Digital Modelmaking E-Book

Helen Lansdown

• Herausgeber: Crowood
• Kategorie: Geisteswissenschaft
• Sprache: Englisch

Veröffentlichungsjahr: 2019

Beschreibung

Digital manufacturing has become an intrinsic part of the modelmaking profession, so today's practitioner must be skilled in both traditional hand-making techniques and digital technology. Relevant to a wide variety of creative industries, including film and television, theatre, architecture and product design, Digital Modelmaking offers a comprehensive insight into the manufacturing processes and technologies used within contemporary modelmaking. Each chapter contains an in-depth explanation of each topic, presents examples of how each process is used and includes case studies from professional modelmakers and students. Topics covered include: making models using a laser cutter, 3D printer and CNC milling machinery; generating 3D digital data using a 3D scanner and photogrammetry; two-and three- dimensional drawing software such as CAD; designing models for digital manufacturing; selecting materials based on their suitability for modelmaking; combining traditional hand-making skills with digital manufacturing; painting and finishing models, and finally, moulding and casting using silicone and resin. This invaluable book will be of great interest for students, young professionals and everyone with a passion for design and making. It is superbly illustrated with 234 colour photographs and 32 line artworks giving numerous examples of the design process. Helen Lansdown has worked professionally as a modelmaker and designer for thirty years and is a lecturer at Herefordshire University teaching on the Model Design programme.

Leseprobe

DIGITAL MODELMAKING

Laser Cutting, 3D Printing and Reverse Engineering

DIGITAL MODELMAKING

Laser Cutting, 3D Printing and Reverse Engineering

Helen Lansdown

THE CROWOOD PRESS

First published in 2019 by

The Crowood Press Ltd

Ramsbury, Marlborough

Wiltshire SN8 2HR

www.crowood.com

This e-book first published in 2019

© Helen Lansdown 2019

All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publishers.

British Library Cataloguing-in-Publication Data

A catalogue record for this book is available from the British Library.

ISBN 978 1 78500 586 2

DEDICATION

To my family, Ken & Jean, Denise, Vic & John. A big thank you to all of the contributors and special thanks to my wonderful friend Claire, without whom I would not have finished.

ACKNOWLEDGEMENTS

The contributions of students and industry professionals are gratefully acknowledged; Justin Adaire Hugill, Rebecca Smyth, Fenella Lundburg, Felix Burke, Paulina Grenda, Jason Larcombe, Isobel McI- nnes, Cora Prazeres, Bob’s Bits, The Alternative Limb Project, Ian McQue, Ben Twiston-Davies, 3DD Ltd, Berry Place Ltd, FBFX Ltd, John Beaufoy and Chris Beach. The author would also like to thank the photographers: BJP Photography, Sonke Faltien and Omkaar Kotedia.

Frontispiece model and photograph by Rebecca Smyth, model owned by Bob Bits.

DISCLAIMER

The information and techniques given in this book have been tried and tested by the author, but the author and publisher cannot be held responsible for any resulting injury, damage or loss to either persons or property. It is the responsibility of the reader to be aware of the correct health and safety procedure for all products, machines and materials that they use.

CONTENTS

INTRODUCTION

1 FUNDAMENTAL MODELMAKING SKILLS

2 LASER CUTTING

3 THREE-DIMENSIONAL (3D) PRINTING

4 COMPUTER NUMERICAL CONTROL (CNC) REDUCTIVE MACHINING

5 REVERSE ENGINEERING

6 SOFTWARE

GLOSSARY

LIST OF MATERIALS

LIST OF SUPPLIERS

FURTHER READING

INDEX

INTRODUCTION

Model by Fen Lundburg. BJP PHOTOGRAPHY

This book is intended for students and recent graduates working in the modelmaking industry and individuals with a passion for design and making. The definition of the modelmaking industry will mean different things to different people, depending on the specialism of the practitioner, but the fundamental skills remain broadly the same. The term modelmaker does not adequately represent the breadth of expertise and knowledge that is possessed by a practitioner. A modelmaker is a designer and an expert on materials, manufacturing processes and technology. The techniques illustrated in this book apply to most areas of modelmaking in the creative industries, including film and TV, architecture, product and packaging design, and theatre.

