Advanced Jewellery CAD Modelling in Rhino E-Book

Jack Meyer

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

Veröffentlichungsjahr: 2022

Beschreibung

This detailed guide is written for intermediate and experienced Rhino 3D CAD users who wish to improve their understanding of NURBS and subdivision modelling methods in Rhino 3D. It explains how 3D modelling applies to jewellery and manufacturing through a combination of step-by-step tutorials, analysis of the software techniques and demonstrations of real world case studies. Packed with essential techniques and strategies, it can be used as a self-learning tool or a classroom text to take your use of Rhino's 3D NURBS and subdivision modelling tools to a higher level. This new book gives a comprehensive and fluid strategic approach to modelling solids, surfaces and subdivision objects in Rhino. The application of jewellery manufacturing tolerances across a range of different jewellery types is covered. The essential tools and holistic strategy of Rhino's SubD organic modelling suite, and how it fits within the greater scheme of Rhino modelling is discussed. Finally, there is an overview of useful practices for creating good CAD renders using Rhino Cycles.

Leseprobe

Contents

Preface

1. Introduction

What You Should Know Before We Start

Setting up Rhino for Jewellery Work

2. Efficient Solid Modelling In Rhino

Proposing a Strategy of CAD Problem-Solving

An Overview of the Six Key Solid Modelling Commands

How Rhino History Fits in with Solid Modelling Strategy

3. Jewellery Manufacturing Tolerances In CAD

What All CAD Jewellers Should Know about Manufacturing Tolerances

CAD Modelling Tolerances for Rings

Tolerances for Earrings

Tolerances for Pendants and Necklaces

Tolerances for Cuff Bangles

Tolerances for Chain Bracelets

Meshing and Exporting for 3D Printing

4. The Logic Of NURBS Surfaces

Anatomy of a NURBS Surface

Continuity, and the Maths of NURBS Surfaces

Building Polysurfaces from Joined Surfaces

Building Forms with the Six Single Surfacing Commands

Using the Six Key Solid Modelling Commands to Make Open Surfaces

Our Combined Surface Modelling Tool Set

Comparing Surface Modelling Strategies

Methods for Hollowing Signet Rings (and other Forms)

Sculpting in NURBS

5. Surface Decoration In Rhino

Overview

The Nine Curve from Object Commands

Surface Inset Method 1: Extrude and Boolean

Surface Inset Method 2: Splitting and Offsetting a Surface

Surface Inset Method 3: Filigree Surface Cutouts

Placing Objects on a Surface

6. Subdivision Modelling In Rhino

The Subdivision Surface Interface Controls

Controlling Solid SubD Surfaces (aka the ‘Doll’ Tutorial)

Piping and Blending Subdivision Surfaces

SubD Skeletons and Surface Controls

Append and Offset Basics

Appending Complex Surfaces

SubD Modelling Strategy in Practice

7. Rhino 7 Rendering Essentials

Optimizing Rhino 7 Rendering for Jewellery

A Good Basic Setup for Jewellery CAD Rendering

Exploring the Rendering Options Tab

Controlling Lighting

Material Types

Physically Adjusting your Model for Better Rendering

Camera Tricks and Post-Production

Index

Preface

I’d like to dedicate this book to three different groups of people.

Since I ran my first official Rhino 3D classes in London in 2006, I’ve taught nearly a thousand students how to use Rhino. They’ve come in from all sorts of backgrounds and all sorts of different places (thirty-three countries and counting, and many more cities). I have welcomed to my classes seasoned jewellers, trade-school students, aspiring hobbyists, sculptors, product designers from many specialities, young heirs to jewellery empires, prisoners on day release, and even several of my former jewellery university professors. These students have always proved a surprise with every class. I have found them stubborn, persevering, cynical, enterprising, determined, frustrating, and brilliant with each new turn. Many were new to using any kind of computer-design software. Some of them were new to using any computer.

Because the concepts I used to develop this book were refined through years of working with them, it is only right that my first dedication should be to these wonderful and hard-working students. In each of these classes, we became so efficient at finding bugs that could crash newly released software we developed a running joke that we could break anything, even Microsoft Word. But through our shared mistakes we all learned how mistakes create progress, and I can confidently say that there is no more efficient machine for finding mistakes in either software or learning material than a classroom of nineteen students hell bent on using newly learned tools to express themselves creatively.

When I look at the jewellery CAD training landscape right now, I see dozens of new CAD tutors who have appeared only in the past few years, each showing off the techniques they’d been working hard to develop through the new tutorials they are creating to train others. I’ve also noticed how the propagation of cheaper and more accessible 3D printers has brought more and more individuals into 3D content design, many of whom are hungry for practical jewellery techniques.

From this group, I’m also seeing new crops of journeyman students emerging armed with the knowledge and practice from these basic jewellery tutorials, and hungry for more. For these hungry intermediate and advanced students, I know they are reaching the point where they are starting to ask why we use that particular tool instead of others.

