Winder – Starting the Loop

Filament is very finicky and a bit difficult to manage.  The way it is looping down from the extruder and back up to the winder looks like a drooping length of string, but it doesn’t act that way.  It is flexible for the first couple of inches while it is hot, and then sets into a shape which may be a straight length or a bend, depending on what it was doing when it cooled.  Then it runs along a path like string, but being semi-rigid it also supports itself along the way.

For the filament to feed consistently, it needs to maintain the same shape as much as possible by keeping the same orientation as it hardens.  If the shape of the bend changes near the extruder, then that bend will push the filament around when it gets to the puller, creating another change in the bend at the extruder which pushes the filament when it in turn reaches the puller in a never ending cycle.  You can see it in action in this timelapse-

The key here is that the filament pushed back behind the nozzle opening, creating a tighter bend in one spot.  When that bend got near the puller it pushed the filament behind the nozzle again.  No amount of tweaking on the speed could compensate for that.  It only ran about an hour, and then developed a kink that was not going to make it through the puller, so I stopped it.

I also took the fan off halfway through.  With the fan, any extra movement of the filament near the nozzle gets quickly hardened into a permanent bend.  If it stays soft longer, there is a chance for it to straighten out again before hardening.  Cooling would be beneficial if it could freeze the filament right as it exits the nozzle, before it has a chance to move around much,.

Here is another attempt at the loop, but this time I moved the extruder or winder back and forth to make sure the filament kept the same angle coming out of the nozzle no matter how it was pushed around.  Eventually the inconsistencies created while guiding it to the puller worked themselves out and it ran steadily for 3 hours until it was time to stop it for the night.

Filament Winder – Puller

The puller controls the speed of the filament coming into the winder, and isolates the tension created by the spool from the extruder.  It’s run by a 37mm 15 rpm gearmotor, mounted by 2 M3x12mm screws.

Print the puller mount, and drill the holes so that they are the correct final dimensions.  Use a 3mm bit for the two holes at the top edge, and the holes for the motor, which are a little above center.  On the back drill the top two holes a short way in with a 6mm bit and push some M3 nuts in.

Mount the motor with M3 screws so that the edge of the motor sticks up above the mount, to allow room underneath for the bolt that holds the mount to the board.

Print the two extruder pieces, and clean out the support and trim any wayward threads from the bearing holder.  The 625 bearing should snap in and spin freely.  Use a short M5 bolt to hold it in place, but don’t use a nut.  Take care that the bolt does not extend from the back, or it will cause the holder to twist away from the mount.

Screw the base part of the extruder on to the mount with a M3 18mm bolt.  Ideally the head of the bolt will hold the part snug against mount without sticking out the back where it will get in the way of the motor.  Use some washers on the front if the bolt is too long.  Attach the bearing holder with a bolt long enough to go through both pieces and the mount.  Cut a section of spring about 10mm and wrangle it into the recess on the base part of the extruder.  Tweezers might help here.

Print the two halves of the tension wheel and glue them together.  Push a 608 bearing in through one side as far as it goes.  Put a M8 bolt through the larger hole of the tension arm, add a nut, and slide the wheel up against the nut.  Tighten another nut against the other side of the bearing in the wheel.

The potentiometer has a little tab that sticks out to keep it from spinning in its mount.  You will need to drill a small hole in the mount next to the hole for the shaft to accomodate this little tab.  Put the shaft a little ways through the first hole and slide on the nut that came with the potentiometer before pushing it the rest of the way through the second hole.  Use some tweezers or skinny pliers to screw the nut onto the threads on the potentiometer shaft.  It’s tricky, but you should be able to get it in a minute or so.

Turn the pot back and forth until you have it near the middle of its range of motion, and press the arm onto it.  Position the mount alongside the wide part of the motor with the wheel lined up with the upper filament guide hole and screw it down to the board.

