Styrene bodies and parts

Polystyrene is a plastic monomer based on styrene (a chemical compound consisting of carbon and hydrogen atoms) that has applications in various fields. In industry it is used to make food containers, packaging for cosmetic and pharmaceutical products, test tubes for laboratories, components for household appliances, packaging, furniture parts and much more.

A fair number of Tamiya models have polystyrene bodies that are also distinguished by their colour, here are some examples:

white (Bruiser model 58048, Mountaineer model 58111, Countach LP500S model 58005, Porsche 936 model 58006…),
blue (Toyota Celica Turbo Gr.5 model 58009, Ford XLT Ranger model 58027…),
light blue (Ligier JS9 Matra model 58011 and 58012…),
black (Countach LP500S CS model 58008, JPS Lotus 79 model 58020, Blazing Blazer model 58029…),
red (Ferrari 312T3 model 58010, Toyota Pick Up 4×4 model 58028, Monster Beetle model 58060…),
green (Porsche 934 model 58001, XR311 model 58004…) and
sand (Cheetah model 58007)

These bodies are richer in detail than an equivalent Lexan body, but weigh more: the specific weight of polystyrene is 3.5 g/cm3 and that of Lexan is 1.20 g/cm3.
F1 and F1CS chassis are supplied with two bodies: a polystyrene one with more detail and a lighter Lexan one.
The polystyrene bodies have a purely aesthetic and not a functional function: they do not protect the chassis from small impacts as they have little elasticity to absorb an impact.
The main advantage of this material is that it is easily machined and repaired.
Excluding cutting tools, the main tool for working polystyrene is acetone; the same liquid found in the best paint shops or DIY shops that is also used for nail care.
The main characteristic of acetone is that it dissolves various plastic forms including polystyrene.
When two pieces of polystyrene are brought into contact after acetone has been brushed onto the surfaces, the two parts join together in an indissoluble manner because acetone dissolves the molecules of the two surfaces and the parts bond together. This technique is not the same as gluing two parts together.
The operation of gluing two parts is also valid in the extreme condition of two pieces of different material held together by a third substance acting as a binder. The three materials remain distinct, can be different, and only come together through the action of the adhesive.

Acetone melts the two polystyrene surfaces, which become one piece by welding them together: once the operation is complete, the two pieces cannot be distinguished from each other.

Tools for working with polystyrene
Obviously, it is necessary to have a set of cutting tools to shape and machine the parts, such as scalpels, scissors or cutters.
It is possible to find sheets or rods of ABS on the market. This material is another form of styrene that dissolves very easily with acetone.
A solution of ABS and acetone makes it possible to join polystyrene parts by welding them together.
To prepare for a restoration of a polystyrene part, it is best to prepare three containers containing

– pure acetone
– acetone and ABS with a predominance of acetone. This solution is very liquid and is best used for joining large, even surfaces or penetrating into cracks.
– acetone and ABS with a predominance of ABS. This solution is very dense and finds its best application for joining small parts that need to be welded onto a surface, the drop of solution remains where it was laid. The denser solution is also good for building parts that have been lost or destroyed.
In order to obtain the solution, prepare many small pieces of ABS by cutting a sheet or bar, place all the pieces in a glass container with a metal cap (avoid plastic caps which are attacked by acetone), pour acetone until the liquid level covers all the ABS pieces, allow the acetone to act; the solution is ready when it appears as one homogeneous viscous substance.
This solution is easily spreadable with a fine-tipped brush. At the end of each use always place the brush in the container of acetone only: it is important to clean the brush of excess solution because after it has solidified it makes the brush unusable for other applications, cleaning the tip of the residue allows the brush to be used again and again.

In order to be able to work two parts, it is important to hold them in place; linen clothes pegs are needed for hanging and metal clips for picking up sheets. The clothes pegs must be made of wood because if they were made of plastic they would melt on contact with acetone.

To machine surfaces, one or more metal files and 3 or 4 pallets with different finish sandpaper are required.
The best solution for the pallets is to have rectangular or curved sections that are suitable for machining flat or shaped surfaces respectively.

