RE: [CAD_CAM_EDM_DRO] Machine Options in CAM Software ?

I may also be FOS but my understanding is slightly different.

Going the other way.

You draw apart in a cad program.
You want to convert that part to G codes that your particular machine
can use to cut with.
Or, you write in G code from the start.

Each machine varies in its implementation of certain g codes or may
actually use proprietary codes.
Post processor interprets codes to achieve a certain move / cut.

My cad program converts from DXF or cad to g code based on a particular
machines post processor.

Or something like that :-)

David
-----Original Message-----
From: Jerry Kimberlin [mailto:kimberln@...]
Sent: Saturday, November 09, 2002 7:02 PM
To: CAD_CAM_EDM_DRO@yahoogroups.com
Subject: Re: [CAD_CAM_EDM_DRO] Machine Options in CAM Software ?


natchamp_87 wrote:

>
> While I'm waiting to buy my mill for the retrofit project I have been
> playing around with different software for the CAD and CAM part. Why
> do the different CAM softwares ask for what type (Fidal, Faunc, etc)
> of machine? I thought G code was somewhat universal for CNC? Is it
> because not all machines use all G codes? Also, is the G code
> converted into step and directions signals in the NC software? Thanks

> for any clarifications!

Mark, a year ago more or less I asked the same question by wondering
what a post processor was. I got some good answers, but nothing
definitive from the development types. Everyone seems to try to answer
this question starting from a drawing on Autocad or what you do once you
have a DXF file drawing of a part to be machined. However, I think the
question should be answered from the other direction.

You have a motor - stepper or whatever.

You will need a driver for the motor, for example a Gecko 320 which will
take pulses to drive that motor in one direction or the other to
accomplish forward or backward movement of the axis in question. The
Gecko drives get their logic sense from the parallel port of the
computer and their power from an auxillary power supply, whose maximum
voltage and amperage should be selected based on the motors you want to
use. Since the Gecko's can drive your motors either forward or backward
and accept pulses at certain rates, you need a program that outputs to
your parallel port to tell them what to do.

It seems to me that Fadal, Fanuc, Haas, Bridgeport, etc., all use
different motor drivers. In those motor drivers there is circuit
controlled by a group of transistors, whether in a microprocessor or as
discrete silicon. Somewhere in there is a read-only-memory chip that
gets in the way of things, taking what it is given and sending out the
direction and number of steps the motor should turn. In the case of the
Geckos which don't have a ROM to govern things, the number of steps and
the direction is controlled by a program in your computer.

As a consequence, you don't need a post processor to use the Geckos.
You do need a post processor to use some of the commercial stuff because
they do not adnere to any standard, letting a translator ROM, which is
propriatary, get in the way of a straight through signal path. Some
commercial stuff does take G-code, but doesn't let it pass straight
thru, necessitating translation thru a post processor program, which
sometimes costs thousands of bucks.

So far as I understand, you can bypass a lot of this by using EMC which
should output the proper logic signals to the motor drivers, bypassing
the need for a post processor program that has to be interfaced between
your motor drivers and the DXF file outlining your part. All you need
to do is customize the EMC program a little and this customization is
based on the dimensions of the pitch of your table screws and whether
they are left hand or right hand.

Now....I have tried from what I understand. Anyone who has both
definitive hardware experience, please tell me what I have said that is
FOS. Somewhere along the line someone has to spoon feed the newbie on
this list and after a year of listening to all the stuff, I know no more
about post processors than I did ten years ago - except that I need one
and I'm not sure that is the case unless I have a commercial machine.
Why do I need a post processor if I am building an amateur CNC machine.

Thanks to all,

JerryK

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