Plastruder MK3

Note: for the upgraded Plastruder MK4 that shipped with Batch 6 (and purchased from the makerbot store) see: http://wiki.makerbot.com/plastruder-mk4

Good to Know

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The Extruder contains certain parts that could be dangerous if used in an improper manner. The extruder tip can become extremely hot. (>250 celsius) There is also an extremely powerful motor that can pinch fingers. Make sure you always run the extruder fully assembled and that you never touch the hot metal tip. Always keep the extruder away from flammable objects and never leave it hot unless you are actively printing.

Overview

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The Plastruder is the 'print head' for your MakerBot. You can think of it as a souped-up, robotic hot glue gun. Its main purpose in life is to heat up the plastic you feed it, and then extrude it out in a fine stream that you can build with. It has two main parts: the filament drive mechanism, and the heater barrel assembly. The filament drive mechanism is the part that grips the plastic and pushes it into the heater for extrusion. The heater barrel assembly is the hot part of the extruder that melts the filament. It also has a small diameter nozzle where the hot plastic is forced out.

Specifications:

  • Accepts 3mm plastic filament
  • Maximum extrusion rate: 16mm/second
  • Maximum temperature: 260C

Usable Plastics

  • ABS - recommended polymer. cheap, ubiquitous, low shrinkage, strong objects. ABS == Acrylonitrile butadiene styrene.
  • PLA - excellent polymer. made from corn, transparent, eco-friendly, biocompatible and biodegradable in the body. PLA == Polylactic acid.
  • HDPE - cheap polymer. very smooth, relatively high shrinkage factor. HDPE == High density polyethylene.
  • CAPA - fairly expensive polymer. very low melting point. low friction. CAPA, aka PCL == Polycaprolactone.

Get one!

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Gathering all the parts for building one of these can be pretty time-consuming. Also, you have to buy a large amount of something (like Nichrome) when all you need is small amount. Not only that, but buying a kit from the creators supports us so we can make it better. That's why we offer a kit that contains everything you need to build one yourself.

You may buy a Plastruder MK3 kit from the MakerBot Store.

Assembly

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Building the extruder takes about 2 hours from start to finish. It's a pretty straight-forward process where you bolt together parts, use tape, cut and solder wires, and other fairly simple tasks. We've simplified the extruder design so that it only requires simple, common tools to assemble. If you have a partner or friend to help you out, it will be much more fun.

View the assembly instructions here.

Source Code

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The design of this extruder is 100% open source. What this means is that we've released all the CAD files used for parts and the documentation under free licenses. The majority of the files are DXF files created by QCad. There are a few different ways you can access the files:

Usage

Your finished extruder is a robust, solid device for extrusion. If you treat it properly, it will extrude for a long time. There are certain things you should know about your extruder in order to avoid damaging it.

1. Never run the motor without extruder being hot.
2. Never feed in a second strand of filament.
3. Always turn off extruder when you are done printing.
4. Double check the target temperature before extruding.
5. Never let your filament run all the way into the extruder.

Steps to First Extrusion

Once you have your extruder assembled, you'll want to get started right away. It's best to take it slow and test the various sub-systems before you do something that could potentially break it. This will also give you a feel for how to actually use the extruder as well.

Measure the Temperature

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Measuring the temperature is really easy. Make sure you have the extruder wired up properly to the Extruder Controller, and then open the ReplicatorG software. It will immediately begin polling the extruder for its temperature and will update the status window. It should read something around 20 celsius which is about 68 fahrenheit.

If it reads something that doesn't make sense, jump to the troubleshooting section.

Initial Burn-in

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If your temperature is reading correctly, it is now time to fire up the heater! Its best to choose a conservative temperature first and then slowly build your way up. That way you can detect a problem and hopefully fix therefore avoiding doing some sort of damage. The latest heater design is pretty foolproof, so you should be fine.

I suggest starting the heater at 50C, letting it heat up (watch the temperature and make sure it actually does rise from 20C to 50C). Let it maintain the 50C temperature for a few minutes. This will prove that it can indeed handle controlling its temperature.

Occasionally during the first startup, the heater does let off a little bit of smoke as the binder on the nichrome burns off. This is completely normal, but if it does get out of hand, simply unplug the extruder and let it cool down. You may want to have a fan setup to blow away any initial out gassings.

If that goes successfully, crank up the temperature to 100C, then to 150C, to 200C, and then finally to 220C.

