I managed to get a decent pin vise at last and drilled out the support nozzle with a 0.011″ drill.  The other day I got around to testing the cleared nozzle to determine if buildup/blockage might be the root cause of my difficulties in running the high-impact polystyrene from New Image Plastics.  I powered up the Stratasys, let the support nozzle come up to temperature, and started feeding it the NIP HIPS.  I noted that the extruded plastic was still curling right around and contacting the exterior of the nozzle – re-boring a 0.012″ nozzle with a 0.011″ drill bit apparently does zilch in this regard (makes sense, as I wasn’t actually removing any metal), but at least I could be fairly sure that any possible blockage was gone.

After perhaps 2 inches of feedstock, the HIPS filament buckled once again between the feed rollers and the liquifier entrance.  I struggled with this for some time, and found that increasing the support temperature to 275° C (10 degrees higher than the normal setpoint) and reducing the feed to 60% (normally at 100%) improved things greatly.  Improved, but not fixed – I could still expect the HIPS to kink very roughly once in every 18 inches or so.  Additionally, I noted very faint wisps of smoke emerging from the nozzle area – I’m pretty sure I was witnessing outgassing of the HIPS as it emerged hot out of the nozzle.  I had never seen this with the OEM material.

I had a little bit of OEM support material left and figured I should try running it to see if it would also buckle – perhaps I still had some sort of buildup inside the liquifier, and maybe the OEM material would act the same way.  I dialed the temperature back down to the OEM setting and bumped the feed back up to 100%.  It ran just as happily as it had done prior to my mad experimentation with alternate materials.  With that in mind, I started to do some light research on what exactly high-impact polystyrene consists of.  Styrene, as Wikipedia points out, is an oily liquid – many styrene molecules need to be linked together in order to create polystyrene, which is the clear plastic used for car windshields and airplane canopies in plastic model kits (modelers hardly ever say ‘polystyrene’, referring to such material as simply ‘styrene’) .  Polystyrene (sometimes abbreviated as GPPS, for General Purpose Polystrene) is itself rather brittle, so to toughen it up, a bit of polybutadiene rubber can be added to improve the impact resistance and we get High Impact Polystyrene (HIPS).  The polybutadiene ruins the transparency of the polystyrene, so uncolored HIPS is a milky white color.  Perhaps this particular HIPS had enough polybutadiene in it that made it buckle more easily than the OEM material?  A brief side note – there are apparently a LOT of ways to mix styrene and butadiene.  I discovered SBS (styrene-butadiene-styrene), which Chris DeArmitt did an excellent job of contrasting with HIPS.  There is also SBR rubber which shares the same CAS # (9003-55-8) as HIPS, even though the two materials seem quite dissimilar (I am not a chemist, so this may all make perfect sense if one is versed in the ways of polymer science). And if that isn’t confusing enough, have a dose of CAS # 91261-65-3, styrene-butadiene block copolymer. Yeah, my eyes glazed over long ago as well, and now my brain hurts.

In looking through various MSDS sheets for different grades of HIPS, I noticed that many formulations contain a few percent of mineral oil.  I wondered if perhaps vaporization of the oil might account for the faint smoke I was seeing – the 265° C nozzle is hot enough to boil some grades of mineral oil.  Once again, NIP was kind enough to provide me with material specs for their HIPS, which turns out to be Styron 487.  The MSDS sheet indicates that less than 5% of the composition is not in fact mineral oil, but is a ‘copolymer mixture’ marked as being a trade secret. Furthermore, the sheet only cautions against temperatures over 300° C as causing decomposition.

I went back to playing with running filament through the Stratasys, remembering that the machine has a torque monitor setting.  If the filament jams in the extruder, the machine will detect that the drive rollers are pushing too hard and pause the system.  I’m not sure that I’ve ever actually seen this torque limit tripped, but when feeding filament through, you can hit the torque button for a realtime display of how hard the feed motor is working.  Comparing the torque when feeding the OEM support material versus the HIPS should tell me…  well, something.  Setting the support extruder for 265° C and 100% feed, I ran the OEM support material through and the torque was around 65 (I’m pretty sure this is a unitless number) – interestingly, I couldn’t see any sign of smoke or vapor with the OEM material.  I then ran the NIP HIPS through with the same settings (as expected, faint wisps of smoke/vapor were visible once more), and it was a whopping…  What?  Only around 60?  What the heck is going on?  I noticed that both materials were extruding much more nicely this time – they would still curve a bit after exiting the nozzle, but not as much as before.  I ran about 6 feet of HIPS through without a hitch before getting tired of waiting for it to kink, which it never did.  As best I can guess, there must have been a little bit of buildup or blockage that the OEM material flushed out.  Could there be some magic cleaning additive in the OEM support material?  Possible, but unlikely – the P400 support MSDS sheet notes the only ingredient as being approximately 99% styrene-butadiene copolymer.  Eh, maybe I was just lucky.

