Pleasant Hardware

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:

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…

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: 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...

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.

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:

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. 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: To press the filament against the M3 groove and to do the same to the M8 threaded rod and the M8 groove, the extruder contains two idler wheels. Each one is adjustable through a single M4 bolt. I already used this technique for my current Printruder design in my MakerBot: This design works quite well (... and I'll publish the new and improved Printruder design, of course. As soon as it is fully tested...) I lathed the idler wheels for both, filament and M8 threaded rod, as wheel rims for 624 ball bearings: To keep the extruder's housing simple (and rigid), I printed it in two parts, a plate which holds the motor and the gears and a frame for the idler blocks. I later glued (or better: welded, with Acetone) the two parts together. The heater section is attached to the extruder more or less the same way as on the MakerBot MK4 extruder: The heater barrel and PTFE insulator are attached to the extruder body with two long M3 bolts. In order to be able to mount the extruder on the Mendel's X carrage, I replaced the large washer of the MakerBot design with a slim piece of aluminum. That way the whole thing fits through the relatively narrow opening in the X carrage. Finally I did a performance test with the completed extruder: This time, the motor started to skip steps at about 9 kg on the balance: That's definitely much more than the 2kg of the direct drive. But it might be still not enough for reliable use. The measured force of about 90N look even worse in account of the 1:33 gear reduction of the worm gear. I guess that most of the force is eaten by friction in the worm gear. Of course, the problem gets worse the more the M8 idler wheel is tightened. I hoped that tests would show, that the M8 idler wheel isn't necessary (which not only would lower the friction but also would simplify the whole extruder design). But if it is too loose, the M8 threaded rod occasionally starts to skip threads. To solve this problem, I'll try to replace the M8 idler wheel by a 608 ball bearing on the free end if the M8 threaded rod. I tried to use the extruder in a real world print on the Mendel (running with MakerBot firmware/ReplicatorG). Although, the XYZ-movement worked quite well, the extruder didn't extrude the ABS continuously enough for a successful first print on my Mendel. So this milestone still isn't reached. Either until I solve the problems with the worm gear extruder or I'll finally order one of these high torque stepper motors... I'll let you know.

My Mendel is almost finished (at least the mechanical assembly).

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…

-

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: :)

-

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!

My Mendel is almost finished (at least the mechanical assembly). 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... - 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: :) - 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!