Hah, weird, I just got one of those too. Well, mine showed up in Feb. It now has CNC mounts, stepper motors, and drivers attached but I'm still working on interfacing it to the driver power supply and computer. It's sure been nice hvaing a real mill, albeit very small, since previously I had to do all such work on the lathe.
Theoretically, the EBB could drive the NEMA 23 steppers that fit the Sherline CNC mounts (Sherline offers Shinano Kenshi SST57D3201 double shaft steppers that draw 2A/phase, which is barely within the capabilities of the EBB, if it's well heatsinked). However, it can only control two steppers. So, for 2-axis work, it would work fine. However, there isn't a way to synchronize more than one EBB, so more axes would require a controller capable of operating more channels simultaneously. Sherline offers a driver box that is (of course) quite capable of the job, but it's a $600 item and I'm handy with a soldering iron, so I'm more likely to roll my own. There are some cheap TB6560 drivers on eBay, but I'm wary of those. There are two major approaches. One is to have a dedicated machine with realtime software which talks to a driver (like a Geckodrive G540) via a parallel port. The other is to have a microcontroller deal with the realtime issues (like the EBB) and talk to it via a modern interface like USB.
You might take a look at the stepper controllers used on the reprap or cupcake. They might need larger power transistors to drive the mill, but the basic design (and open source software) should be usable.
Sherline's use of the parallel port would be enough to keep me from buying their CNC. Reminds me of a company that was selling CNC retrofits for full size machine tools, using an ISA card that had been designed by a consultant. They were stuck stockpiling ISA motherboards because they didn't have enough design info on the system to re-do the interface without reverse engineering their own board.
The NEMA 23 steppers for the mill just need 2A/phase, so the Allegro based drivers should have no problem running them. Sherline claims they use a parallel port for timing reasons. Fullspectrum claims the same thing for their controller board (for a CO2 laser cutter), saying you'll never get their 10ns timing otherwise. I think 10ns timing for a mechanical apparatus is just silly. And the laser itself can't switch nearly that fast: a HeNe can barely manage 1MHz, and a CO2 is much slower. And Linux isn't an RTOS, no matter what extensions you tack onto it.
Both the Cupcake and the Reprap use the same approach as the Eggbot: they use a microcontroller to take care of the timing, and just give it instructions from the host computer. As long as people don't come up with nutty schemes like "go this way this fast until I tell you to stop", it should be fine.
I've done a fair amount of machining myself, and it seems to me that timing just isn't that critical. If you do the steps in the right sequence, it doesn't matter when they
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Sherline's use of the parallel port would be enough to keep me from buying their CNC. Reminds me of a company that was selling CNC retrofits for full size machine tools, using an ISA card that had been designed by a consultant. They were stuck stockpiling ISA motherboards because they didn't have enough design info on the system to re-do the interface without reverse engineering their own board.
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Both the Cupcake and the Reprap use the same approach as the Eggbot: they use a microcontroller to take care of the timing, and just give it instructions from the host computer. As long as people don't come up with nutty schemes like "go this way this fast until I tell you to stop", it should be fine.
I've done a fair amount of machining myself, and it seems to me that timing just isn't that critical. If you do the steps in the right sequence, it doesn't matter when they ( ... )
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