As long as I was looking at torque values, I thought I’d see how the OEM ABS compares to the NIP ABS.  At 275° C and 100% feed, the OEM ABS showed a torque of about 70.  The NIP ABS at the same settings was much higher – about 110.  I also noted that again, faint smoke/vapor was present with the NIP material, but not with the OEM. The MSDS sheet for the Polylac PA-747 that is the NIP ABS notes that additives comprise less than 2% of the material, but it doesn’t say what those additives might be. One possibility is that NIP may be adding some sort of chemical to their batches in order to improve processing, but this is only a wild guess – I don’t know much about the extrusion process and would have to ask Jim @ NIP if they add any sort of special sauce.

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:

1624T012S123 X0520

16/7 415:1K703

HEM1624T16 KW 45/96

It turns out that these 3 lines specify the motor, gearhead and encoder.

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.

After my previous post on alternative ABS use on the Stratasys, I wound up with a pile of informative comments. Jeff directed me towards US patent application 2009/0295032, which contained this gem:

The extrusion runs of Examples 1-12 were performed with a modified ABS material commercially available under the trade designation “CYCOLAC” MG94-NA1000 ABS from General Electrics Co., Pittsfield, Mass. The extrusion runs of Comparative examples A-D were performed with a standard ABS copolymer commercially available under the trade designation “AG700 ABS” from The Dow Chemical Company, Midland, Mich.

We surmised that Dow AG700 ABS may likely be the standard Stratasys ABS, and given the date of filing and material properties, the GE MG94-1000 ABS was likely the newer ABS-M30 material.  I started looking into the AG700 resin first – while I was able to find something of a datasheet for the product, the fact that Dow now only sells to the automotive market (in North America, at any rate) pretty much quashes any possibility of acquiring the resin. Still, we now have a set of material properties to use for comparison, and I’m wondering which properties specifically make for an ideal Stratasys/RepRap/FDM feedstock. The “high flow” and “low gloss” aspects jump out at me in particular – obviously high flow is needed given the small orifice sizes, but I wonder if the glossiness of the extruded filament is indicative of its surface energy, and hence the amount of attraction that two layers will have for each other (thus potentially causing warp).

I had much more luck with the MG94-1000NA resin – GE sold their plastics division in 2007 to SABIC, so I dug around on their site (after needing to create an account, grrr) and pulled up the datasheet for the material. It turns out that the ‘-1000NA’ is simply the color code – they have dozens of colors available, and -1000NA is the plain old uncolored ‘NA’tural one. After a call to sales, I found that the smallest quantity I could order was 55lbs. at a whopping $30.61 per pound. Yowza. However, the price decreases drastically with quantity, and 330lbs. would only be $7.69 per pound. I don’t exactly have $2500 burning a hole in my pocket, but the quantity and pricing certainly isn’t out of reach for a few dedicated hobbyists to try. There’s a few other possibilities to research before falling back to that, however.

Recently there’s been a bit of buzz on the RepRap forums about a low-cost, very RepRap-ish 3D printer from China. What caught my eye the most was that this printer is actually using Stratasys sized 0.070″ feedstock rather than the 3mm RepRap standard. They note an ABS price of $50/kg, which comes out to $22.69/lb. Not as cheap as from NIP or other sources, but if the plastic acts just like Stratasys ABS, it would be worth it.

Speaking of NIP, I called up Donna to see what other possibilities there were for ABS. She and Jim were kind enough to provide me with the datasheet for the specific ABS they use, which is Chi Mei Polylac PA-747. They’re able to get other Chi Mei resins as well, so I took a look at their high flow offerings. The highest flow formulation, PA-756H, looks promising – the low impact strength is one of the properties that stuck out on the AG700 resin. I’ve emailed Donna to see if they can acquire this material.

So much for material musings – I have 5 pounds of HIPS that I need to wind onto spools! I’m not about to wind a half mile of filament all by hand again, so I needed to figure out a good automated system. I originally figured I’d just chuck the empty spool on the lathe and wind it that way, but then I decided to use the mill instead, as the head is variable speed on-the-fly. How to hold the empty spool, though? An expanding collet would be great, but I don’t have any as big as the 2″ bore in the Stratasys spools. A little bit of digging through scrap bins, and I found a Delrin cylinder that would work perfectly for making a pair of bullnose centers mounted on a bolt. Here’s what the assembly with spool looks like on the mill:

What to do on the unwind side was a bit trickier.  Based on my winding by hand of the ABS, I knew that keeping the coil of filament in a rather static shape was very important, so I opted to make a simple spool that could be assembled around the coil itself.  I used Masonite for the sides and drilled holes  through each piece to allow for joining screws.  Multiple sets of holes were drilled so that I could adjust the screw locations to perfectly fill out the center of the coil.

