+1 323 268 0395 kmw@caltek.net

kmw mailing list archives

Draftsmen and boatmakers used [...]

by
Kenneth Wyrick
- 04/21/2018 20:48:23

Draftsmen and boatmakers used mechanical splines to make smooth curvature. 
IJ Schoenberg named the piecewise polynomial formula after these splines. 
Spruce Goose Hangar in Playa Vista still has monuments in the floor that were used to set the spine of the boat/plane.
 (monuments are still used in aerospace to setup virtual coordinate systems and splines when building large aircraft / rockets). 
12
Back in the 1960’s Bezier at renault (the french automotive company),
started using spline curves to define the geometry of cars,
Based on decades of work automating assembly lines and working on replication machines / computerized industrial applications. 
create clay models of cars using electromechanical machines, 
popularized the use of splines through his pioneering work (based on the work of Casteljau)
Developed Unisurf, 1968 (CAD/CAM system)
13

Sketchpad - written by Ivan Sutherland in 1963 (for his PHD thesis)
Pioneered Human Computer Interaction, Breakthrough in development of computer graphics
GUI and Object oriented programming come from this.
First GUI
Insipred Engelbart to design oN-Line system ( mother of all demos)
Ran on the Lincoln TX-2 at MIT, converted to run in interactive mode, was converted back to batch mode after the demo : * (
14
ACM/IEEE Computer Society’s fall joint computer conference in SF 9 Dec 1968.

the oN-Line System or, more commonly, NLS. The 90-minute presentation
: windows, hypertext, graphics, efficient navigation and command input, video conferencing, the computer mouse, word processing, dynamic file linking, revision control, and a collaborative real-time editor (collaborative work).

Inspired Windows and Macintosh. 

Prior, computer science community thought Engelbart was "a crackpot."[18] When he was finished, described as "dealing lightning with both hands."[4]
15
BUILD followed by its commercial spin-off Romulus which went on to influence the development of Parasolid, ACIS and Solid Modeling Solutions. 

Solid modeling kernels 
https://en.wikipedia.org/wiki/Geometric_modeling_kernel
Convergence Geometric Modeler[3] by Dassault Systemes
Romulus was released in 1982 and licensed by Siemens and HP
Parasolid by ShapeData, now owned by Siemens
ACIS by Spatial Corporation, part of Dassault Systemes, is used in many CAD applications.
CGAL, open-source library of geometry algorithms
ShapeManager,[4] is a fork of ACIS developed by Autodesk since 2001.
Granite[5] by Parametric Technology Corporation
Open CASCADE is a freely available modelling kernel
C3D Modeler by C3D Labs, part of the ASCON Group.[6][7]
K3 kernel[8] developed by Center GeoS
SOLIDS++[9] developed by IntegrityWare, Inc.
APM Engine[10][11][12] developed by RSDC APM
16
Modern CAD
Pro Level     -
NX / UG - created in 1973 by United Computing Inc as UNIAPT, 37 versioned releases since 1978
CATA - in 1977 for Dassault to develop the Mirage Jet Fighter, 15 versioned releases since 1981
PTC Creo - First Parametric / variational 3d CAD system, 26 versioned releases since 1991
Small business - 
Solidworks - Dec 1993 by MIT alum Jon Hirschtik, started with blackjack money 26 versioned releases since 1995
Rhino - founded 1980, employee owned, based on nurbs, started the openNURBS initiative http://opennurbs.org/
Inventor - 20 versioned releases since 1999 by autodesk, creater of autocad, one of the earlier CAD systems (1982)
Free  -
Onshape
Not worth mentioning - 
Open source (utter garbage)
Weird finicky CADs
17
How does CAD work?

What’s going on mathemagically?

I recommend chapter 3 in CAD CAM by Chris Mcmahon and Jimmie Browne for a really good derivation
18
What’s a Nurb
It’s a parametric function that defines basically any curvature via piecewise nth degree polynomials that’s curvature are described by weighted control points and normalized. 

And it would take a really long time for me to laymenize that, suffice to say, control points move curve around, can describe any 3d curve fairly exactly, really complex / disjoint curves will be harder to describe accurately and require many more control points / segments.
19
Ok, so just multiply two nurbs together. (add a new index)

So, U and V describe curves with indicies I and J (where it was just U and I before). 

Nifty huh?

The hard part about surfaces is making them smooth and intersect with each other cleanly. 
20
Read about manifolds and be confused by math major silliness. https://en.wikipedia.org/wiki/Manifold#Manifold_with_boundary

This article describes the various strategies of solid representation pretty well
https://en.wikipedia.org/wiki/Solid_modeling

Surface mesh modeling[edit]
Similar to boundary representation, the surface of the object is represented. However, rather than complex data structures and NURBS, a simple surface mesh of vertices and edges is used. Surface meshes can be structured (as in triangular meshes in STL files or quad meshes with horizontal and vertical rings of quadrilaterals), or unstructured meshes with randomly grouped triangles and higher level polygons.
Constructive solid geometry[edit]
Main article: Constructive Solid Geometry
Constructive solid geometry (CSG) connotes a family of schemes for representing rigid solids as Boolean constructions or combinations of primitives via the regularized set operations discussed above. CSG and boundary representations are currently the most important representation schemes for solids. 
Sweeping[edit]
The basic notion embodied in sweeping schemes is simple. A set moving through space may trace or sweep out volume (a solid) that may be represented by the moving set and its trajectory. Such a representation is important in the context of applications such as detecting the material removed from a cutter as it moves along a specified trajectory, computing dynamic interference of two solids undergoing relative motion, motion planning, and even in computer graphics applications such as tracing the motions of a brush moved on a canvas.

