Bring NASA in ( was Re: oz*in NOT oz/in

Folks,

Hmmm. I've been thinking about writing a performance modeling
program to do this sort of calculation for a while now. E.g., how
fast can you move/accelerate and what can you cut, given the physical
constraints of friction and mass vs. motors & drives? Since it seems
like people might be interested, I'll see about putting such a thing
together now that I got my copy of Visual Basic back. CAMAS isn't
bad, but it only spits out Superior Electric part numbers IIRC! Not
helpful if one just wants a quick estimate of whether that 150 oz
motor will pass muster or not before wasting a few days in the shop.

In the meantime, it's not really as trivial a calculation as one
might think. The lead angle of the screw, rather than the pitch,
determines to a large degree how much force you can multiply. So a
1/4-20 will yield less force than a 1/2-20, for the same torque. But
the 1/2" one is a trade-off with more inertia. There's a bit of
torque required just to get something to move at all. And of course,
an ACME does a better job of it than a 60 deg threaded rod, and
ballscrews better still.

Dave Kowalczyk
Everett WA

--- In CAD_CAM_EDM_DRO@y..., "dave_ace_me" <davemucha@j...> wrote:
> Hi Guys,
>
> not to get too far afield here, but NASA
> http://www.grc.nasa.gov/WWW/K-12/airplane/thrsteq.html
> offers this little bit.
>
> " If we are dealing with a solid, keeping track of the mass is
> relatively easy; the molecules of a solid are closely bound to each
> other and a solid will retain its shape. But if we are dealing with
a
> fluid (liquid or gas) and particularly if we are dealing with a
> moving fluid, keeping track of the mass gets tricky. For a moving
> fluid, the important parameter is the mass flow rate. Mass flow
rate
> is the amount of mass moving through a given plane over some amount
> of time. Its dimensions are mass/time (kg/sec, slug/sec, ...) and
it
> is equal to the density (r) times the velocity (V) times the area
> (A). Aerodynamicists often denote this parameter as "m dot" (m with
a
> little dot over the top). Note that "m dot" is not simply the mass
of
> the fluid, but is defined to be the mass flow rate, the mass per
unit
> time"
>
> So mass over time is refered to as kg/sec or slug/sec. So this is
> not the proper measurement for either tourque or force as we use it
> in referring to starting a table to move or moving the table.
>
>
>
>
>
> --- In CAD_CAM_EDM_DRO@y..., "stvdnb" <dsa3@u...> wrote:
> > --- In CAD_CAM_EDM_DRO@y..., Doug Fortune <pentam@c...> wrote:
> > ...
> > > torque is measured in 'force*lever arm'
> > > in other words, oz*in lb*feet N*m
> > >
> > > etc, NOT oz/in , lb/ft etc.
> > >
> > > (Yes I know oz & lb are not exactly units
> > > of force, we should be using Slugs but I'm
> > > afraid that will lead to even More Confusion!)
> >
> > If I remember correctly, the slug is a unit of mass, not force.
> > Pounds and ounces _are_ units of force.
> >
> > - Steve