I clamped a piece of 3/4″ rod in the bench vise and slipped the spool over it (a collar on the rod kept the spool at an appropriate height).  It rotated pretty freely, so I took the loose end of filament and tied it to the inside of the empty spool.  I set the mill spindle to the lowest speed, and hit the power.  60 rpm is perfectly fast for winding, though I cranked the speed up to around twice that once I had a good start on the winding.  I held the filament in one hand (with a rag so that I’d actually have skin left) to provide continuous tension, and the material unwound from my adjustable spool just as nicely as I had hoped, with no snarls.  About a half hour later I had two spools fully refilled.

I gave the NIP HIPS a try in the Stratasys, noting that the Stratasys support material is slightly more brittle than the NIP HIPS.  I ran a small test part with NIP ABS at 250° C, and the HIPS at 265° C.  The HIPS performed admirably, and had good adhesion to the NIP ABS.

The Stratasys is currently running a large plate of parts, and we’ll see if I have less warping this time.

My limited knowledge of plastics has bitten me, as I had half expected (hoped) that I could just run the NIP ABS through the Stratasys and have things ‘just work’.  As noted previously, I had used the exact same extruder temperature on the ABS from New Image Plastics as with the Stratasys ABS, but had sagging filaments as a result. Nophead (who is easily one of the most experienced RepRappers out there) guessed that I likely was using too high of a temperature, which made sense. But shouldn’t ABS run just like ABS? Not a chance, as I found out – I had mistakenly assumed that ‘ABS‘ referred to a specific polymer composition, when in fact you can tweak the ratios of the components (Acrylonitrile, Butadiene and Styrene) to achieve certain properties.  Obviously, NIP is using a different formulation than Stratasys is.  Additionally, Erik de Bruijn noted that he had seen different colors of ABS require different temperatures for optimal extrusion.  Stratasys is apparently doing a great deal of work to make all of their P400 ABS colors act identically at 270° C.  Out of interest, here’s the sticker from a Stratasys reel that lists recommended temperatures for various materials:

E20/E20R is an elastomer (and corresponding support material), ICW06/ICW06R is an investment casting wax and support, P400R (high-impact polystyrene) is the support for P400 ABS, and P400SR is a soluble support material.  It’s interesting that the 0.010″ tip suggests a higher temperature (for one material, anyhow) than the 0.012″ or 0.016″ tips, but I suppose this makes sense – you’d need a less viscous fluid when pumping through a smaller orifice in order to maintain the same linear flowrate.

My latest plate of Mendel parts completed with the NIP ABS, but the results were not as good as with the Stratasys ABS, I’m sorry to say.  I had severe warping on the larger parts, though this could be due in part to me dropping the extrusion temperature down by 15° C early on in the build as a result of nophead’s suggestion.  On the plus side, the NIP peels off of the support material just beautifully (perhaps a little too well, as one of the drive-pulley_3off parts became detached from the raft near the end of the build).  I’m wondering if the lower adhesion between the two materials may have also contributed to the warping – keeping the corners held down more securely may be part of the secret of getting more accurate prints.

I also notice a lot of fine feathery filaments with the NIP ABS at the end of an extrusion path.  Whereas the Stratasys ABS acts like a microscale toothpaste, the NIP ABS acts like a microscale silicone caulk.  The NIP ABS also shows its displeasure at the higher temperatures by turning brown after sticking to the nozzle for a while (meanwhile the Stratasys ABS would simply lose a bit of color, but not appear to actually be charring).  So, time for some testing to see if there is a magic temperature at which the NIP ABS acts like the Stratasys ABS.

I adjusted the white balance on this photo to better capture the filament detail – the parts really do not look this grubby, although it’s interesting to note that the highest temperature pass does look a bit browner than the others.  I created a box with the 0.15″ crosshatch fill in Quickslice, and ran it at ever decreasing temperatures on the Stratasys.  At the recommended 270° C for Stratasys ABS, the NIP ABS is practically dripping off of lower layers.  As the extrusion temperature drops, the filaments droop less, but even at 240° C there is still a reasonable amount of droop.  At this point I started having slippage on the drive wheels (I think this was due more to buildup of tiny ABS fragments than due to lowering the temperature), and more importantly, I was entirely out of Stratasys support material.  As such, the next phase will be to play with the HIPS from New Image Plastics and see how it differs from the Stratasys support material.

