Knurled feeder wheel versus Hubbed (MK8) feeder wheel for filament drive.

[Torgeir 242]

Hi Folks,

As I’ve been testing the hubbed MK8 feeder wheel for some time as it was assumed to be better than the knurled feeder wheel that’s used on the Ultimaker 3D family, I’d simply had to try this type of feeder wheel and here is my findings.

It is important to note this test is done with a MK8 feeder wheel only, having an effective diameter of approx. 7 mm.

This test is done with the feeder wheel driving on the inside of the filaments “memorized curve” when rolled out from the filament roll. Using the inside of this curve drastically reduce the friction between the filament and the bowden tube when printing using high pressure.

The first thing I observed is that the hubbed feeder wheel needed much more torque than the knurled feeder wheel to feed the filament. This is caused by the fact that the small radial “knifes” have to cut across the filament and leave a track line that is notable wider than the track line from the knurled feeder wheel.

What is also counting here is that the distance between the “hubbing” (the radial knifes) that is only 0.6 mm apart, versus the distance between each small squared “pyramid” on the knurled wheel that is approx. 1 mm apart each other. So the knurled wheel make a punched track that is smaller and has a wider grip to the filament.

This explain why hubbed feeder wheel needs more torque than knurled feeder wheel!

I’ve made a picture of the hubbed wheel track here:

Between the every lines the distance is 0.5 mm. (Taken with an USB microscope.)

The above picture is the track line from the MK8 during high load printing first layer. Here you see that the compression and stepper slip can lead to a double track, kind of slicing, but no separation. This slicing reduce the grab on the feeder and lead to grinding..

Here’s a pictures of a grind part of a filament when using hubbed wheel:

As in the previous picture; 0.5 mm between the lines.

I’ll have to mention that the print finished without any issue..

I also made same print with a knurled feeder wheel and made a picture with the two feeders at same place during a printing of exactly the same print object.

OK., I’m using a stepper that’s geared 1:2 for both test.

The truth is, the knurled wheel could extrude without any slippage, but the hubbed wheel could not.

But mind you, this hubbed wheel type also grind during “lots” of retraction under high load!

As you see, the knurled wheel also makes a little more rough looking track during load, but do not slip the filament or grind it. I did this three times with same result, not very scientific but have some indication of a practical result.

This show clearly to me why Ultimaker still go for this type of feeder wheel!

Here is another interesting thing to see, this is that you can adjust the position of the knurled wheel and the pressure on it in order to have a better grip!

And finally, the knurled wheel is sure better for the softer type of filament..

Here’s a macro picture of the two feeder wheels.

This picture is taken after I removed the hubbed feeder and put back the knurled feeder wheel type to the printer.

You’d see the remains of some PLA in between the “knifes” on the hubbed wheel.

It is important to note that this subjective test only made on the MK8 feeder wheel with 7 mm effective diameter. This makes the radius for this wheel only to be 3.5 mm and with this small radius the knifes dig “kind of” hard into the filament!

Other types of hubbed feeder wheel with larger diameter do not dig this much into filament, but need more torque during feed as more knife’s is to be forced into the filament when rotating.

But for this particular comparison, the knurled feeder wheel is a winner in this case!

.. - ..

So, a little breath from my side, I’d see lots of you folks still using the “old” feeder with feeding the filament on the outside of the “normal” filament curve (Ultimaker standard). As the filament is rolled off and cut to proper length in order to have as lo friction as possible, or to put the roll on the side on a chair to obtain the same..

A loose few turns of the rolls make less friction for sure and a roll lying on the side create less friction as the filament rotate during feeding. But with a feeder unit mounted so the that the feeder wheel is driving the filament on the inside of the loop is so much better that you NEVER again have to do this anymore.

This procedure is as follows;

1) Turn your feeder unit around, so that the reverse side become the front, the pressure adjustment will on the inner side of the printer. Oh yes, -hold the feeder stepper motor when loosening the last screw or it will drop down inside.. :( There is a good description of how to do this in the manual.

2) Use the firmware for the Ultimaker 2+, this will change the rotation of the stepper for the feeder.

3) Adjust the E-step pr/mm to same value as before, or requested.

4) Any correction that’s needed due to different heath block, standard Olsson or anything else.

There might be something else, but I’ll assume someone may chime in for correction here.

Sorry folks, but I had to mention this.

Wish you all a happy 3D printing.

Thanks.

Torgeir.

[DeathMachine 23]

Interesting , has any one flipped the extruder over yet?   you could also move it to the other side.  I been looking into the accessory track you can mount on back of machine. (cannot remember the name of it)  I want to move the extruder to the track .

Ed

[Torgeir 242]

Hi DeathMachine,

Oh yes, I've been using this setup all the time since I built my printer.

