K8200 / 3drag GT2 belt extruder

by crashmatt, published

K8200 / 3drag GT2 belt extruder by crashmatt May 22, 2014
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A simple way to change to belt extrusion for less noise and reduced wear. Includes a printable 80 tooth GT2 pulley.
openSCAD parametric cad file included. Can be used to change number of teeth.
Based on this very nice pulleys library:
UPDATE: There was a version posted with no holes and a thin back wall. It didn't work well since it flexed too much. It has now been removed. Thanks to turbotommi for testing.

UPDATE 14/01: RobotDigg changed the GT2 belt pack. See instructions for details

Print Settings


K8200 very modified






0.3mm layers




PLA or ABS. Nylon is too flexible.
Invert to print without support
Print outer perimeters slowly for best tooth resolution (~40mm/s). Infill as fast as you like.


The 80 tooth pulley included puts the motor at maximum adjustment. You may wish to print an 82tooth version or use a 20tooth pulley on the motor side. My preference is for more torque to prevent the extruder stalling.
openSCAD compilation, STL generation and slicing is quite slow due to the high definition teeth and cutout details.

WARNING: The belt changes the direction of the extrude motor compared to gears. You will need to rebuild and reprogram for this to work. See this code line in configuration.h:


The line number changes as the codebase changes. You may need to search for E0_DIR to find it.
The K8200 code has it set true. It should be set to false as follows:
"#define INVERT E0_DIR false"

The ratio is 16:80 instead of 10:44 so you need to change steps/mm from 600 to 682. This is set in the eeprom settings through repetier. The default values are set in configuration.h here as defined value DEFAULT_AXIS_STEPS_PER_UNIT. Extrude step ratio is the last value in the set:

This value is overidden by the EEPROM contents. If you change the default you may not get any real change. Modify using repetier eeprom settings.

Using these parts from robotdigg allows the belt to be tight enough at the end of the motor adjustment range:

16tooth 5mm bore GT2 pulley

188mm GT2 belt : UPDATED 14/01
If this belt is not in stock, turbotommi found GT2 belt at aliexpress:

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This is just awesome! Been using it for over a year now! One of the best upgrades for the K8200.

Thanks for the review.

My favourite upgrade is the auto levelling. It has saved very many prints and time by reliably printing the 1st layer.

any way you can update the links? both links for configuration H. to adjust the steps are dead. Thank you.

Links are updated to the main Marlin repository rather than the old one owned by Erik Zalm.
Please let me know if you need any more help.

Looks like the repository has moved. I will update the links if I can.

Comments deleted.

but the upper reight screw of the Motor is not accessible

So not perfect then.

I can also make it an 82tooth version. The extra teeth will make the motor adjustment range 2mm closer to the motor.
I have much to do right now so I am likely to get distracted from finishing this. Please give me a reminder in a few weeks if I don't get it done.


@Hoplla1 @turbotommi @tanteju, prelimiary 82 tooth pulley with motor mount keyhole added. I have not printed this. I only did a slice to check the keyway does not damage the pulley teeth. Does it look ok?


I second turbotommis comment. The stepper is mounted with three screws on my K8200. The top right one becomes unreachable with the large pulley in place. Increasing one hole would be a great idea.

I really like this mod. No need anymore to avoid slicer modes creating lots of retracts (annoying klick-klack, ...). Special thanks for turbotommi who helped me with getting a closed belt during chinese holliday.

I am currently using a 20 tooth pulley. When printing fast I have sometimes suffered some lost steps on the extruder, so I ordered the 16 tooth pulley to maybe get some additional leeway.

Just an Idea: While mounting all together I had the problem fastening one screw of stepper. The screw is needed to give tension on the belt. Could you add a small 3mm bore to reach this screw through the wheel with an imbus key? drilling it is a bad idea because there is Infill on that position. The stability will decrease. A printed bore is much more stable.

I don't quite see where you mean. The stepper has two screws and I can normally get to them.

A trick I use often is to set the motor position before mounting the large pulley. You get tension as the bearing seat into place. I have to do this every time there is a filament jam in the extruder.

If I have the wrong idea then please post a picture.


Strange, I have three on my extruder. The right top screw on Stepper is not reachable.

I have documented the construction in German K8200 Wiki and referred to your thing.

Today my belt is arrived. I have mounted all together and it works excellent with a 20teeth pulley on stepper. One thing I would suggest: The back wall seem to be too thin. If I give a bit more tension to the belt the pulley bend on it's backwall. So I suggest to fill the pulley up to the screw head with material. Would be great if you could upload such version because you have the cad data. It might be only bend if printed with PLA but I'm not able to print other materials actually.

