Re: Bridgeport servo motors

>
> There is a difference between a real servo and a DC motor. Servos
> have lower rotor inertia, commutators optimized for smother
> operation, and more peak torque reserve.
>

Which is going to equate to overall better, more predictable
performance from the machine.

> 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.
>

I have a 45 volt 800 VA toroid transformer. This should supply
60+ VDC. The motors max volt rating is 60v and I am not sure
I want to go over it. There seems to be conflicting info as to
whether it is ok to go over voltage on servo motors.

So it is your opinion that I will be OK with these motors and a
3:1 reduction as long as I can handle 80 IPM rapids? I will have
plenty of torque for taking nice size cuts in steel?
This makes me feel better because I was second guessing my motors.
I am only a hobbiest and the speed is not all that inportant. Heck,
at least I won't have to stand there and crank the handwheels!

Thanks for your opinion,
Scott