3D cad design sequence

[GreenTwin]

When you go to a 3D model, you are creating one 3D part at a time, assembling them into an overall assembly, creating exploded and isometric views, perhaps a bill of material, and run a motion study to see if the assembly fits correctly at all the joints.

2D drawings are created by dragging and dropping 3D models on a sheet, and then dragging out each view.

Once you have the models, assembly, and 2D drawings complete, then any change to any 3D part automatically propagates to the assembly, the exploded view, the bill of materials, the motion study, and the 2D drawings.
The dimensions in the 2D drawing automatically update to reflect the changes you made to the 3D model, in every view.

So basically everything is linked back to the models.
Like a spreadsheet with a forumula in it; changing another cell can change all the other cells automatically that are linked to it.
The links in 3D modeling are automatic, you don't have to set those up like a spreadsheet.

For 3D modeling, you have to get out of the 2D mindset, and that was what was so difficult for me.

 

[Jasonb]

Gordon. I design in Alibre.

I'll often do a rough 2D sketch first, if it is of an existing engine then I'll use a jpg. image of that in Alibres "trace" option and scale that to the size I want much like in pen and paper days you would draw a grid over a photo or blow it up on a photo copier. I tend to just grab sizes off the trace but sometimes use that to draw out the basic outline if it's a shapely part.

These dimensions can be rounded up or down to more sensible ones an added to my sketch

From that I'll pick a component to start modeling, in this case I started with the frame sketching various features and extruding them or cutting bits away to slowly build up the part, here you can see I have about 4 sketches base, top flange, webs, stiffening flanges and bearings added. I'll probably start assembling at this stage adding things like a cylinder, crankshaft and so on. It's easier to make alterations as the assembly comes together if the parts are not fully detailed.

As I go along I'll add the various holes and finally things like fillets and end up with a finished part like this

I like to make use of teh "Section view" on the assembly as you can see things like if your piston is going to hit the end of the cylinder as you rotate the crankshaft around on screen by dragging it with the mouse. I;ll flit back and forth between assembly and parts tweaking their sizes until I'm happy.

For my own use I don't often produce proper 2D working drawings from the Model, I tend to just pull dimensions off the 3D parts onto a scrap sketch and make from those. If it's one being published or given freely then I'll produce a set a 2D ones to use.

 

[GreenTwin]

When making 2D drawings from 3D models, you can drag each individual model onto its own sheet, and the drag out the respective views, or you can drag an entire assembly onto a 2D sheet, and drag out various views on that too.

Edit:

I create 2D drawings in Solidworks for each part and desired view, and then export that to an Autocad .DWG files, and import the sketches into Autocad, since I can work infinitely faster in Autocad 2D than I can in Solidworks 2D.

Be sure you wait until all the 3D modeling is complete before you pull 2D drawings into Autocad (if you do this), because you lose the link to the models, and so any changes to the 3D models will not automatically update in your Autocad 2D drawings.

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[Jasonb]

You can't drag with Alibre but you just select the part(s) or assembly you want to produce the 2D drawings of. You can add additional parts to the same sheet which I often do if they are small as you can fit a few to each sheet.

One good reason for using a single program if you can is that any alteration will show on the part, assemblies it is in and any 2D drawing of it. As PAT says when you move something from one program to another you will have to start again if you alter it or use the second program to do the alterations.

 

[Gordon]

GreenTwin and JasonB: You basically are starting from an assembly (picture) and then creating parts from that. I think that the best approach for me would be like Jason says to make at least a rough 2D assembly drawing since I am not usually trying to copy an existing engine. Perhaps I should explore making 2D drawings with my 2D program and then importing them into Alibre. The ideal would be if I could operate like in my 2D program and select parts and copy them to the clipboard and then paste them to the new drawing. I am having a lot of problems with expecting the 3D program to do things that I do all of the time in 2D.

 

[Jasonb]

You could do it all in alibre sketching say a basic side elevation. If you build up the general arrangement from a series of sketches rather than just one then it's easy to copy and past into a new part file and then extrude to make it 3D and add in the details

 

[GreenTwin]

You could do it all in alibre sketching say a basic side elevation. If you build up the general arrangement from a series of sketches rather than just one then it's easy to copy and past into a new part file and then extrude to make it 3D and add in the details

You can do your sketching in either a program like Autocad, and then do a copy/paste to your 3D program, or you can do your sketching and 3D modeling all in your 3D program.

For me, trying to sketch in a 3D program is very counterproductive, and almost impossible, so I am the poster child for sketching in Autocad, and then doing a copy/paste to Solidworks.

Jason uses Alibre for everything.

I think it comes down to which method works best for you.

.

 

[GreenTwin]

Perhaps I should explore making 2D drawings with my 2D program and then importing them into Alibre.

Don't confuse drawings with sketches.

A "sketch" is the base shape that you create (like the PlayDoo die), and you use that shape to either extrude or cut into a 3 dimensional object.

A "drawing" is something you create using your 3D program, by dragging and dropping a 3D model onto a titleblock or border, or dragging an entire assembly onto a border.