The focus is on digital technologies, which have been introduced into the industry since the 1990s and have made a significant impact on the way in which companies operate. Digital technologies do not replace traditional methods of making models; they are complementary tools that have become integrated into a practitioner’s toolkit. This book contains information on threedimensional (3D) printing, 3D scanning, photogrammetry, laser cutting, computer numerical control (CNC) machining and 3D drawing software, from the perspective of a modelmaker. Experience of two-dimensional (2D) and 3D computer-aided drawing, and a basic understanding of model construction is helpful, but not essential.

HOW THIS BOOK IS ARRANGED

Each chapter is predominantly dedicated to one subject and written to stand alone, which means that there is some overlapping of information. The reader will occasionally be asked to refer to another section of the book to keep the duplication of content to a minimum. The first section of each chapter contains technical information and useful techniques for each topic. The mid-section provides examples of how these techniques are used to make models. In each of these examples, a description of the design process and software commands that were used to build the models is given, but it is impossible to give a step-by-step guide. Rhino 3D and Illustrator were predominately used to draw the models; it is possible to replace both of them with other software, the command names and approach to drawing are similar in other vector and non-uniform rational basis splines (NURBS) modelling software.

Several case studies from professional and student modelmakers feature at the end of each chapter. These projects are intended to provide context and inspiration. Most of these case studies use a combination of techniques and could, therefore, feature in several of the chapters.

Many of the processes featured in this book need expensive professional-standard equipment and software. Where this is the case, free and easily accessible alternatives are given that provide an opportunity to try the technique without spending money.

Important Note A variety of materials and chemicals feature in this book, it is essential to read and understand the health and safety instructions for each product. Basic information on health and safety is provided in Chapter 1.

MODELS

A physical model is a tangible object that is easier to understand than a computer-generated model. A model is a 3D physical representation of an object made to a scale. For many practitioners, however, the term model will mean different things. For some, a model is a reduced-scale building produced for architectural design, whereas for others it might be a life-size prop for a film. Models can be exact replicas of existing objects or representations of new designs and concepts; they are smaller, larger or made at a life-size scale. Models have many functions: they are used to convey a design intent or as a means of communicating and expressing ideas; they are either one-off commissions or small batch production runs. There are many terms to describe them, including: sketch models, mock-ups, prototypes, concepts and mechanical and display models. They are a feature of numerous disciplines, including product, packaging, toy and automotive design, museums, costume, props and special effects for film and TV; the list goes on. They have different applications, e.g. in product design, they might test a product before it is manufactured or in architecture the client might need a model for planning approval. Whatever the application, the fundamental techniques, materials and processes are the same.

WHAT MAKES A GOOD MODEL

Good models come from good design; they require extensive planning, research, methodical construction and a skilled practitioner to build them with meticulous attention to detail.

ATTRIBUTES OF A MODELMAKER

A modelmaker is a highly skilled, creative designer and artisan of 3D models. They need the technical ability to be proficient with traditional workshop equipment, such as bandsaws, disc sanders and lathes, and possess an understanding of digital technologies, including laser cutting and 3D printing. They have an appreciation of the properties of materials, how they behave when cut, machined and fabricated. They are problem-solvers and innovative designers who can solve complicated technical problems and who can work collaboratively with other people and disciplines.

THE ROLE OF A MODELMAKER

There are various career paths and numerous opportunities for work within the creative industries, including film and TV, architecture, product and packaging design, and theatre, and within each profession, the role of a practitioner will be different. A practitioner can choose to specialize in one aspect of modelmaking and work as part of a team to build a model. This will mean that they are responsible for a single operation, e.g. CNC machining or moulding and casting. They can also choose not to specialize and be solely responsible for an entire project from start to finish. Generally, the larger the company, the more likely it is that a modelmaker will be asked to specialize and work as part of a team alongside specialists in different disciplines; this is simply because it is a more cost-effective way of working. In a smaller company, it is the opposite and a practitioner will have a broader range of skills. In this situation, the practitioner will subcontract elements of the project that they cannot manufacture to external suppliers. Many people choose to work in one discipline, e.g. prop-making for the film and TV industry, but others move between film and TV, architecture and product design, going where the work is.

