Jump to content
Ultimaker Community of 3D Printing Experts
Torgeir

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

Recommended Posts

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:

Filament_PLA_Hubbed.thumb.jpg.21ac49b8b462615dbe1cde5bf1693625.jpg

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:

Filament_PLA_Grinded.thumb.jpg.e9d8c83c71900773d7eef7fcae5e7ee4.jpg

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!

Both_Filaments_Compared.thumb.jpg.6f246f879ed5b39ca1d7f6dd3f760e08.jpg

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.

The_two_feeder_Wheels.thumb.jpg.a1a98409d35db1c62369251c5710882e.jpg

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.

Filament_PLA_Hubbed.thumb.jpg.21ac49b8b462615dbe1cde5bf1693625.jpg

Filament_PLA_Grinded.thumb.jpg.e9d8c83c71900773d7eef7fcae5e7ee4.jpg

Both_Filaments_Compared.thumb.jpg.6f246f879ed5b39ca1d7f6dd3f760e08.jpg

The_two_feeder_Wheels.thumb.jpg.a1a98409d35db1c62369251c5710882e.jpg

  • Like 3

Share this post


Link to post
Share on other sites

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!

SLA_Test_Print.thumb.jpg.7b40f97ab28c511514c9403872c60674.jpg

Happy printing and New Year!

Thanks.

Torgeir.

SLA_Test_Print.thumb.jpg.7b40f97ab28c511514c9403872c60674.jpg

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×

Important Information

Terms of Use Privacy Policy