Mr.RC-Cam

Geeetech MK8 Extruder Tips & Tricks :: 3D Printers

39 posts in this topic

A couple months ago I purchased a Geeetech I3 3D printer so I could use PLA and perhaps some of the exotic plastics. I've been using a daVinci 1.0B with DiY spooled ABS (works great); Given the daVinci's ease of use I had no idea that the Geeetech printer was about to kick my butt. But there is a happy ending, so stick around.

This is not a 3D printer review. But to set the stage, I purchased this printer kit. Rather than order it from the Chinese factory I found one on eBay from a USA supplier. Cost was under $300 USD delivered to my door.

post-2-0-72568100-1440559027_thumb.jpg

 

The Geeetech I3 Pro B kit is a Chinese variant of the popular Prusa I3 design. Mine came with a MK8 direct drive extruder with 1.75mm x 0.3mm nozzle, a Sanguinololu 1.3A (Arduino) controller, and four A4988 stepper motor drivers. Assembly took about 6 hours. But getting reliable PLA prints took several weeks of hair pulling. I'm now getting consistently good prints, which is something that I thought was impossible up until a few days ago.

So I'm here to share my Geeetech war story. I'll provide details on the extruding problem and how I achieved success. Maybe this will help someone else.

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I had zero problems with the X/Y/Z motion mechanics. The open frame makes bed leveling fast and easy. So 90% of the printer is good to go without any fuss.

All my problems were in Geeetech's MK8 hot end, which I'm convinced was created by the devil. I had constant battles with motor cogging (motor stutter), filament jams, and insufficient material flow throughout a build.

The MK8 is a very simple direct drive design. The basic components are a NEMA-17 stepper motor turning a hobbed drive gear to move the filament, a guide pulley, 40 watt heater, and brass nozzle.

post-2-0-35359300-1440560329_thumb.jpg

Online searches exposed a large number of other frustrated Geeetech MK8 owners that reported the same problems. So I was not alone. No doubt there are some proud MK8 owners that have zero problems. But if you are still here, reading about my unpleasant MK8 experience, then I doubt you are one of them.

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If you are having problems with filament jams / flow then start with Geeetech's wiki advice:

http://www.geeetech.com/wiki/index.php/Fixing_Extruder_Jams_and_Flow_Problems

There's not much information published there and I needed to work much harder to solve my MK8 problems. When printing with PLA the main issue I ran into was that the extruder's motor torque is marginal in this direct drive design. But I resolved the filament feeding issues with a few tricks that are discussed below. I recommend doing them all rather than cherry pick those that interest you.

In no particular order, here are the things I recommend:

1. Bed leveling / Z height:

Make sure your bed has been calibrated and recheck it often. It must be perfectly level and at the correct height. It is critical that you do this when the printer is at full temperature. If you make any significant temperature changes on your prints then recalibrate the Z-height. If the extruder motor is making a clicking noise (undesirable motor cogging) when printing the first layer (but not as much on other layers) then your Z-height is too close to the bed. This is a bad thing, so don't print until you recalibrate the Z-height.

2. Filament Tension:

The hobbed spur gear has sharp teeth that bites into the filament. There is a screw adjusted spring that sets the tension for this. You want just enough pressure force to prevent feed slippage, but not so much that the filament's round shape is distorted. Contrary to what is recommended by many others, I suggest leaning towards lighter pressure rather than heavy pressure.

post-2-0-22735800-1440564851_thumb.jpg

3. Filament Lubricant:

Before you load your PLA filament, apply a light coat of clean / fresh cooking (or mineral) oil to the first few inches of it. This will lubricate the nozzle throat and reduce sticking. Re-apply some oil each time you swap the filament. Or, go the extra mile and install one of these on your printer to automatically clean / lubricate your filament: http://www.thingiverse.com/thing:492067

4. Nozzle Size:

A 0.4mm nozzle will take less extrusion motor force than a 0.3mm nozzle. So until you have consistently good results, change your nozzle to 0.4mm (don't forget to revise your slic3r settings). After things are working well you can return to the 0.3mm.

5. Teflon Throat:

Inside the metal nozzle throat is a PTFE Teflon tube. To minimize filament sticking (jams) the Teflon tube must be straight and perfectly round. It must also be exactly the same length as the metal throat (end of Teflon is flush with end of metal throat). Like this:

post-2-0-78152000-1440563138_thumb.jpg

Replace the Teflon tube if it is not perfect. If it is discolored then it has been overheated, another reason to replace it.

