If you don’t speak German but are around Frankfurt, you might come anyway and see the pretty pictures in my presentation, my Makerbot in action and me babbling nervously.

Macoun 2010 is a (the) German OS X Developer conference and will take place in Frankfurt/Main, Germany at October 2nd and 3rd, 2010. Both of my talks are at October 2nd.

Und aus gegebenem Anlaß dieses mal auch noch auf deutsch:

Am 2. Oktober halte ich auf der diesjährigen Macoun OS X Entwicklerkonferenz (2.-3. Oktober 2010 in Frankfurt/Main) zwei Vorträge:

Der erste Vortrag “Drucken in 3D” geht auf die verschiedenen 3D-Drucktechniken im Allgemeinen und das Drucken mit Open Source Druckern wie dem Makerbot im Speziellen ein.

Im zweiten Vortrag “Umdenken in OpenCL” erzähle ich über meine Erfahrungen mit OpenCL während der bisherigen Programmierung an “Pleasant3D” und zeige natürlich auch die grundsätzliche Vorgehensweise beim Programmieren mit OpenCL (an Beispielen).

Alle Vorträge sind deutschsprachig. Weitere Infos und das komplette Programm gibt’s auf der Macoun 2010 Homepage. Eintrittskarten sind bis zum 31. August noch um 20€ billiger zu haben.

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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.

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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!

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As you know, I’m working on the long term project, using Mecanum wheels for a robot with omnidirectional driving capabilities.

Today, I received the gear motors for my Mecanum wheel chassis prototype:

These are 12V gear motors with a 1:50 gear reduction. The spindles are running at approx. 104 RPM.

To drive these motors from an Arduino Duemilanove, I use the motor shield from ladyada.net (at least for the prototypes).

Here’s a short video of testing the controller/motor setup:

Already having printed all 4 Mecanum wheels, I thought I would be nice to assemble the whole shebang and give it a test drive.

Well, there were some bumps on the road.

When designing the Mecanum wheel, I planned to use them with stepper motors. Although it’s generally nice to have exact control of the (stepper) motors’ RPM, I’m sure that the wheels’ slipping on the ground is quickly killing this advantage. Because of the much simpler controller electronics, I switched over to the above mentioned gear motors.

The main problem here: The stepper motors have a 5mm spindle, the gear motors have 6mm spindles. Thus, I ended up with 5mm bores in the wheels for the 6mm gear motor spindles.

I re-drilled the center bores in the Mecanum wheels with a 6mm drill. After that, the wheels fit on the motor spindles but -of course- now the captive M3 nuts for the spindle set screws didn’t fit anymore.

To solve this problem, I needed to file down 4 M3 nuts to about half their height:

Although this solved the problems with the changed spindle diameter, the whole process most likely didn’t enhance concentricity of the wheels. Printing a new wheel (without the rollers), takes more than an hour. Cleaning up the printed object, glueing in the ball bearings and assembling the rollers takes at least another hour. Since it’s a prototype anyway, I  chose to go with the fast, easy and maybe less precise solution.

I mounted the four motors with some quick and dirty printed clamp assemblies to a plywood base plate.

The clamps were printed relatively quick and they give me some freedom in (re-) adjusting the motor/Mecanum wheel positions. However, this sort of mount mechanism might not be ideal for long time use.

And here’s what the first prototype looks like:

The black Mecanum wheel in the front right is the first I printed. I had no liquid rubber then and I didn’t find the time and mood to completely disassemble the wheel in order to apply the liquid rubber to the rollers, yet.

The Arduino controller runs a pretty simple test sketch in the following movie, to test the four general drive modes (forwards, backwards, left, right):

Now I need to beef up the robots sensors and firmware. I really like the idea to add a gyroscope to recognize wanted and unwanted direction changes. And, of course, the thing definitely needs some kind of collision sensors…

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As you might know, 4 Mecanum wheels are needed to build a functional omni-directional chassis. So far I finished only two (at least two others weren’t usable due to failed prints, normally because of filament jams…).

One big problem is still, that due to ABS shrinkage, Makerbot fabrication tolerances and printing with 45° overhang, the holes for the ball bearings are always slightly too small.

Until now I used a Dremel to manually grinding the holes a little bit bigger (as seen here and here). The biggest problem with that (besides the boring work) was that when grinding manually, you never get the final holes exactly round.

Earlier this year, I allowed myself buying a nice, new drill press:

Ever since I wondered, if it would be possible to machine finish the holes for the ball bearings with it. I happen to have a 13mm drill (which is the OD of the 624 ball bearings), so the only thing I’d need would be a jig to position the Mecanum wheel resp. the printed hole exactly centered and horizontal under the drill.

So why not simply print such a jig?

Here’s what I designed:

I then screwed the printed jig on a piece of wood, adjusted it on the drilling table and clamped the whole assembly down:

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jstitner on Thingiverse.com:

The HDPE tubing that is used on the makerbot looks the be the same as the “polyethylene” tubing used to connect refrigerators that have water dispensers.

I found a package with 10m LLDPE tubing in a store, selling refrigerators, washing mashines and stuff like that.

It’s a water tube (I guess some kind of spare part for a water dispenser) with an outer diameter of 6.5mm and an inner diameter of 4mm. Perfect!

Thanks again to jstiltner for the tip!

I already had drilled a hole for the filament into the side of the box:

Now that I had the actual tubing, I printed an object to attach it to the filament box:

Actually I printed two of them. On the one hand, the object prints better when printing two at the same time (the ABS has a hard time to cool down enough between layers when printing only one), on the other hand I used the second holder to mount a spring with about the same OD as the tubing on the inside of the box to flexibly guide the filament. Both parts are bolt down with one M4x20mm bolt:

The tubing (with the filament inside) then goes loosely to the top of the Makerbot. I use a guidance ring, I used before to keep the filament out of the timing belt on top of the Makerbot, to give the tubing some support on its way to the extruder:

I updated the Thingiverse.com thing with the printed parts and added the STL file for the tubing holder part.

