My use of generic ABS and HIPS in the Stratasys finally has caused some annoying issues (more than just drooping filaments on infill). The photo of what awaited me after after the first build weekend with generic materials should speak for itself. It looks like the machine literally barfed all over.
I wondered if perhaps the support filament was to blame, as it had jumped off of the spool and wrapped around the spool shaft in testing a few times (due to me winding the HIPS onto the spool all the way to the rim). I looked in the dry box, but all was well. I then opened up the head for a look inside, and it looked like an accident at a spaghetti factory. HIPS was stuffed all around, and required removal of the motor blocks, so I figured this was a good time to photograph details of the head (the only peek inside a Stratasys head that I’ve found online is at Bouke’s blog) for others to see. Plus, a good cleaning was in order – the generic ABS and HIPS appear to have a great deal of volatile compounds, and there was a good amount of soot and burnt plastic sticking to the nozzles (plus, there was enough melted plastic gunk between the two nozzle rings that the support nozzle wasn’t able to travel up and down freely). This is a big concern when looking for what materials to run through the Stratasys – I had no issues with the OEM material (even with the material left cooking for half a day), but the generics from NIP like to stick to the nozzles and char (note all the brown lumps in the photo).
After cleanup and re-assembly the ABS nozzle is still extruding very nicely, but the HIPS nozzle may very well have some buildup inside. I could only extrude perhaps 10 inches or so of HIPS before the filament would buckle between the feed rollers and liquifier entrance, which is what caused the impressive birdsnest in the head in the first place. I haven’t tried extruding more OEM support material through however, so maybe I’m just hitting a limitation of the material itself. Still, I think the support nozzle has some sort of buildup, as the material is not coming out straight – as soon as it exits the nozzle, it curls back around and sticks to the nozzle, after which some sort of mess is inevitable on a long build. Nophead notes in his latest blog entry that he needed to clear out one of his nozzles with a drill bit to restore proper extrusion. I ordered a 0.011″ drill bit from McMaster-Carr, and then found that the pin vise I have can’t properly grip such a tiny bit, so I await a better pin vise before I can see if this re-boring fixes the issue.
On to the photos!
After the head is removed, this is what you see. There’s three vacuum cleaner hoses that run to the rear of the block – the large center one carries cooling air (which gets expelled from the central nozzle) as well as the two filaments (which poke out on either size of the nozzle through adjustable grommets). The two smaller hoses at the top are for the air return. The brass brush at the lower right helps keep the nozzles clean – after every 2 build layers, the head zig-zags the nozzles over the brush to wipe off excess filament that has oozed out. Of course, this only really works with the OEM filament, as it doesn’t adhere and melt onto the hot nozzle surface like the generic ABS and HIPS likes to do.
This is a top view of the head – there’s a locating pin at the center front and rear to make sure that it is perfectly aligned when the latches are secured. The front cover protects the solenoid.
This is what the rear of the head looks like, with one of the motor blocks removed. Each filament passes first through the black plastic guide bushing, then through the pinch wheels, then finally into the entrance of the liquifier. I’m not sure what type of plastic the reddish-brown liquifier end caps are, but it’s obviously a high temperature material. Right between the two liquifier entrances is the point at which the cool air is directed – it’s important to keep the filament solid before getting to the liquifier.
Here’s a close look at the motor block itself. I’m guessing the amber colored insulator plate is the same plastic used on the top of the head. The toothed roller (appears to be black anodized aluminum) is the driven one. The MicroMo gearmotor label reads as follows:
HEM1624T16 KW 45/96
This is what the underside looks like after the nozzles and protective rings are removed. Note that the black ring on the nozzle is actually a seal (though I’m not sure what material – Kalrez or other perfluoroelastomer, perhaps). Yuck, look at all that black crud. I tried cleaning the rings and nozzles by soaking them in acetone, but it really didn’t help much. I’m assuming that the relatively volatile styrene (which acetone dissolves) had been cooked out already (again, why the OEM material doesn’t degrade in this manner is still a mystery). The rings look to protect the bottom of the foil and insulation wrap. The picture really doesn’t show it, but the heating elements come all the way down to where the foil ends.
Here we have the real guts of the head. Each liquifier (build material on the left, support material on the right) has a thinwall stainless tube at its core (according to Stratasys patents, anyhow – I’m not about to start unwrapping insulation to find out). It looks like there must be some sort of other material around this core, over which the heaters are spiral wrapped and then covered with a layer of what appears to be fiberglass and foil. The cylindrical spring-ended parts that flank the liquifiers are the RTDs that actually measure the temperature. The cylindrical caps at the top of each liquifier are Klixon thermal circuit breakers. If the temperature controllers are improperly set (easy to do, and the manual warns that seeing ‘100’ with the ‘M’ LED on does not mean 100 degrees, but rather 100% output), the circuit breakers should keep the liquifiers from overheating. I don’t know what this cutoff temperature is, however – the circuit breakers don’t appear to have any markings other than ‘Klixon’. Note the rear of the right liquifier, specifically the two aluminum blocks on either side. These are actually pivot blocks – there’s a pin on either side of the support liquifier to allow the whole unit to tilt downwards by perhaps 1/16″ or so. You can just make out the extension spring (and pin that the spring attaches to) at the front of the liquifier that keeps it in the ‘up’ position when not in use. And what moves it downward, you ask?
A Lisk push-type solenoid pushes down on a paddle connected to the bottom of the support liquifier. Note the hex nut at the bottom – this locks in place the set screw that adjusts the downward travel of the paddle. Upward travel is adjusted via a screw attached to the cover that normally protects the solenoid (the solenoid core actually contacts the screw at the top of the solenoid’s travel).
In short, the head is pretty straightforward in terms of design and construction. Would I want to scratchbuild one myself should this one become irreparably damaged? Heck no, but it would certainly be possible.