A modelmaker will either work on their own or within a team and they will work from a brief or a drawing given by their client or line manager; so they must possess excellent communication skills. A practitioner needs the ability to read and understand technical drawings, interpret a brief into a 3D object and make decisions on the most suitable materials and methods of manufacture to achieve the highest possible quality of finish. They are responsible for completing a project on time and within a given budget. A modelmaker will either be employed on a full-time contract or be self-employed. They will be asked on occasion to work irregular hours, including evenings and weekends, and may also be required to travel and work at offsite locations.

TRAINING FOR THE PROFESSION

In the 1980s, models were predominantly made by hand, using manual workshop equipment such as bandsaws, disc sanders, milling machines and lathes. The practitioners were from various backgrounds, from fine art to engineering, because modelmaking degrees did not exist until the mid-1980s. These days several courses provide training, including the University of Hertfordshire Model Design programme. This programme is divided into three pathways: Model Effects, Character and Creative Effects, and Special Effects. Each strand specializes in a specific area of the industry, but with shared skills and techniques used in all three pathways. Graduates work in a variety of disciplines, including film and TV, advertising, architecture, product and toy design. A modelmaker can also train while working; some companies prefer to train their staff themselves and offer apprenticeship schemes.

CHANGES IN THE INDUSTRY

The modelmaking industry, and the knowledge and skills required by a modelmaker, have changed enormously during the last thirty years. They still require the same fundamental hand and machine skills, but professionals must now be experts in digital drawing and manufacturing. It is essential to keep up to date with these changes, otherwise a company, or an individual modelmaker, will have difficulty in finding work. An excellent example of this is in advertising; many companies relied on this stream of work during the 1980s and into the 1990s. These days a lot of that work has gone, replaced by computer-generated rendering, meaning a model is not required. A modelmaker needs to be open to changing their practice to accommodate these changes.

THE AUTHOR

I started working as a modelmaker in 1987. My passion is for accurate, highly finished models and I have worked in product design, architecture, prop making for film and TV and advertising. I have always been keen to learn new techniques and employ the latest technology, and I am continually motivated to learn something new. I first became interested in CNC machining and 3D drawing in the mid-1990s and these days I find photogrammetry and 3D scanning fascinating, all of which have become increasingly important in practice. The modelmaking industry has changed enormously during my career; imagine a time when there was no internet and researching a new project meant a visit to the library. I now work as a lecturer, teaching wonderfully creative and intelligent students the profession that I love. I hope that you find something of interest in this book, whether it is a new technique or inspiration from the professional and student case studies.

Every reasonable effort has been made to trace and credit illustration and textual copyright holders. If you own the copyright to an image or quotation appearing in this book and have not been credited, please contact the publisher, who will be pleased to add a credit in any future edition.

1

FUNDAMENTAL MODELMAKING SKILLS

Model by Paulina Grenda. PAULINA AND SONKE FALTIEN

INTRODUCTION

The focus of this book is digital technology in modelmaking, but models are made using a combination of manufacturing methods, various workshop equipment, different materials and handmaking techniques. In this chapter, you will learn some of the fundamental skills used by modelmakers. All of the techniques, materials and products listed here have been used to make the models in this book. It is only possible to give very general advice in this section; the reader is asked to refer to other books for more in-depth information. The digital manufacturing methods featured in this book are extremely useful but understanding how to construct a model by hand using basic workshop equipment provides a practitioner with an invaluable understanding of materials, how they cut, shape and glue. It is this understanding of materials, hand skills and finishing techniques, used in conjunction with digital technologies, that make a modelmaker a specialist craftsperson.

GENERAL ADVICE

Health and Safety

This subject could form the entire contents of this book and still not adequately address the wide variety of health and safety issues faced by modelmakers. We use hand tools and machinery on a daily basis and work with harmful chemicals, including resins and solvent paints. It is the responsibility of the reader to ask for instruction, read the relevant documentation, thoroughly understand the health and safety instructions for every product, machine and process that they use, and take the necessary steps to protect themselves and those around them.