Use some tiny screws to attach a spring that is 1.5″-2″ long to the arm and the side of the mount.  It should take only a little bit of force to hold the arm upright against the pull of the spring.

 

 

Filament Winder – Spool Mount

The spool mount is made to be easy to take spools off when done and replace them quickly.  The spool itself has printed ends which fit into a 6″ length of 2″ Shcedule 40 PVC pipe. It’s easy to make as many as you need at home, and they are made to fit smoothly onto a 3/4″ PVC pipe.

Start by cutting two pieces of 1/2″ MDF to 16″x8″ and glue/screw them together at right angles.  Drill an 8mm hole about 7″ from the base, and 1″ in from the left side for the threaded rod..  Use a spade bit to drill another hole 3/4″ wide about 1″ down from the top and 2.5″ in from the left edge for the motor arm.  Cut a section of threaded rod about 9″-12″ and put it through the hole with a nut and washer on each side of the board.  Slide the spool stop against the nut on the front of the board.

The spool stop looks like a cylinder with a hole in it, but it is actually shaped like a small spool.  There is a single thread wall (.42mm wide) around the edge to act as support, which should be cut away.  This will be used later on along with a screw to keep the mount from sliding off when you remove a spool.

The Class 200 3/4 PVC pipe has an ID that is slightly larger than a 608 bearing.  If you wrap about 2-3 layers of electrical tape around the outside of the bearings it will make a snug fit.  Place two bearings on the rod far enough to provide good support for the spool, with a printed washer and nut on each side of each bearing.  The nut of the inner bearing should also hold the spool stop in place.  The washers will let you tighten the nuts against the bearings without restricting their motion.   You can save time threading the nuts on by using a drill to spin the rod.

The mount for the hall effect sensors is also pictured, but that will be added in later when the electronics are done.

Cut a section of pipe long enough to reach the end of the spool and slide it on over the bearings, up to the end of the spool stop.  Slide the spool gear onto the pipe with the flange pointed toward the back board, flush with the end of the pipe.  With a 3mm bit, drill through hole in the flange, through the pipe.  Put a M3 16mm screw through the hole.  This screw will bump against the insides of the spool stop and keep the pipe from sliding off when you remove a spool.

There are four small holes in the gear.  Drill them out to 4mm and put 3 M4 18mm bolts through them, with nuts on the other side.  The bolts will slide into matching holes on the spool to lock it in place, and the nuts keep the spool back far enough that it doesn’t drag against the motor gear.

Print Lyman’s gear motor arm and washer and mount them in the 3/4″ hole.  Use M3 screws to attach the gear motor and slip the small spool gear onto the motor shaft.  If it is too tight, drill it out with a 6mm bit.  If the motor arm was a tight fit into the hole, you are done with this part.  If it is a little loose, you will need to hook a small spring to it, with the other end screwed into the back board.  If the gears are not held tightly together, the motor will be pushed away whenever the filament gets a little hard to pull.    If you want the spool to spin freely, simply lift the motor up.

There’s more to come, as I can get it written.

 

Filament Winder – Intro

I’ve been working a few months with the beta of the Filastruder, which will start shipping kits soon from it’s Kickstarter campaign.  I was never very happy with letting the filament extrude onto my (often dirty) garage floor, so I have been working on a winder for the filament.  It has been tricky because filament doesn’t act like string, it is stiff and tries to maintain a shape that may be curved or straight.  There are a few other challenges that need to be addressed by a winder-

A winder needs to sync with the speed of the extruder, which is a bit variable.    If it is a little too fast or a little too slow, over several hours it will outrun the extruder, or let the filament pile up and get backed against the extruder making what looks like plastic ramen noodles.  Also there needs to be some tension on the feed to the spool to force the plastic to coil against it.  The amount of tension depends on how fast the spool is turning, but the speed it has to turn to maintain a given amount of tension will change as it fills up.  Lastly the filament needs to be guided back and forth across the spool so it lays down evenly rather than bunching up in the middle.

