3D cad design sequence

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Gordon

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How do folks design something in 3D? I am thinking something like a single cylinder engine. I am envisioning a sequence like perhaps drawing a piston, a crankshaft and a connecting rod kind of out in space and adding things like a cylinder and frame for mounting the crankshaft etc. all rather crude and without detail. Then once you have the major components in position you would make detailed refined drawings of each piece and insert the refined piece back into the original assembly. I am used to designing in 2D where I would start with an a crude assembly drawing with probably front, top and end view and then making a detail drawing of each individual piece and modifying the original assembly drawing to add the details. I am not sure of how to make a similar assembly drawing in 3D and then refining the individual pieces and replacing them in the original. I guess I am asking a chicken and egg question. This 3D stuff is new to me and I am kind of old to learn new tricks. I started with pencils and triangles etc. back in 1962 and gradually progressed to cad but sold my business and retired (several times) in early 2000's.
 
Gordon (and others looking in),

In the 3-D world, You design in 3-D, then export whatever you want. The specifics kind of depend on the features of the package you have. As you would expect, more features and more flexibility mean more expense and more of a learning curve.

In the 3-D programs I have used, you might design that connecting rod by drawing basic geometry. then you would dimension it, add features like thickness, holes, chamfers, tapers, etc.. From that one part you could then switch to 2-D and export drawings with dimensions, or you could export a section or a 3-D rendering for printing or sharing.

To continue, you might then start designing the crankshaft, using the features of your connecting rod for determining the dimensions and setting points of contact where the two parts match up. You would continue with the crank until you have a part you can make shop drawings, etc. And on to the piston, on to the piston rings, on to the wrist pin, etc.

(I know all this sounds very vague, but I am trying to avoid using terminology and referring to software features that only a program I have used provides. Another thing I feel obligated to mention is that there are usually many means to an end in creating a 3-D model of a part in 3-D CAD, so you don't always do the same steps to make a part.)

I think what I read from your post is well illustrated by the power users here. I think Brian Rupnow illustrates the workflow you are talking about. I believe that you can do some of the same things in lesser packages than the Solidworks that Brian uses, but not EXACTLY like everything he does.

---ShopShoe
 
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This post is an aside, so not directly related to what I said above.

One of the things that I have learned, and others have learned, is that stepping into the 3-D world makes one more conscious of the "project management" aspects of designing. Software features sometimes enhance this. I would suggest that developing conventions for file and version naming become important so you don't lose track of all the steps you have already done. It is useful to have an idea of where you have been in case you have to "rewind" to the "last good one" before you continued.

I handy hint I use is to create new versions saved under a new name every so often. (WOBB2_HEAD_ASSY_v03, v04, v05, etc. I do the same things with video editing projects. I personally use Auto-Save very rarely, as it can automatically save the changes just as you applied a global command to do something really crazy. I usually keep notes to myself in a separate text file as I do this.

--ShopShoe
 
You can tweak your computer to auto-save as frequently as you like. Don't ask me how, because I don't remember. As far as working in a 3D program, start a sketch, draw something close to what you want, then dimension the sketch to lock in the dimensional properties. Then--Extrude it into the third dimension to the "depth" you want. For something like a piston, draw a horizontal centerline from the "origin", then draw a half profile and dimension the sketch until everything including the ringlands are defined (In my Solidworks, undefined lines that you drew are blue. Once they are dimensioned and "defined" they turn black.) Then you choose the "rotate solid" icon, pick 360 degrees, and Presto, the sketch rotates around the centerline and gives you a 3D solid piston. Then, looking at the ass end of the piston, you draw a sketch defining the slot, only this time you choose the "extruded cut" icon and type in a value for the depth of the con rod groove--this will hollow out the bottom of the piston. Then you choose the "make drawing" icon and it opens a drawing sheet and gives you a list of what view you want to start with. It will place that view on your drawing sheet, and then you can have your program set up to project any secondary views or tertiary views from your first view. Your program will also offer you the option of doing any section views. When you go to put dimensions on your views, you only have to tell the program where to put the dimensions (never use auto-dimension). The program will remember the math data entered to make your original sketch, and that value will be displayed on the dimension.
 
How do folks design something in 3D? I am thinking something like a single cylinder engine. I am envisioning a sequence like perhaps drawing a piston, a crankshaft and a connecting rod kind of out in space and adding things like a cylinder and frame for mounting the crankshaft etc. all rather crude and without detail. Then once you have the major components in position you would make detailed refined drawings of each piece and insert the refined piece back into the original assembly. I am used to designing in 2D where I would start with an a crude assembly drawing with probably front, top and end view and then making a detail drawing of each individual piece and modifying the original assembly drawing to add the details. I am not sure of how to make a similar assembly drawing in 3D and then refining the individual pieces and replacing them in the original. I guess I am asking a chicken and egg question. This 3D stuff is new to me and I am kind of old to learn new tricks. I started with pencils and triangles etc. back in 1962 and gradually progressed to cad but sold my business and retired (several times) in early 2000's.
I am not sure how others design engines with 3D, but I can explain how I do it.

I create a 3D model for one part at a time, so there is a part file for the piston, rod, bearing, crankshaft, etc. (each its own separate file, with an extention similar to .PRT ).

Then I create an assembly, which is another file with a different extension, such as .ASM.

I insert one part at a time into the assembly, fixing the first part inserted, such as the base of the engine, so it does not float and move.
The parts are mated as you add them.
Make sure that moving parts still rotate after you mate them, or the engine will not run in simulation.

If I change any part file, that part is automatically updated in the assembly, without you having to do anything.