When using machinery, each person must understand the correct procedure and safety regulations for each piece of equipment; if they don’t, they must read the safety instructions and ask their line manager or teacher for training and safety instruction. Polyurethane, resins, solvent paints and most glues are hazardous, and some people develop a lifelong sensitivity to them. At the very minimum, tie back long hair, wear a dust mask (a respirator for solvent paints and resin), wear safety glasses and disposable rubber gloves, and make sure to cover all exposed skin, including the arms and hands. The intent of this book is not to be a manual for health and safety but as this is such a vital aspect it would be irresponsible not to highlight its importance.

Toolkit

Most modelmaking companies will have a fully equipped workshop of tools, but it is a good idea for a practitioner to have a small personalized toolkit. A basic modelmaker’s toolbox will include: a notebook, pencils (including a propelling pencil), eraser, a pair of compasses, scissors, a 300mm steel ruler, a scale ruler, circle cutter, tape-measure, a scalpel handle and blades (10a Swan and Morton is a good choice), a Stanley knife and cutting mat, a combination square, an engineer’s square, Vernier callipers, sculpting tools, files, needle files, pliers and screwdrivers, a set of drills from 1mm to 6mm, hacksaw, cordless or hand drill, hammers, clamps, a Dremel and a vice. Basic health and safety equipment should include: disposable rubber gloves, safety glasses, a dust mask and a respirator for spraying solvent paint, and moulding and casting.

A range of tools used by modelmakers, including: a cutting mat, scale ruler, circle cutter, steel rulers and a scalpel handle and blades.

A range of tools used by modelmakers, including: a drill set, files, clamps, engineers squares and vernier callipers.

Workshops

The equipment in a modelmaker’s workshop will vary, depending on the specialism of the company. A typical set up will include bandsaws, pillar drills, circular saws, disc, bobbin and belt sanders. Larger machines are likely to include a vacuum former, laser cutter, manual and CNC milling machines, CNC routers and lathes. Also, moulding and casting equipment, including a vacuum casting machine and a spray booth.

PRODUCTS AND PROCESSES

Glues

The glues are listed alphabetically, not in order of importance. Always read the health and safety instructions for each product.

A range of standard glues including dichloromethane and two-part epoxy.

Cascamite This is a powdered glue that is mixed with water to create a paste. It will glue wood, it produces a very strong joint and is typically used for exterior joinery.

Contact Adhesive A common brand is Thixofix and it is used to glue wood, MDF, veneer, laminate and rubber. This glue is applied to both surfaces and left to dry before fixing together.

Cyanoacrylate (Super Glue) This is a general-purpose glue, but the resulting joint is brittle and will fracture under force. It can ‘bloom’ when there is moisture in the air, which results in a whitish powder, but there are low odour and low bloom products. Super glue will not produce a crystal clear joint, so it should not be used to glue clear models. It will stick different types of material together, e.g. plastic to metal or wood, but two-part epoxy is usually a better choice in this instance.

Dichloromethane This is used to glue plastics like acrylic, styrene and acrylonitrile butadiene styrene (ABS). It is water thin and applied with a brush. A brand name for this product is Plastic Weld. Tensol 12 is a similar product that includes dichloromethane, but it is thicker and will fill small gaps between the two pieces of material.

Glue Stick A common brand is Pritt Stick and it is used for card and paper, including fixing paper templates on to material for cutting on a bandsaw or disc sander.

Hot Glue This will provide a temporary fix between two parts. It is useful for attaching a model to a spray stick. Further information on sprays sticks is in the finishing section of this chapter.

Latex Glue A common brand is Copydex and it is used to glue porous materials, e.g. fabrics and paper.

Polyurethane Glue A common brand is Gorilla Glue. This adhesive is activated by water and is used to bond many different types of material, including wood, stone, foam and glass.