Parametric and feature-based modeling[edit]
Features are defined to be parametric shapes associated with attributes such as intrinsic geometric parameters (length, width, depth etc.), position and orientation, geometric tolerances, material properties, and references to other features.[8] Features also provide access to related production processes and resource models. Thus, features have a semantically higher level than primitive closed regular sets. Features are generally expected to form a basis for linking CAD with downstream manufacturing applications, and also for organizing databases for design data reuse. Parametric feature based modeling is frequently combined with constructive binary solid geometry (CSG) to fully describe systems of complex objects in engineering.
21
Real CAD systems have been in development for 10’s of years, and feature powerful features like Direct and synchronous modeling, smart surfacing tools, and lots of industry specific plugins (sheet metal, wing spars, Die design tools, CAM for CNC and meshing tie ins for finite element analysis)
22
Gear Design: The Spreadsheet™ https://docs.google.com/spreadsheets/d/1HwhGyi9gJte60uUocrzMJY-228x4sfKV9r7pKRaXajw/edit?usp=sharing
Involute Profiles from Shigley’s Mechanical Engineering Design (amazon link)

(a couple notes 1: these involute profiles are kinda bad, as you can’t circular pattern splines in onshape yet (bummer)) and 2. I haven’t found really good work arounds to make the parametric model super stable, so large changes may flip shit and break it. This is unfortunately a part of parametric modeling and trying to drastically change dimensions / parameters, so get used to it :P
23
Onshape is free, but at a cost. There’s limited space and all your docs are public unless you pay.

We’re using it because it’s free and you don’t have to install anything. Most heavyweight CAD packages take much longer to get installed and configured, and cost in the thousands just to get started. So be warned, it’s not the best CAD out there by any means. (I like NX personally)
24
When you open or create a part, this is what you’re greeted with. 

Name / Rev control is the name of the part and where you can create new versions or save as / copy the part into a new part

Feature / Sketch Toolbar is most of what you use to create sketches, extrude, revolve, add fillets and create solid geometry in general. 

The main viewport is where all the CAD is going on. You can do all sorts of stuff in this area. 

View control lets you move the model around in space. (you can also do this with the mouse / keyboard shortcuts, in the next slide). 

Help - Where you go to search for features, get tutorials on how to use onshape, and ask for new features if the one you need doesn’t exist yet. 

Feature History - a historic record of each feature you’ve created. You can roll back to earlier features and change / add things, then roll to the end to see how it impacts downstream features. Or you can just directly edit most features and sketches by double clicking them. The filter by name or type lets you filter to just the features you’re interested in. and the eyeball (hover to the right of a feature) indicates whether or not the feature is hidden (click to hide  / unhide)

Part / Bodies - A list of all Bodies / Parts (also hideable) you can right click and assign materials or colors from this list (or right click and export geometry to STL or an interchange format like STEP or IGES
25
Your mouse is your friend.

You can also use a 3d Mouse, it’s up to you. 


26
Help is in the top right, or the lil question marks on each dialog point to the help documentation. A great way to get practice at onshape is to just go through reading all the help menus.

Run through the tutorials to get better!

https://www.onshape.com/videos/topic/tutorials
27
Sketch toolbar
Lefthand side of toolbar is all the curve stuff (circles, rectangles, lines, splines, elipses, points, text, include lines from other parts/features, and convert to construction line)
Next is fillet extend, offset, mirror and pattern, insert DXF/Image (useful)
Then there’s the dimensioning tool, read the help for this to better understand the behavior (it can be complex and unintuitive)
To the right of that is all of the constraints for sketches. This is how you control what’s parallel perpendicular and the what not. 
28
G0 - curves are touching (position)
G1 - Curves are tangent 
G2 - Curvature is Tangent (end circles line up)
G3 - Lots of tangency / smoothness (mostly used in surfacing for cars and aero shapes)
29
Extrude / Revolve / Sweep Sketch

Check out the various versions of the gear to see different types of feature creation.
30
Fillet, Chamfer, Shell
(try it!)

