View Full Version : Parallel cable for CNC use?

09-10-2010, 07:12 AM
I'm about to order a simple breakout board for my little CNC Micromill and it can be ordered with either a DB25 male or female connector.

Checking my stash of cables I find I have tons of DB25/Centronics 36 printer cables and 2 with a DB25 male on one end and DB25 female on the other. My CNC router uses one with a DB25 male on both ends. Are their any electrical differences in the various cables or a reason not to just order the B.O.B with a DB25 male to match the 2 cables I already have?

Seems like a stoopid question but after seeing the confusion over the various serial cable types used with wiring switcheroo going on with the different models of Denford Micromills, I don't want to screw up now that I've switched it to a parallel connection.

09-10-2010, 07:16 AM
Dosnt matter if it is male or female. When I am working with a machine that needs DB-25 on both ends I looks for old Mac SCSI cables. They had all pins through for sure with twisted pairs. Some cheap older parallel port cables tied all the grounds together to get the wire count down to make them cheaper. The fatter the cable the better.

09-10-2010, 08:06 AM
Some cables with DB-25 male on one end and DB-25 female on the other end may have been intended for use as modem cables, and may not have all of the wires that you need, and/or may have some of the wires connected to different pins between one end and the other, so you may want to check the pin wiring to be certain before making a decision or putting the cable to use.

09-10-2010, 08:41 AM
At a minimum make sure that pins 1 through 9 are connected. If that is true then it is a parallel cable and not a serial cable. Fat is good. I recently cut up a printer cable to interface a new telescope relay board I built and was pleasantly surprised to find that the wires were all resistor colour coded.

09-10-2010, 08:53 AM
Thanks for the enlightenment gentlemen.:) I'll check continuity to make sure at least one of the cables is straight through and proceed from there. One of them is pretty old & fat...kinda like me.;)

Just curious; why do you rarely (if ever) see a Centronics 36 pin connector on CNC equipment?

09-10-2010, 04:50 PM
I have seen centronics type connectors, not always 36 pin, on a lot of japanese industrial stuff. I think it just comes down to the size of the connector for the amount of conductors and current handling.

09-10-2010, 05:25 PM
Centronics was very aggressive about defending their intellectual property. Centronics was a spinoff of Wang Labs and it was they that developed the connector type at the time. It was later included in an IEEE specification so that cables could be made by anybody. It is likely that manufacturers avoided the connector because of potential legal issues. The D-25 is a poor choice for cables. Perhaps the best is the IEEE-488 type introduced by Hewlett and Packard. I still have a box full of those and they have much better reliability than the D Shell connectors. They have spring loaded face contact connector surfaces instead of skinny little pins and are very positive when connected even without retaining screws. They are also available in thin format profiles as well as the full size bulky style. IEEE-488 is the protocol, connector and cable of choice for lab instrumentation.

Paul Alciatore
09-10-2010, 08:03 PM
I believe the Centronics printer cables were indeed a pin to pin connection and all pins should have been connected.

Also, virtually all cables made with ribbon cable and crimp on connectors are going to be pin to pin. Although I have done it, it is difficult to make any transpositions with ribbon cable.

The problem is when you have a DB 25 on both ends and the cable is not a ribbon. Now it is just as easy to wire it in any configuration and many cables did cross some or even most or all of the wires. I have a book that lists over a hundred different serial cable arrangements for connecting different devices in the earlier days of personal computers and I am sure it is not complete. The possibilities are quite large (25! would be the actual number).

But it does not take too long to ring it out with a multimeter. If one of the connectors is a female, you will need a single male pin or a solid wire of the same diameter to assist in this. DO NOT USE AN OVERSIZED WIRE as it will spread the contacts. And remember that many cables have one or more pins of one connector connected to two or more at the other. So check all the pins for connections, not just the expected one.