Re: BOBCad and Iges import

Dave,

Nice explanation.

However, I think your etymology(word derivation) is incorrect.

I'd like to add a few pennies...

Parametric is a form of the word parameter. A parameter, as you know,
is "a variable, or arbitrary constant appearing in a mathematical
expression..." (Like "middle" in your example)

para- as a prefix, means "near, beside, or beyond". Also can be used
to mean "resembling", or "similar".

To add to your explanation: A "parametric" program is one in which
parameters, or variables replace fixed numbers. In CAD, these numbers
usually refer to size or location.

So, a parametric CAD program is one in which the size and/or location
of the features OF the part can change, simply by changing the
parameters involved (you used the word "chart" to identify this list
of parameters).

Russell:

Parametric machining programs(gcode) exist as well. Makes sense as
the usual goal of both the CAD and the CNC is to eventually make
parts!

As a final example, a bolt of a given size, thread, and head type
will be drawn/manufactured essentially the same way, regardless of
its length, or material. Only the length and the "look" of the
material will change.
Parameters assigned to the length and material type allow a
parametric CAD program to display any of the whole range of lengths
and materials of this bolt, by simply changing the length and
material parameters.

Moving this example to CNC: Parameters are assigned to the parts of
the gcode program which need to change when making bolts of different
lengths. On a screw machine making these bolts, this would affect the
positioning of the work stop, and the thread length. Parameters for
feeds and speeds will also be set to accomodate different materials
from which the bolt may be made.

Hope this helps,

Ballendo

P.S. Russell, List, Be aware that the word "parametric" does NOT mean
the same thing to everybody who mentions it when trying to sell you
their CAD sofware, or machine control! It is a bit of a "marketing
term" presently, and WIDELY ranging variations exist in the TRUE
capabilities between similar programs/controls which EACH claim to be
parametric... (There were LOTS of examples of this at Westec 2002!)

P.P.S. FWIW, Definitions used above were pulled from the American
Heritage Dictionary, college edition.

--- In CAD_CAM_EDM_DRO@y..., Dave Lantz <dlantz@a...> wrote:
> a solid CAD model is predefined mathmatically by whatever means you
use to
> create it. a 'parametric' model has a variable mathmatic
definition. (you
> can tell it to put the bolt hole in the MIDDLE of that surface--and
when the
> part changes size, the bolt hole will remain in the middle of the
surface!)
> para=changing
> metric=measurements
> so you can design the part by it's intent, not just its
dimensions. you can
> also design a 'generic' part or assembly, meant to be used in a
variety of
> applications, and controll the varied dimensions by a chart. takes
alot of
> the number crunching out of it... very nice for designers &
engineers...
> some of the notable parametric modelers:
> Pro/e--very expensive
> solidworks--very expensive
> prodesktop--free! but has limited assembly abilities
> varkon--free! claims it does 2d parametrics, haven't been able to
get it
> yet, works on linux!
> do a 'google' search, you'll probably find alot more!---Dave
>
> -----Original Message-----
> From: Russell [mailto:rjshaw@i...]
> Sent: Tuesday, April 09, 2002 5:29 AM
> To: CAD_CAM_EDM_DRO@y...
> Subject: Re: [CAD_CAM_EDM_DRO] BOBCad and Iges import
>
>
> onecooltoolfool wrote:
> >
> > Just so you guys know my opinion. Rhino is the most powerful CAD
> > package for the money ever invented. Granted it is not parametric
> > (and that really bugs us engineers) but with some skill and
patience
> > you can model anything. Try that for 800 bucks anywhere else.
> > Besides the fact that you can do most of what you need with the
free
> > demo and 20 saves.
>
> What does 'parametric' mean for a cad tool?
>
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