Parametric Drawings

      Can parametric design simplify change orders? May 19, 2004

In several threads there are references to parametric drawings and models. One post notes that they simplify change orders.

I've used IntelliCAD 2001 in 2D for one-off furniture pieces (I tried 3D but gave up - the 2D did what I needed at the time). I checked, but the help database doesn't list anything under parametrics.

20 years ago, I used a plotter that allowed vector commands and pen control. Is a parametric model similar, with the import feature bringing in dimensions from a spreadsheet or data table? Is there an introductory reference you can cite for the basics?

Forum Responses
(CAD Forum)
From contributor T:
You are close. A parametric drawing is a 3D model which is the "database." It consists of a 3D model made up of individual pieces with an x, y, z dimension. This becomes your database where the individual pieces have the 3 dimensions required to produce a list of parts that can then be used as a cut list.

You start by drawing a 3D picture, then trace off each individual piece and give it 3 dimensions, which go into the database. You must do this for all the pieces in the 3D picture. Then you have your parametric.

Once you have your parametric, you can just change the values of any piece without having to re-draw. Or do various other functions like motion or exploding. Very tedious, but the result has its benefits, because now your 3D picture is made up of all individual pieces which can be modified without having to re-draw them. You just change the values. Mostly for changes or for automation of the cut process with labels to match for assembly.

From contributor V:
IntelliCAD or Vanilla AutoCAD out of the box are not parametric programs. If you are looking for a true parametric 2D design too, you will have to look into Intergraph's SmartSketch. I am not sure what version is current now, but I can say that type of parametric dimensioning was and still is my real wish for AutoCAD.

From contributor P:
Are you referring to parametric symbols/blocks? If so, Ashlar Vellum does this as well. It is pretty handy, but would not be practical for a one-off drawing. Solidworks does this and it is useful for a one-off from this aspect only. But it is pretty cool for submittals, as you can place a symbol of a cabinet and type in the width and height and snap the cabinet right where you want.

From contributor L:
I'd not heard of Smart Sketch, so I visited their site. Looks interesting, but more than I need.

I'd simply run across the term and wondered what it meant. The capability to pre-define elements and insert them as appropriate is attractive, but more powerful than I need.

I'll keep on the learning curve for IntelliCAD.

From contributor N:
One thing very cool about IntelliCAD is that it can run lisp routines just like AutoCAD. One could write a set of routines that could parametrically draw stuff.

From contributor D:
I have a customer that wrote his own parametric drawing routines for ACAD. He has been doing this stuff for a great many years. He can now clearly see the limitations it poses.

What do you do if setting up the drawing takes longer than drawing it in 2D and cut listing it by hand? What do you do if three years from now you see someone create a very similar drawing to something you did, in 1/3 the time, without parametrics? Parametrics has its uses. This is clearly seen. The biggest problem is that the other problems are not usually clearly seen from an outsiderís point of view. Once you have committed to getting it to work, all too often the drafter/modeler is very proud and fails to do the time comparisons to justify the approach. This is especially true when the drafter/modeler is not the owner of the company. Very few employees want to go to their boss and tell them that the 2 years they spent taking the parametrics to the highest level they could is not really saving that much time, if any, and/or that the things it does not do well cannot be implemented because the objects created are custom entities and therefore you cannot take advantage of other third party programs to provide the functionality that is missing. Once committed, you are locked into that company's software.

I think parametrics, as a stand-alone, is a white rabbit. Many of you already know I feel this way. I am currently sitting on parametric ObjectARX code for drawing 3D solids, non-proprietary objects, in ACAD. Implementing it is very easy as a stand-alone approach, as it is always the very easiest coding to do. The trick is to provide an interface that still gets the job done with the very same objects, and to not throw away any parametrics you have built on when you decide to not use them, because at some point you may want to use them again. This requires runtime class modules and/or reactors that can update your formula engine by monitoring the commands and objects when you make changes without the parametric engine. It is much tougher to do, but provides the out needed all too often. It is very difficult to achieve all of this with LISP, as are so many other things, and so I would suggest not learning it, but instead learning C++ or VB and working through a C++ COM object that can provide the complete access and functionality. You do not want to spend a few years becoming a good LISP programmer and then find out its limitations later. Just like parametrics.

The Open DWG Consortium runs IntelliCAD. It is a non-profit organization. They are supposed to have full ObjectARX support by the second quarter of this year. They may or may not pull it off. It will be a great thing if they do because all code written for ACAD could just be ported over, giving everyone a tremendous price break over ACAD.

Keep in mind that the ACIS solid in the DWG database is encrypted and I do not believe they have decrypted the new ACIS solid in 2004. This could be a time setback.

From contributor N:
Parametric drawings and the ability to customize and automate your CAD environment is a good thing and can save tons of time and reduce errors. This is a fact.

Contributor D, youíre absolutely wrong about lisp!

Lisp is fine, simple language to start with, and itís well documented with thousands of examples. It does do ActiveX, Reactors, and it interacts very well with ObjectARX and VB. Accessing the ACIS in a (SAT format) for 2004 with lisp is not a problem. Learning a programming language is never a waste of time. It can only help when you learn other languages and it will help you learn other properties and methods. One language might be better suited for a task than another. Lisp rocks for accessing DXF data. Once one gets hooked, they can buy Visual studio pro, .net download the SDK and start compiling away.

