CAD /Autocad Help

[Zeb]

This thread is becoming epic.

Warbird drawings were pretty bad (and gorgeous..to me). The machinist has to guess as to the enginerd's intent when choosing between two weevils as the ordinates start stacking and the part grows an inch longer than overall.

Old ASME 14.5 had you jumping through all sort of hoops for profile tolerancing. Nowadays you can dial a "grade A" surface (Alias, Rhino 3D) and verify with a FARO. Assembly "in context" work and revision management destroys paper any day. However, I admire the old hats who can sliderule, and I study books on the art. Always nice though to be able to sculpt and print without ever creating a single dimension.

Drafting is a lot easier now than it used to be, and it is also different in terms of the job description. It is a lot more about knowing the software and how to rescue an exploding assembly when the enginerd micro-machines a slivered block in 60 operations....when it could have been done in three.

At the end though, I do like to own my tools. My G'pa's drafting set, Zbrush, Blender, Alibre, all sit there ready to go.

 

[SmithDoor]

This thread is becoming epic.

Warbird drawings were pretty bad (and gorgeous..to me). The machinist has to guess as to the enginerd's intent when choosing between two weevils as the ordinates start stacking and the part grows an inch longer than overall.

Old ASME 14.5 had you jumping through all sort of hoops for profile tolerancing. Nowadays you can dial a "grade A" surface (Alias, Rhino 3D) and verify with a FARO. Assembly "in context" work and revision management destroys paper any day. However, I admire the old hats who can sliderule, and I study books on the art. Always nice though to be able to sculpt and print without ever creating a single dimension.

Drafting is a lot easier now than it used to be, and it is also different in terms of the job description. It is a lot more about knowing the software and how to rescue an exploding assembly when the enginerd micro-machines a slivered block in 60 operations....when it could have been done in three.

At the end though, I do like to own my tools. My G'pa's drafting set, Zbrush, Blender, Alibre, all sit there ready to go.

I learned drafting when building model planes around 1966. Then I in took high school .
Next was buying TurboCAD & Autocad 95 and came they with a training cds .

None of hard even 3D. I found 2D work better and faster for most of my work. The graphics is better on 3D.

Dave

 

[Richard Hed]

There may be an inverse relationship between these two quotes - I have heard it said that one of the hardest things about learning 3d CAD is unlearning 2d. Don't know if that is true, but in my own experience I would at least say that my 2d skills certainly did not help in learning 3d. The first steep climb in the learning curve was getting a handle on how to think 3d modeling, and it is almost entirely different than how I approach 2d drafting. In fact, I just realized as I wrote that sentence that two key words describe the difference for me: 3d is modelling, while 2d is drafting. Not sure that makes sense to anyone else; might just be evidence of my disturbed mind ...

What you said makes sense. However, I thimkpfs that 3D was easier to learn than 2D

 

[RM-MN]

I've had to disassemble a transmission to replace bearings and then use the exploded 2D drawings to try to fit it back together when the parts finally arrived. I could have done it much faster had I had a 3D model on the computer showing where the pieces fit and the ability to rotate the model to show their relationship. I've done a little drafting and a little 3D modeling and from my perspective, 3D is the way to go. Take a complex system and be able to see how the pieces will fit together, change one dimension as the fitment wasn't working out and instead of redrawing everything on paper, the parametric model adjusts all related parts. Those of you who cling to your 2D drawings need to come out of the 18th century.

 

[Klrskies]

I started out on a drafting machine in the 70's ... a big step up from a T Square. I still enjoy drawing sketching and using Trigonometry to design by hand. Part designs back then were simpler and more buildable with just conventional machine tools. A part with complex, swept geometry required a 3D pattern to be developed from a pattern maker, then the pattern duplicated onto the workpiece with a Tracing Mill...a tedious, expensive process.
As computers began being used to develop part geometry and operate machine tools, complex parts were cut more economically and faster. Part design expanded dramatically, taking advantage of what was readily available. Now it's possible to extract 3d shaped and model into a cam system so quickly that CNC machinists don't think much about it But there is a degree of satisfaction in drawing in a simpler, more manual way, be it 2D Cad or with pencil and paper. Slowing down to consider the details is part of the enjoyment for me. I like to design/draw on my notebook while sitting in my recliner with a western on the TV. This supposed to be fun right?
regards,
Ken

 

[SmithDoor]

I've had to disassemble a transmission to replace bearings and then use the exploded 2D drawings to try to fit it back together when the parts finally arrived. I could have done it much faster had I had a 3D model on the computer showing where the pieces fit and the ability to rotate the model to show their relationship. I've done a little drafting and a little 3D modeling and from my perspective, 3D is the way to go. Take a complex system and be able to see how the pieces will fit together, change one dimension as the fitment wasn't working out and instead of redrawing everything on paper, the parametric model adjusts all related parts. Those of you who cling to your 2D drawings need to come out of the 18th century.

The 3D is a isometric drawing.
I do not see that type any more.

3D has it's place which on a done drafting board too.

Dave

 

[awake]

Who makes blocks?