I’ve been in the same position as these new teachers and power-users not even a decade ago. And I know that in several cases I was the one who trained and coached these teachers and power-users to go on and produce their wonderful work. I also know that an instructor is not diminished by sharing their secrets – as your lessons become a part of your student’s foundation, they carry your ideas forward and develop them into something even greater. Therefore my second dedication is to these ambitious journeyman CAD teachers and power-users. Your new tutorials and professional 3D models inspire me to work harder.

I would also like to thank my former colleague and highly skilled CAD designer Sarah Velazco in particular for being so reliable on testing many of the tutorials in this book.

Of course, I cannot ignore the fact that this book was written during the COVID-19 lockdown. This means I have been in the personal space of my wife and daughter more continuously than at any other point in my life, and like anyone else attempting to work from home during this time, this book could not have been completed without their patience, support and understanding. My third dedication goes to them (Helen and Dorothy) for tolerating and supporting my obsessive work during the creation of this book.

Whenever I work with my students, I try to use metaphors to help them understand key concepts. With these metaphors we build up a short-hand that allows us to communicate complex concepts more quickly, and allows students to use them to improvise and develop new interpretations. To use one such metaphor now, consider the literal meaning of the Chinese term kung fu. While most of us in the West know the term for its ties to martial arts studies, the phrase means so much more in its original form. It translates to ‘great insight’ or ‘great skill’, and it can apply to just about any kind of practised knowledge. In this context, when a practitioner reaches a level of skill where they discover their own unique insights into their chosen discipline, they are said to have developed their own kung fu.

If you are one of those hungry journeyman students who is keen to examine and question your own understanding of Rhino, I have written this book for you. If you’re ready, allow me to share with you my kung fu, so that one day it can help you discover your own great insights.

CHAPTER 1

Introduction

WHAT YOU SHOULD KNOW BEFORE WE START

Your Understanding of Rhino

While I will endeavour to make the techniques in this book as easy to follow as possible, I want to reiterate that this book is not designed for beginners. I am assuming you’ve taken the equivalent of the Level 1 McNeel Rhino CAD training course or an equivalent for jewellery (such as one of the beginner courses I teach), and that you’ve practised regularly using the tools on your own work for at least six months.

Specifically, I’m assuming readers are already familiar with the following:

◆ Creating, joining, exploding, and modifying closed curves.

◆ Building solid models using commands such as Extrude, Sweep, Revolve and Loft.

◆ Transform commands such as Move, Copy, Rotate, Scale and Polar Array.

◆ Combining solid objects with Booleans.

◆ How to create individual open surfaces, and Join and Explode them.

◆ ‘Incremental Save’ on a PC, or ‘Revert To’ previous versions in Mac.

If any of these concepts sound alien to you, then before getting too far into this book I would first recommend that you learn and practise the concepts of the McNeel Level 1 Rhino CAD training, or take a Level 1 class from myself (go to cadjewelleryskills.com for more details on my training).

Some of this book will cover the same intermediate and advanced tools taught in the standard McNeel Level 2 Rhino CAD training, but we will be going into much greater detail than the standard course material would normally allow, and we will eventually be covering modelling theory at a level that will go well beyond intermediate courses I’ve seen to date.

Rhino Versions, and the Question of Plug-Ins

Since jewellers first started trying to adapt Rhino for jewellery use in 2001, developers have been working to make plug-ins offering short-cuts and helpful time-saving tools to make certain more complicated processes of jewellery work more easily. The problem I’ve found with all these tools, however, is that they make assumptions about your intended use for them. Once users decide to try to make something not anticipated by the developers, they can find themselves stuck. This is why I’m focusing on only Rhino with no plug-ins in this book. While there may be plug-in tools that can save time with certain processes, this time-saving inevitably comes at the price of control.

I have also written this book under the assumption that you are using Rhino 7 or later. If you are using Rhino 6 or earlier, you will still find that all the chapters and techniques will work the same way, except for Subdivision modelling (which doesn’t exist in Rhino 6 unless you use a third-party plug-in such as Clayoo or T-Splines) and Rendering (which has changed drastically with each version of Rhino up to version 7).

If you wish to use Clayoo or T-Splines, each of those plug-ins will have their own unique interface quirks that may make the various tools behave differently, but the general holistic concepts of SubD modelling should still be the same.

For rendering, again the holistic concepts will still apply, but the interface of other rendering plug-ins will be incompatibly different. Unfortunately, that is the nature of all rendering tools – all of them work in incompatibly different ways.

Using Rhino Mac instead of Rhino PC

Every exercise in this book was written using Rhino PC. But since the user interface between Rhino PC and Rhino Mac has been diverging a bit in recent versions, I should mention a few common variations in the commands:

◆ Instead of using ‘Ctrl’, Mac uses ‘Command’.

◆ Instead of using ‘Alt’, Mac uses ‘Option’.

◆ Instead of ‘Save As’, Mac has ‘Duplicate’, which does the same thing.