PVA (Polyvinyl Acetate) This is water-based and used to glue wood, MDF and wood veneer. It will also provide a temporary fix between two blocks of styrofoam. When diluted, it is used to seal the surface of porous materials.

Spray Glue This has many uses, including fixing paper templates on to material for cutting on a bandsaw or disc sander.

Two-Part Epoxy A common brand is Araldite. This adhesive produces a strong bond between two different types of material, e.g. it will glue wood to plastic. It has two parts, A and B, and because it is thick, the two surfaces do not need to be entirely flat. It cures quite quickly, 5 to 10min depending on the type, and because it does not glue immediately, it allows plenty of time to apply the glue and accurately position the two pieces. A tip is to tape or clamp the two pieces together until cured.

Sketch Models

Sketch models are helpful in the early stages of the design process, for client meetings and to convey an idea in a group discussion. Sketch models are quick to construct and are not precious objects or expensive to make; they allow a designer freedom to try out an idea, discard it and move on to their next design. Sketch models are usually cut out by hand in low-cost materials, e.g. card, foamboard and polystyrene foam.

Foamboard has a foam core sandwiched between two pieces of card; it is light and easily cut with a scalpel. It is manufactured in various thicknesses, including 3mm and 5mm, and when scored with a knife, it will bend into curved shapes. There are different types of foamboard, some are made of polystyrene clad with thin card, which will melt under contact with solvent-based glues. Hot glue, a glue stick, double-sided tape and PVA are good choices for sticking foamboard.

A handmade sketch model of a door; the purpose of this model was to establish the level of detail needed for a 1:15 scale model.

Styrofoam looks similar to lightweight polyurethane modelling board, but it isn’t. It is essential to understand that it does not behave in the same way or indeed glue with the same products. This material is cheap (used for building insulation) and is cut and shaped by hand using knives, saws or a hot-wire cutter. It will melt when heated and cannot be glued or painted with solvent-based products. Water-based glue, including PVA, will stick two parts together, but not particularly well. The best option is to make the model from a single block, where possible, or use strong doublesided tape or display mount. A styrofoam sketch model is typically left unpainted but, when it is necessary to paint it, water-based emulsion paint is the best option.

A blue styrofoam foam sketch model.

Rohacell foam is another material used to make sketch models; this is a relatively expensive material. It is manufactured in different grades and, although it is a foam, it is quite hard, making it a better choice for sketch models that need an extra level of detail. This material is used for better-quality sketch models for clients, rather than by a designer to develop an idea.

Moulding and Casting

In most cases, rubber moulds are made using a condensation cure or addition cure silicone rubber. Both products consist of two parts, the rubber and a catalyst, and they are mixed by hand or in a specialist vacuum casting machine. Condensation cure silicone is the most common product as it is easy to use but the mould will shrink slightly. Addition cure is more expensive and it does not shrink, but it requires careful handling because it will not cure when exposed to specific products, e.g. latex.

A mould box is fabricated from various materials, e.g. acrylic, styrene, MDF or foamboard, and some people even use Lego. The most important thing about the mould box is that it is watertight, so consider sealing the outside edge of the box with hot glue. Depending on the shape of the model, the rubber mould will consist of one part (an open mould) or multiple parts.

A one-part mould box constructed in foamboard and made watertight with hot glue.

A one-part condensation cure silicon rubber mould cast in a square mould box, the pattern painted in grey primer, and two resin castings: one with excess resin on the back, one heated and shaped.

A one-part mould is where one face of the model is flat; this flat face fixes on to a flat sheet of material and a wall is constructed around it. The rubber pours into the mould box in one corner; this enables the silicone to flow across the pattern, making it less likely to trap air bubbles. This type of mould fills with resin from the flat open face and, when necessary, the rubber is cut to enable the part to be removed.

When there isn’t a suitable flat face, or when it is impossible to remove the model from a one-part mould, the object is moulded in sections. In a two-part mould, the model is positioned in a mould box and plasticine is pressed around it to a logical height; this is where the mould will split. The first side is moulded in silicone and left to cure; it is then rotated 180 degrees. The pattern remains in place, but the plasticine is removed and the second is half moulded in silicone. These types need a way of registering the two parts together; dimples pressed into the plasticine is a simple method.

