Well,… no!

1100 hours UTC: Preparing for the big moment

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).

Complextruder

In order to finally get my Mendel operational, I reactivated the insulatorless extruder I built last December. Back then, I didn’t get it working. The ABS got stuck shortly after starting an extrusion.

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:

Insulatorless Extruder

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:

Concept for Extruder by baxsie

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…

No luck – … yet

As you might know, I’m in the process of building a Mendel.

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.

IMG_4765.png

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: :)

IMG_4845.JPG

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.

IMG_4842.JPG

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: