3D cad design sequence

[GreenTwin]

Doing 2D CAD is like driving a car.
You go straight, or left, or right.

Doing 3D modeling is like flying an airplane.
You can go anywhere, in any direction, and so you really have to know where you want to go, else you just crash a lot.

The power of 3D modeling is truly phenomenal though.

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[GreenTwin]

I am sure that my biggest problem is that I am used to 2D and I am having a problem trying to adapt to a different way of doing things. Even the mouse buttons do not work the way I am used to.

I am trying to work on a V twin which I obtained PDF drawings for from another forum. I drew them in my 2D cad because that gives me a better understanding of function and fit etc so I know what I am aiming for. I am having a problem with having my sketch fully defined and that means that I cannot go to the model to extrude , copy etc. I do some operation and the next time it does not work. I have watched some YouTube videos but it is hard to follow them because something happens and I am left wondering how did that happen?

I think what you are talking about is not having a closed sketch.

I never fully define any sketch, and you can see what sort of modeling I do.

I remember that having open sketches was a big problem for me in the beginning.

That is why when I sketch, I let the lines overlap, and then trim them off.
Trimming solves most open sketch problems.

The other problem I had was having stray lines in a sketch.
You have to think of a sketch as a continuous loop of rope.
You can bent, stretch, or manipulate the loop of rope any way you want, as long as it does not overlap, but don't draw a line across it.
You must think in terms of a continuous loop of rope when you make a sketch that you intend to extrude.

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[johnmcc69]

https://www.homemodelenginemachinist.com/members/greentwin.45737/
I haven't used SolidWorks in a long time, so I don't know how that works. But your method works.

In Pro-E, I can create "Family Tables", for instance that's how I create all my fasteners. I have one file for say a 1/4" SHCS. when I assemble it to my project, it will "ask" me what size I want. I can easily "Table" (& edit) these sizes in XLS. Changing the size is a piece of cake. & it all comes through to my BOM. If I want to change the size, I can replace ALL of the ones I don't want.

John

 

[Gordon]

For some reason I am having a problem with just getting back to my defined sketch. I spent a lot of time this afternoon just trying to get a circular array of holes. Still not sure of what I am missing. I did it yesterday and it worked but not working today. I am at the point that I can do a five minute sketch in two hours.

 

[johnmcc69]

Gordon, you don't need to put the holes in your original sketch. close & finish that sketch . There should be a "hole" command you can use to put the first hole in, (You may need to select the CL axis) you should have options for linear & radially (ETC.) where you just need to enter no. of holes & and angular separation of holes. try doing that & After you get the first hole, close that command., you should be able to select it with the right mouse button & select "pattern".

John

 

[GreenTwin]

Another thing that confused me to no end was having to jump onto a plane, do a sketch, and then jump off that plane back into what I call 3D space.

In AutoCad, I was use to jumping between model space and paper space, but in AutoCad you are basically always on this flat X-Y plane.

In 3D modeling, you can get onto any one of the three basic planes, X, Y, Z, or you can create a new plane in any position anywhere, and start a sketch on your new plane.

One I figured out how to accurately insert planes in 3D modeling, I was finally able to do some serious modeling.
Until then, I was just floundering around, trying stuff and praying something would work like it was suppose to.

You sort of have to "get religion" when you are learning 3D modeling, and it takes a while.
Lots of new synapses connections in the brain have to be made, and you have to begin to "think 3D", and get away from the flat earth society.

I was overwhelmed by the options at first.
My brother made the comment (when looking at my 3D models) that it all looked terribly complicated, and I told him it was totally confusing in the beginning, but untimately you end up using about 10 commands most of the time, over and over again.

It is basically pick a plane, make a sketch, extrude a shape, pick another plane or surface, make another sketch, extrude or cut a shape, pick or create another plane, maybe mirror some stuff, etc.

As someone mentioned, it is very much like machining a part from a solid block of material.
You add or subtract, carving or building up, until you have a part (a 3D model).

Its the same few commands over and over.

I look back on learning 3D modeling, and I say "It is really quite a simple process with very few commands, but it did not seem that way at first".


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[GreenTwin]

For some reason I am having a problem with just getting back to my defined sketch. I spent a lot of time this afternoon just trying to get a circular array of holes. Still not sure of what I am missing. I did it yesterday and it worked but not working today. I am at the point that I can do a five minute sketch in two hours.