◆ Instead of ‘Incremental Save’, Mac just uses ‘Save’, and stores all previous versions of the model inside that same .3dm file. You can restore the older version with the ‘Revert To’ command, which lets you browse through previous versions.

◆ When opening a new file, Rhino Mac defaults to your pre-set default template. You can choose a different template with ‘Open Via Template’.

I will also try to mention big differences between individual Mac and PC commands in the text as they come up.

One More Thing…

I would ask you to keep an open mind. Given enough time, everyone develops working habits. But an important part of improving your practice is having the courage to question what has always worked for you. The only thing better than having an ideal solution to a problem is having a selection of ideal solutions to choose from, each with different strengths.

SETTING UP RHINO FOR JEWELLERY WORK

Every time you create a New File in Rhino, you must start with a template that determines initial set-up points such as grid size, absolute tolerance, grid snap spacing, and units. Since we’re working with jewellery often at a small scale, it will save us all some time if we just make one change to the default Rhino template set now, and use that template for every model in this book.

Right-click on Grid Snap to bring up the Settings option: the two grid settings fields that I have changed for my template.

Saving the template: where it will show up when you create a new file.

Making a Jewellery File Template

1.Create a New File, and select ‘Small Objects – Millimeters.3dm’ from the Template Files list.

2.Right-click on the Grid Snap button, and select Settings. A properties menu will come up for Grid.

3.Set the Grid Snap spacing to 0.5mm, and press OK. This means when you use your grid snap, you’ll be able to place points at 0.5mm marks as well as 1.0mm marks. You’ll be able to snap to the middle of grid squares as well as the corners. Later on, you can adjust this down to 0.25mm if you need to for even smaller details.

4.We’ll also set the Major Lines to every five minor grid lines. It makes measurements easier when you are close up.

5.To keep this as a template that will automatically be part of a new file, use File➞Save as Template, and call it ‘Small Objects – Half Millimeters.3dm’. The next time you create a New File, this template will be available for your use.

Unless specified otherwise, we’ll be using this template for every model and exercise in the rest of this book.

CHAPTER 2

Efficient Solid Modelling in Rhino

PROPOSING A STRATEGY FOR CAD PROBLEM-SOLVING

Streamlining Your CAD Modelling Strategy

I’ve felt for a long time that too many trainers make the same big mistake when first starting to teach Rhino – they try to teach students how to use surface modelling and solid modelling at the same time. While this makes sense from a historical standpoint, as Rhino is at its core a NURBS surface modeller, they have spent so many decades perfecting solid modelling techniques in the software as to make this method of thinking completely outdated.

What I would propose instead is to separate the strategy of modelling in Rhino into three different discrete areas of work, through which we move progressively upwards as the situation demands (seepage 14). By separating the program into three different workflows, we narrow down the number of tools we would use in each context, reducing confusion over choice and speeding up the development of problem-solving skills.

If you have completed the Level 1 and Level 2 Official McNeel Rhino training, or have spent years working with Rhino version 6 or older, you’ll already know many of the commands in the first two levels; but subdivision modelling will probably be new to you. If you’re using an older version of Rhino and you already have a subdivision modelling plug-in such as SubD or Clayoo, or you are using the newest version of Rhino (from Rhino version 7 onwards), you will have access to this third way of working involving subdivision modelling. We will go into more detail as to the term’s meaning and how Rhino’s SubD tools work in Chapter 6. For now, we can simply say it involves organic modelling and sculpting.

We’ll be discussing solid modelling strategy for the rest of this chapter. In Chapter 3, we’ll apply all these solid modelling tools to various types of jewellery while we discuss ideal tolerances for manufacturing. In chapters 4 and 5 we’ll be discussing surface modelling strategy. And in Chapter 6 I’ll introduce subdivisional modelling strategy with the new Rhino SubD tools.

Rhino Solid Modelling Strategy in Six Key Commands

For the sake of planning efficiency, we can reduce our entire solid modelling toolset to six key building tools (seepage 13). There are more, of course, but nearly all the other commands are either a variant of a command in this list, or they fit better within surface modelling strategy.

Curves Come After…

Since each of the six key solid modelling commands mentioned above requires a different set of curves to run, we must decide which of the six key solid modelling tools we are using before we can start making our curves. This is the reason why we don’t include curve tools in our modelling strategy.

Breaking Objects Down into Commands

By focusing on using just these six key solid modelling commands in conjunction with the six key transformation commands (Move, Rotate, Scale, Mirror, Copy and Polar Array) and three Booleans (Boolean Union, Difference and Intersection), we can discuss building even the most complex solid models in terms of just these fifteen commands. Considering Rhino boasts more than 600 commands, it’s easy to see how much simpler this makes planning and problem-solving (seepage 15).

The six key solid modelling commands, along with their location in the menu, and a visual summary of how they work.

An example of breaking down a shape into the six key commands.

