Clay, Application to Refinement

 

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 Corvette Scale Model (pt 2)

Armature build (pt 3, page1) (pt 1) (pt 2)

The last section dealt with the backbone of the clay model, the base and the modeling blocks, before applying the foam. Here I will guide you through the process of cutting the foam to the outline of the tape drawing, making sure there's plenty of attention being paid in allowing enough clearance from foam to outer surface. This will help to eliminate the chances of hitting Styrofoam? when clay modeling begins.

This part of the armature build is critical especially during the gluing of the foams. The amount of gap in the foam needs to be minimized to avoid any gap expansion due to temperature change, therefore every joint has to be glued tight. This initial attention to detail in building the foundation solid and correct will prevent unwanted cracks at the later stages of the model when fixing any cracks can be more difficult.

Styrofoam block before shaping to model outline.

The image to the left shows a block of Styrofoam? approximately 30" x 5" x 4". This open cell material will aid in retaining the clay tight to the surface helping to eliminate any chance of delaminating. 

I have purposely made sure that the foam can fit under my small hobby bandsaw with a six inch maximum throat dimension. If I need a taller dimension I will have cut the shape first then glue it together to accommodate the taller profile.

The first process is to take the outline of the foam shape that has been marked on the tape drawing and transfer the shape from the tape drawing to a sheet of tracing paper. I used a tracing paper roll that is readily available from your local art supply at a cost of a few dollars.

The width of the roll that I purchased is eighteen inches, making it wide enough to cover all the tasks that are required for this particular project.

The tracing from the tape drawing placed onto foam block ready for transferring the outline.

Outline of the foam model as marked through the tracing paper.

As you can see from the tracing above, the baseboard is included when transferring the lines. This indicates the shape the foam has to take when cutting, allowing for the staggered baseboard. The tracing is held in place with a few roofing nails, the large head stops the tracing paper from slipping or sliding.

To transfer the lines to the foam, pierce through the tracing paper with a sharp pencil in a dot-to-dot fashion then use a large felt tip pen or wax pencil to indicate the marks. These dots can then be connected to show the shape that the foam has to take.

China marker or wax pencil for marking lines on Styrofoam.

My preferred method is to use the wax pencil, also known as grease pencils or china markers with the serrated paper around the crayon which makes it easy to keep a marking tip. Just peel back the outer paper and untwist to reveal the crayon. I find the best colors are red and black, available from Dick Blick art supplies and McMaster Carr.

All foams cut and temporary placed together on base board.

Foam cut and sprigged together for fit before gluing.

The two images above show the Styrofoam? cut to the outline supplied by the tape drawing minus the clay thickness. I haven't cut the wheel envelope away yet and will probably do that after gluing the foams together and fixing to the baseboard. By cutting the wheel envelopes out later it will maximize the strength of the foam until fully secured into place.

In the back ground the tape drawing shows how the foam stacks up in side view and the plan view shows the overlay of tracing paper with the outline of the wooden baseboard together with the foam outline indicated.

Front view of the foams sprigged together showing the various layers.

When building up the foams I used a maximum height of 5" and a width of 4" for easy maneuverability on the bandsaw. The width of the baseboard for this project is 8 7/8" which meant that I had to place a thin slice of foam at the center. This was not a problem, it just means more joints to glue.

The two outer  foams fit directly to the side of the center foams eliminating any notching over of the baseboard. This way of construction helps to reduce the amount of hand shaping to the foam and lets the bandsaw do most of the work.

At this stage everything is dry fitted together to make sure that it fits over the baseboard easily. The wooden sprigs or stakes are used to hold the foam while register marks are put on the foams with a wax pencil to ensure that the same position is found when glued together.

As you can see from the image, all of the major  angles have been cut on the bandsaw leaving a little hand work to finalize the foam at a later stage when everything is glued together.

Now that the foam has been cut and pre-fitted to the baseboard I can proceed to glue the sections together and this I will cover in the next section Armature Build (pt 3, page2)

Copyright © 2007 - 16 Steven Austin

 

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