Re: Crashing CNCs: what gives ?

David,

This was an excellent post!

Adaptive machining is the nowadays term for what you describe in the
latter part of this post. Also includes would be in-process
gauging,probing,etc. Hopefully these "titles" will helpothers find
more info on what you have posted.

FWIW, two of the current low-cost offerings in CNC controls have
provision and capability for this type of use; Mach2 by ArtofCNC, and
TurboCNC by Dak Engineering...

Hope this helps, Thank you again for the post,

Ballendo

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "David A. Frantz"
<wizard@e...> wrote:

> Hi Kim
>
>
> I have one suggestion for you based on experience obtained years

ago.

> That is to glue your tool post in place with epoxy. Knocking the

tool

> post of the top slide on a lathe, in the event of a crash, is one

way to

> keep the grief level to a minimum.
>
> Now I should mention that this approach was taken due to very

unreliable

> CNC controls that were attempting precision diamond turning.

Since the

> product, in the finshed state was only a few microns thick it

didn't

> take much of crash to damge things. Sometimes the diamond would
> survive the crash and someitmes it wouldn't. The good thing

though was

> that the rest of the lathe did not suffer.
>
> When a upgrade to better CNC equipment took place we moved away

from

> epoxy mounted tool posts. At that point very few crashes where

due to

> anything other than operator error.
>
> As far as other aproaches do make use of your hard limit switches

which

> all machines should have. If you have critical tooling or

product in

> the machine and the machine supports it readjust those hard limits

to

> protect those items. Like wise careful use of soft limts on CNC
> software that supports it will help. Additional switches wire in

with

> you hardstop swtiches may also be of help. All of these take

setup

> time so there has to be some pay off to implementing the

protection.

> Do realize that you have options to the normal hardlimit switch.
>
> Though I've seen it attempted many times I've never seen an

operator

> actuated E-stop that really saves tooling. Generally things

happen to

> fast especially with machines running production code, so man in

the

> loop protection is not a good idea.
>
> Generally fuses can help but they are rather slow. If the

amplifiers

> support it do use current limiting. This can impact your servo
> performance and lead to debug issues so be careful and keep the
> possibilities in the back of your mind. Certain types of crashed
> involving your spindle can benefit from overload protection of the
> spindle also, such an overload should also shut down your axis.
>
> If you in mass production and the process requires operator tweaks

do

> consider moving the required intelligence to a PC. Have the PC
> generate the CNC code and have it update the CNC controller.

Anything

> that removes manual computation and data entry should be looked

into.

>
> So for example if the operator has to monitior the parts for

certian

> dimensions that are key to the process and make program parameter
> changes based on those samplings then it is a very good idea to

have the

> entire process computerized. To get further into this example if

one

> or more of the parameters that the operator is monitoring is

directly

> related to thermal growth of the spindle or growth of the

leadscrews,

> develope a computer program to generate the compensations. It is
> amazing how many unexplained crashes go away once simple validation

for

> rational data is done. While I'm not currently in a situation

where

> I'm up to date on the latest CNC software available I do know that

some

> CNC packages can support such coftware developement within a

modified

> form of CNC code. With modern PC's running CNC interpeters,

there is

> a very real option of running your SPC software right beside the

CNC

> code. It should be noted though that you will have to figure out

how

> to get the CNC side of the machine to re read the CNC code
> automatically. While I realize that these are techniques of mass
> production where you want the cheapest operator possible running

your

> process, it can be very usefull for projects of lesser scale. It

is

> also surprising how many mistakes even a skilled and reasonably
> intelligent operator can make when under pressure or simply
> distracted. The trick is to use accumulated intelligence,

experience,

> a bit of engineering math to remove the human mind from the chain

as

> much as possible. This will save you time and materials due to

mistakes.

>
> Another thing that can be very useful if you go the software route

is

> the concept of traceability. It is amazing how usefull a change

log

> automatically generated can be. What I'm getting at here is to

have

> all paramters touched by an operator saved in a log file. At

one

> point we even had the lathes computing compensations on the fly and

also

> recording those parameters in the log files. So when thinking
> automation software do not forget LOG FILES!!!!. A little bit of
> information can go a long way to correcting or identifiying

problems.

> So things like time and date, before and after values of the

parameter

> in question and what ever other parameters that may be of

importance is

> recorded.
>
> Log files are very usefull beyond the software maintenance issues
> also. If you have a lathe making automatic tweaks to parameters,

and

> that lathe has issues, a log file can be very useful in determining

what

> went wrong. How the lathe was behaving when no body was around

can be

> very useful to the electromechanical maintenance people.
>
> I hope this isn't long winded.
>
> Thanks
> Dave
>
>
>
> Kim Lux wrote:
>
> >I'd like to know what is supposed to "give" when one crashes a CNC
> >tool/slide into a chuck, tailstock, etc ?
> >
> >Lets say we've got a servo/ballscrew set up that generates 1000 to

1500

> >pounds of force when called on. Next, we accidentally command

that axis

> >to run into something immovable: a chuck, tailstock, etc. On a
> >commercial machine, how is this handled without wrecking

anything ?

> >
> >Right now we've got a quick blow fuse that pops in our equipment.

It is

> >the only way that I can see to limit the damage. What is everyone

else

> >doing ?
> >
> >BTW: now that we are experienced, we rarely crash our equipment.

I'm

> >just curious/wondering how others and commercial equipment handle

this.

> >
> >
> >