Every step of building a 3D model has a sketch associated with it.
In Solidworks, the steps are listed in the dialog box on the left of the screen.

If I hover over a particular piece of the 3D model with the mouse, the associated step in the dialog box lights up.
I can open the sketch for any step with a right-click on that step.

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[Richard Hed]

I am sure that my biggest problem is that I am used to 2D and I am having a problem trying to adapt to a different way of doing things. Even the mouse buttons do not work the way I am used to.

I am trying to work on a V twin which I obtained PDF drawings for from another forum. I drew them in my 2D cad because that gives me a better understanding of function and fit etc so I know what I am aiming for. I am having a problem with having my sketch fully defined and that means that I cannot go to the model to extrude , copy etc. I do some operation and the next time it does not work. I have watched some YouTube videos but it is hard to follow them because something happens and I am left wondering how did that happen?

I'm wondering if you are having overlapping lines, or possibly truncated lines without knowing it. If there are overlapped lines, even a millionth of an inch, it will not extrude. It has to be trimmed or extended. It took me a long time to figure out why some of mystuff would not extrude, but that was the reason at least some time.

I'm also wondering if yuou are trying to do too much with one try. You should make all your parts out of simple nd small steps. If hyou can show us part of what you are doing, maybe we can help.

 

[Richard Hed]

Another thing that confused me to no end was having to jump onto a plane, do a sketch, and then jump off that plane back into what I call 3D space.

In AutoCad, I was use to jumping between model space and paper space, but in AutoCad you are basically always on this flat X-Y plane.

In 3D modeling, you can get onto any one of the three basic planes, X, Y, Z, or you can create a new plane in any position anywhere, and start a sketch on your new plane.

One I figured out how to accurately insert planes in 3D modeling, I was finally able to do some serious modeling.
Until then, I was just floundering around, trying stuff and praying something would work like it was suppose to.

You sort of have to "get religion" when you are learning 3D modeling, and it takes a while.
Lots of new synapses connections in the brain have to be made, and you have to begin to "think 3D", and get away from the flat earth society.

I was overwhelmed by the options at first.
My brother made the comment (when looking at my 3D models) that it all looked terribly complicated, and I told him it was totally confusing in the beginning, but untimately you end up using about 10 commands most of the time, over and over again.

It is basically pick a plane, make a sketch, extrude a shape, pick another plane or surface, make another sketch, extrude or cut a shape, pick or create another plane, maybe mirror some stuff, etc.

As someone mentioned, it is very much like machining a part from a solid block of material.
You add or subtract, carving or building up, until you have a part (a 3D model).

Its the same few commands over and over.

I look back on learning 3D modeling, and I say "It is really quite a simple process with very few commands, but it did not seem that way at first".


.

Yes, and ultimately, once you understand your program, it IS ACTUALLY EASIER than any 2D program I know. And also, once you "get it", you wonder why there ever was a problem to begin with LOL.

 

[Richard Hed]

I think what you are talking about is not having a closed sketch.

I never fully define any sketch, and you can see what sort of modeling I do.

I remember that having open sketches was a big problem for me in the beginning.

That is why when I sketch, I let the lines overlap, and then trim them off.
Trimming solves most open sketch problems.

The other problem I had was having stray lines in a sketch.
You have to think of a sketch as a continuous loop of rope.
You can bent, stretch, or manipulate the loop of rope any way you want, as long as it does not overlap, but don't draw a line across it.
You must think in terms of a continuous loop of rope when you make a sketch that you intend to extrude.

.

Ah ah ah, that's it, a closed sketch, or one in which the lines overlap--what's that called?

 

[Bentwings]

i used the same thing when building automated assemble machines that had multiple stations just suppress what’s in the way and add new as needed the issue that came up was who had access to what this lead to Blythe allowing duplicated or modified parts and giving them new names at first it was hard to govern But when a few mistakes were made snd it was shown how to take Ossetian of copied or modified parts it then went pretty smooth we did five large automotive assembly lines using countless stations at meeting we just assigned unique names to stations There were so many stations that naming conventions became issues in them selves one station might have parts from many station that only had small modifications It was important that if a master station was changed that all changes to make it a new station were incorporated a major change to the master could affect everyone on the line so it was important to check your model everytimevyoubworked on it fortunately the software was pretty good at notifying you of changes the more integrated the main model became the more vigilant you had to be on your model for example there might bu be a half of a hole blending in with a hole in your station often you could jut call the owner and ask how to deal with it it might be oh yeah I’ll just move the hole over , will that be ok ? That’s why you had to check for changes I YHINK it was called data management or something like that when you are working on a 100 station machine with 30 or 40 people also working on it things got complicated in a hurry When a major change came the proposed unit was temporally inserted to see what effects it had

