# "Parametrics": Defined and explained

Other Versions
Spanish
An explanation of parametrics in CNC machinery programming. June 13, 2001

Question
Could someone please define parametric?

Forum Responses
According to Webster:
Mathematics. A constant in an equation that varies in other equations of the same general form, especially such a constant in the equation of a curve or surface that can be varied to represent a family of curves or surfaces.

One of a set of independent variables that express the coordinates of a point.

Dealing with CNC matters such as we are, it basically means that you give coordinates relative to other coordinates. A lot of times you will even use a formula instead of an actual X/Y coordinate.

Here's an example: I start my line boring at 62.5mm from the bottom of the panel and end at 65.5 from the top of the panel. So the program line looks something like this: L = Panel length, S = Material thickness, F = a user defined variable which compensates for edgebanding thickness, since I machine before banding. X=L-62.5 Y=37-F Z=15 XF=65.5. Now no matter what size I make the panel, the bottom hole will start at 62.5mmm from the bottom of the panel and the top hole will be at 65.5 from the top of the panel, bearing in mind that all of my panels are on 32mm increments. This formula will not work exactly on a non-32mm increment.

Basically, though, with parametric programming, you are tying your work on the panel to the size of the panel and all operations are at given places relative to the size of the panel.

Brian Personett, forum technical advisor

To common people like me, it just means being able to reference the machining operation(s) to the dimensions of the panel, instead of absolute positions of a single panel.

This allows us to have one program that will work over a broad range of panel sizes. The same program can be used if the panel is 24x36, 23.5x31, etc.

The program can then be saved as a different program or the same program modified by changing the panel dimensions.

I don't understand why everyone wants to go through all this mathematical hassle. If you use a program such as solid, programs are disposable. Use them once and delete them (or throw them away). It's that simple. I hardly ever program a P2P program.

Whether you're choosing a software package like Cabnetware or Microvellum or if you're writing G-code, having parametric capabilities makes a huge difference for custom work.

A simple example is a g-code program used by the P2P operator for drilling pull holes on doors/drawers based on x, y, z header info. Through parametrics, a CAD/CAM program like Microvellum allows you to alter a 3d cabinet structure in AutoCAD and automatically update machining and stockbill output.

Learning parametric syntax is a great step forward for the shop operators in custom or production shops. Similarly, in the engineering room, if your equipment has the horsepower, the 3d parametrics can be a timesaver for custom fabricators. For stock producers it probably isn't necessary.