Z axis speed ?

Software / Firmware
#1

Im running the MPCNC with ESTLCAM saving the cnc program directly in ESTL CAM(new support for arduino is great !) onto an sd card and then inserting the card into the lcd controller unit I bought with the kit, has the firmware that came already flashed.

My question is what dictates the speed the z axis moves. I need the z axis to plunge quickly, I gradually increased the plung feedrate in ESTL but when I got to 8mm/s it seemed to stop actually going any quicker than this. Is there something in the firmware limiting Z to 8mm/s ? Is it unwise to try to make it go any faster than this ? I’m drilling very small holes (0.6mm) through stacked soft plastic straight up and down so there’s not much resistance at 30,000rpm.

Any info/advise appreciated, I’m quite new to milling.

#2

8.7mm/s is the firmware max. If you want to try and go faster you will need to switch to 16th stepping and then cut the z steps in half then you can theoretically go twice as fast.

#3

Great that answers my question perfectly ! Thanks. unrelated question - Do you know of anyone implementing a sensor or similar to automatically stop the router if the bit breaks or other unwanted scenarios ? I was thinking of mounting a ip camera to the middle assembly to watch it as another option.

#4

Back on the z speed topic (sorry I went totally off it into a new one!)

As I understand it all I need to do is change the firmware as follows and re-flash:

From this - #define DEFAULT_AXIS_STEPS_PER_UNIT {200,200,4535.44,200}
To this - #define DEFAULT_AXIS_STEPS_PER_UNIT {200,200,2267.72,200}

It will then be possible for the z axis to move at max 17.4mm per second ?
Is there anything I’m missing here ?

Is there also some limiting factor in the acceleration speed ? If so, over what distance are the acceleration speeds applied ?

Would it be possible/easier to change the speed settings using the lcd screen ?

Sorry if these are stupid questions, Im completely new to all this ! I’m absolutely loving the machine though.

#5

That line is is correct if your are going to 16th stepping.

The next line is for max speed. you’ll need to change the 8.5 to 16 or 17. And the next line is acceleration you might have to play with the 35.

#define DEFAULT_MAX_FEEDRATE {190, 190, 8.5, 25} // (mm/sec) MPCNC
#define DEFAULT_MAX_ACCELERATION {500,500,35,10000} // X, Y, Z, E maximum

Acceleration is linear so it’s mm/second/second. good visual here, http://prusaprinters.org/calculator/, although it doesn’t help visually with a screw. At top speed in 32nd stepping the screw is going 4535.448.5=38,551 steps per second on the z axis alone, that is close to the processor max of about 40,000/sec. you can go all the way down to 1/4 stepping and still be okay. Anything less and it gets a little chunky sounding. What this gets into is max speed of a stepper territory. torque starts to drop off at above 60 rpms. So there are 200 full steps per rev. Just doing the math here, probably best to stay below 200fullsteps/sec = in 32nd stepping that would be 20032=6400. So 3200(16th steps per sec) is keeping the torque at a max. So 16th steps do not help you torque at max speed you are actually going to be running weaker so you will need to accelerate slower.

At 38,551 steps/sec we are running about 360rpm and that is about 57% of full power.

#6

Wow, thanks for the quick and informative reply! I think I follow after reading a few times. I can see the acceleration visual but as you say that’s applying to linear motion on the rails. I will try to come up with a similar graph incorporating the threaded rod/travel per rev. It might not actually be faster overall if the acceleration needs to be a lot slower. The Z axis is only moving 6mm down then back up again.

Is there a setting I need to change to switch to 16th stepping or is that being done inherently by changing the steps per unit ?

#7

You need to pull a jumper or two from under the driver. So when it all comes down to it I don’t think it will matter that’s why I ship it at 32. and limit the max speed. Any faster and you will lose power and possibly miss steps. The only way around this is a different screw, but then you have to worry about backlash. There is some links in the FAQ.

R

#8

Hmmm. Ok this sounds like probably more trouble than its worth. Thanks for the info, very much appreciated.