CAD workflow best practices

[steven yampolsky]

I am a hack when it comes to CAD work and have never been taught proper workflow of drawing up a plan. Can anyone share their process/steps/workflow of drawing up a plan?

[Howard Rush]

It's not too important with CAD, is it?  You don't have a piece of paper that is too small or too large, and erasure isn't a problem.  Layers are useful, too.  You can put preliminary layout stuff on layers that you hide later once stuff gels.  I'm fiddling now with bellcrank size and location, and I have a layer for each candidate.   

[Chuck_Smith]

I'd say the bet practice is practice. Model plans are fairly easy, no real dimensioning or GD&T required. Howard's advice about layers is great, layers are your friends.

The best thing you can do when you start is first do your drawing frame. Draw it out with a title block, make sure you're really drawing full-size and your units are correct.

When in doubt, sketch it witf pencil and the just repeat with your CAD package.

Start in 2-D, and if you can go to 3-D modeling. Thats were CAD gets powerful. If you can get into 3-D you can even animate your controls. If you can model in 3-D you may just have a friend on the forum who can import the model into CFD and test fly it for you before you build it. I happen to know of one supercomputer that was used to test the effects of LEX's on stunt ships, he, he.

Learn how to do splines and polylines too. In the old AutoCAD methods and it's variants PLINE is you friend!

Good on you for learning! It's fun and you'll get good fast, so don't let the learning curve deter you. Warning, it can be addictive.

There are some fun programs that allow you to build a CAD airplane and then performance test it. Some college texts come with them.

Chuck

[proparc]

There is no real workflow with 2D CAD. It just about layer management. The more you break up your items with layers, the easier it is to draw and modify.

[Tim Wescott]

All that, plus this:

I use a 2-D CAD program that lets you group things by blocks, then work inside the blocks.

So I usually get a bare 3-view done, then put wings, stab, and fuselage each into their own block, then I go and fill in the inner structure.  Once I feel like I have the overall view correct, I'll rearrange the blocks in the top-level drawing so they'll print out as construction plans.

[Dennis Adamisin]

I am still at the contemplation stage.  Does anyone use any of the airfoil & wing design packages like CompFoil to design the wing then load that into a CAD file or is that a waste of time?

[proparc]

I am still at the contemplation stage.  Does anyone use any of the airfoil & wing design packages like CompFoil to design the wing then load that into a CAD file or is that a waste of time?

Those packages are good but, when you get to the level that myself and say, Pat Johnston operate at, we don't need no steeenking packages.   One thing I do strongly advise you to do is try to get to grips with something like Autocad LT.

You do not need a current version for our stuff. But you will be able to interface with pretty much the rest of the world once you do. The free equivalent of that is Draftsight. Start there.

The end of the road is pretty much Solidworks. This is serious pain,(trust me I know) but you are now operating in a world without limits.

[Howard Rush]

I am still at the contemplation stage.  Does anyone use any of the airfoil & wing design packages like CompFoil to design the wing then load that into a CAD file or is that a waste of time?

Folks do.  Rather than learn to use another program, I just do the airfoil calculations with Excel and load the upchuck into the CAD program as strings. 

Probably the place to start when confronting CAD is deciding what you plan to do with the output.  If you want to have parts cut by a laser or vinyl cutter, NC machined, or 3D printed, or if you want circuit boards made automatically, be sure your CAD program puts something out that that machinery can use.   Fortunately, the people I deal with who have those machines are patient.

 

[steven yampolsky]

Gents,

I can hack it in CAD. I've worked with AutoCAD, TurboCAD, SolidWorks and now DevCadPro but have NEVER been trained in using them or have formal drafting skills. I know how to draw a pline and how to connect lines, etc. What I am always struggling with is how to organize the process. Do I start with reference lines? Do I start with outlines? when do I add dimensions? How do you organize your drafting process?

