Something which occurred to me this week.

At work we're required to do a "dry run" after setup [CNC mills], but
before running a "first part" (and if the part is one of the "stack 4
sheets and mill together" sort, the first part is "stack one, shim to fit,
and run just the one"). This can take some time, especially when this is
the first time _you_'ve run the program, and you don't know which way it is
going to twitch. (I recall figuring it would be working to the left, it
worked to the right.)

SO, when doing he dry run, "cheat" and put a piece of material in and
do your first part at dry run speeds (which tend, on Robo Mills, to be
about 30% (max) of normal), or dry run & cut an "air piece", and then run
the first piece at normal speeds?

I'm wondering, also, for some of the larger projects, the ones where
high speed production takes an hour or more to run, so 'walking' a dry run
could be an all day adventure in tediousness.

And I do not want to think about the Mag cells, where the eventual
production run times are 72 hours, per piece.

But for the parts which take ten minutes to run ...


tschus
pyotr

--
pyotr filipivich.
as an explaination for the decline in the US's tech edge, James
Niccol wrote "It used to be that the USA was pretty good at
producing stuff teenaged boys could lose a finger or two playing with."

pyotr filipivich wrote:
Something which occurred to me this week.

At work we're required to do a "dry run" after setup [CNC mills], but
before running a "first part" (and if the part is one of the "stack 4
sheets and mill together" sort, the first part is "stack one, shim to fit,
and run just the one"). This can take some time, especially when this is
the first time _you_'ve run the program, and you don't know which way it is
going to twitch. (I recall figuring it would be working to the left, it
worked to the right.)

I rarely do a true dry run anymore, even when making the first part with
a toolpath generated by a custom program. Most of these programs are
based on earlier programs, so I have a pretty good idea how the G-code
will perform. If really in doubt, I might cut the first pass in air
above the real stock, though. I usually run it at a reduced feedrate,
and have my hand hover near the cycle stop button if I think something
looks wrong. At least in my case, the stock is so cheap, and breaking a
$6 carbide cutter is not a major tragedy, either.

Actualy, most of the spectacular goofs have been operator error, not the
fault of the CNC program. For instance, forgetting to zero out the
cutter Z coordinate. So, instead of the cutter approaching the top of
the workpiece while rapid-feeding to the beginning of the cut, the
cutter plunges all the way through the work and then rapid feeds at
60 IPM through the whole depth of the part, while by heart rate hits
200 BPM!
SO, when doing he dry run, "cheat" and put a piece of material in and
do your first part at dry run speeds (which tend, on Robo Mills, to be
about 30% (max) of normal), or dry run & cut an "air piece", and then run
the first piece at normal speeds?

I'm wondering, also, for some of the larger projects, the ones where
high speed production takes an hour or more to run, so 'walking' a dry run
could be an all day adventure in tediousness.

If your CAD/CAM program is reliable, and your part programmers are
reasonably careful, you just shouldn't have to do all this dry run
stuff. If you run the same part for months, the total cost of each
dry run becomes insignificant. But, if you are a mold shop, that would
mean one dry run per part! If your toolpath generation methods are NOT
reliable, don't rely on the dry run, FIX the real problem!

Jon

Hey pytor,

Maybe in the 1960's, 70's, 80,s, but since the early 90's, I can't
imagine that many "production" CNC's don't have a graphic screen page
to watch a fast cutter path on-screen before ever moving an axis.
Nowadays, even the hold-down clamps are shown so you don't mow that
grass. And if you've got an engineering department, there will be
information about all that up front.

Brian Lawson,
Bothwell, Ontario.

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

On Fri, 23 Dec 2005 12:23:08 GMT, pyotr filipivich
wrote:

Something which occurred to me this week.

At work we're required to do a "dry run" after setup [CNC mills], but
before running a "first part" (and if the part is one of the "stack 4
sheets and mill together" sort, the first part is "stack one, shim to fit,
and run just the one"). This can take some time, especially when this is
the first time _you_'ve run the program, and you don't know which way it is
going to twitch. (I recall figuring it would be working to the left, it
worked to the right.)

On Fri, 23 Dec 2005 12:23:08 GMT, pyotr filipivich
wrote:

Something which occurred to me this week.

At work we're required to do a "dry run" after setup [CNC mills], but
before running a "first part" (and if the part is one of the "stack 4
sheets and mill together" sort, the first part is "stack one, shim to fit,
and run just the one"). This can take some time, especially when this is
the first time _you_'ve run the program, and you don't know which way it is
going to twitch. (I recall figuring it would be working to the left, it
worked to the right.)

SO, when doing he dry run, "cheat" and put a piece of material in and
do your first part at dry run speeds (which tend, on Robo Mills, to be
about 30% (max) of normal), or dry run & cut an "air piece", and then run
the first piece at normal speeds?

I'm wondering, also, for some of the larger projects, the ones where
high speed production takes an hour or more to run, so 'walking' a dry run
could be an all day adventure in tediousness.

And I do not want to think about the Mag cells, where the eventual
production run times are 72 hours, per piece.

But for the parts which take ten minutes to run ...


tschus
pyotr

We machine straight from the CAD/CAM model and have done for a decade. But
this is only for 30 ton steam turbine rotor shafts worth £1M apiece. G



Mark Rand
RTFM

pyotr filipivich wrote in
:

Something which occurred to me this week.

At work we're required to do a "dry run" after setup [CNC mills], but
before running a "first part" (and if the part is one of the "stack 4
sheets and mill together" sort, the first part is "stack one, shim to
fit, and run just the one"). This can take some time, especially when
this is the first time _you_'ve run the program, and you don't know
which way it is going to twitch. (I recall figuring it would be
working to the left, it worked to the right.)

If your controller has it...you need to be in the 'command' view (mazak
speak) or in the abs ALL view (fanucked) when you do a single-block step-
through of the program.
Most controllers will show:
Position (relative to your work Zero and including your offsets)
Distance to go (for the current command)
Machine (absolute machine position relative to the machine reference
point)
Buffer (or Next) The next command qued in the buffer.
This last one is the important one...
It will show how much and in what direction the machine is going to move
NEXT.
Many controllers will also show 'next command'.....this tells you what G-
codes are going to be active on the next command (i.e. G0, G1, G3, etc.)
Very handy to pay attention to these....may save your part one day.


--
Anthony

You can't 'idiot proof' anything....every time you try, they just make
better idiots.

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