6. Nozzle / Throat Assembly:

When the metal throat and brass nozzle are mounted in the heater block they must be installed so that they butt up against each other. Do not allow any space between them.

7. Heater Block filament leakage:

The machined threads on the heater block (for the nozzle and throat) are not precise. So during long prints there may be blobs of filament leaking out of the heater block and messing up the prints. This can be avoided by using yellow Teflon gas tape on the threaded parts. I've been told that running a ABS print will seal leaking threads, but I did not have success with that method. Yellow Teflon gas tape solved it for me. You'll find it in the plumbing area at the hardware store.

8. Extruder Heatsink orientation:

The fins on the heatsink should be in a horizontal orientation. Like shown at "A":

post-2-0-82314700-1440563447_thumb.jpg

If the fins are vertical then cooling will be reduce due to the blocked lower side. To remedy this I modified mine so it would be horizontal. This required drilling one new hole and rotating the heatsink 90 degrees.

9. Filament Pulley Cooling:

Filament jams due to a hot feeder can be reduced if the filament is cooled near the entry into the throat. A hole can be drilled in the heatsink to allow the fan to force cool air into the hobbed gear area. It's the big drilled hole shown in this photo:

post-2-0-05676700-1440564620_thumb.jpg

post-2-0-59109000-1440564624_thumb.jpg

BTW, I read that another way to cool the filament in the feeder is with a fish tank air pump. But the drilled hole seems to work fine and avoids the extra hardware and noise.

10. Filament Retraction:

Excessive filament retraction can cause filament sticking due to heat swelling. If the filament is stuck in the throat then you'll probably hear a clicking noise (extruder motor cogging) every few seconds while printing. The jam may have been caused by a filament bulge where it enters the nozzle throat. Clearing it requires pulling out the filament and cutting off the bulged area. If this problem is occurring then turn off retraction (a Slic3r setting); If the problem goes away then you need to work on your retraction and temperature settings.

BTW, I'm currently using 1mm retraction and don't get any strings or spider webs. But each setup is different so you need to determine the best settings for your print jobs.

11. Filament Spool Feed:

Carefully review the amount of force required by the extruder to pull the filament off your spool. You want this to be silky smooth and effortless. If there's too much friction the motor will need to work harder, which may cause uneven filament feeding or other issues.

12. Printing Speed:

Faster printing speed impacts the extrusion motor since it has to work harder to keep up with supplying filament. So slow things down. You can increase print speed later on when PLA printing is reliable.

13. Heater Block Temperature Sensor:

The extruder's temperature sensor must be inside the aluminum heating block. If it extends outside the block the nozzle's temperature will be wrong. BTW, a small amount of thermal paste (CPU heatsink grease) can be applied to it to ensure good heat coupling.

14: Heater Capsule:

Make sure the 40W heater capsule is tightly clamped in the aluminum block. To check for this you can push on it from the open end. If it is loose then tighten the two set screws hidden under the block's thermal wrap.

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15. Motor Current:
Most importantly, you MUST experiment with the motor driver's current that is supplied to your extrusion motor. The current determines the motor's torque. There is a small pot (adjustable resistor) on the A4988 stepper motor driver that is used to do this. The motor will cog and/or stall if the current is too low. But too much current will overheat the motor / driver which also causes similar feed issues. There are plenty of online tutorials on how to do the adjustment.

Here's a helpful video I found that shows what happens when the extruder motor's current is not set correctly:


The current I needed for reliable extrusion caused overheating/overcurrent problems on the A4988 driver module. To solve this I replaced the extruder's A4988 motor driver with a DRV8825 module. The DRV8825 can handle higher current. Other than changing the Sanguinololu jumpers for 16 step operation, the installation was a simple module swap. I set its vRef to 0.85V, which is 1.7A motor current. Due to the high current the extruder's motor gets toasty warm on long print jobs, but it is not excessively hot.

drv8825_1_800.jpg

BTW, don't bother upgrading the other motor driver modules. The A4998 works fine for the X/Y/Z axis motors and they'll be much quieter too.

The frame mounted fan does a good job of cooling the MOSFET transistors that control the two heaters. Likewise, the four stepper motor driver modules MUST have heatsinks as well as forced air cooling from a nearby fan. I found that air flow to the motor driver modules needed improvement. To cool the hot modules, and ensure long term reliability, I created a shroud for the Sanguinololu board that adds another 40mm 12V fan ($3 on eBay).

