OneUp V2 Build Log.

[mr_intensity]

Impasse

Now what?

Okay, get some Blue Painter's Tape (BPT) on the build surface, so prints do not stick to the surface forever.  Using a razor blade, I cut the edges nice and clean.

   

Next, un-level the print bed.

No, that is not a misprint.  It is time to un-level the print bed.  Usually, one tries to level the print bed.  However, the "stock" OneUp X-carriage has this serious "droop" on the right side.  A level print bed would either cause the print head to crash into the print bed (as it went right) or be too far away from the surface to properly lay down a layer (as it went left), or both.  In order to properly print, one needs the "crookedness" of the print bed to match the X-carriage's crookedness.

Of course, your prints will all be skewed (your alignment cube will look like a parallelagram from the side), but the printer will (theoretically) print, which is all I want at this point.

Time for an aside.

Aside:  I never knew what "auto bed leveling" was, until just a few days ago.  I always thought it used small steppers to adjust the screws on the bed corners, or something.  It doesn't.  Also called auto-tramming, it actually uses a sensor (near the print head) to "sense" the bed, figures out how screwed up your bed-to-Xcarriage-unparallelness is, and the firmware adjusts your print to "counterskew" everything so your print comes out right while your print head avoids crashing into the bed.

Anyway, back from the aside, I wouldn't mind hooking up a sensor to this whole thing, and using auto tramming/levelling to "fix" the droop problem.  There are multiple issues with this solution:

• I don't have a sensor.
  
• There's no place to mount the sensor where it does not "miss" the bed at one end/side/corner.
  
• The best/cheapest solution would be an inductive sensor, which would require an aluminum (actually iron) print bed.
  

So, we are back to un-levelling.

Now, someday in the future, I still would not mind an inductive bed sensor.  I could 3d-Print the X-carriage bearing/extruder holder to have a sensor holder on it (behind the bearings, opposite the print head).  I could replace the stock bed with an aluminum plate (longer on the back side, so the sensor does not miss the bed).  Furthermore, I could mount heating elements and a thermistor on the backside of the aluminum plate, to create a heated print bed.

This is, of course, all pie-in-the-sky dreaming.  Right now, I have to un-level the print bed.

I had my procedure all thought up:

• Tighten down the corner bed screws about five turns.
  
• Manually move the print head to the front right corner (same as "homeing" the print head, except we are going right instead of left).
  
• Lower the print head until one could barely slide a business card between the print head and the bed.
  
• Manually move the print head all the way to the left.
  
• Loosen the left front bed screw, allowing the spring to raise the left corner of the bed to meet the print head.  Stop at about a business card's thickness from the print head.
  
• Manually move the print head all the way to the right.
  
• Manually move the bed all the way to the back.  Make sure you do not crash the head into the bed doing so.
  
• The print head should already be a business card's thickness away from the bed.  If not, tighten/loosen the back right screw to compensate.
  
• Manually move the print head all the way to the left.
  
• Loosen the left rear bed screw, allowing the spring to raise the left corner of the bed to meet the print head.  Stop at about a business card's thickness from the print head.
  
• Finally, use the manual control panel in Repetier-Host/Pronterface to move the all the way forward, all the way right, all the way back, all the way left, and all the way forward again.
  
• The head should not have contacted the surface during the moves, and you should now have the head at the home position.  Click the home buttons to let the Marlin firmware know that the print head is homed.
  

It was a disaster.

First, just about five turns is all I could get out of the screws before the springs were completely compressed, and could not go any further.

Second, I needed more than five turns differential between the left and right sides of the print bed.  I either need shorter screws/springs on the right side, or longer screws/springs on the left side.

I just cannot unlevel the print bed enough to compensate for the X-Carriage droop.  This is my impasse.

There are two permanent solutions to the X-Carriage droop.  The first is the Pulley System.  You should use a non-stretchy line, like kevlar thread.  I have that.  The solution I am conidering uses a guitar/ukelele tuning machine head to take up final slack/adjust on the right side.  I don't have one of those, but I live within walking distance of a music store called "Pianos 'n Stuff" (Who'd a thunk it?), where I can pick one up.

The second option is to completely replace the X-carriage with something 3D printed.  This pretty much requires me to replace the extruder as well.  There are many X-carriage solutions that use a Bowden-style extruder.  I want to stay direct, for now.  Forum member floridaservices has turned me on to a direct extruder  X-Carriage solution on Thingieverse.

Really, both solutions require that I get them 3D-printed, and I still have to make a decision.

Until then, I have other aspects of the OneUp to mess with.