Re: Does control s/w affect machine performance? max step rate

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Fred Smith" <imserv@v...>
wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude"
> <davemucha@j...> wrote:
> >
> > > 100 ipm then is 2000 steps/rev * 33.33 rev/second =66,660 steps
> per
> > > second
> >
> > 33.33 times 60 = almost 2,000 RPM.
> >
> > Wear on the nut will increase at those speeds. 1/2-20 is not the
> > typical choce for high accuracy, not longevity.
>
> red herring and not pertinent to the discussion

What I am talking about is the need for the speed of steps in the
first place. That is completely pertanant to the discussion of why ?

> > A 3/8-8 ACME is much more ridgid and in small lengths not
> expensive,
> > and will cut the pulse rate to 26,666.
>
> At 100 inches per minute it owrks, what about 200, or better yet

400

> or 600? That's the speed that routers need to run to prevent
> bitburn. Then there are lasers and I blieve some of the plasma
> machines want to be cutting over 200 ipm on real thin material They
> want to rapid as fast as possible to get from one side to the other
> of a 4 x 10 ft sheet of material, at 100 ipm it takes almost a

minute

> to return to home from the far side of the table.

OK, let me know one shop that uses 1/4-20 screws for a laser table
and has 8 foot of travel. Matter of fact, I'd be interested if there
are more than a small handfull of people on the planet who use 1/4-20
screws on 8 foot tables. Certainly not enough to design complete
control systems for, and I would venture a guess that none are
shooting for 600 inches per minute.

This is exactly what I am talking about. If you are tossing the cash
for lasers, little costs like ball screws are a drop in the bucket.

For 0.0001 accuracy, that is 10,000 steps per revolution right ?
a 200 SPR motor and 10x microstepper and 5tpi offers 10,000 steps per
inch.

That equates to 4.5 inches per second on said table at 45khz.

That equates to 270 inches per minute. or 21 seconds for a full table
travel.

Switch from the laser to a router and 0.0005 resolution is often good
enough. That jumps to 540ipm or 10.5 seconds for 8 feet.
a plasma at 0.001" resolution and you are talking 2,700 inches per
minute or 2.1 seconds for the 8 feet.

The harmonics of the spinning screw will prohibit anything but the
largest screws. And that has brought us to open belts and gear
racks. Those at 45khz can pass 10,000 ipm on a system already.

May be slow to someone with unlimited funds, but as I see it, people
who want to move 5,400 inches per minute in a home shop with a router
is one tiny market. I'm thinking we are gonna start talking inertia
when sizing motors and calculating ramp speeds.

Are there people who want that ? I'm sure, but are there people that
need that ? Not outside of a production shop. Even a jobshop will
not miss the extra 0.10 seconds on a full table travel.

I understand that Ferri sells cars that do 200 mph and people in NY
and LA buy them, but most of us ask why ?

I do understand that people want stuff and will pay for it, but my
question is about proper design and using the stuff we have now. I
showed how one can have 270 inches per minute travel and 0.0001
postioning accuracy today, or 2,700 inches per minute at 0.001".

To double or triple that speed requires heavier screws and much
larger motors.

I'm missing the reason why we require that.

Dave

>
> So the answer is that "NO" the present limits are not satisfactory
> for all , and maybe even many hobby uses.
>
> Fred Smith - IMService