Jim - from what you're saying, I'm not sure if you've gone the right way about setting up your machine. Unfortunately, copying someone else's DIP switch settings sounds like a great idea, but only if your machine is identical to theirs!

Briefly - a leadscrew/ballscrew pitch of 5mm means that the nut moves 5mm for every turn of the screw (or 10mm movement for a 10mm pitch screw, or whatever). A standard stepper motor will turn one revolution in 200 steps, so each step will turn the leadscrew by 1/200 of a turn, and this will move the nut by 5mm/200 = 0.025mm (if I've done my sums right, and assuming that the motor is geared to the screw 1:1). The job of Mach3 is to take a line of gcode that says, perhaps, "move the cutter along the X axis by 10mm" and translate that into the number of "step" pulses that it sends to the motor controller board. This board then turns those pulses into the rather more complex signals with lots more power that are used to actually turn the stepper motor. That's why you have to tell Mach3 about the stepper motor configuration and the pitch of the screw and it can do the sums it needs from that. If you tell Mach3 in the settings dialogue the right numbers, then the movement will be pretty close to exactly what you intend.

It gets slightly more complicated if you use micro-stepping. I said that a standard motor will turn exactly one revolution for every 200 steps sent to it. However, you might want it to move in smaller steps. The controller board can do this for you by modifying the signals that it sends to the motor. What you have to do is tell the controller board how many steps you want per turn. A typical number might be 800 steps per rev. If you look at the manual for the board, you can find the DIP switch settings that specify 800 steps/rev (might also be called 1/4 steps or some such). The motor will now turn one rev for every 800 steps, but you also have to tell Mach3 about this so it knows how many pulses it has to send to move the cutter by any specified amount. So, the settings page of Mach3 asks for the microstepping amount. Again, though, if you put in the right numbers you will get the right amount of movement and while you might want to double-check by measuring it that it's right, you should be very, very close without any need for "calibration". Something else that you need to tell Mach3 is if there is any gearing between the motor and the screw; if you have 1:2 gearing so that the screw turns at half the speed of the motor, then clearly you need twice as many steps sent to the motor to move the leadscrew nut by a given amount because the motor has to go round twice for every leadscrew turn. Again, you tell Mach3 about this gearing and it does the appropriate sums when it calculates numbers of step pulses to send.

Why don't you just use the highest available number of microsteps per rev, then? Won't this give better accuracy because there are more steps per rev so the smallest amount you can move is smaller, so you can position the carriage in smaller increments? Well, in principle, yes, but there are other factors. Stepper motors aren't actually that accurate as the number of microsteps is increased, certainly not when you get to very high numbers, and the actual torque available (in effect, the amount of "shove" that the motor can apply) reduces. Another very important point is that you need more step pulses out of Mach3 to move the carriage by a given amount and there is a limit to how fast Mach3 can generate pulses. As Jazz has said, this is related to the kernel speed setting, and in turn this is governed by the PC hardware. Some hardware is capable of higher speeds than others, but Jazz has given a reasonable value. Now, if you ask Mach3 to deliver more pulses more quickly than its kernel speed setting allows, it will just limit at some lower value. Quick example with 5mm pitch screw. You want to move 50mm in 1 sec. With 200 steps per rev (standard motor setting, no microsteps) you need 10 turns per second which means 10x200 = 2000steps/sec. With 16x microstepping (3200 steps/rev), you will need 16x2000 = 32000 steps/sec. If the kernel speed limits the pulse rate to, say, 20000 steps/sec, then you will not achieve 50mm/sec movement because you just can't send pulses that fast and your machine will move slower than you expect. OK, in practice, there are some other issues involved but this gives the basic picture. This might help explain why Jazz has suggested that your microstep settings are too high.

If you can give the basic settings as Jazz has asked, it gives a lot more understanding of the machine setup and is a good way to move forwards with some better values to try.

Sorry I've rambled on a bit, and this stuff is basic knowledge to a lot of people on this forum, but for people new to the area it might give a little bit more insight into what the numbers mean and how they relate together. Anyway, you only have to go through it all once, and then the machine is set to go!