I do agree for some types of work the 3D great .
But 3D drawings are over use today . The draftsman of today need more 2D drawing training.
Today they call a draftsman a engineer they can do any calculations unless show them how to plug the numbers in.

Dave

Dave, I'm not sure if this is the same thing that you are saying - but I would absolutely agree that when it comes time to build something, I don't use the pretty 3d model; instead I need a 2d plan printed out. (This is for manual machining - if it were CNC, that would be another matter!)

Once upon a time, that meant that I would model something in 3d CAD, then crank up my 2d CAD program to generate the drawings so that I could build it. These days, it is easy to turn the 3d model directly into a set of 2d drawings, from any side or angle desired. As a result, I hardly ever pull out the 2d CAD program any more. Once in a while there is something that is easier to solve using the 2d tools; that is the only time I use it nowadays.

 

[SmithDoor]

Dave, I'm not sure if this is the same thing that you are saying - but I would absolutely agree that when it comes time to build something, I don't use the pretty 3d model; instead I need a 2d plan printed out. (This is for manual machining - if it were CNC, that would be another matter!)

Once upon a time, that meant that I would model something in 3d CAD, then crank up my 2d CAD program to generate the drawings so that I could build it. These days, it is easy to turn the 3d model directly into a set of 2d drawings, from any side or angle desired. As a result, I hardly ever pull out the 2d CAD program any more. Once in a while there is something that is easier to solve using the 2d tools; that is the only time I use it nowadays.

I did drafting work for 30 years with pencil ✏ and paper . Before CAD/Autocad so had to make the 3D on paper.
For some work like CNC 3D CAD is great.
But most work can easily be done with pencil and paper or 2D.

Dave

 

[Zeb]

I've had to disassemble a transmission to replace bearings and then use the exploded 2D drawings to try to fit it back together when the parts finally arrived. I could have done it much faster had I had a 3D model on the computer showing where the pieces fit and the ability to rotate the model to show their relationship. I've done a little drafting and a little 3D modeling and from my perspective, 3D is the way to go. Take a complex system and be able to see how the pieces will fit together, change one dimension as the fitment wasn't working out and instead of redrawing everything on paper, the parametric model adjusts all related parts. Those of you who cling to your 2D drawings need to come out of the 18th century.

A lot of places are moving that way. Check out this demo... Cortona3D Demonstrations Explorer (when opening a demo, click the sheet drop down in upper left).

Comes at an unattainable price.

 

[Ozwes007]

An unfortunate side effect of the newer 3D cad programs is the need for vastly expensive computers to run them on. An example is a basic AutoCad system these days requires a water cooled video card with memory and computing power that is top of the range. Even small to medium Engineering businesses are looking at cheaper alternatives because of these cost. Quite a few go for the Cheaper less bells and whistle programs and even the Free ones. The amount that use Freecad is astounding just in my small part of the world. And LibreCad is used quite extensively by waterjet and plasma cut users as they only use 2D drawings. It basically comes back to horses for courses. I haven’t used Autocad since 2008 version, and testing of units/components can be done in Fusion360 if needed. Jut my two cents.

 

[ajoeiam]

Dave, I'm not sure if this is the same thing that you are saying - but I would absolutely agree that when it comes time to build something, I don't use the pretty 3d model; instead I need a 2d plan printed out. (This is for manual machining - if it were CNC, that would be another matter!)

Once upon a time, that meant that I would model something in 3d CAD, then crank up my 2d CAD program to generate the drawings so that I could build it. These days, it is easy to turn the 3d model directly into a set of 2d drawings, from any side or angle desired. As a result, I hardly ever pull out the 2d CAD program any more. Once in a while there is something that is easier to solve using the 2d tools; that is the only time I use it nowadays.

Hmmmmmmmm - - - what I'm seeing is that using models rather than drawings has resulted in an increase of pieces that just don't work.

To explain - - - - when I look at 2D drawings its easy to see that the shaft MUST be +0.0000 and better -0.0005 to -0.0015 (even) and the mating part needs to be +0.0005 or better +0.0015 to +0.0010. You just can't assemble AND disassemble a tang and receiver without having at least 0.0010 if not better 0.0020 of dimensional difference between the two parts.
When you see it as part of a model - - - - its not as clear that there must be clearance- - - (why) - - because on paper any clearance works.
Using a model makes it far too easy to not understand that GD&T is crucial - - - but then real world experience (re: hands on creation) is becoming ever rarer and of course the model is 'always correct' (NOT!!).

 

[awake]

Hmmmmmmmm - - - what I'm seeing is that using models rather than drawings has resulted in an increase of pieces that just don't work.

To explain - - - - when I look at 2D drawings its easy to see that the shaft MUST be +0.0000 and better -0.0005 to -0.0015 (even) and the mating part needs to be +0.0005 or better +0.0015 to +0.0010. You just can't assemble AND disassemble a tang and receiver without having at least 0.0010 if not better 0.0020 of dimensional difference between the two parts.
When you see it as part of a model - - - - its not as clear that there must be clearance- - - (why) - - because on paper any clearance works.
Using a model makes it far too easy to not understand that GD&T is crucial - - - but then real world experience (re: hands on creation) is becoming ever rarer and of course the model is 'always correct' (NOT!!).