Here's a 3D rendering of the design (created in Autodesk 123D):

fan_shroud_render1_800.jpg


STL Files for Fan Shroud:
sanguinololu_fan_mount_top.stl
sanguinololu_fan_mount_bot.stl


Here's a photo of it after installation:

fan_shroud1_800.jpg


So to wrap this up, after doing ALL these things I'm now getting very nice PLA prints. I'm testing with very low cost eBay and China filaments, which are often troublesome choices. Geeetech advertises that their MK8 can handle exotic filaments too (wood, flexible, fiber, etc.).  I'm hopeful that this is true, but I'll believe it when I see it. :)

 

Edited by Mr.RC-Cam
Added Fan Shroud STL Files.
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Geeetech advertises that their MK8 can handle exotic filaments too (wood, flexible, fiber, etc.).  I'm hopeful that this is true, but I'll believe it when I see it.

Update: I'm having good success printing flexible filament (SainSmart Flexible TPU). It is soft, similar to cooked (Al Dente) spaghetti.

But before I could use the flex filament I had to create an adapter that slips over the MK8 extruder. It supports the filament at the area near the hobbed gear and prevents filament buckling when it is being pushed into the extruder. Try pushing cooked spaghetti and you will see the problem that needs to be solved. :)

Here is a photo of the adapter. It was designed in Autodesk 123D and printed with ABS:

flex_filament_adapter1_600.thumb.jpg.a77

Here's the STL file: flex_fil_adapter.stl

The flex adapter slips over the MK8 extruder. Remove the extruder's cooler/fan (2 screws), slip on the adapter, then re-install cooler/fan. The adapter fits in the extruder like this:

flex_filament_adapter2_600.thumb.jpg.1c8

 

I'm printing the flexible filament at 225C and use slow travel speeds (~20mm/s). The parts come out great and have not had any filament jam issues. Here's a 17mm diameter "rubber" drive wheel I printed for my Filament Monitor project:

flex_puck1_500.thumb.jpg.79d6fc542b135e7

 

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Hi,

thats a very nice post. Im interested in the Sanguinololu Fan Shroud but i dont see a link to i.e. thingiverse like for the other things. So could you post the file/link to it?

 

Thanks

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Quote

Im interested in the Sanguinololu Fan Shroud but i dont see a link to i.e. thingiverse like for the other things. So could you post the file/link to it?

No problem, the STL files for the fan shroud have been added to the post:

http://www.rc-cam.com/forum/index.php?/topic/4034-geeetech-mk8-extruder-tips-tricks-3d-printers/#comment-28231

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On 8/26/2015 at 0:51 AM, Mr.RC-Cam said:

If you are having problems with filament jams / flow then start with Geeetech's wiki advice:

http://www.geeetech.com/wiki/index.php/Fixing_Extruder_Jams_and_Flow_Problems

 

There's not much information published there and I needed to work much harder to solve my MK8 problems. When printing with PLA the main issue I ran into was that the extruder's motor torque is marginal in this direct drive design. But I resolved the filament feeding issues with a few tricks that are discussed below. I recommend doing them all rather than cherry pick those that interest you.

 

In no particular order, here are the things I recommend:

 

1. Bed leveling / Z height:

Make sure your bed has been calibrated and recheck it often. It must be perfectly level and at the correct height. It is critical that you do this when the printer is at full temperature. If you make any significant temperature changes on your prints then recalibrate the Z-height. If the extruder motor is making a clicking noise (undesirable motor cogging) when printing the first layer (but not as much on other layers) then your Z-height is too close to the bed. This is a bad thing, so don't print until you recalibrate the Z-height.

 

2. Filament Tension:

The hobbed spur gear has sharp teeth that bites into the filament. There is a screw adjusted spring that sets the tension for this. You want just enough pressure force to prevent feed slippage, but not so much that the filament's round shape is distorted. Contrary to what is recommended by many others, I suggest leaning towards lighter pressure rather than heavy pressure.

