Re: PC based CNC system architecture

ballendo wrote:

>
> 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'.
>

Wally K. replys

Thats correct ballendo they are doing a industrial job. And not what
many of us want or need.

> Wally wrote:
> >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.


> ballendo replys:
> 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.
>

Wally K. replys:

You could not be more wrong. Header connectors have been used for a
long time in industry. Were vibration is a concern latching headers
are used.

> >Wally K. wrote:
> >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.

> ballendo replys:
> 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!!
>

Wally K. replys

Once again you are incorrect. Plugable connectors are rarely used on
boards that are supposed to be installed and left in place. This
type of connector adds unnecessary cost and adds 2 additional failure
modes. First the plugable portion can fall out as you pointed out
above. And second the plug can fall off due to vibration as you
pointed out above.

Also, in industrial wiring you label the wire so you know what screw
terminal it goes under.

> >Wally K. wrote:
> >Connectors that are external to the box can be of use but not

inside.

> ballendo replys:
> Hopefully I've explained the error in this thinking for a

commercial

> situation with my answers and points above.
>

Wally K. replys

Actually you have not come up with any reason on why external
connectors should not be used, you should reread your post.

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

>ballendo replys:
> 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!
>

Wally K. replys:

And once again you miss the point. Most people on this list do not
want to spend a couple of hundred dollars much less a couple of
hundred dollars extra.

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

control.

> ballendo replys:
> 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

Wally K. replys

No ballendo it does not help. First, what is this supposed to
mean "but I'd say because of the "issues" it's a nice control."
Second, everyone on this list may not be a hobbyist. But it is clear
most of them are, or only want to pay hobbyist dollars.

Hope this helps.

Wally K.