The trick comes in breaking down complex forms into manageable pieces that can be added or subtracted using these six solid modelling commands, three transformation commands, or three Booleans. By doing this, we now have an efficient shorthand for describing our intended strategy when planning to build a complex form.

AN OVERVIEW OF THE SIX KEY SOLID MODELLING COMMANDS

If we are going to use such a reduced list of commands when planning our solid modelling, we should know as much as possible about each command’s capabilities. In this section, I’ll examine every single option for each of these six key commands, and summarize how they can be useful in solid modelling for jewellery.

Examples of extrusions: a ring shape extruded from two closed curves; an extruded cutter for a ring finger hole.

Extrude

Extrude takes one or more flat curves and gives them thickness in a single direction.

Command Requirements

Extrude requires at least one curve and a direction. If you want your extrusion to be closed, you’ll need to make sure the curves are closed, planar (flat) and all on the same level.

Sequence

1.Select the curves.

2.Set an extrusion distance.

Extrude Options

◆Extrusion Distance <in brackets>: Define the thickness.

◆Direction: Define with 2 points the direction of extrusion at any angle.

◆BothSides: Extrudes in both perpendicular directions from the curve(s).

◆Solid: Close the ends if the original curve(s) are planar.

◆DeleteInput: Deletes the original curve(s) used to make the extrude. Since we often need the curves to change a shape later, this is rarely used.

◆ToBoundary: If you have another surface or solid in the path of the extrusion, you can extrude so that the extrusion touches that surface and stops.

Extrude Applications

In jewellery, Extrude is generally used for creating flat forms and straight cut-outs. There are two resourceful uses of the command though. The first comes when you Extrude a shape in one viewport, then another in a different viewport, then Boolean Intersect the two, creating a unique shape matching the profile of each view. The other comes when you inset an extruded form into a curved surface, use Boolean Difference to shave your cutter shape to match the outside contour of the curved surface, and then inset the shaved shape back into the surface for an inset pattern. (SeeChapter 5 for more details on insets.)

Different Extrudes clockwise from top left: Directional Extrude; Extrude with Both Sides=yes; Extrude with Solid=no; Extrude to Boundary.

Common uses for Extrude in jewellery: flat extruded shapes for Boolean Intersection; straight insets (as discussed in Chapter 5).

A Revolve with an open profile; a Revolve with a closed profile.

Variations: While there are several commands that bear the name ‘Extrude’ in Rhino (such as Tapered Extrude, Extrude to Point, and Extrude Along Curve), none of them really fits strategically in the same category as Extrude.

From the six key solid commands, we can frequently replace Extrude with Loft.

Revolve

Revolve takes at least one profile (half cross-section) and spins it round a chosen axis, either partially or fully.

Command Requirements

Revolve requires 1+ cross-section curves, and an axis of symmetry (defined by two points).

See Profile Conventions for Revolve, and Rail Revolve below for more on how the profiles should be made.

Sequence

1.Select profile curve (profiles are different from cross-sections in that they are essentially half of a cross-section).

2.Set your two axis points. The easiest way to use this command is to make your axis in the same viewport as your profile.

3.You can then set a start and endpoint for your revolved object in any viewport. Perspective works best. Alternatively, you can click the FullCircle option in the Command: prompt (see Options below).

Options

◆DeleteInput: Deletes the original line(s) used to make the revolve. Since we often need the curves to change a shape later, this is rarely used.

◆Deformable: By default, Revolve makes shapes around a circle, which is a Degree 2 shape, meaning the surfaces themselves will be Degree 2. This forces your surfaces to be made as Degree 3 surfaces (seeChapter 4).

◆FullCircle: Automatically makes the shape into a full revolution.

◆AskForStartAngle: Determines whether the command will just start from the position of the existing cross-section, or allow you to set a starting angle for a partial revolution.

Partial Revolve; Revolve with Full Circle.

Revolve Applications

Revolve is as essential and commonplace in jewellery as round gemstones. It is also used for gem cutters and various radial forms.

Common examples of Revolve in jewellery: collets and gemstones; gem cutters for surfaces; single profile rings.

Variations: Outside the six key solid modelling commands, Revolve doesn’t have any substitutes. From inside this list, however, some of its common applications can also be covered by Sweep, Rail Revolve, or Loft.

Rail Revolve

Rail Revolve takes a single profile and spins it completely around a rail and central axis, making a non-round revolve.

The components of a Rail Revolve – the profile, rail and axis; a Rail Revolve with a closed profile.

PROFILE CONVENTIONS FOR REVOLVE AND RAIL REVOLVE

When using the Revolve or Rail Revolve commands, there are two mutually exclusive conventions we follow for drawing or profiles, depending on the shape you wish to make and how it sits relative to your axis of revolution:

Open Curve Convention

If the profile touches the axis (like the red shape on the right), then your profile shape should be designed as open on the inside, with both points touching the revolve axis. Otherwise you’ll end up with a double shape or a command failure.