[Bob Kruger]

Gents,

I can hack it in CAD. I've worked with AutoCAD, TurboCAD, SolidWorks and now DevCadPro but have NEVER been trained in using them or have formal drafting skills. I know how to draw a pline and how to connect lines, etc. What I am always struggling with is how to organize the process. Do I start with reference lines? Do I start with outlines? when do I add dimensions? How do you organize your drafting process?

Steve;

I can talk you through all of these with Autocad or any of the workalikes (BricsCAD, etc).  It would probably be easier just to talk you through it on the phone rather than try to describe it here.

A good foundation is to learn the Autocad commands and enter them in the command bar.  Drop down menus are nice, but they take up a lot of space on a monitor.  Back in the pre Autocad 14 days, you had to know the commands and enter them that way.  Painful at first, but still makes me far more productive.  

To snap the ends of lines together, look at the lower right side of your screen. You should see the word "ESNAP".  Right click on it with you mouse and check your settings.  I normally have enabled Endpoint, Midpoint, Center, Intersection, and Perpendicular.  Then, left click on ESNAP until it is highlighted.  Then start your pull the end of the polyline you want to join over until it is at the snap point you want it to be at.  To actually join the two, use the pedit command (pedit, join, highlight the polylines you want to join, then join.

When making airfoils, I rough them out using the polyline command.  Firstly, I draw a line along the X axis, then one intersecting it along the Y axis.  Use your Ortho command (F8 to toggle on and off) to make sure they are true.  Then, offset the vertical line the length of your airfoil.  I do just top half of the airfoil first, and leave the "straight" sections out until I have the shape I want.  Be sure to turn Ortho off when drafting out the airfoil. Then use pedit, spline, and highlight the line.  That will smooth out the polyline.  Pull on the line grips until you have what you want.  Then highlight the airfoil and type "Explode".  Then rejoin them all together with pedit, join, highlight the line sections, and you have the top half of the airfoil.  Then, put your cutouts in for LE, Spars, and draw your trailing edge.  Now, highlight the airfoil half, turn your Ortho and ESNAP back on, and use the Mirror command, referencing your X Axis line.  You now have a full airfoil with LE and spar cutouts.

Methodology for plans.  I assume that you already have your layout template built.  Here is the order I use:

1.  Loft airfoils
2.  Draw wing top view.  Copy, rotate, and lay some of your ribs over their corresponding location to verify accuracy of both.
3.  Draw stab, elevator and rudder.
4.  Draw fuselage side view
5.  Draw fuselage top view
6.  Draw out fuselage formers using copied lines from the side and top view to ensure accuracy.
7.  Draw out any special views.
8,  Draw out landing gear and wheels if necessary.
9.  Put the text in for your special building instructions.
10.  Enter text for part numbers, descriptions, etc.
11.  Enter hatches to depict different materials for cross grain.
12.  Fill in the details in the lower right side.
13.  Send it to someone who hasn't worked on it who will see mistakes that you never imagined.

Does this give you a start?

V/r

Bob

[proparc]

Gents,

How do you organize your drafting process?

You know Steven, that is a good question. No one has really asked that before. My workflow is based on layers-honest,(of course it's honest I'm a stunt flyer LOL).I never based anything on a flow in the sense of point A to point B. Even from a blank screen, the first thing I am thinking of is layers. What goes where on what layer. Quite frankly that is about it-just layers.

Bob Kruger seems to have his finger on the step by step workflow process. Now that I think about it, I really don't work in a rigid step by step methodology. In fact what CAD does for me is to free me from working like that, and allows me to express my natural free form way of thinking.

One thing I can tell you with complete authority is that you absolutely want to add your dimensions as late as possible. The experienced cats know why LOL. No matter how positive you are about a design, there is always something that seems to pop into your head concerning a change. Always, always put your dimensions on a separate layer, (here’s those layers again) and wait as long as possible before you go through the very detailed, and sometimes daunting task of dimensioning.

[steven yampolsky]

One thing I can tell you with complete authority is that you absolutely want to add your dimensions as late as possible.