I ran some more parts with the New Image Plastics ABS, and noticed something odd:

No, not the horrific brightness/contrast I needed to apply (natural ABS does not photograph well if you’re trying to capture detail)  – the sunken, spongelike top surfaces of the parts.  I had been using a crosshatch fill pattern for parts within the Quickslice software which worked just fine with the Stratasys ABS, but the NIP ABS acts a little differently.  Here’s what the internal crosshatch fill should look like:

The pattern is about 0.15″ square – the important part is that the filaments are entirely straight and do not sag.  Unfortunately, this isn’t what happened with the NIP ABS:

In this case, the extruded filament did not stay taut, and the insides of the parts resembled the world’s smallest Golden Gate Bridge convention.  When the final top layers were laid down, they draped over the peaks in the internal fill, leaving a lumpy final top surface (though the outer contours were just fine).  None of the process parameters were changed from the Stratasys material, so I’ve started to wonder what the difference in formulation or processing might be?

In any case, I’m not about to lose sleep over it – the order of magnitude difference in price between Stratasys and NIP materials means that I can dispense with the crosshatch interior fill and use the standard ‘fast’ fill.  Sure, it takes longer to build, but the parts are notably stiffer with the extra density, and the Stratasys has proven to operate reliably when run unattended.

Perhaps tweaking the parameters will help some, but if I have to run with standard fast fill instead of full crosshatch, I can certainly survive.  It’s not as if I currently have a need for ultra low density parts.

In my quest for a better surface finish on FDM parts from the Stratasys (especially with a mind towards having Frankie try some more investment casting), I had decided to try the technique noted in this Stratasys application note. Namely, dipping the parts in MEK (methyl ethyl ketone) in order to fuse the individual filaments together and seal the surface. I poured some MEK into a glass jar and hung two of the Mendel parts onto a length of TIG welding rod. I dunked the parts into the MEK for perhaps 10 seconds, then hung them outside to dry.  I inspected the parts the next day, and I was immediately reminded of the climactic scene in Raiders of the Lost Ark where Toht’s face is melted off.

While the surfaces were most certainly smoother when compared to untreated parts, the side effect of  severe warping and deformation doesn’t make this treatment method a viable option for these small parts.  Spraying MEK onto the parts may work much better, as the loose internal fill pattern I’ve been using makes the parts quite porous, so a little bit of solvent goes a long way.  I’m guessing part dipping may work much better with as solid a fill as possible.

An alternative solvent may also be something to try.  The Stratasys Finishing Touch Smoothing Station uses a vapor bath of a specially formulated solvent, and methylene chloride (the primary component of Weld-On #3) appears to be preferred over MEK in the latest application notes anyhow (earlier versions of the app note recommended MEK and actually mistakenly claimed that Weld-On #3 was MEK – this mix-up had me running in circles for a while).

The treated parts do indeed feel stronger (based on my unscientific method of squeezing them between my fingers to see if they have any discernible ‘give’ compared to the untreated versions), so the treatment certainly has promise beyond just surface smoothing/sealing. So much for the fail – on to the win!

My patience was rewarded on Friday when I had a box from New Image Plastics waiting for me on the doorstep at home – my fresh ABS and HIPS had arrived!  Saturday I ran into work to give the ABS a try, as I still had a reasonable amount of support material left on the spool and wasn’t in a rush to try the HIPS.  Additionally, modifying two parameters of a working system is inviting disaster. Anyhow, if the HIPS doesn’t work out as a support material, it’s not the end of the world – I suppose I could afford to buy name brand Stratasys support material, but if generic ABS doesn’t work well as a modeling material, I may as well start looking to sell the unit given what the official material costs.

The one thing that I had failed to account for was how to take the coil of ABS filament and get it onto the empty Stratasys spool I had. I initially figured I’d just wind it on by hand, but a little bit of math would have told me that 5 pounds of ABS extruded into a diameter of .070″ yields about a half mile of filament. I did end up winding it onto the spool by hand, with a swivel stool seat helping the process a little bit, but it still took a few hours, and my fingertips had a bit of wear. I’ll certainly need to come up with a better solution in the future (perhaps winding the spool on the lathe, or even better, maybe New Image can simply deposit it right onto the spool for me).

Despite being relatively fresh, the ABS had about the same amount of ooze out of the FDM 1600 nozzle as the ‘lobster red’ Stratasys ABS I had been using. Given the high humidity as of late, I suppose this isn’t surprising – I’ll make sure to use plenty of desiccant tins in the dry box. Things were looking good with feeding the ABS through the system, so I ran a single Mendel part for a test.

The part turned out great, though it was a little trickier to separate from the support layer than the Stratasys ABS had been.  The NIP ABS certainly equals the Stratasys ABS in resulting part quality, and I have no more worries about running it through the FDM.  In looking closely at the parts I’ve made thus far out of Stratasys ABS, I’ve noticed a bit of variation in build quality, so it will be interesting to see if the NIP ABS provides more consistent results, or if other factors are affecting the created parts.