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GCode is Complicated
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Does Your Shop Use DNC Software to Move G-Code Around?

Jul 19, 2014   //   by Bob Warfield   //   Blog, Manufacturing, Products, Software, Techniques  //  2 Comments

RS-232CableHow does your shop go about getting g-code part programs on to the various CNC machines on your shop floor?

There’s the old stand bys–usb key, floppy disk, PCMCIA, and so forth.  These involve plugging some sort of media into the machine temporarily to transfer the code.  Newer machines can connect to your WiFi or cabled Ethernet and access folders on a server.  These methods are all fairly manual, but there’s a more automated way to transfer g-code to your CNC machines that is called “DNC,” which stands for “Distributed Numerical Control.”  The idea is to control what g-code winds up on a group of CNC machines from a central server.  A menu can be called up on the DNC software on that machine that causes a particular part program to be sent to a particular machine.

DNC requires connecting every machine back to the DNC Server that’s going to manage that machine.  This is traditionally done using RS-232 serial connections, like the cable on the right.  Newer machines have protocols that work entirely over Ethernet (cabled or WiFi), but this is typically an expensive option, so even newer machines may still be using RS-232.  To make the connection requires either stringing an RS-232 cable from the server to each machine, or there are many WiFi to RS-232 boxes available in the market.  Typically, either a piece of hardware (in the case of stringing many physical cables) or the right software makes it look to the DNC server PC like it has a whole bunch of serial ports ready to pipeline g-code back to the CNC machine on the other end.

Sophisticated DNC software opens the door to a lot of interesting capabilities:

–  Drip Feed;  Older CNC machines may have very limited RAM memory.  Complex g-code programs will often exceed the limits of that memory.  The answer is to Drip Feed, where the g-codes come to the machine a few at a time when the machine is ready to execute them.

–  While DNC software is often used in a “push” mode, meaning the download is initiated from the DNC Server, it is also possible with the right setup to “pull”.  In this case, a short program is executed on the CNC Machine to request a file be brought down.  Here is a typical example for a Fanuc machine:

%
:0001
(/REQ **insert program name**)
%

Such a program is short to punch in manually or to keep around and edit as needed so you can request particular programs from the DNC server.

–  Monitoring:  “Pull” requests are not the only thing going from the CNC Machine back to DNC.  Most DNC software can capture anything sent back via RS-232, and this becomes a channel to be used for machine monitoring.  A g-code function called “DPRNT” lets the g-code program send messages back to the DNC Server.  The Holy Grail of many manufacturing optimization projects is to keep the spindles turning at all times.  It’s hard to do, but the first step is to figure out how to measure how often the spindles are running doing useful work.  One approach is to use DPRNT to tell the DNC server when a g-code program starts and stops.  Appropriate DPRNT messages are sprinkled into the g-code to accomplish that.  Finer-grained monitoring might involve telling the DNC server whenever a tool is changed so that tool life monitoring can start to come into play via an accurate record of how long each tool is actually used in cutting.  BTW, if you need to add some monitoring commands to your g-code, our G-Wizard Editor has some special commands that make it easy to do so.  The linked article describes using the feature to add lock/unlock commands to 4th axis code, but the feature works equally well for adding DPRNT commands at strategic locations in your g-code.

There are lots of other features in DNC software, and the software ranges in complexity from simple free programs aimed at getting g-code over an RS-232 cable and onto a machine to complex multi-machine DNC server software.

Given that brief introduction, let’s do a survey:

How Does Your Shop Use DNC?

Note:  Even if you don’t use DNC, we’d still like you to answer a couple of questions on the survey.  The results should help everyone to understand better the most popular ways to move g-code onto machines, how others are using DNC, and which DNC software is most popular.

Check Out the Survey Results

 

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Does Your Shop Use DNC Software to Move G-Code Around?
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2 Comments

  • Hello, you can buy SD cards with integrated wifi for around 25€. Using them in combination with a batch script that places data on them from a central location can spare you walking around and swapping cards.

    That is not DNC but you could probably extend this if you have a firmware that periodically looks for some sort of file with machine controll commands on the card too.

    • Stoffel, I like this idea. Clever and cheap.

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