It has been about a week since my OrdBot's first successful calibration print and it seems like a good time to write down some of my initial problems, experiences and solutions. However before I get into that a review of my 3D printer stack.
3/8"-12 TPI ACME Z-Axis screws
1.8 degree Nema17 X/Y motors
1.8 degree Nema23 Z motors
Qu-bd MBE Extruder (with some modifications)
AzteegX1 v1.0 (644P processor)
Lava heatbed, I have only used PLA at this point so this is still disconnected.
Pronterface (March 2012 release)
Repetier-host Mac (0.56, lower versionthan linux/windows releases for some reason)
Now for the problems encountered during the past week, approximately in the order which I ran into them.
Pololu A4988 - I have used these before on my ShapeOko CNC machine. They have been so reliable that I completely forgot how to set them up, as such I blew up 3 drivers while setting up the electronics. So be careful, check the polarity and for the love of everything don't measure voltage when your multimeter is in continuity mode!
Leveling the bed - This was tedious but not particularly difficult. The LAVA heatbed has 8 M3 screws along the perimeter so calibration was just a matter of carefully tightening them until the height is just right. To measure the height I lowered the printer nozzle until it had just enough space for a piece of paper to slide underneath with little resistance, at this point I manually jogged the nozzle along the perimeter adjusting the M3 screws as necessary until the bed was level.
Setting the Z-Axis endstop - This step is ongoing and was very tedious without a way to precisely raise or lower the endstop actuator (a screw in sliding t-slot nut). I have it set fairly close, but still find myself hitting the "stop motor" button and manually turning the Z-Axis screws while the first layer is printing. Eventually I will print out something like this and dial in the Z endstop a more reliably.
Configuring steps per mm - This was the longest part of the process, and I'm still not sure why. Fortunately it wasn't difficult, just tedious. I know the steps per revolution on my motors (200), the microstep resolution for the steppers (16x), the pitch of MXL belts (2.032mm) and the number of teeth on the pulley (16). Using the equation on the buildlog.net configuration page gave me a number which ended up being way too small. My calibration object of choice was the nickel test thing on thingiverse, I just kept printing them out, measuring the insides and adding a ratio multiplier until satisfied that things were the correct size.
Pololu A4988 overheating - Once I had my machine calibrated I started trying to print larger objects that took more time. Without fail after 5-10 minutes after starting the machine would start losing steps. Eventually I noticed how hot the stepper drivers were and mounted a fan pointing at them which fixed the problem.
The notorious QU-BD MBE. This thing gave me a ton of trouble, so much so that I ordered a J-Head after the first day of trying to get it up and running. That said I've managed to get it to print very reliably and haven't yet felt the need to install the J-Head.
QU-BD pre-upgrades - Before I even had my printer assembled I performed some upgrades on the QU-BD. First is the QU-BD Modification Kit from the MakerSlide store. Secondly I hobbed the stock raptor gear with a small tap in my electric hand drill.
QU-BD overheating jam - There is a fan and heatsink on the extruder. I wired it (incorrectly) to the Azteeg X1 fan input, making it configurable in gcode (M106 and M107). My slic3r configuration toggled the fan on and off, so occasionally the cold-end of the extruder was heating up too much causing a jam. My current solution is disabling the cooling option in slic3r, but eventually I will wire the fan directly to the 12v input.
QU-BD underheating jam - My printer is in the kitchen and there is a nice crossdraft going through the room now that it is nice outside. The crossdraft was causing the nozzle to drop below 165 degrees, when this happens things usually jam. I need to wrap the hot end in some sort of insulation which will hopefully fix this problem.
QU-BD slicer jam - While printing the nautilus gear thing I was noticing frequent jams during the infill stage. The thing about this object was that there was very little amount of infill needed so the filament moved very slowly. My best guess is that the filament was sitting in one place so long that it heated up too high in the extruder which caused the jam. After reconfiguring slic3r to leave the object hollow there were no more jams on this print.
Pronterface vs. Repetier-host - This could probably be a blog post on its own. They both work but suffice to say that repetier-host is leaps and bounds ahead of pronterface in terms of usability. The one problem I had was that repetier-host allows you to configure the controller buffer size, the default is 63 which causes stuttering when printing complex surfaces with short line segments. I upped this value to 127 when I was 75% finished with the owl print (below) and you can tell just from looking at the surface of the model where I made that change because the surface quality improved dramatically. I just wish I had found that setting before printing all those feathers!
This owl is my longest print to date at 3 1/2 hours. This print was running while a draft was running past the printer, I probably fixed 5 or 6 jams while it printed which caused a several noticeable defects (most of them on the owls back).
After many attempts I finally got the Nautilus Gear to print. Now that everything is dialed in I could print one out in about an hour (~12 minutes for the two clips and ~18 minutes per gear).