More extruder randomness

Recently I’ve been having a great deal of success with the printer, aside from the occasional Z calibration it seems to have been working well.

Over the weekend I was able to print the remainder of the parts for the lower section of a MendelMax with little drama, there was consistency in the print quality and I was able to bang one out after another stopping only to remove the completed parts from the bed.

Yesterday I started on the top MendelMax frame sections, expecting to continue my run of complication free printing. I fear that this (if it already hasn’t) may soon come to an end. As I had taken the printer out for the weekend I knew that the Z axis would need to be tweaked to get the first layer to adhere properly, this however took a lot longer than normal as the resulting distance between the end of the extruder and the bed varied in ways which would not be expected based upon the adjustments made. Furthermore after printing for about 1/2 an hour the offset between the two needed to be increased by .15 of a mm in slic3r in order to obtain the initial, correct gap. I would expect some expansion of the hot end as it heats but I would have thought that this wouldn’t have resulted in such a delayed increase. (note this also happened again when I fired the printer up tonight).

Once I finally got the first layer printing properly I started having a problem that I never had before, the outer perimeter wouldn’t sit properly on the previously printed layer but would droop and hang down the side of the printed part (as on the black printed part below). I stuffed around with the settings in slic3r which dealt with the speed, retraction, z-lift and extrusion multiplier all to no avail.

I then noticed tonight that occasionally the color of the extruded material would change from a light blue to a darker blue as would the consistency, from what I have always experienced, to something what was more akin to 50% PLA mixed with 50% water (like the stuff you get if waterbased paint in a tube separates or is not mixed properly). You can see the areas where this has happened on the print below to the left of the right had bolt hole, below the left had bolt hole and on the left center side of the lower face.

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Initially I thought that I was something in this section of the PLA, some contaminant or change in plastic brew so I swapped out the blue for some purple and tried to print a model of a tornado.

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Greatly improved but the outer face still had some imperfections in it that I hadn’t got on my earlier prints. I also had another test piece behave slightly strangely with the purpler and not adhere to the bed on the outside edge of the extruded path when in-filling the first layer. It almost looked like the printer wasn’t extruding enough plastic for the distance it was covering.

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I then swapped out the purple for some black where once again I had the droopy issue. The final 10 mm of the model (at the bottom in this pic) I dropped the extruder temperature 5 and then 10 degrees to 175 which weirdly seemed to stop the problem.

If it is a case of the temperature being wrong I’m not sure why it would happen all of a sudden and especially why it would be out by 10 degrees. I understand that different colors will extrude at slightly different temperatures but if the poor quality with the blue filament is solved in the same way as with the black (i.e a temperature drop) then what has gone wrong to require this. Nowhere have I heard of the temperature having to be adjusted by such a large factor across approx 50m of filament.

I noticed that the base of the extruder body seems to be deforming slightly in the same way as the first one. There also seems to be some burnt material seeping from between the joint of the PEEK and the brass sections of the hot end. If the base is deforming slightly as it heats up then this would explain the expansion issue that only presents after a period of printing but at the moment I’ve got no idea what the burnt stuff could be.

I guess tomorrow I’ll have to rip apart the extruder and hot end and have a look inside to see how things are, perhaps there are answers in there as to why all this strangness is happening.

3D printers are cool, really cool, but man they can be a pain in the ass. Badly behaved, they don’t tell you how they are feeling and then just when you think everything is fine they go and crap themselves. Bugger it all

Extruderplosion

Took the extruder off the carriage tonight to have a look at how bad the damage was. To be honest I was hoping that it’d be a simple matter of screwing the brass back into the PTFE but no such luck.

As you can see the actual body of the extruder has deformed and cracked. I wouldn’t have thought that the PLA would buckle this easily but I guess that the heat from the hot end will have risen and softened the plastic a bit. Anyway looks like a new body will have to be sorted before repairs can proceed. To prevent this happening in the future the only thing I can think of would be to decrease the limit on the extrusion speed to reduce the pressure in the hot end.

Average

I actually thought I was getting somewhere with this…

Managed to get one good print of something other than a box the other night, namely the knob for the display panel that will eventually be mounted on the front. Since then however its been a complete mess. Firstly there’s been no end of trouble getting the bed level, mostly this has to do with its design and the decision to have 4 mounting holes (one in each corner). Whilst this may be great for support its a right pain in the ass when it comes to adjusting them all. Secondly I wonder if the perspex that the heated bed is mounted on is too thin and flexes too much. This could explain why after I’ve spent 20 minutes leveling the whole thing when I go to print its sits too close to the extruder and appears to not be level again.

Tonight I also noticed an issue with the actual extruder. During another attempt at printing the knob I noticed that the large gear on the extruder seemed to be stalling at times that made no sense, i.e in the middle of a long pass (not near the end, when moving or any other times when you would expect the machine to not want to extrude material). Initially I thought that either the current limiting on the motor controller was set too low and the motor was stalling or that the limit was set too high and the controller was shutting down from overheating. Neither of these turned out to be the case, different current settings didn’t help and the heat-sink with the added fan was defiantly below the + 150 degree limit.

It turned out that the screw attaching the smaller of the gears to the motor shaft was slipping which left the motor still turning during these times but the gears and extruder stationary.

This was duly tightened.

I then gave the extruder a test, extrude 100mm of filament so I could check that it wasn’t slipping anymore and so I could reset the current limiting and this was when it all went wrong.  Whilst fiddling with the motor controller I heard several clicking sounds coming from the extruder. I then noticed the brass lower section descending from the PTFE rod that attached the hot end from the extruder body. By the time I was able to hit the emergency stop button the brass section was most of the way out of the rod and only held on by the leads coming off the thermistor.

Needless to say this is a real bugger of a thing to happen, looks like tomorrow night is going to be spent ripping apart the x-carriage and extruder to see how bad it all is, hopefully the threads in the PTFE rod will be fine and the brass can just be screwed back in.  At the moment the brass section is completely out of the ORFE rod and hanging from its power cables above the heated bed.

I’m not sure how to prevent this happening in the future however, I’ve had a look at the graph and the temperature never dropped below 183 so I know that it wasn’t an issue with the filament clogging up from being too cold. It looks like it just came down to too much filament being forced in the hot end and it not all being able to exit the nozzle quickly enough.

Proper printing

The couplers between the Z-axis motors and the threaded rod that acts as a screw arrived on Tuesday night. On the couplers that I ordered, the holes in either end had a diameter of 6mm so in order to connect the rod to the couplers and the motors some machining was required. Peter came to the rescue once again by turning down the ends of the threaded rod to 6mm and turning a spacer to fit on to the 4mm shaft of the motor to enlarge the OD of it to 6mm.

I only needed two of them but at $1.50 each ordered 2 extra, Probably a good thing as the machining on them is less than accurate. You can see on the top of the one on the left the threading for the grub screw has broken through the top face.
After a few firmware tweaks to get the Z-axis moving at the right speed with the right steps per unit this was produced

One very rough 20 x 20 x 10mm cube.

Both the belts on the X and Y axis need to be tightened, the bed needs to be leveled and the frame squared up still but as a first print with all this alignment / calibration stuff to do I’m pretty stoked. Looking at the top of the cube it looks like the extruder may have stalled a few times, I suspect this was because the motor controller was overheating and shutting down, Since mounting a fan above the RAMPS board this hasn’t seemed to have happened again.