[Nickolaus]

I am trying to understand a few things but there doesn't seem to be any single resource that outlines the entirety of this. With that being said here are my thoughts and questions.

(Reference to any CNC conversion)

What I think I know:

1. In basic form for CNC conversion you need steppers, a driver, software, and a computer. The computer communicates from your parallel port to your driver (say G540), then outputs to each stepper. It seems like some people have no issues with the parallel port and others swear by adding a smooth stepper.

2. In the smooth stepper form you would have a computer output via usb or Ethernet to the smooth stepper, then the smooth stepper to driver via parallel port, then driver outputs to each stepper. People are stating that the feed rates can be doubled and there is no issue where the machine skips a step or stops mid motion.

3. Most stepper drivers seem to communicate through parallel ports via enhanced parallel port which is has a theoretical maximum of 2MB/sec at 8bit packets at a time.

My Questions:

1. Is the smooth stepper in place because the parallel port can't output data fast enough for some milling operations? If this is the case why are so many of these drivers using parallel ports? Was there some sort of form factor everyone had to adhere to?

2. If the option of smooth stepper is the best/only way to go for high speed applications or precision which route is any is better? Ethernet or USB?

3. Is the 8 bit packets of information and maximum throughput of 2MB/sec causing the stepper motors to skip steps and have issues? In my mind I am visualizing that without a smooth stepper the computer outputs information to the drivers and the drivers directly output stepper motion. If the program requires extremely fast commands the driver does not have any buffering ability and is simply consuming data faster than it is being outputted. Does a smooth stepper take in all of that data and process the motion more efficiently than the drivers can?

Thanks and looking forward to the feedback (and mild flaming too).

[Novett]

1. Yes it enhances speed of the machine.
2. Ethernet has a faster transfer of data than a USB
3. The SS may help the steppers. But my opinion is steppers are a waste of time.I built my
machine with steppers and then switched to servos. Much improved.

[Torchhead]

The issue with the parallel port is not the speed of the parallel port . It is the process of MACH having to generate up to 60,000 pulses per axis per second and handle reading inputs and reading the G-Code , while doing all of the math for a coordinated series of moves. You have to do all of that while living under the Windows limitations of how it talks to peripherals and handles everything from video to keyboard and mouse. MACH was the first and only CNC controller for Windows that could even come close to generating more that about 20.000 pulses. One of the side effects of MACH generating all of the pulses is ANYTHING that could interfere (communications and background programs and processes) can cause anything from minor to major "jitter". Jitter is where the signals should all be exactly the same width and evenly spaced but have variations. We are talking about usec down to nsec timing. Steppers have limitations but if you understand what those are (biggest being non-linear loss of torque at RPMS above about 1/2 max RPM) and design accordingly they can be both accurate and reliable.

Now, to the Smooth Stepper. It has a driver that REPLACES the parallel port driver in MACH and takes all of the real time pulse generation overhead off MACH. It has its own high speed processor that generates nice clean even PARALLEL pulses at high rates All MACH has to do is read the G-code and turn it into "trajectory" commands (something it did anyway) but now it just runs like any Windows application at normal speeds. No lost steps , no jitter no limitation on speed. So the main difference is WHERE the pulses are generated.

The advice is to use a parallel port MACH as a dedicated CNC controller with NOTHING else running or anything that can leave a background process running even after it is closed. That largely goes away if it no longer needs to use the parallel port driver in MACH. Downside is that the actual motion and the MACH engine are no longer directly connected. There is now a disconnect as to what is happening in MACH and what is happening in the real world. It's like a really bad echo so reading inputs and syncing them with where the motion really is can be a challenge. Warp9 has worked most of that out and the Ethernet Smooth Stepper is much more noise tolerant and reliable than a USB connected pulse card.

TOMcaudle
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[Nickolaus]

Thanks guys!!!

Tom: Your explanation makes perfect sense. Thank you very much for explaining this in detail. This has cleared everything up for me.