Extruder Problems

The most frustrating thing about my Mendel is my extruder. I've had lots of problems with it since I completed the build. It's Adrian's Geared extruder with the hot-end epoxied into the base rather than held in by a PEEK block.


The first problem that I had was caused by my wimpy stepper motors getting too hot. The excess heat caused both the extruder base and the X-carriage to distort. This has since caused all sorts of meshing problems for the extruder gears as they no longer line up. 


The second problem that I had was the hot-end dropped out completely while working on a print. Frustrating, but easily fixed by liberal application of more epoxy.


Today I resolved to fix the meshing issue which causes the gears to skip, resulting in poor extrusion. I completely dismantled the extruder body to fix the alignment between the motor mounting plate and the extruder base. After they had become distorted they developed a slight kink in both parts, and whenever I tried to align the gears the parts would prefer to slip back to align with the kink. 

Note the kink in both parts and the buried washer.

The solution was to file the kink flat on both parts and make up for the missing material with an M4 washer. I also found that the excess heat had partially closed the bolt slots on the base, preventing the bolts from sliding as needed. After opening these back up again I could position the motor so that both gears engaged successfully.


Several tests showed that everything was working perfectly, so back to printing. In this case some new frame vertex with feet, since my Z-axis pulleys stand a little proud for the current feet to handle.

Previously the wires were flush with the PTFE.

Unfortunately, half-way through the print another extruder problem developed. The threaded brass insert that makes up the extruder was pushed out of the PTFE block. Shifting it down about 5mm and leaking molten PLA out over the nozzle.


I'm not sure if I can salvage this extruder hot end, I might need to build a new one using the PEEK block to attach the nozzle to the PTFE. This should solve at least two of the extruder problems I've experienced in the past two weeks. It wouldn't be so bad if I've been churning out hundreds of Mendel parts, but I've only managed to print a couple of small objects and two vertex's. Reading other RepRappers blogs, I can see that others have far more success with their extruder than I do with mine.


Oh well, time to research new hot-ends!