Test the Motor

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Now that your heater control is working properly, you will want to test the drive motor. Enter a PWM value into the speed box. The value should be between 127 and 255. I run my extruder motor at full speed, so I recommend using 255 as the value. Enter 255 and then click the 'forward' button. Your motor should turn on and rotate forward.

You'll want to watch it and verify that it is actually moving. If you peek down the filament feed hole, you should verify that the motor gear is moving in the right direction. You can also verify this from the side. If it is moving in the wrong direction, check out the troubleshooting guide.

First Extrusion

Now that your motor, heater, and temperature control have all been verified, its time to try for your first extrusion! This is a very exciting time, so feel free to do a little excitement dance to get yourself ready. I'll wait, its okay.

Alright, first triple-check that your Target Temperature is set to 220C (for ABS plastic) and that the heater barrel is at that temperature. If you are using a different plastic, make sure you know what temperature to extrude at.

Now, turn your motor on forward at 255 pwm. You need to set the PWM first, then turn the motor on. Verify again that it is indeed moving.

Feed the Filament

Finally, get a long length of plastic filament that you will feed into the extruder and actually feed it into the extruder. The motor will change sound slightly since it is actually exerting force, so don't worry. Push gently on the filament and soon the motor will grip it and start pulling it into the extruder itself. You can pull against the filament to see if it has a good grip. You should not be able to pull it out of the extruder without using excessive force. That is good.

You should watch the filament move down through the extruder body, and can also see through the back of the extruder housing and see the notches slowly moving through the extruder. Alternatively you can either mark the filament with a marker or slightly dent it with some pliers to give you a reference to watch the filament as it is fed into the extruder.

It works!

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It takes about 1-2 minutes for the filament to feed all the way through the extruder and come out the bottom. Be patient while this is happening. It will definitely start to extrude. Eventually, you'll see your very first extrusion come out of the nozzle! Congratulations, your extruder works! You should 'burn-in' your extruder and let it extrude for 5-10 minutes just to verify that it is actually working properly. Be careful that your filament does not pull all the way into the extruder housing as it is a bit of a pain to remove if it does.

If your extruder stops extruding during this first extrusion, check the troubleshooting guide for steps you can take to fix this.

Daily Printing Operation

Replacing the filament

The basic process to replace the filament is:

1. Heat up extruder to operating temperature
2. Reverse the extruder motor to pull filament out
3. Pull out old filament
4. Turn extruder motor on forward
5. Feed in new filament and wait for extrusion

If you want to be lazy and/or efficient, here is a pre-made GCcode script that you can run which will prompt you for the various steps:

M104 S220 (Heat up extruder to 220C.  Change if you use non-ABS)
M108 S255 (Set PWM speed to 255)
M06 T0 (Wait for extruder 0 to warm up)
M102 (Reverse the motor)
M00 (Click 'Yes' once the filament has been removed.)
M101 (Motor on, forward)
M00 (Insert the filament and click 'Yes' once it starts extruding.)
M103 (Motor off)
M104 S0 (Temperature 0, heater off.)

Keeping it Clean

It's important to keep your extruder clean for proper functioning. Always make sure you are using clean filament with no dust or debris. You may want to have the filament pass through a rag or something in order to remove the dust from it.

Also, during operation your extruder will probably pick up globs of plastic on the nozzle. These should only be removed when the nozzle is hot with a pair of tweezers. You can use needle nose pliers, but be very careful that you do not clamp the nozzle as you may destroy it accidentally.

Keeping Things Tight

Hopefully when you tightened down the idler wheel, you gave it a good twist. If you didn't, it may possibly work its way loose during normal operation. If this happens, you just tighten it back up. You'll need to remove the filament before tightening.

Depending on your tools, you may need to remove the electronics to tighten the idler pulley. If you have a 13mm wrench that fits between the board and the acrylic, then you can just use that. Otherwise, off with the electronics!

The rest of the nuts and bolts should be kept tight, especially the ones holding the heater barrel assembly to the extruder housing. Don't tighten things too much so that the acrylic breaks. A good rule of thumb is 1/4 or 1/3 of a turn past hand-tight.

Troubleshooting

My Extruder does not report the right temperature.

Reality Check #1: Is your thermistor actually hooked up?

The thermistor should be wired to the two-pin screw terminal labeled 'Thermistor'.

Reality Check #2: Is it actually your thermistor?

Your thermistor should have a resistance of ~80K at room temperature. Measure the resistance with a multimeter. If it reads low, like say 6-12 ohms, then you have hooked up the heater to the thermistor port instead. Swap the heater and thermistor (double check the heater resistance to make sure!!!).

