Re: Bridgeport servo motors

The RPM of my motors is 1200 at 50v. I will be running them at
60+V, so maybe I will run a 4:1 reduction just to be safe- and I
should still get 80+ IPM because of the higher voltage. I would
rather err on the slow, but safe side. I don't like doing things
twice. The motors are maybe a bit on the "light" side, but I am
just a hobbiest making telescope parts and I don't mind if the
mill is a bit slow. As long as I can overcome the motor "lightness"
by running a higher ratio, I am happy. The mill may only see
several hours of use a week. I'll have to start checking out pulleys
at SDP.


Thanks,
Scott

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "cnc_4_me" <cnc4me@g...> wrote:
>
> Hi Scott, i was thinking about your setup some more and I am sure you
> should use at least a 3 to 1 reduction. In the example below I
> estimated your continuous torque by dividing your peak torque by 5.
> I used 5 because many servos work out this way, but many also work
> out to be 7. If you divide your peak torque by 7 you get 600 / 7 =
> 85.7 oz-in = 5.4 in-lb. Multiply this x 3-1 belt reduction = 16 lb-
> in, or just enough power for heavy cut in steel (using my friends
> estimation of force on hand wheel).
>
> You also may have a little reserve in there, as Jon Elson pointed out
> your peak torque may be 880 0z-in not 600. The reason being your
> torque constant per amp is 44 oz-in and your peak safe current is 20
> amps. Multiply them and get 880 oz-in. This would give you 880oz-in
> = 55lb-in / 7 = 7.86 lb-in x 3-1 belting = 23.6 lb-in with 15 lb-in
> estimated needed.
>
> Wally
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Polaraligned"
> <polaraligned@o...> wrote:
> > > Well, this is what my research shows on required torque, speed,
> and
> > > reduction ratio.
> > >
> > > Most people on this forum agree the servo size used for
> commercial
> > > Bridgeport retrofits is around 30 lb-in or 480 oz-in.
> >
> >
> > So this is the Peak torque rating for these motors?? I have been
> > assuming that this is a continuous rating and my motors are a little
> > small as opposed to being a little big.
> >
> >
> >
> > > Also I seem to
> > > be getting the consensus that the pulley reduction is around 2-1
> to
> > > 2.5-1.
> > >
> > > Now let's look at a practical example. A friend has been using a
> > > Bridgeport for 15 years. He is estimating that on average with a
> > > heavy cut he is pushing 5 lb on the hand wheel. The hand wheel
> has a
> > > 3" lever length. So 3" x 5 lb = 15 in-lb continuous torque
> needed.
> > >
> > > You motor has a peak rating of 37.5 lb-in. Estimating constant
> > > torque we would divide peak by 5 = 7.5 lb-in. So you need 2x
> this
> > > number for the estimated 15lb-in force required. This tells me
> you
> > > need a minimum of 2-1 belt reduction.
> > >
> > > As you noted earlier more reduction gives you more power but
> less
> > > speed. A 3-1 reduction would give you a 22.5 lb-in at 80 IPM. A
> > > nice continuous torque rating but a little slow on rapids.
> > >
> > > Lets talk about 80 IPM, I can tell you this. A typical power
> feed on
> > > a Bridgeport will give you a maximum speed of around 90IPM. If
> you
> > > have access to one of these you can see for yourself if you like
> this
> > > speed.
> > >
> > > From a personal standpoint, and this is coming from someone who
> has
> > > no patience….I get irritated using the power feed to go from one
> side
> > > of the table to the other. One time I actually disengaged it and
> > > turned the crank by hand because I thought I could go faster (I
> was
> > > wrong). The reason for going from one side of the table to other
> was
> > > I had 2 setups on the table, one on each end…
> > >
> > > With that in mind I am shooting for a rapid of 120 IPM minimum on
> my
> > > machine.
> > >
> > > With all that said, if I were you I would probably go with 2.5
> or 3-
> > > 1 ratio, a fast rapid is nice. But if you can't take the cut you
> > > want it doesn't do you any good.
> > >
> > > I also think you should use a 70 volt supply, with your current
> limit
> > > set to 20 amps. This way you will get maximum RPM without
> running
> > > over current.