Originally I tried pulling the plastic directly from the extruder like the industrial machines do, stretching the filament down to the desired diameter which is determined by the speed of the pull.  I wasn’t able to get close enough tolerances doing this because the speed of extrusion isn’t constant.  When the filament can drop freely, variations in pressure inside the extruder cause the filament to come out faster or slower without really affecting the diameter.  When filament is being pulled out at a fixed speed, variations in extrusion will change the diameter instead.

What I have done is let the filament drop into a loop and then get pulled up again into the winder.  This way any pulling by the winder will act on the loop and not the filament at the nozzle.  There are two photo sensors at the bottom of the loop with a line laser shining on them.  When the winder pulls too fast, the loop will rise and shade the upper sensor which slows down the motor.  When the loop drops low enough to shade the bottom sensor the motor speeds up again.  The bottom of the loop then slowly rises and falls within about .25″ which maintains a steady enough pull on the plastic coming out of the extruder.

The winder has a puller which syncs the takeup with the extrusion and isolates any other handling of the filament from the extruder.   There is a mechanism to regulate the tension on the spool, and a guide arm waved back and forth by a servo.  The whole thing is powered by an Arduino Uno.

It is still a work in progress, but close to being finished.  I wanted to start documenting it so others can begin to play along, and maybe begin getting parts together.  There a lot of printed parts, which you can find at Thingiverse.  I don’t have a detailed BOM down to the size and number of screws, but I will list enough to get going.  I haven’t decided if I will set up sales of a kit somehow, but at the very least I would like to get custom PCB’s made.  This is set up on a breadboard at the moment which works, but is a bit clunky.  There will be a mix of metric and imperial which I apologize for.  I like to use metric whenever possible, but some things in the US are imperial only.

In addition to printed parts you will need-

• 2 pieces of MDF 8″x16″
• 2 37mm gear motors 15 rpm.  Ebay, probably from China.  Order now and start printing while you wait for the boat to come in.  These are for the spooler and puller.
• HiTech standard servo – Amazon or the local RC hobby store for the filament guide.
• 625zz bearing for the puller idler
• 3 608 bearings for the spool mount and tension roller.  Get a pack of 10, it’s always good to have extras around.  I’m working on a spring loaded caliper to measure the filament which will use 2 more of them.
• A short spring for the puller idler
• 1/2″ OD latex tubing from http://www.latex-tubing.com for the motor shaft on the puller. Some easier to get rubber tubing may work, but latex is soft and has a good grip
• M8 threaded rod for the spool mount
• 3/4″ Class 200 PVC pipe for the spool mount (thinner than schedule 40)
• 2″ schedule 40 PVC pipe for the printable spool
• Arduino Uno rev3
• Half size breadboard
• 12v power supply.  I found a pile of them at the thrift store.
• Solid wire for breadboard jumpers
• Stranded wire for hooking up hardware
• 2 photo resistors
• 4 10k resistors
• 2 MOSFETs for the motors
• 2 1N4001 diodes for the motors
• Some Molex single row wire housings like these – a handful of 2, 3, and 4 wire versions.
• Crimps to go with the housings like these from Mouser
• Straight PCB headers, 30 or so
• A small spring, about 1.5″-2″.  The kind with loops on the ends, meant to stretch.
• Various M8 nuts and washers
• Short wood screws
• M3 nuts and bolts ranging from 12mm-20mm
• 2 10k potentiometers, 16mm diameter with a long shaft
• 2 hall sensors for detecting spool rotations.  Mouser has them for less than $1
• Cylindrical neodymium magnets, 1/4″ to go with the hall sensors.  Amazon has a pack of 20 for $10.  You only need 2, but they are useful to have around.
• A coupe of microswitches with levers, similar to endstops on a printer.  Adafruit has some, you can probably track down an equivalent at Mouser.

Next I will start with the spool mount.