Repairing body damage
The easiest way to repair damage to a polystyrene body is to have the part that has broken, cracked or bent available. Using the dense solution of ABS and Acetone to join the parts, the dense solution ensures that the liquid stays where it is smeared. A metal or wooden clip holds the parts together in the right position.
Four hours after the first application, another solution of acetone and ABS in the less dense form can be brushed onto the fracture line, the solution enters the cracks and closes them. Repeat this every hour or more until the crack closes. The time between applications depends on the thickness of the solution being applied, on average after 15 minutes a thin solid coating forms all around the solution, the inner part takes longer to solidify completely.
Wait as long as it takes for the solution to solidify completely to work the surface with 600 grit paper and apply a layer of putty. The putty should not replace the ABS and acetone solution, the solution is an integral part of the body and ensures its rigidity and structural integrity; the putty serves to shape and close the pores.

If you apply a thick layer of putty to give the right shape you have proceeded clumsily with application of the ABS and acetone solution. If you apply a thin layer to fill the micro-pores that form when acetone evaporates you have proceeded clumsily with application of the ABS and acetone solution.
When the putty has dried, work the surface with 1.200 and then 1.500 grit sandpaper to completely remove all traces of the breakage.
The following sequence of pictures shows the procedure for welding the front grille pin:

– locate the exact spot where the part is to be welded,
– apply a drop of the thick solution that remains at the point where it is applied,
– position the broken piece and
– remove the excess filaments.

Use the same procedure to join together body parts that have broken off. The following sequence of pictures shows how to join together two broken body parts for a Lamborghini Cheetah model 58007:

– locate the line of breakage,
– spread liquid solution so that it adheres to both sides to be joined,
– hold the parts together with a wooden clothes peg.

It is possible to reconstruct small and large missing parts of polystyrene bodies. Before starting to rebuild the part, search the chassis for an intact part that will be the sample to be used to replicate the missing part.
The following sequence of pictures illustrates the procedure for repairing a small wing end part of Ford XLT Ranger model 58027, which frequently breaks off due to a small bump or a bad landing:

– the body is symmetrical with respect to the axle, so it is possible to draw a template of the missing part using the undamaged part of the body on the opposite side as a sample,
– cut a piece reproducing the template from a millimetre-thick ABS sheet,
– use the thicker solution of Acetone and ABS to weld the new part onto the body in the exact position to be repaired,
– apply several coats of solution to give volume to the weld both on the outside and inside,
– apply a coat of less dense solution to fill all remaining pores and cracks,
– apply a thin layer of putty,
– work with file or 400 or 600 grit sandpaper to optimise the shape,
– if there are any marked lines, mark them with a scalpel or sharp blade,
– make the surface smooth with 1.200 or 15.00 grit sandpaper.

Other small parts such as window deflectors, side lights or arrows, door handles, etc. can be repaired with this method.

Entire body sections can also be repaired using this method. In such cases, it is useful to proceed by machining two or more panels in order to better construct the missing piece.
The following sequence of images illustrates the procedure for repairing the left front side panel of the Countach LP500S model 58008, which was torn off after a head-on collision:

– the body is symmetrical with respect to the axis so it is possible to draw a template of the missing piece using the intact part of the body on the opposite side as a sample,
– use cardboard and a felt-tip pen to draw the arch shape of the wheel,
– apply painter’s tape to the part to be repaired,
– apply the cardboard wheel arch template you have just cut out and use a felt-tip pen to fill in the figure of the missing part,
– cut a piece reproducing the template from a millimetre-thick ABS sheet,
– use the thicker solution of acetone and ABS to weld the new part onto the body in the exact position to be repaired,
– the side profile is slightly curved so first weld the upper part and then weld the lower part using a metal clip to hold the ABS template in place

– cut a strip from a two millimetre thick ABS sheet as high as the mini skirt,
– cut out the concave profile with a round file,
– cut the panel one millimetre thick so that the miniskirt can be inserted,
– use the solution to weld the mini-skirt to both the panel and the nose of the car,
– construct a semi-arc for the wheel arch using the wheel arch of the opposite side that is intact as a template,
– the wheel arch is slightly curved so first weld the upper part and then weld the lower part using a metal clip that holds the ABS template in place
– make the repair more solid by applying a coat of dense solution along the entire break line between the panels and the body on the inside
– apply several coats of dense solution to give volume to the weld on the outside, when applying the coats of dense solution wait fifteen minutes or as long as it takes for a surface film to form, use your fingers to shape the part (protect your skin with disposable gloves)
– wait for the solution to solidify completely
– apply a coat of less dense solution to fill in any remaining pores and cracks,
– outline the body lines with a box cutter or scalpel in a back and forth motion along the line,
– apply a thin layer of putty,
– work with a file and 400 or 600 grit sandpaper to optimise the shape,
– mark the lines again with a scalpel or sharp blade,
– make the surface smooth with 1.200 or 1.500 grit sandpaper.

