Re: PC based CNC system architecture

Wally,

(snips,inserts below)

First let me say that Jon and Matt seem to be following some pretty
standard industrial control wiring practices. As has been said on
this list many times, What you can 'get away with' is very different
from what is 'right'.

>First, header connectors do not pull apart that easily. But it
>would depend on board size. Second, how in the world would anything
>unplug inside of a control cabinet.

Depends on how often they are unplugged. A well made and wired
machine can be in service for DECADES! As to your second question,
VIBRATION! Or 'accidental human intervention' :-). Like when cleaning
the dust out of the cabinet.

>There is no reason to put connectors that unplug on the axis cards.
>Once the cards are in place why would you want to unwire them.

Again, this is a fairly regular wiring practice. A screw connector
for good contact and non-specialty tool initial assembly; de-
pluggable so that a board can be swapped later if necessary without
having to rewire the harness, keeptrack of bare wires, etc.

Once more, think in terms of decades of use. Also think in terms of a
machine which may be making a product which is a significant part of
the business income. When it "goes down", you DON'T want to
be 'messing with the wiring'. You want to 'swap the axis card' and
get back to work!!

>Connectors that are external to the box can be of use but not inside.

Hopefully I've explained the error in this thinking for a commercial
situation with my answers and points above.

>My point is, depending on card size and layout you do not need
>expensive backplane connectors and removable external connectors or
>a card cage.

Their/our point is, over the expected life and usage of the machine,
a couple hundred dollars is a REALLY SMALL price to pay for some
reliability, and/or ease of maintennance!

>I would like to say with the cost and miscellaneous construction
>issues aside that it sounds like you are making a very nice control.

I'd say you got this part right; but I'd say because of the "issues"
it's a nice control.

Not everybody on this list is a hobbyist!

Hope this helps.

Ballendo