This is the part I don't get. When I draw a line, it asks me how long it needs to be so I enter the actual size. Does your statement mean that there is a way to set the size of a part? What about size relative to other components. What I used to do draw a fuse I would start with a horizontal ref line, a perpendicular vertical ref line and offset another refline by specifying the distance which would be equal to fuse length. Are you saying I don't have to do that?

[Howard Rush]

I'm not sure of what you're asking, but always enter the actual size of a part in whatever units you are using.  Then zoom in or out as you please.  I presume you know about absolute and relative dimensions.  You will probably be happiest selecting relative. 

[steven yampolsky]

I'm not sure of what you're asking, but always enter the actual size of a part in whatever units you are using.  Then zoom in or out as you please.  I presume you know about absolute and relative dimensions.  You will probably be happiest selecting relative. 

Eh, What's an absolute vs. relative dimension? 

[Tim Wescott]

You may be confused about what people mean by dimensions here.

Proparc and Howard are talking about the dimension callouts; I think you might be thinking about "the size of the parts".

You do want to add the callouts last.

Absolute dimensioning is when you choose one reference point and call out all the dimensions relative to that point.  Relative dimensioning is when you call out the distance from point A to point B, then the distance from point B to point C, etc.

[Bob Kruger]

This is the part I don't get. When I draw a line, it asks me how long it needs to be so I enter the actual size. Does your statement mean that there is a way to set the size of a part? What about size relative to other components. What I used to do draw a fuse I would start with a horizontal ref line, a perpendicular vertical ref line and offset another refline by specifying the distance which would be equal to fuse length. Are you saying I don't have to do that?

Actually, that is the process that I use in CAD.  The offset command is one that you want to use all the time.

For example, when laying out the top view for a fuselage for a plane from the "Fox 35" days:  

1.  Draw your horizontal reference line.
2.  Draw vertical reference lines based on the side view that you just did.
3.  Fox 35 size ships traditionally have 1 1/4" between the inside of the motor bearers.  Offset the horizontal reference line .625".
4.  Now, you have to add on for your fuse doubler.  If using 1/32" plywood, offset .031".
5.  Offset for the fuse side thickness.  If using 1/8" balsa, offset .125"
6.  Bring up polylines from the side view were the doubler ends and where the taper start.  Use thess to trim the fuse side and doubler lines.
7.  Using the end of the trimmed inner fuselage line as a starting point, ESNAP and start a polyline to rough out your taper from the inner line of the fuse side.  Use the pedit ->spline to smooth out and and get the shape right.
8.  Explode that line, then reconnect it using pedit -> join.
9.  Offset that tapered line the thickness of the fuselage.  Use ESNAP to move the end of line grip to properly align with the polyline that is parallel to the reference line, e.g. the front part of the fuselage prior to tapering towards the tail.
10.  Clean up everything you have, and then mirror it on the X-Axis line.  You now have a fuse top view, less formers.
11.  Bring up vertical polylines from the side view for the formers.  Trim on the inside fuse or doubler sides.
12.  You now have the lines you need to draw your fuse formers.  Copy from the side view and top view.  You will have to rotate the top view lines 90 degrees, but that's easy.  Then use the copy and ESNAP function to put the lines together.  Voila - a fuselage former.  

I use this lock step method because each step after the first feeds the next, minimizing changes and errors.  And when you work with Walt Umland, he will find your errors.  Every time.....

Bob

[John Miller]

I am still at the contemplation stage.  Does anyone use any of the airfoil & wing design packages like CompFoil to design the wing then load that into a CAD file or is that a waste of time?

I use compufoil, and have for years. I haven't used other lofting programs, so my remarks relate to my experiences  with this fine program only.

Modern lofting programs are powerful, versatile, and a huge library of airfoil coordinates. There's a lot of power in the program that allows you the ability to modify airfoils easily, and accurately. Beyond that, there's the abi.ity to loft an entire rib set, as well as generating a great top view, or a 3D view of the wing itself. All of this can be impoprted directly into a CAD drawing as a .dxf file.