Rebuilding missing parts
Polystyrene bodies are full of parts that are always made of the same material or styrene derivatives.
The image below shows the additional parts for the Toyota Celica Turbo Gr.5 model 58009: there are 14 pieces

Obviously, some parts are likely to be lost or broken.
It is possible to reconstruct these parts using Oyumaru paste, which is a children’s game for making moulds of small objects to recreate.
To reconstruct a part with the paste, you need to have a part to replicate.
The following sequence of pictures shows the procedure for preparing a mould for the construction of the rear radiator, part number 5 in the picture above of the Toyota Celica Turbo Gr.5:

– prepare tweezers + paste + glass container,
– heat water in a saucepan,
– as soon as water boils, pour the water into the glass jar,
– immerse the dough, after a few tens of seconds the dough is soft enough to be pressed over the shape to be replicated,
– remove the dough from the water using tweezers,
– manipulate the paste, if the paste contains solid lumps heat the water again and repeat the operation,
– press the piece to be replicated into the dough, for small pieces it is better to press the piece into the dough,
– wait several hours for the paste to cool back to solid,
– remove the sample piece,

– fill the mould with acetone and ABS solution,
– wait 3-4 days for the solution to solidify, once solidified the solution has receded so supplement by adding new solution,
– wait 4-5 days for the solution to solidify, remove the part and
– finish the lines with a screwdriver tip or toothpick

If it is a very complicated and large shape, the dough must be quite soft; to achieve this, make more than one pass through the boiling water. In this way the dough is also completely heated inside; it must be possible to manipulate it with the hands without feeling any parts or lumps that offer resistance to manipulation.

The following sequence of images shows the procedure for preparing a mould for the construction of the front bumper of Countach LP500S model 58005 and Countach LP500S CS model 58008:

– prepare tweezers + paste + glass container,
– heat water in a saucepan,
– as soon as the water boils, pour the water into the glass jar,
– immerse the dough, after a few tens of seconds the dough is soft enough to be pressed over the shape to be replicated,
– extract the dough using tweezers,
– manipulate the paste vigorously, if it contains solid lumps heat water again and repeat operation,
– place the bumper on a flat, smooth surface that is strong enough to withstand the pressure while pushing the soft paste onto the bumper only then will the paste take the shape, for large pieces it is better to press the paste onto the piece,
– press the paste into the workpiece
– wait several hours for the paste to cool down and become solid again,
– remove the piece,
– fill the mould with acetone and ABS solution, as it solidifies the solution loses volume, add solution daily to supplement the evaporated part,
– wait 3-4 days for the solution to solidify,
– after the last application wait 4-5 days or more, remove the part, cut off the excess,
– finish the lines with a screwdriver tip or toothpick,
– apply a layer of filler to close the pores and
– work the surfaces with a file and 1.200 and then 1.500 grit sandpaper or a toothpick

There are parts that are not available for mould making or that cannot be rebuilt with a mould.
Some parts are easy to replicate with just the use of ABS sheets and rods, suitably shaped and welded together with acetone and ABS solution or directly with ABS. The rear-view mirror is a part that is almost always missing from models. The picture below shows the ‘rear view mirror – Ruckspiegel’ for the Lamborghini Cheetah model 58006.

The following sequence of images illustrates the procedure for constructing this part:

– from a four-millimetre thick sheet of ABS, cut out two rectangles with dimensions proportionate to the frame (take the cockpit medicine chest as a reference in this case, which has the same dimensions),
– sandpaper 600 sides to make the corners rounded,
– sandpaper one of the two bases to create a truncated pyramid with a rectangular base,
– prepare the mirror support by cutting from a two millimetre square bar two bars as long as the smaller base of the truncated pyramid,
– drill a hole along the axis of each bar using a millimetre-thick hot iron wire to allow installation of the mirror on the body,
– round off one of the two long sides of the bar,
– weld the mirror to its support with acetone,
– colour the parts,
– prepare the metal bracket from a drawing paper clip and install the mirrors on the model.

