September 19, 2018 at 6:43 pm #69757
I’m just starting to use my mpcnc and I’m noticing my cuts aren’t as deep as I’m expecting them to be. It has me wondering if I didnt set something up right.
I attached a pic of repetier host where it says my z axis is 6, I assume mm? But looking at the actual depth, it cant be more than 2mm.
My assumption is I didnt set it right in the source code when I uploaded the firmware to my ramps board? This is just my speculation and I’d love to get a second opinion before i redo my firmware.
Thanks in advance
Attachments:September 19, 2018 at 6:54 pm #69761
This depends on your Z steps in the firmware, driver, step rate of the driver, Cad settings.
You you tell your Z axis to move 10mm and give us an exact number of how far it moved we can usually narrow it down.September 19, 2018 at 7:32 pm #69767
This is a noob question but…. one step is one mm right?
My first assumption is it’s in the firmware, but I haven’t found the original firmware I setup. What places should I look, and is there a good way to narrow it down?September 20, 2018 at 4:26 am #69775
No, one step is way less than a mm.
One step means that your stepper motor moves by one increment, for nema17 motors this is usually 1.8°, meaning it takes 200 steps for a full rotation.
With a 16 tooth GT2 pulley you get 16 * 2mm = 32mm movement per rotation, so 32mm / 200 steps = 0.16mm per step.
And then you have microstepping, which means you can also move the motor in half steps, quarter steps or even smaller, commonly used are 1/16 steps and 1/32 steps.
So with 1/16 steps you’d only move 0.01mm per step.
On the leadscrew of the Z axis this works similar, but without knowing what your setup is I can’t tell you how many steps per mm you have to set in your firmware…
Edit: The steps per unit setting is in the section “Movement Settings” in Configuration.h, search for DEFAULT_AXIS_STEPS_PER_UNITSeptember 20, 2018 at 4:35 am #69778
One more thing, Prusa has a bunch of calculators on their website to help with this stuff, here’s the one for calculating steps/mm for leadscrews:September 24, 2018 at 3:55 pm #70236
ok so it’s been a bit since I last posted. I am starting to dive into this a bit more. I uploaded fresh firmware to make sure I was starting with something correct. From this page: https://www.v1engineering.com/marlin-firmware/ – I downloaded the MPCNC813_GLCD_T8 since I’m using an M8 rod for my z axis.
What’s confusing me is, in repetier host, when I use the manual controls, if I tell it to move “10” on the X or Y axis, it moves 1CM. the Z axis is significantly less. I have to move it “60” to show a rise of ~1CM.
I understand the comment about steps, but shouldn’t they all travel the same distance on each axis and let the ramps board/marlin firmware figure out the steps? what am I missing?September 24, 2018 at 4:05 pm #70237
Also… This on a ramps 1.4/arduino mega board.
16T pulleys, M8 threaded rod for the z axis… and lemme know what else you need to know?September 24, 2018 at 8:43 pm #70268
An M8 Threaded rod is not a T8 leadscrew (the firmware you have). You need to set the proper Z steps.September 24, 2018 at 8:47 pm #70271
I understand the comment about steps, but shouldn’t they all travel the same distance on each axis and let the ramps board/marlin firmware figure out the steps? what am I missing?
No, you have to figure out the steps. There is no way to put thread/pitch/diameter/teeth information and have it calculate the amount of steps. That’s why that calculator that was posted was created in the first place.
You say you are using an M8 rod, generally that means a threaded rod very similar to a screw (1 start) , while the T8 firmware is for a 4 start T8 leadscrew, which I am theorizing as the reason your steps are off. M8 rod is 1.25mm per revolution, while the T8 screw is 8mm per revolution.September 24, 2018 at 9:30 pm #70278
Steps will be 5102, I think. And you need to limit your max Z speeds to 7.5 mm/s or under.September 25, 2018 at 8:02 am #70304
This makes a lot more sense. I’ve never really taken a dive into the settings like I probably should have and I definitely made some assumptions along the way. I understand now on the steps, though if you don’t mind educating someone just a little more, why does the max Z speed need to change? I’m guessing it’ll just push the motor a little too hard? Shouldn’t matter at this point, but I am just curious to hear from someone with infinitely more experience than I have, lol
Regardless, thanks for the help guys!September 25, 2018 at 9:19 am #70312
The CPU can only do so many step pulses per second. You can see and X or Y move is about 200 steps, your Z is 5000 that means it can only go roughly 1/25th the speed. try and go too fast and it will just disregard steps and will not move. On top of that the faster your run a stepper the weaker it is.October 3, 2018 at 5:45 pm #70976
Glad I found this thread! I accidentally bought a M8 leadscreaw too.
I’m just buying the proper T8 part and saving myself more troubleshooting woes.
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