Since I prefer my tip airfoils to be a few percentage points thicker, and want he high point moved slightly forward, to help delay the tip stalling before the root airfoil, I like being able to morph two different airfoils. My lofting program allows me to do that.

When I drew the plans for Walter Umlands version of the Sterling Spitfire, I had to use the older system to loft the ribs similar to what Pat J. does. It works, but I was unable to have the modified tip sections described above. Rectangular wings, like the Pathfinder,  I used a straight loft, without the modified tips. All other designs, those with tapered wings, have been drawn with the modified tips.

These powerful and accurate lofting programs do have a learning curve. In the case with Compufoil, there's little guidance, except the tips box. You must sit down at your computer and devote the time needed to become proficient with it.

I've been using the program for almost 20 years, and it comes pretty easy to me with that experience.

Why did I invest so much time learning the program? Well, usually within an hour or less, I cam loft all my ribs, with spar cutouts properly located, along with Rod style jig holes accurately placed, or tabs set to support building the wing on a flat surface. I'll have web and rib sections placed and sized the way I want them, and have an accurate top view of the wing. All of this can be imported directly into my drawing. It really can save me a fair bit of time.

I have many plan forms available from straight wings to pure elliptical, with ribs from straight fore and aft, form, to Geo Style.

Lots of good advice has been given in this thread, let me add a few additional thoughts.

Use Layers

Set up start files, with all your layers already set up, with your basic title block.

I usually start all my drawings with two lines. 1 is my thrust line, the other, crossing 90 degrees to the thrust line. This line will become the back of the spinner.

Most of the rest olf the drawing is done with offset, fillet, and trim commands.

  Cheers

[Bob Kruger]

Good point on layers, John.  Layers help simplify the process when the drawing gets complicated.  Turning them on and off certainly helps.

It sounds that Steve Y. (Steve - if I am wrong, let me know) is trying to use a number of programs.  For the life of me, I have never mastered TurboCAD, although from time to time I use an older version of it just to get absolute lengths and widths that is far more difficult to do in Autocad. 

Those of us who do CAD have all developed our personal tips, techniques, and procedures to get the job done.  It just requires getting 30 or 40 sets of plans behind you until you hit your stride.  But I am a slow learner.

V/r

Bob

I use compufoil, and have for years. I haven't used other lofting programs, so my remarks relate to my experiences  with this fine program only.

Modern lofting programs are powerful, versatile, and a huge library of airfoil coordinates. There's a lot of power in the program that allows you the ability to modify airfoils easily, and accurately. Beyond that, there's the abi.ity to loft an entire rib set, as well as generating a great top view, or a 3D view of the wing itself. All of this can be impoprted directly into a CAD drawing as a .dxf file.

Since I prefer my tip airfoils to be a few percentage points thicker, and want he high point moved slightly forward, to help delay the tip stalling before the root airfoil, I like being able to morph two different airfoils. My lofting program allows me to do that.

When I drew the plans for Walter Umlands version of the Sterling Spitfire, I had to use the older system to loft the ribs similar to what Pat J. does. It works, but I was unable to have the modified tip sections described above. Rectangular wings, like the Pathfinder,  I used a straight loft, without the modified tips. All other designs, those with tapered wings, have been drawn with the modified tips.

These powerful and accurate lofting programs do have a learning curve. In the case with Compufoil, there's little guidance, except the tips box. You must sit down at your computer and devote the time needed to become proficient with it.

I've been using the program for almost 20 years, and it comes pretty easy to me with that experience.

Why did I invest so much time learning the program? Well, usually within an hour or less, I cam loft all my ribs, with spar cutouts properly located, along with Rod style jig holes accurately placed, or tabs set to support building the wing on a flat surface. I'll have web and rib sections placed and sized the way I want them, and have an accurate top view of the wing. All of this can be imported directly into my drawing. It really can save me a fair bit of time.

I have many plan forms available from straight wings to pure elliptical, with ribs from straight fore and aft, form, to Geo Style.

Lots of good advice has been given in this thread, let me add a few additional thoughts.

