heart was made from ply and fastened to support table

making armature with ply strips

Building up the heart profile using templates and ply strips

Heart shape in ply strips

Rough heart shape defined by ply strips

Hessian covering over ply

Ply framework covered with hessian

Plaster applied over hessian

Casting plaster was applied over the hessian covering to make it rigid.

second layer of plaster and hessian applied

A second layer of casting plaster and hessian is applied over form work

To smooth the heart shape a thick layer of Gyprock top coat filler was applied using a spatula taking care to make the layer as smooth as possible.

Applying Gyprock

Applying the Gyprock top coat filler over the plaster form. It was carefully filled out to match the heart outline defined by the base ply template.

Smoothing the form

Form ready for smoothing after the Gyprock dried

In the rush to get the mould made I decided to save time by not making the heart form super smooth before applying gelcoat and matting. Instead I would apply a double thickness of gelcoat when making the mould and then sand any irregularities from the mould directly. A quick coating of wax mould release was applied before applying the gelcoat and fibreglass matting over the heart form. This was a big mistake. The wax soaked into the not quite dry Gyprock allowing the gelcoat to stick firmly to the heart form making its easy removal impossible.

Mould completion

With the fibreglassing completed the mould was ready to be removed from the form but it would not budge.

Removing the heart form

The mould was firmly stuck to the heart form. Weighing in at over 100kg the mould had to be lifted from the work table so the form could be cut out from underneath the mould

Removing formwork

Once the bottom of the mould was exposed the timber formwork could be dug out

Plaster removal

Removing the plaster and hessian reinforcement

Once the ply form work and hessian had been removed there was still a thick layer of plaster and Gyprock stuck firmly to the fibreglass. The only way to remove it was to use a hammer and chisel. The chisel had its corners rounded and the cutting edge dulled to minimise the inevitable damage that would be done to the mould interior surface.

Removing the plaster and Gyprock

After 4 hours work only half the mould had been cleaned.

More plaster removal

About 8 hours later the last of the plaster and Gyprock was removed from the fibreglass surface

Cleaning mould

Wet’n’dry was used to sand the irregularities and scratches from the mould inside surface

Waxed mould ready for use

The mould after being cleaned and waxed ready to have a cast taken

Red gelcoat in mould

First layer of gelcoat with red pigment applied to the mould. This was followed by two layers of matting.

Fibreglass casting from mould

The first fibreglass heart shell removed from the mould. It popped out very easily because the mould release was applied correctly this time.

The shell of fibreglass was very flexible and had to have bracing fitted inside to make it rigid. This was done by hot glueing pieces of cotton rope on the inside and applying fibreglass matting over the top. The front shell also had a steel framework fitted so it could be attached to the wing mechanism.

Internal bracing of heart shell

The internal bracing in the front heart shell showing the cotton rope before being fibreglassed.

Completed 3D heart

Heart shells join line covered with cloth tape and polished