When I did so, I installed the feeder unit as the designer meant it to be installed, with the knurled wheel toward the inside of the filament loop. I've never had any problem with the feeder!

As there was complains about to lo torque at the feeder, I just installed a 1.8 deg. stepper motor (200 step/rev) (At that time I did not have a 400 step/rev stepper). So I used a belt gear with 2 pulleyes (1:2 ratio) and same belt as used for the X/Y steppers (the short belt). This to avoid to many different parts and to lift the feeder a little bit higher (can use shorter bowden tube, if you want = less friction).

By doing this, I was able to use exactly same firmware as the original UM2 with better torque for the feeder and avoiding a "heated" knurled feeder wheel.

Today I can lift and lock up the roller and feed the filament easily all the way to the extruder using the original UM2 feeder unit. Yes, this original feeder unit is good!

Here's the little test print that Wizard bought up for us to use.

http://www.thingiverse.com/thing:704409

I've just used standard adjustments with lo temp at nozzle 0.25, 70 micron at 183 deg. C., so here's a little stringing and some opening in the top layer. But overhang and angles is perfect, those printers is great!

Happy printing and New Year!

Thanks.

Torgeir.

[fergazz 60]

That's a cool test... thanks for share! I was thinking to try this until I find your post a couple of days ago.

 

Have you ever tryed Bondtech feeder? Cause those MK8 looks like the Bondtech gears (but just gripping one of the sides).

I know that Bondtech gives much more torque... do you know the diameter/ratio of those? Cause as far as I know Bondtech is 

a very good gear for TPU and soft filaments. Did you test this MK8 for 1.75mm or 2.85mm? I found those difference sizes ratios

to grip the filament:

 

and that one, well machined from E3d, is for 1.75mm (internal ratio 3mm; external ratio 3.5mm) for 8mm shafts:

https://youprintin3d.de/hardware/schrittmotoren/505/hobb-goblin-8mm-id-drive-gear.html

 

By the way I will try the knurled wheel with Meduza's feeder and see how it perform. Bondtech doesn't ship to my

country but when I trip to Europe or USA I can grab one, if necessary

 

I'm just curious if you keep the same setup or did you test anything else?

 

Cheers!

 

 

 

 

 

 

 

[Torgeir 242]

Hi fergazz,

 

Thanks for the flowers.. 

 

Yes, I did many test and found that I do not need the Bondtech feeder.

I'd actually made a test using double knurled and double hubbed feeder wheel. I found that the friction increased (of course) but the stepper had to be geared to a higher ratio as well in order to handle this extra "drag". It actually worked well, but I did not want to change the firmware from the original UM2! 

So I installed a 200 step/ 360 deg. and made a belt gear using same belt as the short UM2 for X/Y axes. The pull eye's I'm using for the gear is (16 and 32) tooth type 2GT.

By doing this, no firmware change and your feeder now have close to double torque. This feeder unit make very little noise, just the humming from the stepper motor.

Meduzas feeder unit is having the same gear ratio as mine, just go for it, but one very important thing to do is to mirror the original feeder housing.

 

So to the question, why turn around the feeder?  

 

Ok. then, when we buy new filament from a shop, do you think we will have the one just arrived from the producer? If they have this filament in the shop, you'll have the oldest one, for sure. Meaning there will be some memorized curved filament for you to use, and even fresh filament have some effect -like this.

 

Try this; mark the inner loop side of your filament (in same length as your bowden tube) with black (permanent) marker. Let it dry and manually feed this marked filament into the bowden tube. See that the filament line up its curved path into same curve as the bowden tube has, yes the black line will stay mostly on the inner (lo) side of the bowden tube. The black line represent where my knurled track line is located on the filament! On Ultimaker setup, the trackline is on the top and this make "some" added friction. Using hubbed drive wheel add much more friction in such setup..

 

I've always wonder why Ultimaker choose the outer side of filament to put the drive (knurled) wheel, but no one ever answer this question..  :(

 

So I'll think Ultimaker always have a super fresh filament that's behave different, than "some aged filament" we the users got from shops around wherever we are.

 

My printer can push approx 5.2 Kp input to bowben tube.. Then the bowden lock often just come off..  If you need this much force to drive the filament, there is some serious problem with your 3D printer. 

 

If you like to see my setup, I can share this -but need to be home in order to send pictures files etc..

 

Anyway, keep up your good work.

 

Thanks.

 

Torgeir.

 

[Torgeir 242]

Sorry, but forgot to mention that you have to swap two wires on the feeder stepper motor, as it have to turn in the other direction.

Either, pin 1 and two, or three and four on the stepper connector.

But this is very easy to do.. 

The thing is; your printer will be (act) as a standard UM2 printer, so no firmware change!

 

If you can improve your 3D printer with software, this is good, -but if you can improve your printer by hardware -it is even better!

 

Thanks.

 

Torgeir.