Wireless DNC: connect RS-232 CNC machines over Wi-Fi or Ethernet

Many shops still run machines whose only link is an RS-232 port, often far from any PC. Instead of long serial cables or a laptop carried to each machine, a small adapter at the machine puts its serial port on the network. On the DNC PC the adapter appears as an ordinary COM port, so DNC software works with it unchanged.

How it works

At the machine: an Ethernet-to-serial device server or a Wi-Fi serial adapter connects to the control's RS-232 port with a short cable.
On the network: the adapter has an IP address on the shop network or Wi-Fi.
On the PC: the adapter's driver creates a virtual COM port, for example COM12, that forwards everything to the adapter. One virtual COM port per machine.
In DNC Precision: each machine uses its own virtual COM port, with the same port, handshake and format settings as with a cable.

DNC Precision works with Ethernet-to-serial device servers and Wi-Fi serial adapters as long as their driver creates a virtual COM port.

When it is worth it

Machines are far from the DNC PC, or spread over several halls.
One PC (or one server running DNC Precision as a Windows service) should serve all machines, and programmers should send programs from their own desks.
Laptops with serial ports are getting rare, and carrying one to each machine wastes time.
Together with the server mode, the operator requests programs from the control itself, so nobody needs to be at the PC.

Setting it up

Choose the adapter. It needs a Windows driver that creates virtual COM ports for your Windows version. For drip feed, prefer one that passes the RTS/CTS lines (hardware handshaking).
Give it a fixed IP address (or a DHCP reservation), so the virtual COM port always finds it.
Connect it to the control with the right cable. The adapter's serial port may be wired as a terminal or as a modem; the control's manual and the adapter's manual decide whether you need a null-modem cable. See RS-232 pinouts and cables.
Set the adapter's serial side to the control's baud rate, data bits, parity, stop bits and handshake, if the adapter does not take them from the PC.
Install the driver on the PC and map one virtual COM port to each adapter. Note which COM number belongs to which machine.
Add the machine in DNC Precision with that COM port and the same settings as with a cable. Send a short program first, then receive one, then try your longest program.

Pitfalls

Buffers and delays. The adapter and the network add buffering and delays. After the control sends XOFF, data already on the way can still arrive and overflow a small control buffer; a slow link can make the machine wait between short moves during drip feed. Hardware handshaking, a lower baud rate or wired Ethernet help. See drip feed.
The adapter must be reachable. If the transfer suddenly fails, check that the adapter still has its IP address and that the virtual COM port is connected. Some shops power-cycle their adapters now and then; a fixed address and a good power supply avoid most of it.
Driver updates. After a Windows upgrade, check that the adapter's driver and configuration tool still support the new version.
Security. Put the adapters on a separate network or VLAN: anyone who can reach them can send data to the machine.

Editions

Each machine needs its own virtual COM port in DNC Precision. The Free Edition handles one machine, Professional three and Enterprise any number; Professional and Enterprise add drip feed and the server mode. The full version can be tried with one machine first. Compare the editions or download DNC Precision.

Questions

Can I send programs to an RS-232 CNC machine over Wi-Fi? Yes. A Wi-Fi serial adapter connects to the control's RS-232 port, and its driver creates a virtual COM port on the PC. DNC software then sends and receives through that port as if the machine were connected with a cable.

Does DNC Precision work with serial device servers? Yes, with Ethernet-to-serial device servers and Wi-Fi serial adapters whose driver creates a virtual COM port. DNC Precision uses such a port like any other COM port.

How many machines can one PC serve over the network? One virtual COM port per machine, as many as the adapters' driver creates. DNC Precision Professional serves three machines and Enterprise any number; the Free Edition serves one.

Is drip feed reliable over Wi-Fi? It can work, but network delays and the adapter's own buffer can starve or overflow a control with a small buffer. Use hardware handshaking where the control and the adapter support it, test with your longest program, and prefer wired Ethernet for machines that drip-feed all day.