Closed Curve Convention

If the profile sits away from the axis (as the blue shape on the right), then your profile shape should be closed. Otherwise you’ll have an object with naked edges (openings in the shape).

Command Requirements

Rail Revolve can be found by right-clicking on the Revolve icon in the Surface menu.

Rail Revolve requires one profile (cross-section) curve, a closed rail, and an axis of symmetry (defined by two points).

See Profile Conventions for Revolve and Rail Revolve above for more on how the profiles should be made.

Sequence

1.Select a profile. The profile should be perpendicular to the rail. It doesn’t have to touch, but it is easier to understand what is happening with this command if it is.

2.Select your rail.

3.Set your two axis points. Your axis points must make a line that passes somewhere inside the rail, ideally perpendicular to the rail. The easiest way to use this command is to make your axis in the same viewport as your profile.

4.As your rail gets further away from your axis, the cross-sections will scale 1D larger. Conversely, if it gets closer than your initial starting point, it will scale 1D smaller.

As the rail gets further from the centre, the cross-section stretches.

Options

◆Scaleheight: Only works if your rail curve is not Planar (flat). If Scaleheight is turned on, then where you place the start of your central axis now becomes important. The profile will now scale vertically larger or smaller based on its distance relative to the starting point of the central axis.

A Rail Revolve with a sheared rail; Rail Revolving those curves with ScaleHeight=no; the same Rail Revolve with ScaleHeight=yes.

Examples of common uses for Rail Revolve: non-round gemstones and stone settings for symmetrical stones; domed forms.

Rail Revolve Applications

If we want to use a Revolve on a shape that is not round, we use Rail Revolve.

Variations: Outside the six key solid modelling commands, Rail Revolve doesn’t have any substitutes. For some applications, Rail Revolve can be replaced by Revolve, 1 Rail Sweep, or Loft in some cases. In particular, Loft is the other way of making a domed shape or gemstone.

1 Rail Sweep

1 Rail Sweep (aka Sweep 1) takes one or more cross-sections and passes them along a single rail.

Command Requirements

1 Rail Sweep requires one rail and one + cross-sections. All cross-sections should ideally be perpendicular to the rail. In practice, this means you’ll never create the rail and cross-sections in the same viewport.

The set-up for 1 Rail Sweep – rail, at least one profile, and aligned seams; an example of a closed sweep two cross-sections.

A Sweep 1 Rail with a twist caused by a 90-degree change of seam points between cross-sections.

(Left) A Sweep 1 Rail that has been twisted to the point where the shape now becomes a bad object. This can be caused by two different causes: if the seam is on opposite positions across different cross-sections (middle), or the seam wrapping directions are set opposite (right).

Sequence

1.First, select the rail. The rail is the curve along which all the cross-sections pass. It can be either open or closed. For a ring, the rail shape is usually the finger hole. For 1 Rail Sweep, there can be only one rail.

2.Select the cross-sections next. These cross-sections should be perpendicular and upright to the rail. You can select as many as you like before pressing <Enter>.

3.Adjust the seams. At this point you can choose whether to make the sweep straight or twisted just by positioning the seams. Make sure all seam points are aligned to the same relative position on each cross-section. On a ring, this means where the rail and the cross-section touch.

4.Make sure the direction of seam points is the same for all cross-sections. There are only two choices for direction: clockwise and counter-clockwise.

5.The options menu will now come up before you finish.

The Sweep 1 Rail options box.

1 Rail Sweep Options

◆Chain Edges: Available in the Command: prompt before you select the rail. If your rail is made up of unjoined curves, you can use this to allow you to select a series of unjoined touching curves instead as your rail. This is useful when you’re using surface edges as your rail.

◆Frame Styles (drop-down menu): As the cross-section moves along the rail, the Frame Style determines how it orientates itself, as well as the angle and position of the isocurves left along the sweep. There are three Frame Styles options:

◊Freeform (the default): Tries to keep your cross-section and isocurves perpendicular to the rail.

◊Roadlike: Will orientate the rotation of the cross-sections and isocurves according to an axis you set with Set Axis. The default is perpendicular to the rail for planar rails, or the Z-axis for non-planar rails. The Roadlike frame style can occasionally prove useful if you’re working with a non-round rail such as we’d use for a crossover ring or wishbone ring.

◊Align with Surface: This only works if your rail is a surface edge. This will cause your cross-sections to twist along the surface edge, potentially keeping the newly swept surface tangent to the original surface.

◆Freeform is the default (it will just stay in its current position throughout); the other modes will keep the shape’s rotation relative to a chosen construction plane. In practice, this doesn’t get used much.

◆Closed Sweep: If you’re sweeping along a closed rail, this will complete the sweep along the rail, making a closed shape.

◆Global Shape Blending: When this is on, Rhino will find the average amount of blending the surface goes through between every cross-section (A and B, B and C, C and D, and so on), and then equalizes the surface blending over the whole surface based on this.

