With a second working 3d printer in the house, I needed an extra filament spindle box. It was easy enough to build the first one for my Makerbot, so why not build a second, improved one?

The most wanted improvement was a window.

It turns out, that it’s not only nice looking but sometimes also important to see what’s going on inside the box. So I changed the design slightly to sport a window on the front.

Since it turned out, that the second disk above the filament spool on the turntable isn’t really needed (the spindle’s construction is self-supporting and the box’s top keeps the filament on the spindle), I recycled the spare plywood disk in the second filament box: It got promoted to be the turntable. (If you don’t have an extra plywood disk at hand, see here how to cut the disk out of a rectangular sheet of plywood with a Dremel).

Needing even less wooden parts (no front side, no plywood for the turntable), the remaining material was even cheaper to get. Including the sheet of transparent plastic (“Hobby Glass”, a sheet of 2mm transparent LDPE, 25x50cm), the whole stuff cost me less than 5€ (!).

Here’s the updated part list for the box:

There were some requests for detailed drawings, so here you go:

(These drawings are also available as PDF. I added them to thing 3640 on thingiverse.com.)

The change in design is, that -instead of a front wall- there’s a groove for a sheet of transparent plastic (or acrylic, or glass, or whatever).

If you got a circular saw, the grooves are quite easy to make: Adjust the circular saw blade’s height to about half the MDF thickness (i.e. if you use 10mm MDF, adjust the saw to 5mm). Then use the saw’s stop to saw the groove 10mm from the front side of the bottom, top, left and right parts (I hope I’ve got the technical terms about right in English…).

If you don’t have a circular saw at hand (I don’t!), you might use a Dremel to cut the grooves. That’s slightly more work and probably not as exact, but it’s good enough:

After cutting the grooves and drilling all holes, the assembly of the box is quite easy. I used some glue for additional stability.

Then I did measure the final width of the front window (including the depth of the grooves).

Cutting the LDPE sheet was very easy: After slightly slitting the sheet with a box cutter, the sheet can be broken at a table’s edge. It’s like cutting glass, only with a knife and without the cullets.

Now I was able to mark the final height of the window:

Another LDPE-cut later, the box was almost finished:

I didn’t change the inner construction of the box. So all printed parts, ball bearings and rods are the same as in the first box.

I added one last improvement to the box’s turntable: Since the filament roll tends to loosen up a little bit on the turntable, it can happen that some loose filament “falls” from the turntable. That’s usually not a big problem, but it could lead to a turntable-jam.

To avoid that, I used some paper (160g/m²) to build kind of a “cake setting ring” around the turntable (maybe one could actually use a real cake setting ring for this?).

The paper ring catches the loose filament windings, but it doesn’t interfere with the unwinding mechanism itself.

Besides some delays due to massive lack of time, the main problem was, that I couldn’t manage to build a working extruder to print with PLA. There were several attempts to build the original “direct stepper” extruders. These failed because I haven’t had a high torque stepper motor back then.

Some experimental geared extruder designs followed. None of them really worked.

There was even a try to mount a Printruder II on the Mendel (which generally works great). However, I used the Printruder II to test an experimental “insulator less” hot end – … which was a fail :)

Finally I printed different versions of Wade-inspired geared extruders. In the meantime I received two “RepRap-tested” high torque stepper motors (SY42STH47-1684B), so this shouldn’t be an issue anymore. But it was…

Since early tests on mine, to get the RepRap host software running on my Mac, weren’t too promising (I somehow managed to build and launch it, but there were a lot errors and GUI issues), I decided to install the Makerbot firmware on the Mendel boards and use it with ReplicatorG.

When doing first tests, I ran into problems with the motor driver chips on the extruder board. They ran really, really (really!) hot within seconds when driving the extruder’s stepper motor. When reducing the motor’s current by reducing the PWM value, the problem got slightly better (but the chips still got really hot). But  also the stepper motor lost most of it’s torque (and  the extruder got jammed again).

Finally, a reader of this blog (“renoir”, thank you!) wrote a comment on the blog post “Well, …no!”, linking to Tony Buser’s “RepRap host on Mac OS X Snow Leopard” blog post. This nice, short instructions solved most of the problems I had with running the RepRap host software earlier (I guess, Adrian also improved the software’s compatibility in the past half year).

Anyway, having the RepRap host software up and running on my Mac, there was no reason not to try the geared stepper extruder again, this time with the “originally intended” firmware. Behold: It worked like a charm, the motor driver chips’ temperature gets only to about 40-45°C.

I still don’t what went wrong (or what I did wrong) when trying to use the stepper extruder with the Makerbot firmware. But it works just great with the RepRap firmware.

