CNC Bridgeport mill for sale

Yes, I moved it to my warehouse.

I have a 2-1/4 HP Hitachi M12VC and a pair of precision collets for it which ought to handle the task well. Some day, when it grows up, it may have a real spindle on it. ;)

-- Doctors prescribe medicine of which they know little, to cure diseases of which they know less, in human beings of which they know nothing.

--Francois-Marie Arouet Voltaire, about 250 years ago

In my opinion, the drivers which accept step and direction pulses to run a servo motor throw away some of the benefits of servo motors, including smooth motion and the ability to traverse intermediate values without leaving steps in the workpiece. After all

-- even though the motor is capable of intermediate positions, the controller is not capable of commanding them to reach those positions if it has to treat them as steppers.

Enjoy, DoN.

What difference does it make if the steps are small enough?

Digital commands will always have some finite resolution, even if it's nanometers.

Best regards, Spehro Pefhany

If its servo no problem for that size machine. The G320X is rated 80VDC 20 amps. Viper is rated higher, but support is slower.

If its stepper, most people think of the G540 which really doesn't handle much larger than about 380oz/in and then only those that will get to full torque at 50VDC and 3.5 amps or less per stepper. However while the G540 is a nicely packaged combo of a breakout and 4 250 stepper drivers its one of the less powerful controllers they sell.

The 201, 203, 210, and 213 will all handle 80VDC and 7 amps per driver.

The claim they design with about a 20% safety margin.

Absofrigginglutely. VFDs are awesome. I will probably wind up with 3 of them inside the high voltage cabinet on the Hurco by the time I get it done. I already have two in there. (Main spindle and spindle cooling fan currently, going to add a 4th vertical axis (Linear A that I can swap with Z when I need it) with a high speed spindle eventually.)

...

prettys sure its a 2000 oz/in stepper that doesn't do microstepping. It may do 1/2 steps IIRC. I seem to remember my AHHA drivers were rated 12amp at 50 volt and they were still undersize.

Karl

Because the steps may *not* be small enough. This is certainly the case with my Emco-Maier Compact-5/CNC lathe. A little lathe made mostly for teaching CNC machining. The minimum step (from the program point of view) is either 0.01mm or 0.001" depending on the position of a front panel switch. The steps are in metric units, so the inch units wind up with patterns like:

And -- to make it worse, the cross-feed steps have to translate into diameter, so a slow taper like a Morse is visibly stepped.

And if you are going to say -- finer steps and step faster, that machine *can't* step fast enough as it is. As an example, when threading with a fairly coarse thread, you have to slow down to 180 RPM (or sometime slower) on the spindle so the CPU can keep up with stepping the longitudinal feed at the right times. The CPU is an ancient 6502, and has little enough memory so finer steps would reduce the nubmer of program lines possible -- because the input is fixed format.

Of course. But steppers run fast can introduce resonance in the leadscrews -- and the same applies to servos pretending to be steppers.

Oh yes -- the fineness of the steps with a servo pretending to be a stepper is limited by the resolution of the encoder on the servo's shaft. Used as a true servo, the computer simply outputs a voltage saying "go so many RPM" and the servo amp takes care of keeping that happening. The computer simply checks every so often to make sure that the speed is right, and if it is a little too fast or slow, it changes the output voltage just enough to fix that speed. And this gives a smooth travel between the two end points, even in the areas where the encoders don't have resolution to tell the difference.

The only disadvantage to true servo operation that I can see is that if the computer hangs up (say a Windows box which experiences BSOD

-- Blue Screen Of Death), each axis will keep going at the last commanded speed -- until it hits a limit which should be wired to shut it down fully. With steppers, a hung computer will stop outputing pulses, and the motor will stop. Likely a spoiled job in either case, but less potentially exciting with the steppers.

And with servos in home machines, it is likely being controlled by what used to be called EMC, and is now LinuxCNC, which runs in a real time engine under the linux OS' kernel, so a hang is less likely.

Enjoy, DoN.

There is a solution for this also, pulse input that requires pulses from the controller all the time, and if pulses stop (controller hangs), it disables drives. My mach3 system is built like that. In Mach3 it is called "change pump" output.

Kristian Ukkonen.

Kristian Ukkonen fired this volley in news:K2NBr.7556$ snipped-for-privacy@uutiset.elisa.fi:

In other parlances, that's called a "dead man signal". Common on all mission-critical computers.

The name comes from the pedal or lever that railroad engineers had to keep depressed all the time for the locomotive to move. If they fell off the "dead man switch", the engine stopped.

Lloyd

I believe you meant "charge pump", Kristian.

-- Doctors prescribe medicine of which they know little, to cure diseases of which they know less, in human beings of which they know nothing.

--Francois-Marie Arouet Voltaire, about 250 years ago

Unless the engineer put a big piece of wood on it to hold it down.

My dad was a trainman and I rode the engine a few times as a boy.

But since Mach3 does not do "true servo" operation -- only servos pretending to be steppers, so if the computer hangs up, Mach3 stops producing pulses anyway.

The "servo pretending to be a stepper" is accomplished by a counter controlled by the step and direction pulses, and another one by the encoder on the servo motor. The Gecko servo driver is an example of this design.

Typically, there will be a circuit comparing the count in each of the two counters, and producing a voltage proportional to the difference between the two counts. The step and direction pulses get a burst to move to a higher value, and the voltage difference starts the motor moving (speed dependent on the difference) which starts counting encoder pulses until the two are equal again. This circuitry is totally separate from the computer, so if the computer hangs it stops outputting pulses, so there is no problem. (This unless the computer is asked to be part of the driver too, which I have not yet encountered.

So the only place where I would expect this problem to show up is when using a servo as a true servo -- controller outputs a desired speed voltage, not pulses, and the servo amp (driver) simply runs the motor at that speed until it is changed.

As for the hanging problem, computers designed to run unix have in their hardware a "watchdog timer" -- the OS pokes at it once every so many milliseconds, and if it does not get a poke in so-many + 10% or so milliseconds, it generates a pulse which resets the computer, starting a reboot, and hopefully, the card generating the speed command voltages will sense that reset and adjust the output voltages to zero. But in any case, the axes with true servos should have limit switches to shut down the servo amps to prevent crashes. Again -- something which does not depend on the computer.

Enjoy, DoN.