The engine manufacturing line I worked on was probably a classic it was changed from v8 to v6 I don’t remember how many million that one cost all of the tooling had to be removable or inter changeable The amount of inspection items was a book in itself


Getting way over head here do I back out for now

Please keep up with the latest cad ideas I’ve been away from it for just long enough to see that there are new things I need to learn so I’m going to center in that for a while

By.ron
I think John is saying this in his post above, but he brings up a good point that I had forgotten.

The question was asked "How do I design the engine so that all the parts will fit?".

I sketch the first part, and then I can copy that sketch, and start a second sketch and part, and like John said I can use the same hole pattern or shaft size and sketch to begin a new part, and so I know the parts will fit because they originate from the same sketch.

Another trick I have discovered is if two parts are very similar, then save Part 1 and Part 2, and then suppress some pieces of Part 1 to create Part 2.
No need to actually create Part 2, just supress a few things and leave it like that.

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[Bentwings]

there was a course plus a nice book called geometric tolerance for engineers and machinists I’d guess it’s available on the inter net now this covered bolt holes and fasteners then got into thing much more complicated I’d also guess you can find some calcularorscthatvyounonly have to plug features into . Most cad programs have interference checking so you basically model a part. If it goes in a hole you neither mak evthe part smaller or the hole larder you do this in your sketches
Doing 2D CAD is like driving a car.
You go straight, or left, or right. You can set any number of decimal places both English and metric . Your only real limit is how close the machines will machine to for 3 sprinting you may have to follow a guide or depend on the printing service It used to be that it was hard to get a large hole really round but with the advent of servo motors an encoders rather than stepper motors that’s pretty much a thing of the past unless someone used a small diameter tool to hog with our shop had onboard measuring so out of round holes just didn’t happen It’s really amazing the machine tool development the r and dept I worked in had precision laser welding done either in vacuum or inert gas

I don’t send many parts out now but if I do all I need is to send the file in the formate the place uses if there is any questions I just get an email or call

Doing 3D modeling is like flying an airplane.
You can go anywhere, in any direction, and so you really have to know where you want to go, else you just crash a lot.

The power of 3D modeling is truly phenomenal though.

.

 

[Jasonb]

Gordon, you can still extrude a non defined sketch.

More likely you have something out of place in the sketch, simple example would be 4 lines to form a square but they don't meet in one corner so the sketch is "open" you need to correct that gap to "close" the sketch

When you "deactivate" the sketch you will get a warning "status - sketch problem deleted" if you then click the "show me" tab it will list the problems which won't mean much to you at the moment.

Now click one of the items in that list and it will be highlighted on the sketch so you can see where to alter things. Sometimes the "Heal" tab darkens and you can use that but usually its a line crossing another or not quite reaching it.

 

[Jasonb]

As John says best to sketch the basic shape possibly a cylinder head or the cylinder in your case and extrude that.

Then start a new sketch either on a plane or a surface of the part. You can then either use the limited hole options in Atom or simply use the circle drawing tool to draw one hole. Extrude cut that. Then select circular pattern, click the hole as that is what you want for the pattern and then number of instances (6) click tab for equally around a point rather than along an arc and then click the ctr axis.

 

[Jasonb]

Gordon Why not start a thread on "designing an engine with Alibre" or some such title, put a link to the engine plans you are drawing and suggest a couple of parts you would like to see drawn preferably not starting with the crankcase!

Your questions are getting somewhat lost in general discussions about CAD use

 

[ajoeiam]

Hmmmmmmm - - - - someone (its not clear who) wrote that "parametric design has 'improved things".

