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i3 config and Extruder settings in Marlin: Am I missing something?

Posted by SupraGuy 
i3 config and Extruder settings in Marlin: Am I missing something?
December 03, 2014 12:47PM
I'm used to being able to handle DIY stuff better than this.

I could probably work it out myself, but since I'm somewhat stalled

Steps per unit. I'd been working with the default settings in Marlin for initial configuration, and the X and Y settings of 78.7402 seem reasonable with the motors and cogs that I've got. I haven't actually measured travel, but it seems at least very close to 100mm when I tell the printer to move 100mm. The default setting for Z was WAY out to lunch (200*8/3 = 533.3333) I have it set to 4000 now, and at least it moves when I tell it to go 10mm, though I don't expect it to be really accurate, but I've still got bigger fish to fry. Since I know that the Z motors are driving a threaded rod with a 1.0mm thread pitch, the steps per unit (Assuming that 1mm is the unit in question) should then be the number of steps per revolution for the motor. I've seen some people leave a shrinkage factor in, but I would think that's dependent on the material.

I think it's close enough now that I could actually print something, then measure the resulting object, and come up with a factor that gets me real steps per unit based on what's already in place, but I want to make sure that I've got a handle on the math, because I like to be able to improvise.

So if I've got it right, the Z axis is easy, and probably the one least likely to cause me grief where real world components look like their theoretical models. As stated above, take the thread pitch of the rods, (1mm) divide by the desired unit (1mm?) and multiply by the steps-per-revolution of your motor. (or whatever your driver thinks are steps, if you're using microstepping, as I appear to be, I'm less sure how that works, since I don't know where that is in the configuration.)

X and Y should be the steps-per-revolution divided by the product of the cog pitch of your belt (2.5mm) and the number of teeth on the motor gear (12) then adjusted for the desired units... With some adjustment made since rubber belts may have some amount of stretch to them when tightened. PROBABLY not an issue for the size builds that we're doing, but I like to keep it in mind. (Working it backwards from this, I'm getting 4724.4 steps per revolution on the motor, maybe I should further adjust my Z axis, or re-measure...)

For the extruder, it will be steps-per-revolution divided by the circumference of the drive wheel in desired units. Simple enough geometry.

Does this sound correct?

Current status on my build, I have working X, Y, and Z axis. I can heat the hot end and bed, I can home the extruder, but I can't get it to move, so my 3D printer can do everything that it is supposed to do, except actually print. sad smiley

Planned troubleshooting is to connect the motor to a different axis (Say X) on the RAMPS board, and unthread the hot end to allow filament to pass through unheated, then play with pronterface and get the filament to move. The steps per unit should be similar, so should work... Right? Or am I just missing something in Marlin somewhere and it's trying to make my printer do something that it can't? Maybe it's trying to move the wrong extruder motor? Have I just missed something?

Sorry for the rambling post, I'm kind of thinking 'out loud'
Re: i3 config and Extruder settings in Marlin: Am I missing something?
December 03, 2014 01:17PM
Right, I forgot to ask because I distracted...

X, Y and Z Home positions...

looking at the printer from the front, I have the Y axis homed with the bed all the way forward. Moving it + moves the bed away from you. the X axis is homed all the way to the right, moving it + moves it to the left. (This seems weird to me, but is how I interpreted the assembly instructions.) The Z axis homes to about a sheet of paper's width off of the bed. moving it + moves it away from the bed.

I have the bed levelled so that it maintains that sheet of paper's distance with X=0,Y=0, X=200,Y=200, X=0,Y=200, and X=200,Y=0 I am working under the assumption that my sheet of glass on the bed is flat, and that even if it is not, I can't do anything about it.

Edited 1 time(s). Last edit at 12/03/2014 01:18PM by SupraGuy.
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