 

hobbed1_800.jpg

 

 

3. Filament Lubricant:

Before you load your PLA filament, apply a light coat of clean / fresh cooking (or mineral) oil to the first few inches of it. This will lubricate the nozzle throat and reduce sticking. Re-apply some oil each time you swap the filament. Or, go the extra mile and install one of these on your printer to automatically clean / lubricate your filament: http://www.thingiverse.com/thing:492067

 

4. Nozzle Size:

A 0.4mm nozzle will take less extrusion motor force than a 0.3mm nozzle. So until you have consistently good results, change your nozzle to 0.4mm (don't forget to revise your slic3r settings). After things are working well you can return to the 0.3mm.

 

5. Teflon Throat:

Inside the metal nozzle throat is a PTFE Teflon tube. To minimize filament sticking (jams) the Teflon tube must be straight and perfectly round. It must also be exactly the same length as the metal throat (end of Teflon is flush with end of metal throat). Like this:

 

throat1_800.jpg

 

Replace the Teflon tube if it is not perfect. If it is discolored then it has been overheated, another reason to replace it.

 

6. Nozzle / Throat Assembly:

When the metal throat and brass nozzle are mounted in the heater block they must be installed so that they butt up against each other. Do not allow any space between them.

 

7. Heater Block filament leakage:

The machined threads on the heater block (for the nozzle and throat) are not precise. So during long prints there may be blobs of filament leaking out of the heater block and messing up the prints. This can be avoided by using yellow Teflon gas tape on the threaded parts. I've been told that running a ABS print will seal leaking threads, but I did not have success with that method. Yellow Teflon gas tape solved it for me. You'll find it in the plumbing area at the hardware store.

 

8. Extruder Heatsink orientation:

The fins on the heatsink should be in a horizontal orientation. Like shown at "A":

 

cooling1_800.jpg

 

If the fins are vertical then cooling will be reduce due to the blocked lower side. To remedy this I modified mine so it would be horizontal. This required drilling one new hole and rotating the heatsink 90 degrees.

 

9. Filament Pulley Cooling:

Filament jams due to a hot feeder can be reduced if the filament is cooled near the entry into the throat. A hole can be drilled in the heatsink to allow the fan to force cool air into the hobbed gear area. It's the big drilled hole shown in this photo:

 

heatsink1_800.jpg

heatsink2_800.jpg

 

BTW, I read that another way to cool the filament in the feeder is with a fish tank air pump. But the drilled hole seems to work fine and avoids the extra hardware and noise.

 

10. Filament Retraction:

Excessive filament retraction can cause filament sticking due to heat swelling. If the filament is stuck in the throat then you'll probably hear a clicking noise (extruder motor cogging) every few seconds while printing. The jam may have been caused by a filament bulge where it enters the nozzle throat. Clearing it requires pulling out the filament and cutting off the bulged area. If this problem is occurring then turn off retraction (a Slic3r setting); If the problem goes away then you need to work on your retraction and temperature settings.

 

BTW, I'm currently using 1mm retraction and don't get any strings or spider webs. But each setup is different so you need to determine the best settings for your print jobs.

 

11. Filament Spool Feed:

Carefully review the amount of force required by the extruder to pull the filament off your spool. You want this to be silky smooth and effortless. If there's too much friction the motor will need to work harder, which may cause uneven filament feeding or other issues.

 

12. Printing Speed:

Faster printing speed impacts the extrusion motor since it has to work harder to keep up with supplying filament. So slow things down. You can increase print speed later on when PLA printing is reliable.

 

13. Heater Block Temperature Sensor:

The extruder's temperature sensor must be inside the aluminum heating block. If it extends outside the block the nozzle's temperature will be wrong. BTW, a small amount of thermal paste (CPU heatsink grease) can be applied to it to ensure good heat coupling.

 

14: Heater Capsule:

Make sure the 40W heater capsule is tightly clamped in the aluminum block. To check for this you can push on it from the open end. If it is loose then tighten the two set screws hidden under the block's thermal wrap.

Is the teflon in the throat, is to be but against the nozzle? I purchased a mk8 and the hot end was not put together, and it came with 2 throats and 2 nozzles I notice that the teflon is only at one end of the throat, I think the throat is half full of teflon..  Thanks 

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The nylon tube on mine is shorter than the metal barrel. So yours is probably the same. But when the nylon tube is firmly pressed into the barrel (as far as it can go) it must be flush on the nozzle side. When the nozzle is installed it will butt up against the nylon and form a tight connection for proper filament flow.

