MontyFlange wrote:I thought the speed settings where set in the software. Makerbot Desktop seems to get the times right .
Yes, default print speeds are set in software. Slicing a file will then generate the different locations the toolhead should move at, accompanied with a feedrate, which tells how fast to execute the command. The firmware, however, ultimately decides how to interpret and execute the travel move. Say, for example, a command is sent to a printer to move from point a to point b at 7500 mm/min (125 mm/s). The firmware itself will have its own max feedrate, for example 3600 mm/min (60 mm/s) and even though you set the speed in software to print at 7500 mm/min, the firmware will execute the move at 3600, since it has been programmed not to travel any faster than that. There's also acceleration to take into account. For example, if you tell the printer to move at 7500 mm/min, and say it is able to move at that speed, but the move itself is only 1mm, it won't actually have made that move at 7500mm/min, but a fraction of that, depending on what the acceleration value is set in the firmware. There are also other values such as jerk, max allowed acceleration, homing feedrates, PID of your heaters (it can take 10 mins sometimes to heat my large build volume to 100 degrees) etc etc.
With all of these different variables to account for, you also have to remember, not all printers have the same values for any one of these values, it's actually more common printers will have different values than they do equal values, depending on the hardware and build. If you're using a Makerbot printer in conjunction with MakerWare, it's quite possible they take into account some of these firmware level values, as they are the makers of it and know the values and don't care if other printers have values that are off since they only really support their printers.