Re: [CAD_CAM_EDM_DRO] Looks Like tonight is the night for questions

Jon,
What I am trying to do with this setup of course it to "mostly" eliminate
belt changes:-})
Obviously, this will take some experimentation to see how well everything
reacts, but if I use the listed belt speed of 1040 (motor is rated at 1720
rpm at load) and use a MOTOR range of 172 - 4300 rpm then I will have my
desired 104-2500 rpm spindle range. If this works, this will satisfy 98% of
the speed ranges that I need for the type of work that I do. Never will be
able (from a practical side) to be able to twist up that 1/16" end mill for
AL to its proper speed but then I don't do that on a regular basis.

I understand the problems with slow speeds and heating, but can watch that
easier and take measures easier and quicker to halt the problem than I
could if the motor decided to become a grenade:-}) That's why I am more
concerned about the high speed factors.

After I had searched the net for a while (and not getting any answers), I
wrote to this group for answers and then while doing another search (funny
how things work when you use the right search string), I did find one
manufacturer that rates his
"Motor @ 1800 rpm
Frame Direct Belted*
56-184 5400 2250
*Belted per NEMA MG1-14.41 (dated 1993)"
More searching turned up some white papers regarding the subject also.
Obviously, the torque starts going to pot after base speed, but usually
when doing milling at high speed, one needs less torque as the end mill
will be a lot smaller so guess its time to experiment and see what happens.

Now to get off my fat duff and out into the chill and go to the shop:-})


Thanks for the reply.At 06:47 AM 1/6/02 +0000, you wrote:

>Doug Harrison wrote:
>
> > Hi Art;
> >
> > How fast your motor will run is one of those "yer on yer own" things. I
> > once asked a Baldor engineer at a trade show this same question with regard
> > to his vector drive system. He said Baldor vector drive motors are rated
> > for 5500 rpm. I asked where such information was published in their
> > literature. I think his next comment was about the free hot wings being
> > offered by the Hooters girls across the room. You get the picture.
> >
> > The tech guy at YCI Supermax told me I could easily run the 1740 rpm motor
> > on my knee mill at 4000 rpm. I inquired who was doing this, to which he
> > replied "lots of people." I've yet to try it.
>
>If you look at the construction of 1140, 1740 and 3420 RPM motor rotors, you
>won't find much difference. There may be some changes in the integral fan,
>so the higher speed motors won't waste excessive power churning air
>around. Otherwise, I don't think they make much of an adjustment for
>safety factor in the lower integral-horsepower motors. 5500 RPM doesn't
>sound too hairy. (Funny thing, 5500 is a standard speed for 8-pole 400 Hz
>motors. I wonder where he pulled that number out of the air - maybe they
>use standard rotors in 400 cycle 8-pole motors!)
>
>I wouldn't get very worried running a 1740 RPM motor at 2x speed, ie. 120 Hz.
>4000 RPM isn't much over that. It will increase vibration and shorten bearing
>
>and belt life. Now, if you ran the motor up to 4000 RPM on the highest speed
>setting, you'd get a spindle RPM something like 7000 RPM on the spindle, at
>least the way a Bridgeport 1J head is set up. I don't know what that will do
>to
>your spindle bearings, which cost a LOT more than the motor bearings. But,
>it has to shorten their life at least linearly, and may do worse than that.
>
>Jon
>

Bubba

OLDER THAN DIRT
Country Bubba
(Actually the inventor of Country and Bubba)

axtein@...
LaGrange, GA

http://www.surfsouth.com/~axtein


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