Once you start using 3D modeling, you no longer create any drawings; the 3D program does that for you when you drag and drop models into a border.

If you want to change the drawings, you change the 3D model only, and those changes are automatically reflected in your drawings that you created in the 3D program, in every view (and thus the parametric or linked approach for 3D modeling).

The power of the parametrics of 3D modeling cannot be understated.
Parametrics is like the invention of the wheel, or the striking match; or the airplane; it changes the design process dramatically and forever, for the better.

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[HMEL]

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 think its necessary to reflect on what a drawing is for. Its primary purpose is to convey information to others. In that regard I have seen designs based on a restaurant napkin, sketches, 2d drawings, and 3d drawings. There are times when I use only a sketch pad for myself when I make something.

Modern use of digital drawings has progressed to the point that you can check for interference's, do heat and stress calculations, bill of materials and a host of other valuable information on a platform.

But all of this starts in your head and you choose the information and how you wish to display it.

I have given these techniques a name . I call it virtual engineering. It is the present and the future. But in all honesty the simple sketch is what I start with and in some of my notebooks all you will find is a sketch along with a description of how it is supposed to work.

Its not the drawing that is important its the idea you wish to convey. So use whatever method you want to do that. But remember whatever you choose it is to convey an idea and some are better then others. And often you are the one who the drawing is speaking to.

Take Care
HMEL

 

[kvom]

I don't design in 3D but rather convert 2D plans to 3D parts in order to check fits and dimensions, and then to output DXF files for CNC machining or STL files for 3D printing.

That said, there's something to be said for using this technique on an existing plan set in order to learn 3D CAD.

As for using constraints, in SolidWorks at least you'd get some implied. For example, if you draw a vertical line in a sketch it will have the vertical constraint automatically. But in general they are very useful in parameterizing a design so that modifying it is easier. One example might be a steam chest cover. If you apply the equal constraint to all the holes, then it's easy to change all their diameters by modifying one.

 

[GreenTwin]

One example might be a steam chest cover. If you apply the equal constraint to all the holes, then it's easy to change all their diameters by modifying one.

That is a really good example of how constraints can be useful.
Thanks for that.

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[petertha]

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.

Maybe just to expand on this a bit.

SW may run in motion simulation or make a nice movie, but it has no concept of physical surface conflicts unless you toggle on diagnostic evaluation modes (interference, collision detecting..) in conjunction with specific parts of interest. For example SW will happily allow a 0.5" diameter shaft to spin in a 0.4" hole because the only instructions provided in an assembly is mate them concentrically. But of course that doesn't work in real life... without a big hammer & lots of grease LOL

The reason why you typically select specific parts or features for interference vs going auto-pilot mode of all parts is it will dutifully complain about everything it finds - fasteners in holes, a lid sitting flush on a box... things that are understood to be contacting/somewhat interfering, but are of no consequence. So you can selectively pick & choose. This can chews on processing btw depending on part complexity & motion range.

However the point is diagnostics in 3D modelling is super powerful. You can have it paint the the conflicting surfaces a different color to highlight, make an audible ping & stop at the conflict position... things like that. This is where the computer & software earn their pay, very difficult to 'visualize' things like this with hundreds of parts mated together in different orientations & degrees of motion. And better than machining parts that go clunk in real world assembly

 

[petertha]

very nice molds & castings btw @GreenTwin

 

[GreenTwin]

Thanks much.
I was very lucky to have a local art-iron foundry teach me how to do that.

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[GreenTwin]

Maybe just to expand on this a bit.

SW may run in motion simulation or make a nice movie, but it has no concept of physical surface conflicts unless you toggle on diagnostic evaluation modes (interference, collision detecting..) in conjunction with specific parts of interest. For example SW will happily allow a 0.5" diameter shaft to spin in a 0.4" hole because the only instructions provided in an assembly is mate them concentrically. But of course that doesn't work in real life... without a big hammer & lots of grease LOL

The reason why you typically select specific parts or features for interference vs going auto-pilot mode of all parts is it will dutifully complain about everything it finds - fasteners in holes, a lid sitting flush on a box... things that are understood to be contacting/somewhat interfering, but are of no consequence. So you can selectively pick & choose. This can chews on processing btw depending on part complexity & motion range.

However the point is diagnostics in 3D modelling is super powerful. You can have it paint the the conflicting surfaces a different color to highlight, make an audible ping & stop at the conflict position... things like that. This is where the computer & software earn their pay, very difficult to 'visualize' things like this with hundreds of parts mated together in different orientations & degrees of motion. And better than machining parts that go clunk in real world assembly

I recall creating the assembly on the green twin, and it would not run in simulation, and would not rotate using the mouse.
I can't recall exactly why this occurred; whether it was a mating problem, or dimensional problem (I think it may have been a mating problem).
I was learning 3D and simulation while using it for the green twin, so I was not really up on how it all worked, and am still a bit hazy.

I remember having to start the simulation assembly all over again, and this time I rotated each piece with the mouse as I mated it, to make sure things would move.
Sometimes I would add and mate a part, and the assembly would lock up, so I knew that mate or dimension was not correct.