Slicer Shootout Pt. 4

One of the other models that Make Magazine used in their 3D Printer reviews was Cushwa’s Owl from Thingiverse.  I thought it would be a good test for the slicer comparison as well, something more sculptural than geometrical.  This was printed straight from Thingiverse without any cleaning or modification other than scaling it down 60% to save time.  I have two KISSlicer prints because I accidentally ran one scaled at 50%.  Since I still had hairspray and kapton on the bed from trying to prevent warping in the Torture prints, the Owls were stuck pretty hard.  I broke the Cura print just above the talons trying to get it off, so that isn’t a printing artifact down there.

The Owl has some challenging texture in its feathers.  The tips are largely unsupported, which gets complicated in the lower half of the body since the perimeters have a bit of overhang due to the body widening from the talons up to the middle of the chest.  An additional challenge is the unsupported underside of the beak which needs support to print properly.  It’s another chance to see how the slicers deal with a bad situation.  The back of the owl is a smooth, even curve which provides a good contrast to the texture in front, and the top of the head is a shallow dome, which can be challenging.

Between the Slic3rs, 072b seemed to do the best at overhangs, with few loops at the feather tips and under the beak.  However the surface of the feathers is cleaner in 097, especially in the upper chest.  The upper chest is also very good in Cura, but it suffered a lot in the inward slope toward the talons.  Not a lot of dropped loops, but it’s possible that the perimeters aren’t laid out with enough overlap between layers to maintain a consistent alignment.  KISSlicer has the smoothest surface on the feathers and maintains it the best in the underside of the body.  There are a few misaligned layers however.

KISSlicer also handled the underside of the beak best, but had some odd lines across the face.  They are happening at the same spot in both prints, so it isn’t some random wiggle from the printer, unless there is something about those layers that is difficult for the printer to execute properly.  Those misaligned layers are very similar to the ones above and below, so there shouldn’t be anything unusual about those spots. Cura is inconsistent there as well, with Slic3r handling it the best.

Slic3r 097 is the clear winner at the back of the owl with no blobbing or misalignment.  Slic3r 072b has the blobbing from perimeter ends, and KISSlicer has a visible seam as well, though it was mostly flush to the surface.  It also had a few odd perimeters that were shifted in X, recessed on one side and sticking out the other.  It looks like layer shift, except the rest of the layers are in the right place.  It also happens in the same places for both prints.  Cura failed here with a bunch of bad layers.  It is possible that there was an issue with the Z axis of the printer because it looks a little like squished layers.  If so, it was intermittent enough to not show in the other prints.

Cura looks like it overextruded a little bit at the top of the head, yet still left some gaps, and the tufts are a bit rough.  Slic3r 072b has perimeter starts in the middle of the tufts, which 097 hid better.  The perimeters are a little uneven in 072b which 097 improves on, but still left some gaps.  KISSlicer has the most steady lines and solid fill.

It’s a close call between Slic3r 097 and KISSlicer for the owl, only because of the way KISSlicer handled the back.  There is a new version coming out soon however, and I’ll have to see if it shows any improvement in this model.

Torture Test Quality Check

I’ve been wondering why the columns on the Torture Test printed so badly for all of the slicers when I’ve seen them all do better than that before.  I tried a single column with Slic3r 096 which was one of the worst for that section.  I also wondered if there might be a problem due to the model coming from Tinkercad, so I printed one column from Tinkercad, and another from Alibre-

They both look pretty good, aside from where I gouged them with my scraper.  My concern with Tinkercad was that STLs generated there are typically fairly low resolution.  You can make out the increased faceting in the print but it didn’t cause a problem otherwise.  I thought there might be a difference due to the bad columns being part of a larger print.  I cut out the rest of the model and tried a print of only the column section.