 

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On 5/6/2016 at 5:15 PM, Mr.RC-Cam said:

The nylon tube on mine is shorter than the metal barrel. So yours is probably the same. But when the nylon tube is firmly pressed into the barrel (as far as it can go) it must be flush on the nozzle side. When the nozzle is installed it will butt up against the nylon and form a tight connection for proper filament flow.

 

Can you tell me where I can get a  Push Fitting and  PTFE Tube??  I have the same as your mk8, didn't come with it.. That part in the picture I circled 

post-2-0-82314700-1440563447_thumb.jpg

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I purchased the push fit connector and one meter of PTFE tube on eBay. There are many sellers for them there.

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Hi! Thanks for sharing your findings on the Geeetech I3 Pro - I got the same kit some weeks ago, and I'm still struggling with finding the optimal settings as well as meaningful extensions. Amongst others, I have created my own cooling fan, but it is not working as effectively as I imagined. In one of the pictures above, I can see your cooling fan - would you share your design? Are you satisfied with the results it gives? What type of fan are you using (i.e. specs)?

 

Thanks,

kind regards,
Momme

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Here is the STL file for the hot end fan: fan_duct_set.stl

The fan works fine for me. I have a toggle switch on it that allows me to select always-on or GCode control. You might want to add a simple on/off switch so you can turn the fan off when it is not needed.

I could not find the invoice to the 12V fan I bought. It came from one of the many online China sellers. I found this one on eBay and the photo looks the same as what I have:
http://www.ebay.com/itm/75mm-x-30mm-DC-12V-0-36A-2Pin-Computer-PC-Blower-Cooling-Fan-TP-/171916843021?hash=item28070ad80d:g:SFsAAOSw0JpV5mpz

Edited by Mr.RC-Cam
Revised STL File
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Thank you so much! I will try to set it up. Looks like you used a much largen fan than I did - mine was only 40x40mm, thus having much lower throughput.

 

Edit:
I downloaded the stl file, it has approx. 210kB, but I can neither import it into any of my 3D modelling applications nor load it into the Repetier Host software - could it be that the file upload did not work properly? Sorry for the hazzle...

Edited by Mommsen

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Sorry for the bad file. I re-uploaded it so try again.

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Can someone tell me how many Volts and Amps I should supply to this to make it heat up to required temperature without destroying it?

I think I'll supply 12 volts, but I don't know how many amps to give it.

Is it like a heatbed and uses tons of current? Please tell me the number of amps i need asap.

Thanks, mitch

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The Geeetech MK8 hot end's heat cartridge is rated at 40W @ 12V. So when powered with 12V the current is 40/12 = 3.3A.

That said, you can't just apply 12V and expect it to heat up to the required temperature all on its own. The printer's controller (with the hot end's thermistor) are used to regulate the required temperature.

 

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Quote

 

14: Heater Capsule:

Make sure the 40W heater capsule is tightly clamped in the aluminum block. To check for this you can push on it from the open end. If it is loose then tighten the two set screws hidden under the block's thermal wrap.

 

Thank you for your precious help on MK8, may I ask to show where the screw are located on the hotend? I don't want to remove the kapton since I don't have at home. Are there 2 screws? Thank you!

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I'm sorry but I don't have any photos that show the location of the two screws. You may be able to find them by probing the side of the heat block with a sewing pin. If that is not successful then I recommend that you purchase a roll of Kapton tape so you can remove & replace the existing tape.

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hello,

I've bought a Geeetech MK8 extruder, and I want to know which kind of thermistor is used for this extruder. I know it's a 100K NTC one, but when I'm building firmware I need to know the specifications. Which one do I choose? Can someone tell me what kind of thermistor it is please?

Also when I'm building firmware, I need to know specifications for the gear attached to the stepper. Can someone tell me how many teeth it has and what the pitch is also?

thanks a lot, Mitch.

Edited by mitch25

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9 minutes ago, mitch25 said:

hello,

I've bought a Geeetech MK8 extruder, and I want to know which kind of thermistor is used for this extruder. Can someone tell me what kind of thermistor it is please?

thanks a lot, Mitch.

Hi mitch25, as long as I searched for, it seems to be a 100K thermistor, you can find it almost everywhere. 

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I'm sorry but I edited my question. the one you replied to was the non-edited one. I know its a 100k ntc thermistor but when i'm building firmware, I need to select what kind of thermistor it is, like the specifications. which option do I select?

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