The simulation tool is extremely powerful.
The translucent cylinder wall and steam chest wall (allows you to see inside the engine) are also extremely useful to make sure your piston and valve travel are equal.

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[Gordon]

The more I work with Alibre the more confused I get. I managed to actually make a part but I had a drawing that I was copying from so there was no real design by me. Once I was done with that I thought that I would see about importing a DXF drawing and try creating a part from that. I could import the DXF and select the items. Then the instructions say copy to the clipboard. Then start a new drawing and paste the copied items. Nothing happens. I have looked at the help file several times and I certainly seem to be following the instruction.

I still am confused on how to actually start a new design. I can see creating individual parts but without an overall assembly I have no idea what those parts are going to fit. I can draw a crankshaft and a connecting rod etc. but I have no idea if that is going to even fit in the final design. It looks like my best bet is to produce a 2D drawing and then import individual items into Alibre. No working. See above. About ready to give up on this again.

 

[petertha]

I recall creating the assembly on the green twin, and it would not run in simulation, and would not rotate using the mouse.

Hard to say but likely a mating issue. Mating to parts is analogous to constraints in sketches (sorry about that haha). But kind of with a twist. It is possible to over or under-define mates in assemblies. Both are legal as kind of a static model, but when it comes to motion, certain combinations of mates may need to be turned on/off. There's a couple techniques depending on complexity & desired result, but usually configurations are a good starting point. Think of them as a copy of the model but you can selectively turn on/off mates (or even parts for that matter) & that logic sticks with the configuration.

 

[kuhncw]

Don't give up Gordon.

As you said, creating individual parts without an idea of what the assembly is going to be doesn't work well. Yesterday, Jason gave a good description of the design process for an engine or other assembly. He drew a pencil sketch showing centerlines, diameters, heights from the base, etc which gives a picture of where the design is headed. You could call this a layout sketch or drawing. Sometimes I do the layout step with paper and pencil but more often I use my 2D Visual Cadd to layout crank and cam centers, base to top of the block distance, con rod centers, cylinder bore, valve centers, ports, etc. Usually this is a cross section view. Once I've got a picture of where I'm going and I'm happy with how the proportions look, then I'm ready to design the individual parts in 3D and modify them as needed as things progress.

I don't import my 2D layout parts into the 3D software as usually my 2D layout parts are pretty simplified. The 2D layout may just show the con rod as a line from the crank pin to the piston pin. That is my approach and it reminds me of the drawing board days when we had layout drawings followed by more detailed drawings of individual components and finally detailed production drawings.

Keep at this and you'll get there.

Regards,

Chuck

 

[Richard Hed]

The more I work with Alibre the more confused I get. I managed to actually make a part but I had a drawing that I was copying from so there was no real design by me. Once I was done with that I thought that I would see about importing a DXF drawing and try creating a part from that. I could import the DXF and select the items. Then the instructions say copy to the clipboard. Then start a new drawing and paste the copied items. Nothing happens. I have looked at the help file several times and I certainly seem to be following the instruction.

I still am confused on how to actually start a new design. I can see creating individual parts but without an overall assembly I have no idea what those parts are going to fit. I can draw a crankshaft and a connecting rod etc. but I have no idea if that is going to even fit in the final design. It looks like my best bet is to produce a 2D drawing and then import individual items into Alibre. No working. See above. About ready to give up on this again.

That's right. Don't give up. You can change an already finished drawing so if it has been extruded tothe wrong size, you can change it. I gave up once but after a couple months, tried again, found it very confuzing but managed to continue until I begain to get how it works. I make a lot of use of editing, both edit sketch and edit extrusion. I was really surprized by the video someone placed on HMEM yesterday--I didn't have a clue that one could do the magic that was in that vid.

I make new drawings ffrom my old ones, I don't bother with importing. It is easier just to make new drawings plus I get the practice in Alibre.

 

[GreenTwin]

The more I work with Alibre the more confused I get. I managed to actually make a part but I had a drawing that I was copying from so there was no real design by me. Once I was done with that I thought that I would see about importing a DXF drawing and try creating a part from that. I could import the DXF and select the items. Then the instructions say copy to the clipboard. Then start a new drawing and paste the copied items. Nothing happens. I have looked at the help file several times and I certainly seem to be following the instruction.

I still am confused on how to actually start a new design. I can see creating individual parts but without an overall assembly I have no idea what those parts are going to fit. I can draw a crankshaft and a connecting rod etc. but I have no idea if that is going to even fit in the final design. It looks like my best bet is to produce a 2D drawing and then import individual items into Alibre. No working. See above. About ready to give up on this again.

I gave up on learning 3D modeling many times over a year period.
Learning 3D was very confusing for me, coming after so many years of 2D work.
I "gave up" perhaps 10 times, and swore I would never be able to learn 3D.

But like carving a statue out of a block of marble, you take a few tiny chips every day, and one day a light goes on in your head, and you say "I got this".

If you are going to learn 3D, you have to have reasonable expectations.
I think many struggle at the beginning with trying to understand the fundamental concepts; I know I did.

Keep at it, you will get it.
You have some really good 3D people here that can support you.

Pat J