So having a Mendel, printing with the RepRap host software, I am somehow puzzled about how to generate usable gcode with it. When using the host software’s built-in gcode generator, I always end up with fancy 5D gcode, but printing objects with a fill rate of about 80-90%. I searched the settings, I browsed the RepRap wiki, I googled the forums… no word on how to configure the gcode generator in order to be able to change basic (and important) settings like “fill rate” or “raft / no raft” or anything. I cannot believe, that the official RapRap gcode generator works like “one size, fits all”. Does anyone know more about this? Renoir? Tony?

What I did find was the hint to use Skeinforge to generate gcode for the Mendel. I tried this, but so far, I wasn’t able to generate working gcode  for the Mendel with it. For the Makerbot, I still use an older version of Skeinforge (v2009-11-06). My settings for this version are well tested and fine tuned. Also my raftless tool works very well with this version. Since this old version doesn’t support 5D gcode generation yet, I downloaded a more recent version (2010-06-29). But somehow I couldn’t manage to generate usable gcode with this version. Also the newer versions of Skeinforge seem to be much less liberal with “unproven meshes” in STL files. I ran into a lot of non-recoverable errors with some of my STL files (which work well with the old 2009-11-06 version).

I also tried to use Erik’s 3D-to-5D-Script with gcode I generated with the old Skeinforge version. But the resulting gcode wasn’t printable. I guess, I need to read more on the use of this script…

Generally, I’m surprised how hard it is to find instructions or how-tos on generating gcode for Mendel. Maybe I looked in the wrong places. I googled a lot in the past few days, but besides some posts with partial Skeinforge settings I couldn’t dig up much.

Any hints or links are highly appreciated!

After printing a Printruder II extruder block (slightly modified, for better maintainability of the pinch wheel), I still needed a way to mount the Printruder II on the Mendel X carriage.
So, here’s the simple 2 parted solution:

Theoretically, this holders should also work with a standard MakerBot Extruder MK3/4 (I didn’t try!). Probably you’d need to exchange the retainer washer to a slim-line retainer bar as described in my yesterday’s post.

I published the design for the holders on Thingiverse.com (thing 3151).

After successfully mounting the Printruder on the Mendel, I feeded some PLA into it and…

1230 hours UTC: Houston, we have an extrusion

Looking good, so far.

To test things out, I loaded the original whistle_v2.gcode into Replicator G and hit “print”:

Well, that looked really promising.

The scrapped blue tape in the front came from some unexpected movements during my first try to print something. I use MakerBot firmware and ReplicatorG to drive my Mendel (unfortunately, I’m still not able to run the RepRap host software on my Mac and, as already mentioned yesterday, I also have trouble to get my stepper motor extruder working), and I forgot to adjust the machines.xml and to add custom settings for the Mendel. Thus the Z axis didn’t work as expected first.

This was the first time, my Mendel actually printed something! Great joy!

It turned out, that the stepper motor controllers needed some adjustment (too low current for the motors, the y stage lost some steps).

So I aborted this first print to adjust the potentiometers properly.

After finishing the adjustments, I started another print, but…

1530 hours UTC: Houston, we have a problem!

The extruder got stuck. Again…

I tried different extruder temperatures, removed the filament, fed it, removed it again…

Nothing really helped. There was some oozing, but no extrusion.

Finally, I tried to push out the remaining PLA with some white ABS. Not sure if this was a good idea, but after a few tries, the ABS seemed to have reached the nozzle. Although I got a little bit of ABS extrusion, the nozzle seemed still somehow jammed.

Long story short, here’s the final result after another 15 minutes:

Well, that looks like a jammed extruder :)

And indeed, here’s the lower end of the mess:

That retainer bar isn’t supposed to hang there in this strange angle!

Have a closer look:

The leaking ABS plastic is definitely not supposed to be there!

2200 hours UTC: Looking for a friendly bar in the neighborhood

Well, I’ll try to disassemble the whole mess and to find out what happened to the PTFE tubing…  Tomorrow (at the earliest).

For the Mendel, I tried it again (with PLA this time). I cleaned the whole thing, rewound the nichrome wire and attached the extruder to a special variant of the Printruder II:

This Printruder II has a special mounting hole to directly screw the insulator-less extruder to the body with a single captive M8 nut.

Although the whole setup looked very nice and I even was able to extrude PLA at 185°C by pushing the filament manually, it got stuck again as soon as I tried to extrude more than 5cm with the motor.

I really don’t know why the extruder doesn’t work, but I guess the problem is the long brass barrel. Probably, the plastic melts way too early in the barrel and forms some kind of plug.

