Basic overview, solid model design

[bbussey]

As we don't have a CAD forum, this is the best location for a basic CAD overview I believe.

There have been some questions in a couple of the 3D conversations regarding basic technique on designing digital 3D models.  As discussed there, the basic concepts and procedures are generally the same regardless of the CAD program used.  The following is my attempt at showing that learning the how-to and executing it is not a steep learning curve and, once you understand the concept, design becomes very easy.  You mainly have to train yourself to look at all objects as a series of geometric shapes that are manipulated by or joined with other geometric shapes.  While there are some features that take some mastering (for example, a canvas tarp over the top of a loaded trailer, or a coal load in a hopper), the overwhelming majority of features on a model are relatively simple in nature and simple to create.

Your basic features in any CAD program are extruding, cut-extruding, rotation and cut-rotation.  As with any feature, you must begin with a sketch.

This is a very general example of creating a base extrusion from which to start your 3D model.  The picture below shows the side (X), top (Y) and front (Z) planes from a dimetric viewpoint.  Normally in SolidWorks the standard planes are hidden , but I turned them on for this presentation.  Hidden objects can be selected from the project tree so there is no need to have everything visible at all times.



I've created a simple rectangular sketch on the top plane, centering it and locking it to the Origin object.  The coordinates of the Origin always are (0, 0, 0) regardless of the unit of measure.  This particular rectangle is 10mm x 20mm.



I'm now using the sketch as the basis of an extrusion feature.  I'm extruding the sketch for a length of 30mm.



Once this is accomplished, I have a solid box with the dimensions of 10mm x 20mm by 30mm.



So to continue on this theme, we’re going to look at the beginning steps of a model I recently finished, a Strick 35’ drop-frame trailer in N scale.  You've seen this model featured in some of my other 3d threads.  The finished body with all of its surface relief has this appearance in the SolidWorks workspace window:



But in the beginning, we start with a simple rectangular box that matches the height, length and width of the prototype.  I always start in 1:1 scale for the general dimensions, then reduce it to N to add the detail relief and any scale-specific necessities.  This is looking up at what will be the bottom of the trailer body from below the rear of the trailer.



The drop frame behind the nose is added via a cut-extrusion from a sketch on the front plane.



Split lines are added to the sides as indicators for the side ribs.  Again, these are 1:1 so the real widths are used.



The front of the trailer with the rounded corners is added via a sketch on the top plane.



Clearance for the rear wheels is a cut-extrusion via a sketch on the front plane.



The extended rear frame is added via a sketch on the front plane.



At this point, the model is scaled down to 1:160, as the relief will begin to be added, which is scale-specific as some features will be oversized to be visible as appropriate.

The flanges of the vertical ribs are added via a sketch on the front plane that was created by tracing the split lines on the body.



The ribs are added via a sketch on the front plane, created by drawing vertical centerlines off the flanges.



The nose flanges are created via a sketch on the side plane, created by tracing previously added split lines on the body (not shown previously).



The nose ribs are created via a sketch on the side plane, same method as with the side ribs.



All of the electrical connection appliances are added to the nose with a series of features.



The roof overhang is added via a sketch on the top plane.  The sketch was created by offsetting from the top perimeter of the body.  A fillet is applied to the top edge of the roof (not visible from this angle but visible in the screenshot of the completed bodyshell above).



The bottom trim is added via a sketch on the front plane, to take account of the wheel well clearance.



With the basic relief in place, the body is shelled out via a sketch on the top plane, to allow the eventual floor component (a separate part) to be inset.



Additional clearance is cut via a sketch on the top plane, so that there is a stop to prevent the floor from being pushed into far into the body.



That’s the basic design for this model.  Additional features were added such as the rivets, marker lights, rear door detail, etcetera.  But this gives a general idea of what it takes to flesh out a new model.  Just basic geometric shapes one simple step at a time, to get to the finished big picture, instead of worrying about rivets and door chains before even the first sketch is created.

[peteski]

That is a good tutorial and it all makes sense. I see the end result of the operations accomplished in each step, but how they are done eludes me.  The first extrusion you show is clear, but how are the rounded corners, ribs, and roof overhangs done exactly.  That is the part of CAD I'm lacking.

