# Manual milling using a CNC mill & MPG question.



## Reddinr (Jan 19, 2017)

I have a CNC converted mill from International Hobbies.  It is one like Charter Oak does now.  I think it is called a column mill.   It has been a pretty good and useful mill.  I'm running Mach 3, still using a parallel port.  It is a pretty fast computer running Windows XP.   At times, I just need to do some simple operation and I try to use the MPG (manual pulse generator) pendant to do an axis move.   The MPG is set up for 1X, 10X and 100X motion which can be selected.  If I move at 1X, I can get smooth axis motion, but really slow.  If I select 10X or 100X, the motion is jerky, like the software catches up, then pauses, etc..  Is there some setting in Mach 3 where it will provide some ability of moving the axis faster but smoother with an MPG?   I don't want to change anything that makes the CNC control change as it works well now.   I know moves can be entered in Mach but I'm just wondering if I can make the MPG more useful for  simple cuts.  Would external hardware like an ethernet smoothstepper help with this?


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## Boswell (Jan 19, 2017)

Not sure how to solve that. When I need to make simple cuts, I just use the MDI and input GCODE directly. You only need to know a few GCODES to do straight cuts. Start the spindle with the control panel, set the cut speed with the control panel, Zero your X and Y, then issue gcode like G1 X=1   (one inch movement to right).


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## jbolt (Jan 20, 2017)

Does the mill move properly when using the virtual MPG in Mach3?


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## Reddinr (Jan 20, 2017)

I don't know if the virtual MPG works better or not.  I really have not used it that much.  I was hoping to have the hand-held so I could be standing by the part as it was being cut.  Maybe I'll start just inputting the G-code moves as my back-up plan but I would still like to cure this.  I think the X10 and X100 settings just tell Mach to scale up the pulses by those factors.  I think that Mach just isn't doing that smoothly.  I could be wrong.


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## rdean (Jan 20, 2017)

On my big router I have Mach3, ethernet Smooth Stepper, and a C22 board from CNC4PC that connects to the MPG. 
I am not sure what you are saying about the speed as that is set in the fly out manual screen in Mach3.  On the same screen you have a "Cycle Jog Step" button that shows how far the axis will move for each input.  I didn't say for each click of the MPG as that has to be calculated.  There is also a button at the top of that screen that says "Calc" and that is the first thing you need to do after installing a MPG.  Read through the Mach3 docs on this subject as it can be involved.
Evidently your machine came with the MPG installed so this step should be already set up.

Actual use
When you turn the hand wheel 10 units the machine will move that distance but if you spin the hand wheel not all of the units are counted and the machine may not move to where you want it to be.  By using the C22 board it keeps track of the number of units moved on the hand wheel and feeds that info to Mach3 without missing counts.  If I turn my hand wheel 1 turn and then while the machine is actually moving to that spot I turn the wheel another turn the machine will come to a stop for a split second before moving to the second input.  

I do not use the MPG for anything except for positioning and not for actually cutting.  If I want to make a manual feed cut I will use the jog buttons after I have set the speed, and moved the cutter to the desired depth.  By using the jog buttons you have more control and a smooth feed.

Send me a PM if I can help

Ray


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## jbolt (Jan 20, 2017)

Reddinr said:


> I don't know if the virtual MPG works better or not.  I really have not used it that much.  I was hoping to have the hand-held so I could be standing by the part as it was being cut.  Maybe I'll start just inputting the G-code moves as my back-up plan but I would still like to cure this.  I think the X10 and X100 settings just tell Mach to scale up the pulses by those factors.  I think that Mach just isn't doing that smoothly.  I could be wrong.



If the machine moves smoothly with the virtual MPG then it is something t do with the hand held MPG (settings etc.). If it exhibits the same behavior with the virtual MPG then it may be a Mach3 setup or a hardware issue.


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## spumco (Jan 21, 2017)

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


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## Boswell (Jan 21, 2017)

When I am jogging the machine for various reasons and need to move large distances (.5" or more) I put it into continuous mode. When I do that, as long as I am turning the jog wheel it moves along the axis I have selected. When I stop turning the jog wheel, it stops moving. I have never used this for cutting but I guess it could. I think the jog speed is controlled by the "Rapid" setting so you will have to figure out how to manage the speed properly. For me, way more work than using the MDI field. There was also some sort of proportional control where the speed that I turned the jog wheel effected the speed of the movement but that did not seem to work well and had limited value for me so I never spent any time trying to figure it out.


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## jbolt (Jan 21, 2017)

+1 on the xbox controller.


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## Reddinr (Jan 21, 2017)

Thanks very much for your replies.  I'll try out some of the ideas in the next few days.  I do think my MPG and setup are in good working order.   I kind of had an idea that the MPG was squirting out a bunch of pulses as you said spumco.   The Vistacnc prices don't look to0 bad.


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## coherent (Mar 1, 2017)

I  know this thread is a little old, but thought I'd chime in anyway.
I have a VistaCNC pendant and use it for manual cutting on my CNC mill quite often for simple things especially like squaring or surfacing a part or edge.
I simply set the slow jog speed in mach 3 to match my desired cut speed and use continuous mode. It will move at the slow jog speed as long as the wheel is rotated. The speed the pendant wheel is rotated doesn't matter and the cut speed doesn't vary and is consistent as long as the wheel is turning no matter how fast or slow. As soon as I stop turning the wheel, movement stops. Rotate clockwise for axis positive movement and counterclockwise for negative movement. Select which axis to move by the press/selection of a button. I can fine tune position by selecting step mode. Set any step amount (hundreth, thou, 10 thou etc) in Mach3 and select step mode and it will move one step each wheel detent very precisely. Most models have a LCD that shows the "DRO" position of the selected axis without having to even look at the computer screen. All in all really handy... like a DRO and powerfeed on steriods. I'm not affiliated with Vistacnc in any way but I highly recommend their pendants. Once you use one a bit it becomes pretty much second nature to quickly do "manual" milling on a CNC mill.


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## Wreck™Wreck (Mar 1, 2017)

Servo or stepper machine?


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## coherent (Mar 2, 2017)

Wreck™Wreck said:


> Servo or stepper machine?



If the question is meant for my me and last post, my mill has steppers but I doubt as far as the pendant goes its an issue one way or another. Cut speeds are so slow compared to the machines max feed rate capabilities that torque isn't an issue nor lost steps. Also, most of what I machine is aluminum. A servo driven closed loop/encoder setup would be best I suppose.


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## spumco (Mar 3, 2017)

The servo vs. stepper question, while always interesting, is not really applicable to the OP's question.  Either drive system will accelerate, move a certain distance, and decelerate when used with a 'dumb' MPG in step mode resulting in the not very smooth motion he was experiencing.

The difference in drive systems might only become obvious when a stepper system drive is set to full-steps (no micro-stepping) and moved very slowly at a constant rate.  The magnetic poles would then cause some 'clunking' at very low speeds, and a 'throbbing' at slightly higher speeds, especially if they're direct drive on the ball screws.  Enabling micro-stepping should smooth things out, as does switching to 3-pole steppers, or the rare stepper that has more than 200 steps per rev.


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## lens42 (Mar 3, 2017)

I used to use jog dials for manual machining, but I now find manual data input much easier. I don't use Mach 3, but in my machine, an "up arrow" runs through previous commands so repeating a move is very easy - do a pass, drop z 0.05" with the dial, then repeat the x move that's already in the manual data window. 


Sent from my iPhone using Tapatalk


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