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Re: [GrizHFMinimill] Re: feeding itself

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  • Barry Young
    Thank you Ian: That cleared up a few items I was missing. Barry Young ... ____________________________________________________________________________________
    Message 1 of 105 , Oct 1, 2007
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      Thank you Ian:

      That cleared up a few items I was missing.

      Barry Young


      --- Ian Foster <fosterscons@...> wrote:

      > g'day Gary & Dave.
      > Daves expalnationis pointing in the right direcction
      > but may confuse
      > some, particularly those wanting to set their drive
      > up.
      > As dave says IR is the product of resistance and
      > current which
      > through Ohms law =E the voltage.
      > All motors generate what is called a back emf, even
      > you humble
      > single phase ac motor and can act a generators. For
      > a dc motor as
      > used in our lathe the back emf is prortional to the
      > speed. This
      > motor has a constant field strength because of the
      > permanent magnet
      > field. At zero speed the resitance of the armature
      > circuit (which
      > includes the windings, brushes and wiring) limits
      > the current; we
      > will give this resistance a value of R ohms. BTW
      > Without the current
      > limiting function of the control board a very high
      > current would
      > flow when the motor stalls.
      > When started the motor will accelerate until the
      > motor speed
      > generates a voltage which balances the voltage
      > applied by the
      > controller. The resistance R is still in the circuit
      > and the motor
      > current flowing through this resistance effectively
      > lowers the
      > voltage which the motor has to generate to balance
      > the control
      > voltage. As the current increases the voltage
      > developed across the
      > resistance increase so reducing the amount of
      > voltage the motor has
      > to generate, consequently the motor slows down.
      > To enable the controller to keep the speed more
      > constant with
      > different loads and currents the IR compensation
      > adjusts the output
      > voltage from the controller so that it rises with
      > increasing current.
      > To adjust the IR compensation you run the motor at
      > about 30% speed
      > and apply a load. The compensation adjustment is
      > increased until the
      > slowing of the motor under load motor is only just
      > perceptible; too
      > much compensation may make tthe drive unstable with
      > speed hunting.
      > To load the drive I used a friction pad applied to
      > the perimeter of
      > the chuck with high speed engaged. Speed changes can
      > be indicated by
      > the stoboscopic effect of a fluorescent light,
      > adjust the speed
      > until you get a stationery image effect, slowing of
      > the drive will
      > cause the image to rotate in reverse.
      > Because resistance rises with temperature the
      > adjustment must be
      > made with the motor warm.
      > Hope this helps.
      >
      > One good turn deserves another.
      > Regards,
      > Ian
      >
      >
      > --- In GrizHFMinimill@yahoogroups.com, "Dave Mucha"
      > <dave_mucha@...>
      > wrote:
      > >
      > > --- In GrizHFMinimill@yahoogroups.com, Barry Young
      > <barryjyoung@>
      > > wrote:
      > > >
      > > >
      > > >
      > > > Why would a motor controller be infra red
      > compensated
      > > > and why do electonics people always think
      > everybody
      > > > understands their acronyms?
      > > >
      > > > Thanks though, I do appreciate it even if I
      > don't
      > > > ubderstand it.
      > > >
      > > > Barry Young
      > >
      > >
      > > yup, WORDS are the biggest barrier to learning !
      > >
      > > I.R. both caps, separated by periods.
      > >
      > > if you are familiar with Ohms law E-IR
      > >
      > > you are probably familiar with I representing
      > current and R
      > > representing Resistance.
      > >
      >
      >
      >
      >
      > Yahoo! Groups Links
      >
      > (Yahoo! ID required)
      >
      > mailto:GrizHFMinimill-fullfeatured@yahoogroups.com
      >
      >
      >



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    • ronpat
      -In my photos is a couple pictures of one of my bars of Aluminum made with a big coffee can, a small propane bottle cut in half, and charcoal. About 30 min
      Message 105 of 105 , Oct 17, 2007
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        -In my photos is a couple pictures of one of my bars of Aluminum made
        with a big coffee can, a small propane bottle cut in half, and
        charcoal. About 30 min from start to pour. I have found an unlimited
        supply of scrap Aluminum around here, is old gutters laying out for
        the trash truck to pickup. As far as what grade ect. it is I have no
        idea. But it machines great



        -- In GrizHFMinimill@yahoogroups.com, David Patterson <odd_kins@...>
        wrote:
        >
        > Extruded aluminum is just fine for casting, it's gummy because
        you've taken the temper out of it. I demold while the casting is
        still real hot and quench in cold water, away from the furnace, and
        you'll get some of the temper back. if you wait until it's cold
        you'll have to heat treat to get it back.
        >
        > walker_lyndon <walker_lyndon@...> wrote: For brass, it
        seems to work well. Aluminum, not so much because a lot
        > of the scrap aluminum people get are extrusions and they are
        horribly
        > gummy to mill.
        > I didn't actually build anything with it. My friend had shown me one
        > of the brass ingots (about 3 lbs) that he cast and I wondered how it
        > would machine, so I took a couple of facing cuts acrosss it. As far
        as
        > I could see, it machined as nicely as the brass rod I purchased.
        >
        > The brass is melted in a charcoal furnace and melts at a slightly
        > higher temp. than aluminum. Google "Gingery furnace" for more info
        on
        > building your own.
        >
        > --- In GrizHFMinimill@yahoogroups.com, rick201m <rick201m@> wrote:
        > >
        > > How difficult is it to start to do one's own melting
        > > from scrap/cheap brass? Are the metals used in those
        > > items found in thrift store of good enough quality to
        > > mill/lathe well?
        > >
        > > Thanks much,
        > > Rick in CO
        >
        >
        >
        >
        >
        >
        > Dave Patterson
        > odd_kins@...
        > http://home.comcast.net/~oddkins/foundry_home.html
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