Terms like cut-extrusion, "rounded corners is added via a sketch", "tracing the split lines", "overhang is added via a sketch on the top plane.  The sketch was created by offsetting from the top perimeter of the body.  A fillet is applied to the top edge of the roof" are all voodoo to  me.   

I guess the only way I could experience those operations would be to find videos specific to the CAD program of my choice, hoping to see someone demonstrate something similar to what I'm trying to draw.

[Chris333]

I just fake it till I make it. 

I would have made one side of that trailer. Then copied it and mirrored it around to make the other side. Something like a boxcar I make one side and one end then mirror it around to make the other 2 sides.

[Chris333]

In Sketchup I have a "round corner" extension.

[John]

That is a good tutorial and it all makes sense. I see the end result of the operations accomplished in each step, but how they are done eludes me.  The first extrusion you show is clear, but how are the rounded corners, ribs, and roof overhangs done exactly.  That is the part of CAD I'm lacking.

A lot of those things are dependent on the program you are using .. Fusion360 has specific "tools" or commands to round corners ..  Tinkercad allows you to round corners on a square, but its more involved.  Other programs may have the same features ..

Terms like cut-extrusion, "rounded corners is added via a sketch", "tracing the split lines", "overhang is added via a sketch on the top plane.  The sketch was created by offsetting from the top perimeter of the body.  A fillet is applied to the top edge of the roof" are all voodoo to  me.   

Basically, it's adding or subtracting from the starting box .. again, that comes with familiarity of the software ..

I guess the only way I could experience those operations would be to find videos specific to the CAD program of my choice, hoping to see someone demonstrate something similar to what I'm trying to draw.

this video (while based on Fusion360) explains the process really well . it's 20 minutes - well worth watching ..

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[narrowminded]

@peteski What you're asking about is what the tutorial will demonstrate in pretty short order.  They will probably have you design a house or something which will use the different commands and features that you will use for designing whatever.

[bbussey]

I just fake it till I make it. 

I would have made one side of that trailer. Then copied it and mirrored it around to make the other side. Something like a boxcar I make one side and one end then mirror it around to make the other 2 sides.

Depends on the model for me. The nose and back of the trailer are not symmetrical, neither is the rivet pattern on the sides. And when I have specific dimensions of the prototype, I draw it whole 1:1. On freight cars however, I usually draw one side and then copy/rotate around the Origin. I draw the A end as a separate object and then copy/rotate after complete to add the brake hardware details of the B end. Passenger cars I usually draw the entire part, although difficult features such as roof end caps I may draw the quarter corner and mirror on both the front and side planes, or draw the full end cap and mirror on the side plane.

[Maletrain]

Thanks for the taking the time to produce this concept intro, Bryan.

As I guy who took mechanical drawing for 6 semesters in high school (about 60 years ago!) I am comfortable with the process of representing solids with various projections (orthogonal, isometric, diametric, etc.).  And, I am comfortable with using computers and have done a lot of programming, but none of it to manipulate graphics.

What takes me some time to get really good at is the particular human interfaces that are more or less unique to specific software products.  And, I realize that some products are more intuitive to learn, and some products are more powerful when used to their maximum capabilities, and not necessarily the same program maximizes both of those attributes.

So, before I jump into 3D printing, I want to pick a program to learn that is as easy as I can find that provides really good capability for home 3D printing.  Something with good tutorials available is probably better for me than something that is more intuitive but lacks instructions on how to use the interface to maximum advantage.  I don't have any local friends who I can lean on for learning by doing.

I am interested in your recommendations.

[bbussey]

I'm probably not the best person to ask because the overwhelming bulk of my experience over the past 20 years has been SolidWorks, so it is extremely familiar to me over the others.  I've dabbled with Sketch-Up and Rhino, but my comfort zone is SolidWorks.  But there are a number of programs out there that will fill all model railroading requirements.  Inventor is another.  Sketch-Up is at the lower end of the scale but many such as @Chris333 have created extraordinary models that could not have been created any better in SolidWorks or Inventor.  So it's more a matter of picking one and jumping into the swimming pool.

