UM original with direct extruder

[foehnsturm 969]

Stepper: SY20STH42-0804A (http://cncshop.at/index.php?a=4076&)

 

[foehnsturm 969]

A short extrusion test video.

With years old UM silver PLA @ 210°C, underextrusion starts at 115 mm/s (9.2 mm3/s).

But it's not the stepper skipping steps but filament slipping. If I increase the idler arm pressure by hand it would go beyond 140 mm/s. 100m/s @ 0.2 layer is ok for me but more should be possible with a stronger idler arm.

 

 

[jonnybischof 60]

That's impressive

What's the motor rpm at 100mm/s?

 

[foehnsturm 969]

If I did math right:

approx.140 rpm and 950 steps / s (half stepping)

 

[foehnsturm 969]

I decided to run a true retraction torture test:

Longo-Tetrahedra-Lamp-Shade-by-Dizingof, 90x90x180mm.

Look's good so far. I'll report back once it's finished. But this will take another 20 hrs ...

 

[foehnsturm 969]

After 33 hrs printing time, with 9 hrs left and some 400.000 retractions I noticed some underextrusion. Nothing related to the direct extruder but a f***ing clogging Merlin hotend.

EDIT:

I stand corrected. The Merlin was fine. The drive gear (glued to the shaft due to space limitations) became loose.

Disassembled the entire hotend two times while the print was paused. Unintentionally displaced the printhead during re-assembly. :evil: Needed several additional print pause / disable steppers cycles to realign the printhead with the print again (not easy with that weird printing paths here ...). It looks like I was successful. :cool:. Hopefully the fix will last long enough. :wacko:

 

[jonnybischof 60]

Could it be that your thermal barrier heated up too much?

I've read something about the Merlin briefly, also got one here, but haven't used it yet. Having a small fan blowing at the PEEK is supposed to help, but not be necessary.

 

[foehnsturm 969]

Well, there is a lot of air flow due to the crossflow fan. Nevertheless something must have happened. It didn't recover completely this night so I will cut off the top 3 cm of the print. The remaining part came out very well, considering that I used ColorFabb PLA/PHA which definitely is more prone to stringing than Faberdashery.

EDIT: Not the Merlin, the drive gear became loose.

 

[macua85 52]

I love this mod and would like to give it a go. Would you be prepared to share the STLs and BOM?

 

[foehnsturm 969]

I'll do that in the near future. However there are at least three obstacles to overcome, which requires some machinery.

Most worm gear sets with module 0.5 have drive worms with a 2 mm bore. It cannot be widened to the 4 mm of the stepper shaft as the overall diameter is too small. So you have to machine down the stepper shaft to 3 or 2 mm or manufacture a small adapter with a 4 mm bore and a 2 mm shaft.

The usual drive gears (MK8 ..) feature a 5 mm bore. This would require a 5 mm shaft, ball bearings with 5 mm ID and widening the worm gearwheel bore to 5mm ... parts would become quite bulky and heavy. I took a 3mm shaft and made a bushing with 3 mm ID and 5 mm OD fort the drive gear.

The design offers not enough width for a drive gear with a set screw. I removed the half with the screw and glued the remaining part to the shaft.

 

[foehnsturm 969]

When printing 0.1 mm layers and quite slow the stepper sound with halfstepping became an almost unbearable low frequency rattling. So I tried other microstepping settings and ended up with eight step resolution. Max revs / min stayed the same, what I didn't expect.

Works perfectly now and is much more pleasing to the ear.

Layer height 0.1 mm, 3.5 hrs printing time

 

[aviphysics 9]

What are those connectors you are using for the hotend?

BTW I am surprised you have done so much with modding the print head, but you are still using stock tension blocks.

 

[foehnsturm 969]

The type which came with the UBIS hotend: Molex http://help.printrbot.com/Answers/View/5181/What+molex+type+numbers+to+purchase.

I simply had no issues with the tension block so far. Or at least I think so ...

 

[mararuo 0]

For the record, your mod has been the most accomplished piece I have seen since Chopmeisters Nanoblock regarding direct drive extrusion with the Ultimaker 1. I consider it the next logical step after bowden extrusion, it just enables you to do so much more with a simple machine. So many different materials to test!

I am very excited about your work, keep at it!

I don't know if you know the hyena bolt of shop.arcol.hu, and its owner László Krekács, I had his Bolt running in one of my U1 back when I was a student and it worked very well, maybe you could ask him to machine a custom drive gear for your build, with your specifications, his prices are very reasonable and he seems to be an overall nice guy.

I did a humble homage to your work in order to adapt my newly purchased E3dv6 Hotend to your modular printhead design, I posted it in youmagine, for some reason I cant open youmagine so the link will have to follow soon.

Again, thank you for sharing your amazing work !

[foehnsturm 969]

Thanks a lot!

I didn't expect this to be possible, but it looks like I can print the same part with flexible filament (FlexiFil).

Stay tuned ...

 

 

[foehnsturm 969]

Turned out to be no problem at all.

All joints move freely.

0.15 mm layer, 0.8 mm shell, no infill, FlexiFil @ 218 °C

 

[aviphysics 9]

Prints pretty well without infill, though the overhang on the ears isn't perfect. I have been meaning to print a max print volume sized one of those. My son loves the little one.

[foehnsturm 969]

As I sometimes had layer adhesion issues with the flexible filament and it's only a 0.8 shell to allow easy deformation I printed quite hot.

 

[foehnsturm 969]

... still very happy with it. QuickSteel (aka JBWeld) is a very suitable material for that air deflector. Well, my sculpting skills are quite limited.

 

 

[foehnsturm 969]

Another retraction madness test.

That's how it started.

8 hrs later

 

[mararuo 0]

that is absolutely impressive!

I don't see any strings from here.

Do you need any beta testers?

 

[aviphysics 9]

@foehnsturm

How is this project coming along? Can we expect a release of something anytime soon?

 

[foehnsturm 969]

Just posted the stl and step files at Youmagine https://www.youmagine.com/designs/modular-printhead-nema8-worm-gear. But still no BOM due to the reasons I mentioned earlier in this thread.

 

[aviphysics 9]

Thanks.

BTW, is your design setup to use a stepper with a ground down shaft or an adapter to go from the stepper to the worm gear?

 

[foehnsturm 969]

There is enough room for an adapter. You can use both, it depends on the length of the shaft. The second NEMA8 I bought hat such a short shaft that I had no other choice as to use an adapter.