It’s a little better.  The misaligned layers seem to be gone, leaving only blobbing and artifacts related to the start and end points of the external perimeters. I had used Tinkercad’s STL import feature to convert the original torture STL to solid, and easily add other elements.  There is some decimation that happens in the process and who knows what else, so I decided to compare meshes.  This is the original-

Those columns are pretty high res, but completely uniform.  Here is the mesh from Tinkercad-

This is a lot more jumbled, with the surface resolution of the columns changing from bottom to top.  Compare this to the Slic3r 096 print-

The columns start out smooth at the bottom, and become more blobby where the resolution increases.  The column with the chamfer shows the pattern as well.  In the mesh, the column starts out simple, becomes more complex rising toward the chamfer, then becomes consistent and well ordered after the chamfer.  The effect of that change is clearly visible in the print.

I decided to print the original, unaltered Torture Test in Cura and see how much difference the mesh made in the final print.

There is a small improvement, but it isn’t drastic; a few less lines in the columns and a smoother surface on the arch.

Here is a simpler set of columns drawn in Alibre:

And here is the print in Slic3r 097:

It seems as if the columns were all rendered with the same number of faces, but on the smaller columns those faces must be much shorter.  It seems that with Slic3r, it begins to have more and more trouble as the mesh gets denser.  Here is a KISSlicer print of the same STL:

KISSlicer seems to have a little trouble as well, but unlike Slic3r, it only shows in the smallest columns.  It seems like the slicers have a minimum length of segment that works well.

I also wanted to test perimeter speeds.  You can get a much better surface quality by keeping the speed of the outer perimeters low, while letting the inside of the model run faster.  I printed the column set in Skeinforge once at 50mm/s like all the other prints, and once with the perimeters at .25mm/s.

The poor quality only begins in the thinnest column as it was with KISSlicer.  The slower speed noticeably improved the surface of the last columns, but didn’t eliminate the errors completely.

This really was a torture test, not just in the features, but also the inconsistent mesh.  This exercise wasn’t about finding the best settings and creating the nicest print, but seeing how the slicers perform relative to each other.  The torture model happened to test how well each of the slicers dealt with a mesh that was  disorganized, and I think KISSlicer handled it with the most grace.

In the next post I will try some owls for a more organic print.

Slicer Torture Test

One variable I was concerned about in making the test prints was the USB connection.  Sometimes the flow of instructions can get interrupted, causing the printer to pause and wait, leaving a blob in the process.  If a little too much CPU gets tied up for a moment, it can create one of these pauses.  To prevent this, I ran the test prints from an SD card mounted on the printer itself..  I did a comparison between USB and SD with Slic3r 096, and there is a slight, but noticeable improvement in the SD print-

Overall it looks pretty horrible, at least in the columns.  On to the overall results.  At the end I will have a link to download all of these at high resolution since the viewer on the blog doesn’t let you really get into the detail.  Warping at the corners was always a problem.  These were printed on Kapton with hairspray in a closed case.  On some I used a heater to get the ambient up to 60C which helped keep the corners down, but never completely eliminated the warping.  Even though the corners lifted the prints were very hard to remove even at room temperature.

I’m surprised to see stringing across the holes in the Cura print, even though the retraction settings were the same for all.  The sides of the cube with Cura and SF39 split in a few places because the narrow walls were left hollow and weak.  Slic3r had a consistent problem with the end of the arch coming loose.  The echo pattern to the left of the holes is supposedly due to the outer perimeter speed being too fast.  Ideally you would set that to a low speed, and run inner loops and infill faster to save time, but not all of the slicers had that ability.  The Slic3r 096 print doesn’t have the holes because I had already run that one before I thought to add them.

Kisslicer wins for best arch.  Slic3r might have been better, but it is hard to tell since it knocked it over every time.  Kisslicer and Slic3r also had more consistency in the flat walls.  The columns were a challenge to all slicers, and I don’t know why they all came out so poorly.  You might think it would be mechanical issues with the printer, however they sucked in different ways, and did it in a consistent manner. I did some more testing related to that, which I will get into later.

