Since my last post, I have worked to print and put together all six legs for the first version of the StIRLing Platform. I finally succeeded in this process, but it took longer than expected.
A Jammed Extruder
After the first test leg was tweaked and the design finalized, I decided to bulk print five of the first leg bracket. This bracket connects the first servo (which provides allows the leg to move back and forth) to the second servo, which functions as a knee joint, allowing the leg to pivot up and down. I set up a print in Repetier-Host made up of five of these brackets, a print that would take around 5-6 hours to complete.
A couple of hours in, the extruder jammed. I stopped the print, removed the failed brackets and started to open the extruder. I noticed that the extruder had managed to squeeze filament out through the threads between the barrel and the heater block, a defect called retrograde extrusion. This, however, wasn't the biggest problem. The main problem was a length of cold filament inside the barrel (the threaded tube that passes filament from the extruder motor to the hot end).
After much research, I found that I needed to isolate the barrel in order to remove this filament. At first, this proved very difficult. I spent hours with a couple sets of channel locks in an attempt to remove the barrel from the block with the heater (there may be a name for this, but I'll call it the heated block for now). The retrograde extrusion had pushed filament through the threads connecting the barrel to the heated block, locking the two pieces together very firmly. I eventually came up with the idea to heat the extruder to a low temperature (100 °C) in order to weaken the plastic, allowing me to unscrew the barrel. I used two sets of channel locks (one set on the heated block and another set on the barrel). After removing the heated block, I inserted a small 1.5mm drill bit into the barrel and hammered the two parts together, to push the filament out.
After clearing the barrel, I reassembled the extruder, almost. The block of aluminum that holds the barrel under the extruder motor (I'm calling it the mounting block for now) has two holes in my case, one tapped (threaded) and one not tapped with a set screw. I that the barrel was originally in the untapped barrel, but I lacked the screwdriver bit for the set screw (this later turned out not to be true), so I decided to put the barrel back into the tapped hole, assuming I could screw it in and reassemble the extruder. After doing this, I realized that my barrel was on the wrong side of the extruder motor (in my defense, I was doing this at about 11:30 pm), something I hadn't anticipated when I decided to screw in the barrel.
Bearing this in mind, I took apart the extruder and began to unscrew the barrel. Then, right as I was a few millimetres from freeing the barrel, it seized, having likely become cross-threaded. Nothing I tried (heat treatment, channel locks, lubricant) could remove the barrel from the mounting block. I was able to free it the next morning after C-clamping the barrel to a table and using channel locks to unscrew the mounting block. When it finally came out, it was followed by a little sprinkle of metal dust, a testament to just how stuck the two parts were.
After I freed the barrel, I found the right screwdriver bit (a star-shaped bit works well in place of a small allen key) and put the barrel in the correct hole. I reassembled the extruder and was just about ready to go back to printing.
Bed Leveling
Before I returned to printing, I had to level my print bed. This is a key task in any 3D printer, one that must be completed after any major change to the structure (moved endstops, new printing surface, etc.). I leveled the bed quickly, but was eager to return to printing. The first thing I did was give my printer the exact same job as before, a five hour print containing all of the first brackets of my hexapod legs. I later came back to find a jammed extruder. This time, the cause was an un
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