To make 2D drawings from a 3D model, in Solidworks, you open a separate drawing file (perhaps a file with a .DWG or similar extension), drag and drop the 3D model onto the sheet, and then drag off top, left, right, bottom, side, and isometric views.
You can change the views from wireframe, show hidden lines, don't show hidden lines, color, etc.
I usually show the isometric in color, and the rest in wireframe black and white.
I dimension the drawing as desired.

Any changes made to any 3D model after you create the 2D drawing file is automatically updated, including dimensions, without you having to do anything, and thus the "parametric" feature of 3D modeling.

I started drafting pencil on vellum in about 1978, and created hand drawn engineering drawings pencil and ink on vellum for four years, before the advent of the IBM PC and CAD programs.

Learning CAD was a bit of a shock, but was pretty similar to pencil and vellum drawing.

Learning 3D modeling was a whole new mind twist, and that took a while to get my head wrapped around the concepts required to make a 3D model, since it is so different in many ways to the old pencil and paper approach.

I have never used constraints on any engine I have modeled.
I am told I MUST have constraints, but I don't use them, and have never had a use for them.

.
 
Here is an engine that was developed from three photos of an old engine from England.
I modeled one part at a time, assembled the parts, 3D printed patterns, cast the engine, machined and assembled it.

Did not use constraints on any of it.

6in-Grn-Twin-Flywheel-11.jpg
Crank-Arm-04.jpg
Crank-Arm-Pin-02.jpg
CylinderHead-UpperR2-01.jpg
CylinderHead-UpperR2-03.jpg
Outer-Support-01.jpg
Outer-Support-02.jpg
Piston-01.jpg
Piston-Rod-02.jpg
Quarter-Bolt-01.jpg
 
Assembly of all the parts.

If the parts are assembled correctly, with no conflicts, you can run the engine in simulation, and watch all the pieces move.
If the engine won't run in simulation, it won't run in real life either.



Final-Assembly-Rev2-01.jpg
 
I am trying to learn Alibre and you are correct. It is a completely different concept from 2D. I am working on a crankshaft because it looked rather straightforward. I can draw the cheeks (throw?) and extrude the shaft out one side. I thought that since it would be symmetrical I should just be able to mirror that and have the complete part. There is a mirror command but it certainly not working the way I expected it to. In my 2D cad I can select parts or features and then pick an axis to mirror the parts. Not in Alibre apparently.

I have tried looking at YouTube videos but I certainly cannot follow what they are doing. They click here and here and here and enter a value and everything happens the way they expected it to. The problem is that I have no idea what and where here and here are. Most of the videos are moving too fast and without showing the steps so I have no idea how that happened. I have looked at a few territorials and that tells me how to make some simple part but does not get into the details and next steps.

As GreenTwin states you can make the parts and then insert them into an assembly but without some type of overall assembly how do I know what the crankshaft should look like?

Sorry to be so dumb but the whole concept is just completely beyond my experience.
 
I am trying to learn Alibre and you are correct. It is a completely different concept from 2D. I am working on a crankshaft because it looked rather straightforward. I can draw the cheeks (throw?) and extrude the shaft out one side. I thought that since it would be symmetrical I should just be able to mirror that and have the complete part. There is a mirror command but it certainly not working the way I expected it to. In my 2D cad I can select parts or features and then pick an axis to mirror the parts. Not in Alibre apparently.

I have tried looking at YouTube videos but I certainly cannot follow what they are doing. They click here and here and here and enter a value and everything happens the way they expected it to. The problem is that I have no idea what and where here and here are. Most of the videos are moving too fast and without showing the steps so I have no idea how that happened. I have looked at a few territorials and that tells me how to make some simple part but does not get into the details and next steps.

As GreenTwin states you can make the parts and then insert them into an assembly but without some type of overall assembly how do I know what the crankshaft should look like?

Sorry to be so dumb but the whole concept is just completely beyond my experience.

I was in your same position just a few years ago.
I wanted to build an engine, and had no clue how to design an engine, or how to create 3D models for it.
I had never used 3D modeling.
Been there, done that, and yes the tutorials are not very good when trying to learn the basics.
For me, getting a grasp of the fundamentals of 3D modeling was the most difficult.
I really had no idea where or how to start.

There is a mirror command in 3D programs (I use Solidworks, but I know others have this feature).

And I often mirror things across a plane.

You have the three planes, X, Y and Z, and you can mirror across any of them.

For engine designs, I start inside the engine, with the piston, and work out.
Once the piston dimensions are selected (make it any size you want), then the bore has to match, and the crankshaft has to be on the bore centerline.

I generally use some existing engine as a go-by to get rough dimensions of flywheel, crankshaft diameter, etc.

When you get good, you will know about what size things need to be for a model.

.
 
I have designed and built 20+ engines and also built engines from plans by others. I have no problem with making 2D drawings and I usually make my own 2D drawings even of the engines designed by others because that clarifies the design in my mind and I can make changes to fit my equipment and available material. I could make a 2D assembly using top, front end views etc but the idea was to generate a 3D assembly to check the operation and then make the 2D drawings for actual machining.
 
I tell people it is like the PlayDoo machine.

Create one sketch at a time, extrude or cut that shape, and repeat until the part is a complete 3D model.

Extruder-01.jpg
 
Here are some sketches I did to show the differences between a 2D approach and a 3D approach.

For 2D, all of the drawing views are taken from the actual engine, or from the design you come up with.
Changing any dimension in any view does not affect any other dimension, and this causes terrible problems (at least it did for me).

SW-Overview-2D-01.plt.jpg
 

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