It seems I have to count the insulator-less extruder as a fail after all.

Speaking of fail: I finally recieved two new stepper motors: SY32STH47-1683B from Zapp Automation. This motor is recommended on the RepRap  site for use in the Mendel Extruder 2.0. However, after connecting it to a standard MakerBot extruder controller and trying to drive it with the MakerBot firmware (recompiled for driving a stepper extruder motor), it turned out that even when just driving the bare stepper motor (no gears, no filament, no nothing), both A3949 motor driver chips on the extruder board heat up to 70-100°C in just a few seconds and start to smell funny. The stepper motor turns as expected during this time, so I’m quite sure the 4 wires are connected in the correct order.

I switched of the whole thing quickly, so I’m not sure if 100°C is the top temperature or if the chips would just burn out (I really don’t want to know…).

Do I something wrong? When reading the Mendel documentation on the RepRap page, it looks like there is no additional electronics needed. Just hooking up the 4 stepper wires to the 1A/1B/2A/2B connectors on the extruder board and go.

When asking for help on the RepRap forum, nophead answered that I’d need to limit the current by using a smaller PWM value than 255. I tried that already, but the chips still get very (!) hot and if using a lower PWM value, the stepper motor looses a lot of its torque, of course.

Does anyone successfully use a stepper motor in an extruder with MakerBot firmware? I’d really appreciate any help on this.

But back to today’s main feature :)

The “Complextruder”

When reading about a “Concept for Extruder” in the Makerbot mailing list some days ago, I really liked the first illustration, Brent Crosby (“baxsie”) attached to his post:

This sketch shows a heater section where a PTFE tubing goes all the way down from the extruder body to shortly before the hot zone in the extruder tip. This should reduce friction in the extruder significantly. And since it seems, that too much friction killed my insulator-less extruder design, I decided to give this design a try.

Please also have a look at the “Concept for Extruder” mail thread in the MakerBot mailing list. Brent documents there the build process of a slightly different extruder design (derived from the above, but using a rather large melting chamber).

Here’s a drawing of what I try to build:

Although I used the general idea of Brent’s design, I changed it in order to get an extruder I could easily use with a standard MakerBot extruder body (and of course with a Printruder II).

To avoid leaking plastic, I designed the PTFE tubing to be threaded at the end where it goes into the brass hot part. This also makes the whole thing somehow more rigid.

The brass nozzle

Here’s the nozzle blank, before drilling the stepped bore:

The completed nozzle. Although out of focus, you can see the M6 threads inside the nozzle:

Another shot of the finished nozzle, this time in focus (kind of):

The PTFE tubing

I presume, that the PTFE tubing in Brent’s original design is meant to be a piece of simple PTFE tube. But since this part is slightly more complex in my design (and I don’t have any PTFE tubes lying around), I turned this from a piece of 15mm PTFE rod.

The outher PTFE shell

This part was rather easy to build. It’s simply a piece of 15mm PTFE rod with a 9mm bore in it:

Assembly

Once the three parts are manufactured, the assembly of the extruder is straight forward:

1. Screw the PTFE tubing into the end of the brass nozzle

2. Press the above part into the outer PTFE shell

3. Insert the holder

I build the holder (my version of the MakerBot Retainer Washer) from a 2mm thick piece of aluminum bar. The part has a centered 6mm hole for the nozzle and two 3mm holes for the M3 bolts (holding the whole thing on the extruder body). Using the aluminum bar instead of a large washer also allows you to use such an extruder nozzle in a standard Mendel carriage.

Finally, I wound the nichrome wire onto the brass nozzle:

And here’s the completed extruder nozzle, after attaching a thermistor and some insulated wires to the nichrome:

So far so good. I hadn’t a chance to test the new nozzle, yet.

I need to print another Printruder II first, since I don’t want to risk dissasembling my current (and only only working) extruder to test the new nozzle. I hope, I find the time to test it tomorrow.

I’ll let you know, as usual…

There are two reasons why it’s not printing yet:

On the software side, I still didn’t manage to bring the Reprap software to life on my Mac. After tinkering around with some Java frameworks, settings and class paths, I was eventually able to launch the host software. But somehow I wasn’t able to establish a connection between the host software and the RepRap firmware on the Mendel.

Right now, I switched back to the MakerBot firmware, in order to be able to use ReplicatorG to test drive Mendel’s mechanics. When I solved the remaining problems on the hardware side (see below), I’ll probably try again to use Mendel’s native RepRap firmware/software.

On the hardware side, I still don’t have a high torque NEMA 17 motor on my hands. However, I have a NEMA 17 stepper laying around. It’s the same cheap, low torque type, I’m using to drive the X,Y and Z axis.