[wcfn100]

 

I guess the only way I could experience those operations would be to find videos specific to the CAD program of my choice, hoping to see someone demonstrate something similar to what I'm trying to draw.

Every program I've used has a glossary where you can look up the different functions and how they are used.

The best way to learn is to just start drawing and ask questions later.


Jason

[rodsup9000]

  Bryan, Thanks for taking the time to do this.

  I started with Sketchup in about 2008 and bought the Pro in 2013. Upgraded to Pro 2019 and still use it. It works for me so far. After all the years of using it, I'm still finding shortcuts and extensions that helps.

 I have Solidworks ($20 a year for veterans) and just cannot figure it out. Out of habit, I try to use it as it was Shetchup. Just hard for me to unlearn Sketchup and use it. I keep it cause I would like use it someday.

 I also have licensed copy of AutoCad 2010 and cannot figure it out either.

[wcfn100]

It should always be noted that there are multiple ways to create almost any object.

For example:



If you're more comfortable with 2D design, this shape could be made with a side profile that could include the drop frame cut, the wheel cut and even the frame extension  (you would have to cut some relief later) all in a single line drawing, then extrude the width.  But when I started drawing 3D, you had to save you file and say a prayer if you ever tried a Boolean operation like a cut because there was a better than 50% chance you machine would crash.  So I learned a different way.

This is why the best way to start, is to just start.  Because we don't all think the same, you need to find what works for you.

Jason

[Chris333]

I use AutoCAD2004 and keep my finger over the enter button. Click on a command and smack the button. Then in Sketchup it doesn't work that way.

I can't recommend anything cause I don't know enough to know. If I run into something I can't figure out I have AutoCAD for dummies and Sketchup has all of Youtube.

[Sumner]

I'm using Fusion 360 and would do all the steps basically the same as Bryan outlined.  Haven't used Solidworks but looks to be the same type concepts in a number of ways.

I started with the free download and this guys video and still use a lot of what I learned in it for most of what I do....

Lots of videos out there on Fusion and when I need to learn something new or a new situation I look for one and usually a few minutes later I'm using a new command.  Just from the past few days and from various threads here including this one I'm now using 'off-sets' and 'draft' commands to do things quicker than what I was doing before.  Don't overwhelm yourself thinking you have to learn dozens of commands to be able to design something.  It will come to you.

If I was doing this commercially I'd look around before deciding what I was going to spend money on either one time or yearly.  For me since I'm not, Fusion 360 was a no-brainer.  It is powerful as indicated by the $500 a year license fee but for hobby use it is free.  Free means I'm really happy to have such a powerful but still easy to use program at my disposal. Here is the renewal link along with a link to initially download it....

https://knowledge.autodesk.com/support/fusion-360/learn-explore/caas/sfdcarticles/sfdcarticles/How-to-renew-your-hobbyist-enthusiast-license-for-Fusion-360.html

Sumner

[peteski]

Thanks everybody - keep the info coming!
I dabbled in SketchUp several years ago, but couldn't figure out how to do some things and gave up.  I now realize that I can load bunch of extensions which expand the program's capabilities. Too bad that those do not come with the program.
I also bought a copy TurboCAD, but I quickly gave up on that one.  Still have the CD.

Seeing what people can accomplish with even free or inexpensive CAD apps I should really revisit SketchUp (or some other inexpensive or free program).

The only success I had with Sketchup was a church steeple roof I made for Spookshow (Mark).  It had lots of interconnected odd angles, and I figured out that a CAD program would work out all those angles for me.  It did.

Prototype:


My CAD rendering:


Since Mark wanted to make it out of folded paper, I flattened all the parts:


I then exported that as a bitmap into Corel Draw, and created a paper model for Mark to cut out and fold. Saver it as a PDF, then sent it over to Mark to print and fold.:


I'm sure there was a way to create the flat paper model in SketchUp, but I'm more familiar with Corel Draw, so I too the easy (for me) way out.