Damn Google foo not working today. Who can tell me where to find the value for the maximum number of step commands an arduino 2560 can send per second.
Not enough
http://umforum.ultimaker.com/index.php?/topic/1734-marlin-bug-the-myth-of-retraction-speed/
Short answer: 40000, assuming you’re using Marlin. If you’re looking for a more general “How fast can you signal a stepper to go using an arduino?”, I dunno.
@Whosa_whatsis Thanks fella, I am using Marlin and whatever incurs a limit first is what I’m interested in. What I know need to work out is; does the 40K steps per second limit applies to all drivers simultaneously or to each driver?
My understanding is that that limit applies to each axis individually
Nice, thanks 
@Whosa_whatsis Related question: I recall you use 1/32 drivers on the Buko. Does that mean you are using1.8 degree steppers? I ask as I recall you recommended some 0.9 degrees ones a while back. I’m running 0.9 Wantai steppers and DRV8825 on the big Tantillus but i’ve set the drivers to 1/16 as i figured 1/32 would limit top speed too much…
The .9 degree or 1.8 degree is a parameter of the physical poles in the stepper. So a .9 motor has twice the number of pole locations as the 1.8. The microstep size is interpolating smaller steps in between those physical pole steps. So if I’m not mistaken, if you use 1/32 microstep on .9 motors, your angular resolution would be .9/32 degrees. But keep in mind, torque and speed drop with micro steps. But switching from 1.8 to .9 only affects speed and resolution.
Also, higher microsteps mean less noise. Nothing I build from here on out is using those A4988s after listening to the DRV8825s on other printer builds.
I did not know that. Very good thing to know though
@John_Ridley they make apps for your smart phone that can make it sound like a muscle car. Just mount your phone on the nozzle carriage
We’re using 1.8 degree motors for those. I do like those .9 degree motors, but I would advise against using them at 1/32, at least for X/Y. Using the numbers above, I calculated that our maximum X/Y speed is 355mm/s with this setup. Your results will vary based on effective diameter of your pulleys, but for most it will probably be in the 200-500mm/s range with 6400 microsteps/rev.
Note that switching from 1.8 steppers to .9 on my cupcake with 1/16 made a much bigger difference to noise than switching a Bukobot with 1.8 motors from 1/16 drivers to 1/32. It’s anecdotal, but the higher step rate seems to make it quieter either way, at least when you have a frame that resonates, as it pushes the frequencies produced out of the audible range.
@Whosa_whatsis sweet, thanks for clarifying, I figured as much. My step/mm on x/y with 1/16 is ~125 so max speed will be 320 and I think I can live with that. As I intend to run separate infill and perimeter extruders, I have considered going crazy and running the perimeter at 1/32 with a. 9 to get uber resolution and making do with 160mm/s. I might give it a try just to see if there is a noticeable difference in surface quality.