That's where the step of turning it into a drawing is vital, at least for me. I model the "ideal" part, as if there were no such things as tolerances; this lets me make sure everything fits together as intended. Then I use the model to generate drawings. When I put the dimensions on the drawings, I can put the tolerances for any given dimension.

That bit doesn't seem any different to me than 2d CAD - when I draw up a part in 2d CAD, I can't draw it plus-or-minus; I draw it to a particular size, and have to note the tolerance when I take the dimension.

To say it another way, the CAD tools do not (or rather, should not) take the place of understanding good design. We've all heard the stories of newbie engineers proudly showing their CAD drawing with clearance holes specified to 4 decimal places ...

 

[SmithDoor]

That's where the step of turning it into a drawing is vital, at least for me. I model the "ideal" part, as if there were no such things as tolerances; this lets me make sure everything fits together as intended. Then I use the model to generate drawings. When I put the dimensions on the drawings, I can put the tolerances for any given dimension.

That bit doesn't seem any different to me than 2d CAD - when I draw up a part in 2d CAD, I can't draw it plus-or-minus; I draw it to a particular size, and have to note the tolerance when I take the dimension.

To say it another way, the CAD tools do not (or rather, should not) take the place of understanding good design. We've all heard the stories of newbie engineers proudly showing their CAD drawing with clearance holes specified to 4 decimal places ...

Specified to 4 decimal is problem with CAD drawings. Like 9/16" or .5625. You round off to .56 . I just edit the dimension to 9/16" diameter.
Clearly is 9/16" diameter hole not 0.56"

Dave

 

[cds4byu]

I had a student this year put a clearance hole for a 7/16 inch bolt at 0.40 inches.

Oops!

Carl

 

[SmithDoor]

I had a student this year put a clearance hole for a 7/16 inch bolt at 0.40 inches.

Oops!

Carl

That would be a drive fit.
In old paper drawings you did not see mistakes like that.

Length of long parts are interesting. They put to 0.0001 of inch. Try holding that on 240" part. The part only need +- 1/2" to work. Typically is most shops hold to under +- 1/4"

Dave

 

[cds4byu]

And if you don't specify the temperature, you don't have a prayer of having a 240" part to even within .010, let alone .0001.

Carl

 

[cds4byu]

Actually, the 9/16 diameter hole probably doesn't have a 9/16 diameter (as measured with a true cylindrical go/no-go gage). So instead of putting a diameter, I usually just say to drill with 9/16 drill (or whichever size I prefer -- 9/16 is too small for a clearance hole on a 9/16 bolt).

Carl

 

[SmithDoor]

And if you don't specify the temperature, you don't have a prayer of having a 240" part to even within .010, let alone .0001.

Carl

I know
At best for most work is +- 1/32"

Drilling a 9/16" is +- 1/64"
Dave

 

[Ozwes007]

I’m not following you believe that a cad drawing and a paper draft drawing could be different if drawn to ISO specs. The dimensioning tolerances are expressed in the iso specifications on the drawing notation block. Unless other countries don’t use specifications on cad drawings, which by the way I have never seen. I have worked with American, Chinese, Taiwanese, German, Swiss, Indian and undoubtably others and the drawings all have the specifications drawn on them. There are differences from ISO to DIN and American drawings, however never have I seen a drawing in Cad or hand drafted(by a competent drafts person) that didn’t include all that was required to complete the job. I have definitely seen some pretty crappy drawings using relative instead of absolute dimensioning for production drawings, however they still contain the ISO specs.

 

[Zeb]

That's where the step of turning it into a drawing is vital, at least for me. I model the "ideal" part, as if there were no such things as tolerances; this lets me make sure everything fits together as intended. Then I use the model to generate drawings. When I put the dimensions on the drawings, I can put the tolerances for any given dimension.

That bit doesn't seem any different to me than 2d CAD - when I draw up a part in 2d CAD, I can't draw it plus-or-minus; I draw it to a particular size, and have to note the tolerance when I take the dimension.

To say it another way, the CAD tools do not (or rather, should not) take the place of understanding good design. We've all heard the stories of newbie engineers proudly showing their CAD drawing with clearance holes specified to 4 decimal places ...

Yes, my favorite is the concentric GD&T callout that makes the part 100X more expensive. My favorite callouts to bewilder inspectors are "use Ø3/8 drill bit".

It is true that engineers have gotten worse in terms of real world experience, but I think it's a symptom of a different problem. The same tolerancing data is transferred, but in a different way. A lot of 2d drawings I worked with from very talented drafters had all sorts of ordinate stacking errors along with missing constraints required for manufacture.

Here's an example of PMI. Tolerances are transferred down to the measurement inspection tools, so the job only needs to be done once. Just a different way to define tolerance (in 3D).


This spitfire drawing has several ordinate errors. A CAD workflow caught all of them, because it forced fully defined sketches. Production aircraft have even more deviations from the drawing. But yes, the drawing is glorious to look at, and who am I to judge when they were at war when they drew it? Still admirable, and still they won in the end.



*edit grammurly