dreadnaut
Posts: 625
Joined: 3/13/2004
From: Vista,
CA, USA
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quote:
ORIGINAL: r72cnvt
Just input from someone who make parts from cad files. Try to use p-lines instead of splines and ellipses. Undefinable Bezier curves cause the G code (machine language) to go through the roof. A simple ellipse traced with p-line may have 20 lines of code where a true ellipse may have 200 or more.
Some controls can't hold big files, or they have to be broken into multiple files. The problem is slowly going away with PC based controls, but there are a lot of older controler out there with limited file capacity.
Ask your machine operator and programer for advice if you plan to do production type drawing. They will tell you what they want to make it easiest for them. Remember, they charge for the amount of time they have to mess around with your drawings, and the amount of time the machine is running. It all adds up to some serious dollars if you are getting abrasive waterjet cutting or laser cutting done.
Been an AutoCAD user since 1990, and agree completely. Some people seem to be in love with splines, and do not realise the problems that they cause at the ''number crunching'' level.
I do use them when I want to generate a smooth curve. But then I use the ''divide'' command to generate points. Then I use the ''list'' command then copy that output from the text window into MS Word, where I use find and replace to format it so that I can generate a script file that will draw a polyline.
A script file is nothing more than a .txt file where you rename it to a .scr file. I would look like this;
pline
<xvalue1>,<yvalue1>
<xvalue2>,<yvalue2>
<xvalue3>,<yvalue3>
<xvalue4>,<yvalue4>
<xvalue5>,<yvalue5>
etc.
Go to the command line and type ''script'', then brows to the file you created, and *poof* you have a pline. (If you have a couple hundred points, these extra steps are worth it)
A simple explination of whay splines are troublesome is that the algorythms that drive CAD programs are based on the mathematics of linear matricies. This involves the simultaneous calculation of large numbers of linear equations. These are equations where tha variables x, y, and z are all raised to the first power, as opposed to second power (squared) functions, and third power (cubic) functions. Splines are cubic functions.
< Message edited by dreadnaut -- 5/24/2008 9:17:18 PM >
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RE: Tips And Tricks for CAD Programs. - 