This stepper is rated to provide a holding torque of only 0.23Nm, which is obviously too low for using it in a RepRap Thermoplast Extruder v2.0.

I tried it anyway: :)

To grip the filament, I put a treaded pulley on the motor’s shaft. I built it on my lathe and tried keep the shaft’s diameter as low as possible: the pulley only adds 1mm to the motor’s shaft diameter, so it now has effectively 6mm diameter.

According to the rated torque, theoretically this motor should be able to pull the filament with about 76N (i.e. around 7.5kg on the balance).

But when I tried this setup, the motor started to skip steps at about 2kg on the balance (i.e. ~ 20N). That’s way to low, even for PCL filament.

I guess, the main problem is, that I don’t use a real stepper driver to power the motor, but the RepRap/MakerBot extruder controller with the “2x DC motor drivers  -> stepper motor hack”. So the stepper motor probably doesn’t get enough current to produce it’s rated torque.

The obvious solution for this problem would be to buy a high torque stepper motor and/or use a well dimensioned stepper driver. Well, maybe I’ll eventually end up doing exactly this. But then again, I had this idea some time ago, when I lathed my first threaded pulley, to use one of these threaded pulleys as part of a worm gear.

I decided to first give this idea a shot…

Here’s the design, I came up with:

I drilled a 5mm hole in a piece of M8 threaded rod and added a set-screw, so it can be attached to the shaft of the stepper motor:

The central part of the gear box is the following part. It’s made out of brass and has two threaded grooves, one M8 (for the worm gear) and another one (M3) to grip the 3mm filament:

All printed parts were successfully printed raftless in black ABS on my MakerBot with heated build platform.

Although I’m quite fond of Mendel’s overall construction, I changed the design of a few parts.

For example: the timing pulleys. In order to attach an original timing pulley to the motor, one’s supposed to file two flats onto the motor’s shaft. I tried it on one motor and it was a pain in the ass. Maybe it’s all about the right tools, I don’t know. I used a full sized file and a vise, but I didn’t manage to get the flats right. In addition to that, I rather don’t do any irreversible modifications to expensive parts (i.e. stuff I have to order, like stepper motors). After all, once you messed up a motor’s shaft, you cannot use it anymore…

So I aborted my luckless attempts to get the drive shaft right and rather changed the pulleys’ design to have normal, round holes. I designed the holes to be exactly 5mm wide, but due to ABS shrinkage they turn out a little bit smaller. After cleaning the holes with a 5mm drill, the pulleys fit very snugly on the original motor shafts.

Since the force on the X/Y/Z axes aren’t that high, I’m pretty sure that the pulleys won’t slip on the shafts. And if they do, it’s probably much easier and more reversible to drill a hole for a splint pin through the whole assembly…

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Another problem to solve was the pinch wheel part in the pinch wheel extruder. I decided to go with a threaded pulley.

In order to keep the diameter as small as possible, I lathed the threaded pulley with an outer diameter of about 9 mm; with the 5mm hole for the shaft and a M3 thread groove, the pulley adds only 1 mm to the drive shaft’s diameter.

Unfortunately, the steppers I have are way to weak for a Mendel’s extruder. So I hadn’t a chance to test the pulley in a working extruder yet.

If anybody has easy access to one of these high torque NEMA 17 motors and likes to send me one of these in exchange for one of my threaded pulleys, please feel free to contact me!!

Actually, I’m really thinking about selling these threaded pulleys. Anyone interested? Here’s my official pack shot: :)

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After completing the mechanical assembly, I’m now about to wire the whole thing up.

Which brings me back to my concerns on doing irreversible (or better: hard to undo) modifications on expensive parts: According to the build documentation, several “adaption” on the motherboard and other PCBs are needed.

Although I’m ok with desoldering the RJ45 connectors for the endstops on the stepper boards (I always found the Ethernet cables way to clunky for connecting the endstops…), I really don’t like the idea to remove the ATX power connector from the motherboard.

Besides the technical challenge and a childish “must-have” attitude, one reason for building a Mendel was (and is) to have a mutual backup for/by my MakerBot. That not only includes the convenience of being able to print replacement parts for the other machine, but also the to use the identical electronic hardware as a backup. By removing the ATX power connector from the Mendel motherboard, I’ll loose this advantage. And I’d rather not.

I hope I’ll find a way to use the unmodified motherboard in the Mendel (adding the I2C connector is ok, that’s adding, not removing…). There must be a way, maybe by doing a few firmware changes…

Does anyone have experience with this? Any help appreciated!