A two-part mould fills with resin through a pour hole designed into one side. An easy way to achieve this is to glue a rod on to the model, which, when moulded, becomes a hole in the silicone rubber. A common problem with casting in two-part silicone moulds is air bubbles trapped in the resin casting. To resolve this, several small rods are glued on to the model in places where it is likely that air will become trapped. Like the pour hole, these rods become holes in the silicone mould and act as air holes, allowing the resin to flow into the mould and any trapped air to escape.

Setting up of a two-part mould: a styrene mould box with plasticine pressed around the pattern at different heights to create the split line between the two mould halves. One side of the box is not glued into position merely to show the mould set up. The large white styrene tube is the pour hole for the resin, the three smaller rods are the air holes, and the five dimples locate the two halves of the mould together.

A two-part mould showing a method for registering the two halves. The grey part is the 3D printed pattern; the beige is the polyurethane resin casting. This mould is part of a student project by Jason Larcombe.

Resins

Polyurethane resins are easy to use; they consist of two parts that are mixed together and cure at different rates. There are many varieties; some that cure within 5 minutes, and others that take hours to set. The fast-curing polyurethane resins are often referred to as ‘fast cast’ resin. They have different properties, e.g. several are strong in thin sections and some will flex. Fast-curing resins are usually mixed by hand because there is not enough time to use a vacuum casting machine. When mixing by hand, shake the resin container to combine the contents, as they tend to separate. Put the correct volume of parts A and B in separate cups and leave the resin to settle. This allows any air bubbles in the resin to escape before the two parts are mixed. When mixing both parts of the resin together, be careful not to add any air bubbles into the mixture. When pouring the resin into an open mould, it is helpful to pour it into one corner and allow the liquid resin to flow across the silicone; this means that the casting is less likely to trap air bubbles. If the resin is slow-curing (this is referred to as its pot life), then a vacuum chamber or vacuum casting machine is used to remove all air bubbles before filling the mould. There are two types of products for casting clear parts: polyurethane and polyester. The health and safety instructions must be read, understood and adhered to.

Jigs

Making jigs is a fundamental skill for a model-maker. They have many uses: for example, to hold a model in position to drill a hole, to fix something onto a milling machine or to glue two pieces of material together in the correct place. Using a jig will make many tasks easier, quicker and more accurate. They are usually made of cheap materials, such as MDF and scraps of wood.

This support jig was laser cut in MDF for accuracy. Its function was to keep each beam at the correct height and width while the model was assembled and glued.

A jig made in MDF to hold a turned cylinder upright on a milling machine.

Templates

Templates are helpful for ensuring accuracy when making a model by hand, especially when the shape is curved. They are made in card, styrene or MDF, and they are cut out using a scalpel, bandsaw or a laser. In the example of a computer mouse, a bandsaw cuts the basic shape, and the curves are sanded by hand with files and sandpaper. The templates are put on to the model to check the accuracy of the shape and to note where material needs removing.

These two card templates were used to check the shape of a block of polyurethane modelling board during sanding.

A curved styrene template used to check the shape of a part turned on a lathe.

Finishing

Finishing is often the most time pressure point of a project, and it is highly likely that this is when something will go wrong. In an ideal world, plenty of time is set aside for finishing, but usually the deadline is looming and this stage is compressed into the last few days of a project. It is due to this time pressure that a model must always be designed and made using materials and processes that will achieve the highest quality outcome. When constructed correctly, using high-quality materials, a model will not need extensive finishing. Model-makers will give themselves a deadline to finish building a model, adequate time to finish it and, when possible, time to deal with any problems.

A common mistake made by students and early career practitioners is to ignore imperfections on the surface of a model and believe that a coat of paint will cover or disguise them. Paint will never compensate for poor finishing; in fact, it will generally do the opposite and highlight the flaws even more. Modelmakers must train themselves to assess the quality of their work, scrutinize every nook and cranny, and be their own worst critic. They must be able to see where the problems are and, importantly, understand how to repair them. This section covers the preparation and painting of a model.

