Prusa i3 Clone Bed Leveling Issue

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SMatthews95
Posts: 4
Joined: Sat Nov 03, 2018 5:37 am

Prusa i3 Clone Bed Leveling Issue

Post by SMatthews95 » Sat Nov 03, 2018 6:31 am

I am relatively new to 3D printing. I've used them for projects at my university, but I came across Tom's Dolly tutorial and decided to build one (see pictures below). I didn't go for absolute lowest cost. Instead I used an aluminium frame, trapezoidal rods, and mini-RAMBo 1.3a as a control board (all knock offs sourced from China).

The mini-RAMBo came pre-loaded with the latest Prusa MK2 firmware. My bed is an aluminum Chinese knockoff and while it's the same size and is painted to look like a MK42, it doesn't have the correct heat trace pattern or the calibration points (as far as I can tell). As such, I don't expect the XY calibration feature to work correctly. However, the mesh bed leveling should work fine as far as I understand it.

When I try to run bed leveling, it performs a check in the front left, performs a check in the front middle, then the problem happens. The extruder assembly travels too far to the right on the x-axis such that when it comes down, the inductive probe is off the bed and the part cooling fan shroud hits the print surface.

Given that all of my dimensions should be virtually the same as an actual MK2, what am I doing wrong?

I'm currently fiddling with flashing the board with some Marlin firmware, but I'd still like to understand why this is happening.

Any help would be appreciated.
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Stefan
Posts: 223
Joined: Thu Jun 15, 2017 12:46 am

Re: Prusa i3 Clone Bed Leveling Issue

Post by Stefan » Sat Nov 03, 2018 7:48 am

Hi SMatthews95,

Welcome to the forum and congrats on your Dolly! If I had to guess, I would say that the difference in the Prusa bed leveling and the mesh leveling is the culprit. The Prusa system depends on the special calibration points, exclusively, so the print head comes down only when the probe is in the correct spots. The mesh leveling system moves to points over the bed that do not guarantee that the probe is still over metal. This can be adjusted in the firmware so that all the points are on the bed.

My Dolly uses mesh leveling and does a great job with first layers.

-Stefan

SMatthews95
Posts: 4
Joined: Sat Nov 03, 2018 5:37 am

Re: Prusa i3 Clone Bed Leveling Issue

Post by SMatthews95 » Sat Nov 03, 2018 4:29 pm

So the option in the Prusa calibration menu that says "Mesh Bed Leveling" still relies on the calibration points on the MK42? Based on the motion of the extruder head for the first two successful points, it seems as if it is simply doing a proximity check using the inductive probe - not doing the side to side scanning motion for the calibration points.

If it is looking for the points and not finding it, that could explain the error. However, if it isn't looking for the points, why would the firmware not come with leveling travel limits suited to its geometry?

Here's a video:
[youtube]https://www.youtube.com/watch?v=Lpyrc49 ... e=youtu.be[/youtube]

Stefan
Posts: 223
Joined: Thu Jun 15, 2017 12:46 am

Re: Prusa i3 Clone Bed Leveling Issue

Post by Stefan » Sat Nov 03, 2018 6:57 pm

I don't think the mesh leveling ever relies on the calibration points, just Prusa's leveling. Beds vary a bit in dimensions, roughly 200 to 230mm; setting the firmware for all configurations would be impossible. (Or they didn't bother to check?). It is adjustable, so dive into your firmware and look in configuration.h (or equivalent depending on what Prusa did to Marlin).

SMatthews95
Posts: 4
Joined: Sat Nov 03, 2018 5:37 am

Re: Prusa i3 Clone Bed Leveling Issue

Post by SMatthews95 » Sat Nov 03, 2018 9:11 pm

It occurred to me today that I had gotten both 16 tooth and 20 tooth pulleys in my order. I may have put the wrong one on, accounting for the over travel issue. I have a strong suspicion that's what happened.

Stefan
Posts: 223
Joined: Thu Jun 15, 2017 12:46 am

Re: Prusa i3 Clone Bed Leveling Issue

Post by Stefan » Sun Nov 04, 2018 4:38 am

That would certainly explain why your first calibration point is so far from the left side! Just try sending the carriage to 100, 100 in x & y. If it isn't near the center you may be right.

SMatthews95
Posts: 4
Joined: Sat Nov 03, 2018 5:37 am

Re: Prusa i3 Clone Bed Leveling Issue

Post by SMatthews95 » Thu Nov 08, 2018 3:05 am

Yep. That was it. I swapped out the pulleys and now the bed leveling works fine.

I got my first print off and it came out pretty well all things consider- a bit of under extrusion, but pretty good. However, I had a pretty significant layer drift issue. (See photos below.) Each layer was increasingly offset from the one below it, but in a very regular way.

My theory is that there was some specific/repeated rapid movement in the G-code for resetting between layers and each time that movement happened, the y-axis stepper skipped a step. From my limited understanding this is a current setting issue. If I was using RAMPS I would adjust the trim pot on the board. However I'm using and mini-RAMBo 1.3a, meaning I have to adjust the setting in the firmware, correct?

Also if anyone has any other suggestions on the cause, I'm all ears.
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