◆Untrimmed Mitres: This option is only available when your rail has sharp corners. If this is turned on, then all component surfaces of the sweep will be made as if they have been Trimmed and Shrunk (seeChapter 4).

Sweep 1 Rail with Closed Sweep turned off (notice the open faces); the Closed Sweep option; Sweep 1 Rail with Closed Sweep turned on.

The three cross-section curve options from left to right: Do not simplify; Rebuild to 20 points; Refit to 0.01mm tolerance.

Cross-Section Curve Options:

◆Refit Rail: Runs the Fit Curve command on the rail before completing the sweep, using the absolute tolerance of your file as the tolerance for your curve. In practice, it doesn’t do much in most jewellery modelling circumstances unless you’re working with imported curves from other software (such as Illustrator).

◆Align Cross-Sections: Gives you one last chance to change the seam wrapping direction for each seam point. Turn this button on and you can flip any cross-section’s seam. Unfortunately it doesn’t let you change seam point locations.

The next three options are controlled by a radio button, and so are mutually exclusive:

◊Do Not Change Cross-sections: The default look of the sweep. Passes the shapes around the curve as they are.

◊Rebuild Cross-sections with X control points: Takes every single cross-section and applies the Rebuild command to them, softening them and making the control points on the shapes uniformly distributed. In effect, it melts the ring. Also, it has a side effect of making the ring a single piece, making it now possible to modify it with control points.

◊Refit cross-sections within X millimetres (tolerance): Rethinks every surface generated by the Sweep command to a new level of absolute tolerance. In other words, it changes the precision of the isocurve structure on the shape.

1 Rail Sweep Applications

One could make an argument that the 1 Rail Sweep command is the most important solid modelling command in Rhino for jewellers without exaggeration. You could potentially make jewellery using nothing but 1 Rail Sweep if you wanted to. Any shape that follows a curve can be made.

Variations: Of all the six key commands, 1 Rail Sweep has the most alternatives. Pipe is an important and common replacement for 1 Rail Sweeps with only circular cross-sections. Similarly, in some contexts, Extrude Along Curve could also be used. From inside the six key commands, 2 Rail Sweep, Loft and Rail Revolve can replace it in some instances.

Examples of common 1 Rail Sweep uses: prongs for a claw setting; a ring with two different cross-section shapes.

2 Rail Sweep

The 2 Rail Sweep (aka Sweep 2) takes one or more cross-sections and passes them between two rails, watching the shapes scale between the rails.

The set-up for a 2 Rail Sweep – two rails, at least one cross-section, and aligned seams; an example of a 2 Rail Sweep on a closed surface.

Command Requirements

2 Rail Sweep requires one rail and one + cross-sections. All cross-sections should ideally be perpendicular to the rail and should touch both rails. In practice, this means you’ll never create the rail and cross-sections in the same viewport.

A 2 Rail Sweep of a ring with one cross-section at the bottom. The preview on the left shows the sweep with MaintainHeight on, and the one on the right shows the sweep with MaintainHeight off.

Sequence

1.Select the two rails. These can be selected in any order, but where you click on the rails does matter. Specifically, you want to pick on the same side of a rail.

2.Select your cross-sections in order. It will morph your shape starting from your first cross-section and proceed through the shapes along the rail to your last selected cross-section. Press <Enter> to proceed.

3.Adjust the seams. Make sure all seam points are aligned to the same relative position on each cross-section. On a ring, this means where the rail and the cross-section touch.

4.Make sure the direction of seam points is the same for all cross-sections. There are only two choices for direction: clockwise and counter clockwise.

5.Press <Enter>, and choose your options.

Options

◆Cross-Section Curve Options: These behave the same way as with the 1 Rail Sweep.

◆MaintainHeight: By default, when the two rails of this command get further apart, the swept form gets both wider and taller. And the reverse happens when the two rails get closer together. But when MaintainHeight is turned on, the swept form does not get taller, it only changes the size of the shape between the two rails.

◆Closed Sweep: Behaves the same way as with the 1 Rail Sweep.

◆Add Slash: Normally when the sweep generates a surface between the two rails, the isocurves will be placed according to the location of the original cross-sections and the number of edit points in the rail curves themselves. If you use Add Slash, you can manually determine where the isocurves will be placed between the two rail curves by placing waypoint lines that the isocurves must pass through. This in turn can have a big effect on the way the surface sweeps.

Upper row: A 2 Rail Sweep with two convoluted rails and a single cross-section at the beginning; a single slash being placed at a problem area; the resulting fix.Lower row: The same sweeps in Perspective View: no slashes; after the single slash was added.

2 Rail Sweep Applications

2 Rail Sweep adds an extra level of control to any swept form. It can be used to make a tapered form along a curve. When sweeping a ring, your two rails can either be inside and outside ring shapes (forming a silhouette of the ring), or the left and right sides of the finger hole.