The following sequence of pictures shows the procedure for building the rear wing of the JPS Lotus 79 model 58020. The aluminium V-profiles and wings indicated in the picture as “rear Fin” are available, the rear wing indicated in the picture as “rear Wing” is missing.

This is the sequence of operations to be performed:

– from a two-millimetre-thick sheet of ABS, cut a strip as wide as the V-shaped metal support
– draw two working lines; the first dotted line marks the fold that copies the shape of the wing and the second continuous line marks the cut
– heat the sheet of ABS with a standard 2 kWatt hair dryer, hold the hair dryer at a distance of 5…10 mm from the strip that heats up enough to work ABS
– position a wooden board along the dotted line to shape the future wing, once it is in position lift the free end of the strip by pulling it upwards, the round profile will not be guaranteed by the shape of the wooden board it will be ABS itself which by bending it will take a shape that covers a perfect curve
– repeat the operation until the bend ensures the desired shape. Better to do one more operation than to strain and stress the ABS strip

Wooden board is large enough to hold it firmly to the bearing surface, the part that will be the future wing is clamped between the board and the bearing surface: this ensures that the initial part of the wing will be flat. The strip of ABS is long enough so that one end will be held firmly under the wooden board and the other end will be long enough to allow it to be pulled up by forcing ABS which, although hot, offers a lot of resistance to the bending action. Once the desired shape has been obtained, cut the ABS strip along the continuous line.

Construction of the two supports:

– cut two pieces as long as required from a 5 x 5 mm section bar, use the distance of the two holes on the side supports as the unit of measurement, leave space for installation,
– round off the two ends of each support using 600 grit sandpaper,
– use the side support as a template for drilling the holes for the screws,
– heat a 1-1.5 mm diameter metal wire over an open flame and drill the four holes at the four screws,
– finish the parts with a standard utility knife by removing the melted plastic and
– with a pencil, mark the size of the nut for each hole and use the modeller’s drill with the appropriate blade to make the cut and cut out the recess to fit the nut inside.

– Install the two ABS bars on the aluminium supports,
– place the wing on the brackets and draw two lines at the screws to be used as a reference to always find the correct position of the wing between the two brackets
– then use the acetone and ABS solution to glue the parts,
– install the brackets by fixing the 2+2 screws and nuts,
– prepare the solution in the most liquid form, brush the solution onto the sides of the brackets and into the part of the wing that will be glued together
– prevent the solution from flowing out of the sections to be welded, ruining the surface of the wing,
– join the parts, use clothes pegs to hold them together,
– wait 2-3 days for the parts to weld,
– machine the upper and lower surfaces to get the right shape for the wing inlet and outlet profile by working it with 800, 1.200 and then 1.500 abrasive paper.

The following sequence of images shows the procedure for building the rear wing of Countach LP500S model 58005 and Countach LP500S CS model 58008. A wing is available as a sample, but you can also proceed following the same procedure in its absence:

– use wing as a template to cut a sheet of ABS two millimetres thick,
– cut a second sheet with the same shape from a one millimetre thick sheet of ABS,
– cut the one-millimetre thick sheet into three parts that fit with the two rear vertical supports of the body,
– better shape the two millimetre thick sheet by comparing it with the original wing,
– smear pure acetone on the two millimetre thick wing by applying the three one millimetre thick pieces to leave the two rails needed to install the wing on the two rear supports,
 test installation,
– cut strip six millimetres high from the one millimetre thick sheet,

– with the thick solution join the six millimetre high strip with the central body of the wing, abound with the solution by applying several consecutive coats, when the surface film forms on the solution manipulate the correct shape to the solution to replicate the curved profile (protect your skin with disposable gloves)
– work with sandpaper in this sequence 400-600-1.000 to replicate the airfoil – the wing curves,
– apply a thin layer of putty,
– work with sandpaper 1.200 and then 1.500.

Take care to properly handle hot – boiling water, scalpels, cutters and tools in general; wear disposable gloves to protect your skin from contact with the acetone solution and ABS, use a mask when working on surfaces with sandpaper or a file, take all possible precautions to avoid damaging yourself, others and the surrounding environment.

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