From contributor D:
Itís not the parametrics that helps avoid mistakes, but the fact that you are modeling in
3D. Yes, it can make things faster, but then it can make things slower too. I think the other proponents of parametrics on this thread have already stated the same.

The stuff I detail is a waste of time with parametrics. It can be done, but then I would be throwing money away.

From contributor D:
Yes, there is no problem doing it. How to do it, though, is dependent upon your situation, end goal, etc.

If you did it in lisp, you can use the same approach. VBA allows you to add more GUIs and makes the coding process easier if you create programming objects (not talking about anything drawn in CAD) instead of using straight variables.

From contributor R:
If you've used Cabnetware or Cabinetvision, you immediately appreciate parametrics. Some years back, because of CW's CAD limitations, I started creating blocks in Ashlar Vellum (Ashlar Vellum calls them "symbols") of 2D sections and plans that directly reflected the CW input fields. Yes, the learning curve took some time, but for most of us who love what we do, it's absorbed personally and not by the business. The end result is accurate, it's absolute and it manages the revision process far better than stretching vectors.

With AutoCad, parametrics isn't an "out of the box" alternative, so trying to convey its advantages is a bit difficult.

From contributor T:
Parametrics has some great advantages and amazing abilities. Unfortunately, it is not for one-offs or truly custom (one of a kinds), which is 100% of what I do. Contributor D hit my experience with parametrics right on the head, but I do not want to discourage someone from exploring parametrics, especially if they are into automation or a production line type of operation. This could truly be what they are looking for and I wouldn't want them to miss out. Explore as much as you can. It will only make you better at what you do.

From contributor R:
On the contrary, contributor T, everything I do is one-offs. Configured accordingly, parametrics can be a great supplement to the process.

From contributor D:
Yes, contributor R does stuff with parametrics that does not appear to make sense to be done with anything else. His assemblies are complicated and there really is no other way to update them with just stretching, because of helixes and curved objects. He needs to be able to change his model fast based on design and field changes.

No one else does what he does. He is clearly an advanced user with extraordinary abilities. The fact that he is the only one around doing what he does is proof enough of the complexity of what he does. He is also taking these curved shapes and unrolling them for export as a flat panel to CNC.

The questions that should be considered are:

How much extra time does it take to add the associatively for updating and creating the drawing from scratch vs. drawing it from scratch without the ability to just punch in a number and change it, but instead redraw in 3D what needs to be redrawn without creating parametric objects at all from the start to adjust for design and field dimensions?

You also have to factor in other ways to unroll the curved shapes, create true helixes and get the rest of the cut list. There may be a faster way to do it, for what he does, but it appears several different programs would need to be used.

He is in a class by himself because of the constant need to unroll curves and generate helixes. As a detailer, I have run across this many times over the years, but it was never a daily need and I do not think it should be considered needed for most users, as long as they have work around when they need it. You can create helixes in many programs and bring them into ACAD to finish up the drawing and then still go back to some programs that created them to unroll them to generate the flat panel layout.

If I knew how to detail stairs, like he does, I would try and do a time comparison. This is only something he can do and eventually I am sure he will.

Remember, parametrics can do pretty much anything in the right program, but the time to set them up and use them may not be cost effective. Every situation is different and has to be evaluated accordingly. Some programs cannot be tweaked because of the user interface. Some programs can, but some take longer than others and require better skills, higher pay and lock the company into keeping the detailers because replacing them can be very difficult. Training a new employee is very expensive, as you all know.

Keeping it simple (easy to understand and work with, regardless of the assemblyís complexity), generic, exchangeable, flexible and get out manufacturing information is the balance we strive for. Sometimes you need to use something more complicated because the math necessary to generate the shape you want requires serious processor computations.

From contributor P:
I use parametrics for submittals. It is effective for cabinets. Contributor R has parts of an assembly that are used over and over, and in this way parametrics are useful.

From contributor R:
Absolutely! For example, in Ashlar Vellum (Graphite), parametrics are fantastic for shelf standards, system holes, cabinet sections, etc... you name it. The rationale is that it is so much simpler to highlight one grouped object, as opposed to lots of entities and related vectors/grips/points. And upon editing, lines remain at 90į and don't accidentally become 89.99999į, as what frequently happens when we're under extreme duress and revisions need to get out the door.

Maybe this strategy isn't for everyone, but as a custom woodworker, it's worked for me for the last 8 years. Given the right combo of software and user, this strategy shouldn't be ruled out.

From contributor T:
I never meant to downplay parametrics. I agree that if you understand what it does, it can be very beneficial in certain kinds of production. I just don't want to turn someone off to a good system that can make some producers a lot of money. The foreign competition have just about put us out of the production line business now and parametrics can do a lot to get us back into it.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor M:
I went through the parametric/non-parametric debate a few years ago when deciding which CAD system to buy. A friend who had used Cadkey (now KeyCreator) for years steered me away from the parametric direction, and I could not be happier I chose Cadkey. Whatever I want to model I just do it, not spending time building Swiss watch parametric models. When I want to change something I just change it, no restraints.

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