Thanks in advance

Tommi, the previous version 7 is much stiffer. The version 8 was done just to be nylon printable. Nylon is less stiff than pla so it was worse than what you have. With your feedback I will remove or properly comment that model.


I'll give a try on V7

You are totally right! The V7 is a lot more stable and shows no bending at all. I printed it with 30% infill with PLA. Now it works as expected. Thanks for sharing your idea!

The yellow Version in this make is my final solution

K8200 / 3drag GT2 belt extruder

Tommi, I removed the V8 model to make sure others don't have the same problem.

Can you make model for original T5 belt ?

Yes but you probably don't want it.
A belt pulley has to have the belt in contact with a minimum number of teeth, preferably no less than 5. It is also difficult to make a pulley of the right shape with much less than 10 teeth which is what I used. This means that the driver pulley scales up by 5/2 and so does the driven pulley. They end up touching together and becoming a direct cog system again. You could choose to mount the motor offset on the rail somehow.

You have to use a loop of T5 belt. Its very difficult to effectively join the belt. Once you have bought new T5 loop belt you might as well have bought the T2 belt instead. With T5 you might get away with printing the driver pulley as per the X-Y axis driver pulleys.

Alternatively you could purchase a geared stepper motor and have a 1:1 pulley ratio. This would look sweet but probably cost more than buying the T2 belt and pulley.

The one best feature of T5 is the ability to print it easier. You need a well setup and fairly modified printer to do T2.

I would offer to print and sell the large T2 pulley but the local tax system hates any form of individual innovation or creativity that leads to any exchange of money. It would amount to a small business transaction and the mountain of paperwork is simply not worth the after tax reward.

hello :) can i have your firmware configuration, step for mm ????? and, how to change rotation motor?? please tell to as :)

My K8200 is quite modified so my configuration.h will only bring you trouble. I updated the instructions to match the updated Marlin codebase. If you still have problems following the instructions then I will modify them again.

Velleman has not published the location of their Marlin fork (if they have one). For this reason I am not using their codebase but a fork of the original codebase. I can only give you guidance on the original Marlin and not the Velleman one.
-10 karma points to Velleman for not sharing :-(

My marlin fork is here for reference:

Hello! The sources of the firmware for the K8200 (and other infos) can be found here: http://3dprint.elettronicain.it/2012/09/06/software/
This 3d printer has been designed by Futura Elettronica, an italian company, not by Velleman. I live close to their headquarter.
I don't know why they haven't translated the website in english! Italians are a bit narrow-minded!

Yes, K8200 is a rebranded 3drag. The core Marlin software is not written by Futura or Velleman but is an open source project on github lead by Erik Zalm. Futura/Open Electronics/Velleman have simply modified Marlin to fit the printer. There are several 3drag owners who are using the original Marlin source code because there is a github repository available with the latest features.

It looks like Futura is also guilty of not maintaining a github fork for users. At least they link to the original github repository.

I really don't mind if websites are not translated. It is not their responsibility or useful for their business. Italy has Austrian, French and Slovenian borders to cope with before thinking of English.

The firmware must be changed. When you change from gear to pulley it goes in the opposite direction. It confused me the first time I tried the extruder and it ejected the filament.
The 80 tooth pulley is not quite as tight as I would like with the motor at full adjustment. An 82 tooth pulley would probably be better.

I see. I know how to upload and modify the firmware, but could you point my in the direction of what should be changed for this to work?

I have modified the instructions to be clearer about the code change. Please check if it makes sense and you can follow them.

I used a 188mm GT2 belt and a 16tooth pulley. A 20tooth stepper pulley would also do it.
You could use belts of slightly different lengths and modify the pulley diameter to fit. There are more details in the instructions. Please ask if you have more questions.

So today I received my belt, it looks way too short for your gear to fit. I think I've ordered the wrong item... This it the item I bought http://www.ebay.com/itm/140917500572?var=440103245714&ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649http://www.ebay.com/itm/140917... can you please confirm if it's wrong or right?
the text on the belt says "188-2gt"
Best regards

I double checked the belt on my build and it shows 188-2gt, just as you have. The pulley you print has less diameter than the gearwheel that comes as standard. This is compensated by the 16 tooth driver pulley on the motor which is also smaller. You can't fit the belt by adjusting the tension on the motor. You need to fit the belt as you tighten the bearings on the hobbed bolt.

Thank you very much, I've ordered the parts. Have you changed anything in the firmware for this mod to work?

I like your design, which belt and gear on the extruder stepper are you using? :-)