If the multimeter reads as a short or as 0 ohms, then your thermistor is shorted. Unfortunately, you're going to have to take apart the heater barrel, pull the thermistor leads apart to fix the short, and then re-assemble it.

If your multimeter reads infinite resistance, or no connection, then one of your connections is bad and you'll need to re-attach the lead wires to the thermistor somehow. This involves taking apart and re-assembling the heater barrel assembly.

My extruder does not heat up.

Reality Check #1: Is your heater hooked up?

The heater wires should be hooked up to the B+ and B- ports on the MOSFET output port. The polarity is not important, but it is important that its hooked up and screwed down nice and snugly.

If that doesn't fix it, make sure that you have your heater hooked up. Measure the resistance between the two ends of the heater wire. It should be from 6-12 ohms, depending on the length of nichrome you used. If it is much higher, you have hooked up the thermistor to the heater and should switch them (double check the thermistor resistance to make sure!!!)

If they are shorted, then you have a short and need to fix it. Unfortunately, you need to take apart the heater barrel to fix it.

If that doesn't fix it, or there is infinite resistance (no connection) then one of the joints may be bad. You'll have to disasseble the heater barrel for this as well.

My extruder motor is not running.

Reality Check #1: Is your motor hooked up?

The motor should be hooked up to output 1 of the h-bridge outputs. The red wire should be hooked up to 1A, and the black wire should be hooked up to 1B.

My extruder motor is running backwards.

Easy! Simply swap the red and black wires. Remember to turn the power off first!

My extruder has stopped extruding.

This can be a bit tricky. There are a few tricks / techniques to make it work again. Just be patient and you'll have a working extruder in no time.

New Extruders

If you had your first extrusion, but it stopped shortly afterwards, you might have debris in your extruder nozzle. This happens when you do not properly clean your barrel/nozzle before using it.

The solution is to reverse the filament, cut off all the filament from where it got chewed up and below, and run new filament in. The old filament that you pull out will also pull out most of the junk that is in the extruder. Do this a couple times and it should be totally free of debris. You may even see tiny particles on the surface of the melted filament when you pull it out. If you see that, then that is definitely your problem.

Does pushing on the filament start up extrusion again?

If it starts extrusion again, then awesome. Chances are that the drive gear just chewed up the filament too much and lost traction. If you just had to push for a little bit to start extrusion and then the extruder continued to extrude then that was your problem.

If the extrusion starts, but stops as soon as you stop applying pressure, then most likely your idler wheel is not tight enough. I recommend removing the filament, tightening up the idler wheel, and then re-feeding the filament down through the extruder again.

Does your extruder slowly lose grip and not extrude very well?

Potential problem #1: Your heater barrel does not fix exactly into the PTFE barrel.

Some of the heater barrels in the latest batch are not beveled to match the internal structure of the PTFE. If you have a lathe, bevel the edge at 31 degrees (to match the standard 118 degree angle of a jobber bit) If you don't have a lathe, you can use a file to get the desired bevel as well To check to see if you need to do this fix, its pretty easy:

# Remove the screws holding the heater barrel assembly to the heater barrel.
# Cut the filament just above where it goes into the housing.
# Turn the extruder motor on forward at 255 rpm to eject the filament along with the heater barrel assembly. no need to heat it up, as the whole assembly will be pushed out with the filament.
# Unscrew the PTFE from the heater barrel and pull it off over the filament. If the plastic has flattened and 'pancaked' over the heater barrel, the barrel does not match the ptfe receptacle and you'll want to bevel the edge to eliminate this gap. you'll need to heat up the heater barrel and remove the filament first in order to get access and to be able to load filament later.

Potential problem #2: The idler wheel slot may be slightly undersized.

We tried to make it the perfect size, but it may be too conservative. Check the filament and see just how deep the teeth are. I press on the idler wheel moderately hard when tightening which may give me an extra 0.1 or 0.2 of a millimeter. If the teeth marks do not look deep, you may need to widen the slots on the retainer plate and the motor plate. Unfortunately you'll need to take apart your extruder for that. Once you've done that, then file (or dremel) away the slot in the direction of the pinch wheel pulley. That should give you the added grip to make it work nicely.

Does nothing work to start extrusion?

This could be bad. You may have a really bad blockage in the nozzle. If you're using ABS plastic, then your best bet is to take apart the entire heater barrel / nozzle assembly. You should then soak the nozzle and heater barrel in Acetone overnight. The acetone will dissolve the ABS and you can then thoroughly wash the nozzle / heater barrel to remove the blockage. It may be extreme, but it does work.

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