SANDING AND DEGREASING

The most common sandpaper is wet and dry. As the name suggests, it is used both with and without water. There are various grades: 60 grit sandpaper is very coarse and will remove a lot of material very quickly, whereas 1,200 grit is very fine. A model is sanded through the grades of sandpaper until the sanding marks are small enough for the paint to cover them, typically 600 grit paper. The best approach is to go through the grades of paper, starting with the coarsest, and change the sanding direction between each grade. Sanding in two perpendicular directions makes it possible to see when the sanding marks left by a rougher grade of paper have been removed. If a model is shaped with 240 grit paper and painted, the sanding marks will be apparent, so it is sanded with 360, 400 and finally 600, each grade in a different direction. This technique of sanding in two directions is particularly useful when preparing acrylic for polishing.

Sanding also provides a key for the paint to adhere and removes all of the oil and grease that may have built up during manufacture or just from handling. In cases where the model was machined, and could be contaminated with oil, or when a part was moulded in silicone, it is advisable to degrease it with a solution; a widely used product is lighter fluid.

SANDING BOARDS

Sanding boards are extremely useful; a model-maker will make various sanding boards in different shapes and sizes, with varying grades of sandpaper. Using a sanding board is a more accurate way to shape a model than sanding with paper held in the hand.

Lighter fluid for degreasing and a variety of sanding board shapes and grades.

FILLER

The most widely used product is polyester car body filler, commonly called P38. It consists of two parts: the filler and a catalyst. It is necessary to mix and apply it quickly because it cures within 3 to 5 min. During curing it achieves a semi-cured stated, often called ‘cheesy’. As the name implies, it has a cheese-like softness, which means that any excess filler is easy to remove before it fully hardens. This filler is used to repair surface imperfections before applying paint. It is not good practice to put polyester filler on top of paint, as doing this will leave ugly witness marks in subsequent paint layers. In this instance, it is better to remove the paint around the imperfection with sanding paper and apply the filler on to the material.

MAKING A MIXING PAD

A tip: pour leftover silicone rubber into a shallow container to create a mixing pad for polyester filler. Cured filler does not stick to silicone, so it is easily removed, meaning that the silicone pad is reusable. An alternative is to mix it on a scrap of plastic, e.g. styrene. The filler will, however, stick to this material, so any excess is removed before it sets.

This product is also used to create shapes, including internal radii. The filler is mixed and spread on the model between two surfaces, and a styrene template is dragged across it; this pulls the filler into the shape of the template. It is also used to make one piece of material fit precisely to another. For example: two parts are cut to shape, one is produced accurately and covered with brown packing tape or Vaseline, the other is made to fit approximately. The filler is mixed and applied on to the piece without the brown tape and both parts are pressed together. When cured, the two parts separate, the brown tape is removed, and the pieces are a perfect fit.

On the left: radii made using filler and a plastic template, the brown tape protects the material from the excess filler. On the right: the filler is used to make two blocks fit together precisely.

Car body filler, acryl green and red, cellulose putty, a silicone pad with a spatula and a square of styrene for mixing the filler.

Left to right: a repair on top of paint using cellulose putty, acryl green used on top of acrylic primer to repair a scratch and acryl green on an FDM 3D print before painting.

There are situations when it is necessary to put filler on top of paint. Perhaps the model has been masked and sprayed with several colours, and in the final coat, the paint is damaged; in this situation a putty is used instead of polyester filler. There are different types of putty, e.g. cellulose and acrylic. The putty must match the paint; if the model is sprayed with acrylic paint, then use an acrylic putty. Putties are air-drying, they do not have a catalyst and they dry at different rates. Two popular products are 3M Acryl green and red; the green dries very quickly, the red dries slightly slower, which allows for more time to apply it on to the model. Acryl green and red putties are also used to fill surface imperfections before painting; they are particularly suitable for filling FDM 3D prints.

There are other types of filler, not all are listed here, but in all cases filler is applied sparingly; there is a tendency to use too much, which results in more work. Valuable time is wasted sanding off excess filler, so put on a small amount and sand between each application.