I would posit exactly the opposite.
Having this supposed error proof method is what has cars that need an engine removed to change spark plugs, has 'features' on other engines which mean that I need to have hands that are about the size of a 4 year old's to get at things and a lot more other things I could mention. What we have lost is the hands on knowledge gained by physically doing the stuff. The software says things are great - - - - well its a classic GIGO routine - - - the assumptions written into the software say its ok but - - - in the real world - - - - those assumptions are pure deluxe 'garbage'.
Even better is when the errors are pointed out the amount of time used on justification far exceeds the original work - - - - sometimes by a factor of 10 or more.
I am of the opinion that a lot of our tools today are not near as useful as the are purported to be.

(Reminded of when I looked at a turret lathe that was for sale fairly reasonably. The sales guy told me that the company had replaced the machine with a cnc after the old timer that ran it for a very long time retired - - - - he told me that the company hadn't been able to get the cnc to even equal the productivity of the very very old iron - - - - but that was likely because they had a hugely skilled and quick old timer and they bought a mid road cnc and maybe a top end cnc would have improved things but its the HAND skills (includes knowing how to use equipment) their people have that makes a difference - - - - not their 'paper' skills.)

 

[Richard Hed]

As John says best to sketch the basic shape possibly a cylinder head or the cylinder in your case and extrude that.

Then start a new sketch either on a plane or a surface of the part. You can then either use the limited hole options in Atom or simply use the circle drawing tool to draw one hole. Extrude cut that. Then select circular pattern, click the hole as that is what you want for the pattern and then number of instances (6) click tab for equally around a point rather than along an arc and then click the ctr axis.

Where is this "limited hole option" ? I would like to use it but I have never seen it.

 

[Jasonb]

I did not go and look at Atom 3D when I wrote that reply but actually I don't think it has a hole option at all. So you just need to sketch a circle and cut extrude that.

 

[awake]

Every step of building a 3D model has a sketch associated with it.

That may be true for some 3d CAD programs ... but there are others that work, not from extruded sketches, but rather from geometric primitive solids (cubes, spheres, etc.), which are then combined / cut / differenced / etc. This approach is called CSG (constructive solid geometry). An old, old, old CAD program with this approach is BRL-CAD, which was developed by the army (? I think?) to model ballistic data - I believe the BRL stands for Ballistic Research Lab, but I am going on fuzzy memory, so take that with a grain of salt. It is (or at least was) hard to use, but immensely powerful. It has undergone development since the last time I used it, so may be easier now, but one of the challenges (which also comes with certain advantages) is that it is a programmatic approach rather than a WYSIWYG - you give it a set of instructions to follow, and it generates the resulting shapes, rather than drawing and manipulating things on the screen.

OpenSCAD is a more recent but more limited program that also primarily depends on CSG. You *can* generate or import a 2d sketch, and then extrude it, but in general this is not the primary approach.

FreeCAD actually includes BOTH approaches. You can work entirely or primarily from sketches that are extruded in various ways and on various planes, or you can work entirely or primarily from primitive solids which you then combine / cut / subtract / etc. And the really nice thing is, you can mix these approaches as needed.

Hmmmmmmm - - - - someone (its not clear who) wrote that "parametric design has 'improved things".

I would posit exactly the opposite.
Having this supposed error proof method is what has cars that need an engine removed to change spark plugs, has 'features' on other engines which mean that I need to have hands that are about the size of a 4 year old's to get at things and a lot more other things I could mention. What we have lost is the hands on knowledge gained by physically doing the stuff. The software says things are great - - - - well its a classic GIGO routine - - - the assumptions written into the software say its ok but - - - in the real world - - - - those assumptions are pure deluxe 'garbage'.
Even better is when the errors are pointed out the amount of time used on justification far exceeds the original work - - - - sometimes by a factor of 10 or more.
I am of the opinion that a lot of our tools today are not near as useful as the are purported to be.

I would say that this is a result, not of parametric design in particular, but rather of CAD in general. Parametric design simply makes it easier to change dimensions without having to go back through the entire design process ... but typically it is not used to change the position of things.

 

[Gordon]

OK A question for Alibre users. I have worked on two part sketches. I have extruded them and one is complete and the other is partial. I cannot figure out how to get back to my original basic sketch. The original sketch was fully defined and turned black so I extruded it and added features and extruded them etc. Now I cannot find a way to get back to the original sketch. There is nothing shown in the tree view which brings me back to the original basic sketch. I can get the individual later extrusions witch are things like a single circle which I extruded but what happens if I want to change something on the original basic sketch? Suppose that I wanted to make it bigger or just modify a chamfer or a fillet.