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I liked the the horizontal design of the “official” Makerbot filament spindle, so I decided to build my own filament spindle box based on (or rather inspired by) this open source design.

Since I don’t have access to a laser cutter, I re-designed the enclosure box for the filament spindle to be build from rectangular parts. It’s cheap and easy to buy custom pre-cut wood in almost any larger hardware store. I got the pre-cut wooden parts for less than 15€:

Here’s the part list for the wooden parts:

Qty	Size (mm)	Material
2	310 x 310	MDF 10mm
2	310 x 120	MDF 10mm
2	290 x 120	MDF 10mm
2	280 x 280	Plywood 4mm

I printed all smaller and more complex parts in ABS on the Makerbot. The STL files for these parts are published on Thingiverse: http://www.thingiverse.com/thing:3640

Finally the following non-printable parts are needed:

Qty	Part
1	M8 Threaded rod (approx. 135mm long)
2	608 Ball Bearing
2	M8 nut
2	M8 washer
4	M4 x 12mm bolts
6	M4 x 55mm bolts
16	M4 nuts
26	Chipboard screws (35mm)

The only non-printable parts (too big) in a non-rectangular shape are the two disks, holding the filament in place. I used my Dremel with its circle cut tool to cut the two square plywood sheets into (more or less) round shape. It was the first time I used the circle cutter and I learned a lot about how to not use it :) However, the disks are hidden inside the box anyway…

Building the box is straight forward: Pre-drill and countersink the holes for the chipboard screws (the hole for the axle in the center is a stepped bore 8/13mm. More on this later)…

… and assemble the box, using some glue and a bunch of chipboard screws:

(Well, I guess 3 screws per edge would have been more than enough…)

The axle inside the box is stationary. The lower M8 nut is counter-sunk on the “outside” of the box (that’s why the center hole is a stepped bore). Inside the box, the axle holds a sandwic containing a M8 washer, a 608 ball bearing, another washer and finally a second nut:

The 608 ball bearing holds the bottom plywood disk (and therefor the filament roll). I know, the ball bearing isn’t designed to hold load in axial direction. But the  approx. 2.5 kg shouldn’t be any problem for a 608 ball bearing (even in axial direction) and the spool turns rather slowly. According to wikipedia, the maximum axial load of a radial ball bearing is usually between 25 and 50% of it’s maximum radial load. And a 608 ball bearing is able to handle a static radial load of about 1400N (!)

The axle is cut to length, so the upper end should end “inside” the top cover (approx. 5mm):

The top cover plate also gets a center bore (8mm diam.), but only half way thru.

That way, the top cover plate hold the stationary axle centered.

To attach the bottom plywood disk to the 608 bearing, I printed an ABS bearing holder part:

This part is bolt to the plywood disk with four M4 bolts.

The 608 ball bearing should fit snugly:

(The 608 ball bearing in the photo above was only inserted to check its fit. Later, the ball bearing is already mounted on the axle as described above and the plywood disk (with the ABS bearing holder bolt to its lower side) is pressed onto the ball bearing on the axle.)

… back to the headline

Initially I planned to use the chipboard screws only for building the wooden box. But when designing the printable parts, I ran into an old problem: how to connect the printed parts with the non-printed parts? In case of the lower bearing holder it’s no problem to use bolts and nuts to attach it to the plywood disk. But in case of the inner distance parts it’s not that easy. Using the T-slot technique (normally used with laser cut assemblies) isn’t that easy with printed ABS parts. The T-slots likely aren’t printed with enough detail and ABS is probably too soft to hold the pressure from the tiny M3 or M4 nuts.

Finally it struck me: Why not simply use chipboard screws and screw them directly into the ABS? After all, when disassembling industrial plastic objects, you almost never find bolts and nuts but self-tapping screws. So why not use the same technique with printed objects? The design gets even simpler: just print the parts with “pre-drilled” bores for the screws and you’re ready to go. No captive nuts. No fiddling around.

Granted, some nice, black socket cap bolts with self-locking nylock nuts look usually much more elegant. Also parts you want to disassemble frequently are much better off with some kind of nut & bolt connection.

But all other connections are great candidates for “direct screwing” with chipboard screws. Chipboard screws are available in all kind of sizes and they are cheap!

That said, I designed the inner distance parts with a “pre-drilled”  bore for a 35mm chipboard screw, holding it on the plywood disk:

To hold the upper end of the inner distance parts in place, I designed a second ball bearing holder:

This second holder contains slots for six M4 bolts, used as spokes:

Since I put the Makerbot on top of the closed filament spindle box, there’s no need for any additional closing mechanism.

Things to do

As mentioned above, I still need to design and print some kind of snap-in mechanism for the upper plywood disk.

A much bigger problem is, that I still don’t have any tubing to guide the filament from the box’s outlet (a hole on the right side of the box) to the extruder. It’s harder than I thought to get hands on a small amounts of plastic tubing (at least around here in my hometown). In order to minimize friction, I guess the best material would be PTFE. So far I found PTFE tubing only in online stores in large quantities of 25 or 50m (which is quite expensive, especially since I need only 1 or 2m).

If someone knows a good, cheap source for PTFE tubing in small quantities (preferably in Germany), please let me know.

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Anyway, here’s a short movie of a new feature I implemented some weeks ago:

Although there seem to be some issues with more complex DAE files, the import of “printable” objects usually works very reliable.

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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).

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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…

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