Kisslicer handled the columns best, with some slight gapping at the point where the outer perimeter turns inward to the fill.  In Slic3r I left Randomize Starting Points unchecked.  That setting is supposed to prevent a seam running up the side of cylinders from the perimeter starting at the same point in every layer.  However it usually causes blobs to be spread all over the surface.  I suspect Slic3r 096 was randomizing anyway, while 097 respected that setting.

Cura and SF39 had a lot of variations in the flat wall, and especially the column perimeters.  Kisslicer and Slic3r 097 had the best walls and a little variance in the column perimeters, while 096 had a lot of random blobbing. 072b is OK, somewhere between 096 and 097 with a little more pronounced seams.  In the 097 print you can see a little blobbing on the face of the cube toward the bottom. This is from moves between the column and wall, so retraction is a little less effective there than the Kisslicer print.

Kisslicer, Slic3r 097 and 072b are doing the best on the texture wall.  072b managed to avoid dropped loops and maintain layer alignment all the way through.  Kisslicer and 097 also didn’t drop threads, but had some layers with a little setback.

Cura had the best solid top layers, watertight and consistent.  096 was decent, 072b borderline, and 097 and Kisslicer were far too loose.  This could be fixed in 097 by reducing the nozzle diameter so the threads get placed closer together.  I’m not sure how to fix that in Kisslicer.  Increasing the flow rate will close up the gaps, but it will also make the perimeters wider, making the outer and inner dimensions incorrect.

Cura and SF39 left the narrow walls of the cube unfilled, which weakened them so much that some of the layers split apart at the corners.  096 filled the thin wall with a zig zag fill, executing it better than 096.  Kisslicer and 072b seem so have used straight lines to fill the wall which I prefer since it looks a little neater.

096 didn’t handle filling the thin wall of the hollow column at the upper left very well.  072b did a little better but mangled the inner perimeter.  Kisslicer’s is decent with some concentric fill, but Cura has the best one, as well as the smoothest surface of the arch.  The corners of the arch show quite a bit of overshoot, demonstrating that 50mm/s is too fast for the Solidoodle to be running outer perimeters.
Slic3r 097 and 072b predictably had the best bridging performance.  Slic3r has the ability to run the fan for bridges, though 096 seems to have ignored that setting.  Cura and Skeinforge can only speed up and lower the flow to stretch the filament over open space (which Slic3r was also set to do) and was moderately successful.  Kisslicer doesn’t have any bridging settings at all.

The chamfer under the large cylinder was a challenge that none of the slicers was able to handle, though 096 came close.  If the placement of the thread is a little too far to the inside, it won’t stick and get pulled into a straight line instead.  I’ve printed this kind of feature without trouble at 60-70mm, but at 20mm or so the curve is too tight.  A slower speed might have helped, to provide as much time as possible for the extruded plastic to bond to the lower layer.  Even though it didn’t do very well on the chamfer, Kisslicer handled the overhanging perimeters on the underside of the arch better than the others.

The overhanging corner is something that no printer will accomplish neatly without support, but Slic3r 097 managed with the fewest dropped loops, most likely due to the fan.

I was surprised at how badly the columns came out overall, which would seem to point to a problem with the printer.  However the errors were different for each type of slicer, and consistent between versions.  Also they happened the same when the same print was run twice as in the SD/USB comparison.  These prints were scaled up 150% from the original model so it wouldn’t be too torturous, but I did also print them at the original, smaller size.

 Skeinforge 39 still mangled the columns, Kisslicer had small gaps up the seams, 096 was blobby, and 097 had misaligned layers.  All of the Slic3rs still knocked over their arches.  I did a few tests to try and figure this out, which I will cover in the next post.

Later I will have tests with Cushwa’s Owl from Thingiverse for something a little more organic, as well as tiny Yodas at .1mm layers.