Variations: Outside the six key solid modelling commands, the closest we can find to a replacement for 2 Rail Sweep would be the Surface from Network of Curves command (also known as the Network Surface). However, Network Surface fits better within surface modelling strategy, as we shall see. From inside the six key commands, 1 Rail Sweep and Loft can replace it in some instances.

Examples of uses for the 2 Rail Sweep: a horn shape with one cross-section; a bombe ring with two side rails made with Curve from 2 Views; an S-shaped filigree element made from two sweeps joined together.

Loft

Loft behaves like a sweep command without any rails, morphing directly between at least two cross-sections. It is also one of the only commands that can use a provided point as a cross-section.

Three examples of the most basic set-up for a Loft: two cross-sections positioned in 3D space with aligned seam points. The first Loft shape is made with two different curve cross-sections; the second Loft is made with two rectangles of different dimensions; the third Loft is made with one curve and one point.

The Loft Options menu: four cross-sections (including the point) laid out vertically in Z, all with seams aligned.

Command Requirements

Loft requires at least two cross-sections, positioned in 3D space.

Sequence

1.Select the cross-sections in order. The command will travel between your cross-sections in the order you select them. Press <Enter> to proceed.

2.Adjust the seams. Make sure all seam points are aligned to the same relative position on each cross-section. On a ring, this means where the rail and the cross-section touch.

3.Make sure the direction of seam points is the same for all cross-sections. There are only two choices for direction: clockwise and counter clockwise.

4.Press <Enter>, and choose your options.

Options

◆Style: Determines how the lofted shape is generated using the cross-sections used. There are many choices for this command:

◊Normal: The default for lofting. The curves pass through every cross-section.

◊Tight: A lot like normal, but with greater tension applied to the surface.

◊Loose: The first and last cross-sections will touch the surface, but everything in between will simply ‘pull’ on the surface, creating a much softer shape.

◊Straight Sections: Makes straight surfaces between each cross-section.

◊Uniform: Works rather like Global Shape Blending under 1 Rail Sweep Without History.

◆Closed Loft: Causes the last cross-section to double back on to the first cross-section, making the solid into a loop. To use this without creating a surface that crosses through itself, you’ll need to ensure the cross-sections are spaced to create both inside and outside surfaces.

Examples of each loft style, shown in their order from the Styles menu: Normal, Tight, Loose, Straight Sections, and Uniform. Note how similar Normal, Tight and Uniform appear to be. It’s common to get the same results from these three styles.

A normal-style Loft with four cross-sections with Closed turned off; the same Loft with Closed turned on. Notice how the form changes for the whole shape when you close it.

◆Cross-Section Curve Options: These Loft options work in much the same way as they do for Sweep 1 and Sweep 2.

◊Do Not Simplify: The default look of the sweep. Passes the shapes around the curve as they are.

◊Rebuild to X control points: Takes every single cross-section and applies the Rebuild command to them, softening them and making the control points on the shapes uniformly distributed. In effect, it melts the ring. Also, it has a side effect of making the ring a single piece, making it now possible to modify it with Control Points.

◊Refit to X tolerance: Rethinks every surface generated by the sweep command to a new level of absolute tolerance. In other words, it changes the precision of the isocurve structure on the shape.

Loft Applications

Loft allows us to make shapes in terms of contours or rails. This makes it ideal for creating connecting shapes between two existing forms, tapered forms, and domes. It can also be used as an alternative for gemstone or stone setting creation, and can be used as a primitive method for making signet rings (seeChapter 4).

Examples of uses for Loft: a lofted dome; lofted cabochon setting; one type of signet ring.

With Record History turned on, moving the parent shapes that were used to make a surface will cause the surface to be recalculated to follow the new positions.

Variations: Loft can sometimes be replaced by Extrude to Point. From inside the six key solid modelling commands, the functions of Loft can sometimes be replaced by Rail Revolve and 2 Rail Sweep. In particular, Rail Revolve makes a good alternative for creating non-round gemstones.

HOW RHINO HISTORY FITS IN WITH SOLID MODELLING STRATEGY

What Rhino History Does

One easy way to think of Rhino History is with the following phrase: ‘Where the parent goes, the child follows.’ Rhino History creates a relationship between the original parent objects and the subsequent child objects, such that if you make changes to the original object, the child objects will adjust themselves accordingly.

As of Rhino version 6 onwards, all the six key solid modelling and transformation commands listed above, as well as all deformation and array commands, observe Rhino History.

What Breaks Rhino History

While we can chain multiple levels of Rhino History links between parent and child objects, these History connections themselves are easily broken. Any command which directly affects a child object will break the History connection with its parent objects. And once that History is broken, it cannot be restored without undoing the change.

In practice, this means that Transformations, Booleans, Caps, Join, and Explode/Extract Surface commands are the points in the modelling process where Rhino History ends.

One easy solution to preserving your Rhino History links in case you need them again is to get into a habit of Incremental Saving your files whenever you know you are about to break Rhino History with any of the above commands.

