Assuming nothing is actually broken, your issue is that the MPG - if it's a simple dial type - sends individual pulses to Mach3. Each MPG click/pulse causes Mach3 to send a number of pulses to the axis drive (stepper or servo) depending on the steps/microsteps of your drive. Mach3 accelerates the axis and then decelerates the axis an amount that depends on your steps per inch settings. Repeat for each 'click' of the MPG and you get jerky motion, because you are telling Mach3, in effect, "step-stop, step-stop, step-stop."
The same situation will be observed if you put the Mach3 jogging panel in 'step' mode and press the keyboard or screen jog buttons as fast as you can. "Thump-thump-thump-thump" as your axis moves .001" (or whatever step value) in individual movements.
Switching to the 10x or 100x setting causes the MPG to send 10x or 100x the pulses for each click. Mach3 has more time to accelerate the axis per MPG click, so the start/stop appears even more jerky.
A smooth-stepper or other motion control hardware will NOT improve this, because whatever you think you're doing, you're actually commanding Mach3 to move in discrete steps. If you have jerky motion when running a gcode program, that's when the smooth-stepper should improve things dramatically.
To get smooth motion you have, I think, four options. Someone else may have additional suggestions.
1. Use the keyboard or screen buttons - when you jog and make sure you've set the jog to "continuous" mode. Set up the cut position with the MPG (sneak up on the location where you want to start), and then use the arrow keys on the keyboard to move the axis once the spindle is running. The keyboard buttons cause Mach3 to simply move at the jog % rate without the acceleration/deceleration that individual MPG pulses cause. If you want a certain feed rate, then determine your max axis IPM rate (max rapid), and set the jog % to cause a jog rate you want. For example: you want 20IPM while machining, and your max axis speed is 100IPM, set the jog to 20%. You axis will now move at a smooth 20IPM with the buttons while in continuous mode.
2. Use the MDI (manual data input) field on the main screen as you indicated in your reply earlier. In this case you would again use the MPG to sneak up on start point of your cut and then type a Gcode command in the MDI field. Let's say you want to clean up the edge of some 4" wide stock held in a vise. Assuming the vise is pointed front to back, and the stock is side to side, you'd jog the table or tool to your cut point where you are about to shave the rough edge. Zero the X/Y/Z screen DRO's. The actual cut will be in the Y-axis, so you'd start the spindle and type "G1 F20 Y-5.000" then hit enter. The Y-axis will then move at the feed rate to the commanded location and clean up the end of your stock. Practice a few times with the tool above the part ("air cut") and you should get the hang of it.
3. Replace or augment your MPG with a "smart" MPG. There are a number of MPG's available for not much money that have a 'constant velocity' or 'continuous' feature. These plug in to a USB port on the computer and usually have a nice plug-in (software control) for Mach3. You can set them to move the axis continuously instead of just in individual steps. In this mode when you turn the dial the MPG just sends out a continuous stream of pulses without the start-stop problem. Vistacnc.com is one source of reportedly high-quality smart MPG's that should permit you to treat your CNC mill/router like a manual machine with power feeds.
4. Replace or augment your MPG with an Xbox controller. I have one of these and it's pretty slick; it also plugs in to the USB port. The plug-in for Mach3 permits the joystick(s) to function as a proportional 'throttle' in continuous jog mode. Again, you would set your jog feed rate to whatever IPM you want to cut at, and then - once you're in position - mash the joystick in the direction you want to cut. Result: smooth motion at the speed you want. The danger here is that if you accidentally move the joystick at an angle you're going to move BOTH the X and Y axis at the same time, probably wrecking something and causing a ferocious fecal-shorts encounter.
Trust me, it's frightening to jog a small mill around at 200IPM with joysticks. The Mach3 Xbox plug-in has a safety feature that optionally prohibits multi-axis moves, regardless of what you do with the joystick - thus saving you from the crash described above.
In summary - dial MPG's cause the axis to move in individual steps; they move the axis in precise amounts but are not designed for continuous axis motion. If you want smooth motion for quicky cuts, you need to tell Mach3 (or whatever the controller software is) to move in continuous mode.
Hope this helps. I'm new at CNC, but have had to deal with this exact problem when I bought my mill.
Regards,
Spumco