There are other features you can add like threads, holes, ribs, and draft (for molds and stuff)
31
Try assigning different materials, and see how the mass properties change
32
Evaluate the properties of parts after you assign materials

To measure distances
Select a point or surface, and another point or surface, and look in the bottom right of the main viewport for the measurement. 
Click the arrow to the right of the measurement to see the Deltas in XYZ (relative to the global coordinate system

To get Mass Properties
Select Part in Part / Bodies List
Click small balance / scale icon in bottom right of main viewport. 
33
ISO 10303: STEP files (https://www.iso.org/standard/63141.html)

IGES files - Initial Graphics Exchange Specification - first published in 1980 by national bureau of standards. Can exchange data on circuit diagrams, wireframe, freeform surface or solid model representations. First ANSI standard to be documented using itself https://en.wikipedia.org/wiki/IGES

STL -An STL file describes a raw, unstructured triangulated surface by the unit normal and vertices (ordered by the right-hand rule) of the triangles using a three-dimensional Cartesian coordinate system. In the original specification, all STL coordinates were required to be positive numbers, but this restriction is no longer enforced and negative coordinates are commonly encountered in STL files today. STL files contain no scale information, and the units are arbitrary. https://en.wikipedia.org/wiki/STL_(file_format)

Higher end CAD systems tend to have macros to check geometry and make sure self intersecting curves, surfaces, and sliver surfaces or gaps in solid bodies don’t exist. This makes sure your downstream CAD CAM or FEA experience doesn’t grind to a horrible halt mid run. Use them if it’s important. 
34
Assembly tools are somewhat different between various CAD systems. My strong recommendation is to make a few parts, experiment for a bit, then read the documentation. I’m a pro at NX assemblies, but not so much at onshape, so don’t take my word as law. 

With onshape, you can fix and unfix parts, and mate using mate connectors and various mates. Cylindrical mate and parallel mate with all the min and max distances set to zero are pretty useful right off.

Once you have two cylindrical mates setup, you can set a gear relation, and you can animate mates with a right click. Pretty nifty huh?
35
Assembly tools are somewhat different between various CAD systems. My strong recommendation is to make a few parts, experiment for a bit, then read the documentation.

With onshape, you can fix and unfix parts, and mate using mate connectors and various mates. Cylindrical mate and parallel mate with all the min and max distances set to zero are pretty useful right off.

Once you have two cylindrical mates setup, you can set a gear relation, and you can animate mates with a right click. Pretty nifty huh?
36
CAD for hobby stuff (like garage projects and making figits on your 3d printer) is way different from professional use.

Most of the big difference are:

A lot more time is spent in CAD. 
Many people will depend on and interact with your model
You need to make a drawing and a part as the end result of the work and it should match the CAD. 
You will be working with many more / highly detailed parts. 
37
CAD for hobby stuff (like garage projects and making figits on your 3d printer) is way different from professional use.

Most of the big difference are:

A lot more time is spent in CAD. 
Many people will depend on and interact with your model
You need to make a drawing and a part as the end result of the work and it should match the CAD. 
You will be working with many more / highly detailed parts. 

The entire system pictured exists in a CAD model, with all designs reviewed,  drawings checked and released. Despite being designed by about 30 people in a year, and operating at vacuum with a vehicle north of 100 m/s there have been no major system failures through hundreds of hours of operation. It consists of about 40,000 unique components. 

I setup the process and built the top level assembly, and released all tube and track drawings, and served in a review function for the motor, airlock, and all major subsystems. 
38
True Position Excerpt from GD&T wall chart
http://www.iigdt.com/Products/Images/0f390980.jpg

This is 1994, but is close enough
Basic Views
Dimensioning
Tolerances
Geometric Tolerances

Dimensioned drawing image from autodesk. 
39
Spacex Drawing template is pretty good. You too can use it! Found pubished publically here: 
https://cdn.atraining.ru/docs/TubeSpecs.pdf
http://www.spacex.com/sites/spacex/files/2018_hyperloop_competition_rules.pdf

Drawings are used to : 

Communicate Design intent
Provide acceptable tolerance ranges for Manufacturing
Control QA process. 

They are not meant to:
 Restrict manufacturing method (as long as tolerances are achieved).
40
Example Drawing that I can actually share (Spacex competition hyperloop tube published drawing). 
41
Don’t Model Threads

Hide or don’t load extraneous geometry ( for example, molding in a room, threads on a fastner / hole, every nut in a 3,000 bolt assembly)
Don’t model stuff that doesn’t matter (lockwire, grease etc) it can get called out on a drawing. You might need to include mass estimates at some point, every company handles it differently
Consult with your CAD vendor frequently
42
PLM / PDM

Database to store your cad
Pretty Drab
Exciting for ensuring quality work, tying issues to parts, and freezing designs so changes aren’t inadvertantly made in CAD after stuff is built (you can tell what was supposed to be built). 

43
Spaceballs: The CAD Mouse https://www.3dconnexion.com/ 
Online / Free CAD https://grabcad.com/ 
Grabcad
McMaster https://www.mcmaster.com/ 
Digikey / Mouser  https://www.digikey.com/ 
Most high end suppliers have great CAD models (igus, Joyce Dayton, Parker, etc.)
(some will want an NDA or a website sign up first). 
44 Next Classes

Code Basics with Kit! - Kit Class (5/19) will sell out fast! Link to go up tomorrow (sunday)

45
46
Onshape actually has a config management tool now.

I have not used it. 

This normally requires a herculean effort on the shoulders of one or two very experienced engineers. In short, listen to whomever that is, until you start to understand the basic strategies they’re employing. 
Subdivision and typing is a nightmare, try to stay away from it in a group setting unless you have a strong dictator, and can maintain that indefinately. 
47