If You Choose to use Rhino History, use Always Record History

To turn on Rhino History, you can click on the Record History. This will activate Rhino History for only one command before turning itself off again. Managing this for every command can prove quite cumbersome, so I recommend leaving Rhino History always turned on until you need it turned off.

Always Record History can be found by right-clicking on the Record History button: an example of a broken history warning.

If you are recording history on multiple Rhino commands, you can end up with chains of commands each dependent upon another. These can prove very time saving when editing shapes.

To leave Rhino History turned on indefinitely, right-click and go inside the Record History menu and tick Always Record History. This will reverse how the Record History button works – Rhino History will always stay on unless you temporarily turn it off for one command by clicking on the Record History button.

This will lead to your having many more warnings of Rhino History being broken, which can be a nuisance. However, by leaving it on you enjoy the time-saving benefits of being able to rework almost any object made with the six key solid modelling commands or transform commands by simply changing the curves. For example, you can adjust all the piped claws in a polar array around a gemstone by changing the edit points on the original curve; or you can change a sweep by resizing or reshaping the cross-sections.

CHAPTER 3

Jewellery Manufacturing Tolerances in CAD

WHAT ALL CAD JEWELLERS SHOULD KNOW ABOUT MANUFACTURING TOLERANCES

Disclaimer

Whilst every manufacturer has their own experience with working with various types of jewellery, and everyone seems to have strong, individually formed opinions as to what the ideal thickness of a ring might be, I have found from speaking with hundreds of casters, goldsmiths, mounters and manufacturers over the years that there is a common range for most jewellery tolerances and dimensions. This chapter focuses on all these standard common ranges of measurements for manufacturing various common types of jewellery.

Whilst this is not meant to be an exhaustive list of dimensions that would or would not work in jewellery manufacturing (it would be impossible to make such a list), it does provide some ‘safe zones’ for jewellers to fall back upon in order to ensure their models will work for manufacturing. In this chapter I have therefore sorted common manufacturing tolerances and design considerations by jewellery type, and provided a sample exercise to help you experience how to ensure these tolerances when making your models.

What Are Tolerances?

There are several related meanings to the word ‘tolerance’ when doing any kind of product design work in Rhino. It can mean any one of the following things:

◆The smallest decimal place worth paying attention to. Anything smaller will be rounded off.

◆The smallest precision measurement we can consistently guarantee in manufacturing.

◆The minimum thickness a particular component can have and still survive the manufacturing process.

◆The maximum thickness a component can have and still be usable for purpose.

Quite simply, if you try to make a component that does not meet minimum tolerance, it will not work for its intended purpose – details will fail to 3D print, rings will buckle and crack, claws will break during manufacturing, and so on.

When I discuss tolerances in this chapter, I am referring in particular to the last three definitions in the list above. But understanding how to control the first one will have an effect on how surfaces and models can join together. This control over decimal places in Rhino is common to all product design CAD programs, and is known as Absolute Tolerance.

Why Every CAD Jeweller Should Know Manufacturing Tolerances by Heart

Perhaps the foremost complaint of jewellery manufacturers and stone setters who work with CAD modellers is their failure to provide correct thicknesses and structures for casting and manufacturing. In particular, they complain about having to make poorly constructed stone settings work in supposedly professional pieces. The problem is, like modelling any other type of object, the more the CAD modeller has physical experience with the object they are making in CAD, the more likely they are to understand what they are making.

This is not helped by the fact that most stone setters cannot seem to agree on standard numbers. The best we can do is define a range of numbers, and then let our own experience (or the experience of the setter we’re working with) fill in the gaps.

Therefore, if you are going to build jewellery in CAD, you should either have experience working with the real thing, or should maintain a dialogue with the manufacturers and stone setters with whom you will be making the piece. As a general rule, any proven tolerances or measurements that come from actual real-life bench experience will be better than those I have written here.

What is Absolute Tolerance in Rhino?

Within Rhino, Absolute Tolerance controls how close two curve ends or surface edges must be before they are close enough to be joined together. This not only affects the joining of curves, but also the construction of solid forms using commands such as Sweep.

The advantage of having a higher tolerance (that means the smaller Absolute Tolerance number) is that your models will be made to greater precision. This is important for finer detail work. In exchange, your models will have a larger file size, and you will have to be more precise when working.

Conversely, lower tolerances make for smaller models and allow for ‘sloppier’ use of tolerances, and more relaxed precision when using Join.

One major issue that can happen if you set your Absolute Tolerance too low is that commands that rely on intersections such as Splitting and Boolean commands may start failing because Rhino loses the ability to find complete intersections between surfaces. This is another reason why it is good to use a tolerance appropriate for the size and detail of your object.

Adjusting Absolute Tolerance in Rhino

We can find the Absolute Tolerance setting in Units Settings, under File➞Properties.

◆Network Surface

◆Sweep 1, Sweep 2, and Loft

◆Match Surface

General Tolerances for Precious Metal