Use Layers

Set up start files, with all your layers already set up, with your basic title block.

I usually start all my drawings with two lines. 1 is my thrust line, the other, crossing 90 degrees to the thrust line. This line will become the back of the spinner.

Most of the rest olf the drawing is done with offset, fillet, and trim commands.

  Cheers

[Chuck_Smith]

When you pick your units in an AutoCAD type system, it's nice if you can stay on the grid, sometimes you move off if the units are not optimized.

Another secret is to draw a square, then plot it to your printer. You may need to do some scaling to ensure your full-size plot is actually to scale in both directions.

But, in a pinch, grab a piece of paper and learn how to do conic lofting. To my eyes the most beautiful aircraft ever built were the flowing lines of the Grumman Banshee and Cougar, and if you understand how conic lofting works you'll see how all those beautiful sexy curves evolved. You can do conic lofting with PLINE in ACAD. Once CFD and CAD came along aircraft got uglier and uglier. CAD can lend itself to an ugly aircraft if you aren't careful!

[steven yampolsky]

Once CFD and CAD came along aircraft got uglier and uglier. CAD can lend itself to an ugly aircraft if you aren't careful!

I always thought that it was my lack of talent that made all my planes look ugly. Now I know the real reason: it's the Autodesk people that are to blame! 

Seriously, thank you everyone for the pointers. I will start posting DWG's looking for comments. I know it takes a village to teach an idiot to draw in CAD. 

[CircuitFlyer]

the Autodesk people that are to blame!

Ya got that right!!!

it takes a village to teach an idiot to draw in CAD

It takes a village to teach anyone to draw in AutoCAD!  The reason: It's an antique.  It was developed 30 years ago (primarily for architects) and hasn't changed all that much since.   Would you use a 30 year old computer system? Then why learn old software.  Don't agree with me? Then imagine all of the above forum posts with a date stamp of 1985 rather than 2012.  No difference, huh?  Same crap existed then as does today.

Save yourself some grief, skip the old stuff, jump right in and learn a more modern 3D CAD modeling system.  I found SolidWorks intuitive and easy to learn.  My suggestion - Alibre Design is a very affordable SolidWorks wannabe very capable of what you need.

Enough ranting, back to the original post, in a nutshell:

1) Create a sketch, constrain and dimension it.
2) Extrude the sketch into a 3D part.
3) Repeat 1 & 2 for the other parts.
4) Mate the parts together into an assembly (just like building a virtual model).
5) Don't like the look of something?  Go back to one of those original sketches and change a dimension or two - viola, everything automatically magically updates.
6) Create the 2D drawing by dragging and dropping any view (top, bottom, side, cross section, etc) onto your drawing sheet (it even scales it correctly for you)
7) Dimension and add notes to your drawing
8  Print your drawing.  (Who uses a plotter anymore? Oops, sorry, ranting again)
9) Remember: any time you want - repeat step 5.  Even the drawing & dimensions automatically update.
10) More advanced but useful:  assign materials to the parts and determine your C of G on the computer.

Paul

P.S. - that reminds me, does "oops" still work on the command line in AutoCAD 2013 as it did in version 1.0?

[steven yampolsky]

Save yourself some grief, skip the old stuff, jump right in and learn a more modern 3D CAD modeling system.  I found SolidWorks intuitive and easy to learn.  My suggestion - Alibre Design is a very affordable SolidWorks wannabe very capable of what you need.

I had access to SolidWorks 6 years ago a thought it was fairly easy to use. After my father retire, I lost access to SolidWorks and quickly forgot the very little I knew in it. I wanted to get a permanent verision of solid works their stuff(AutoCAD's too) is ridiculously pricey.

[steven yampolsky]

I finally settled on the free one from the makes of Solid Works called DraftSight. This software is 2D only, has the functional equivalent of AutoCAD 2000 and the user friendliness of it's bigger sibling, the SolidWorks. In other words, it's perfect! I started the process! Here's my inspiration for the model: