UM original with direct extruder

[jasonatepaint 18]

Hi Jason

There was talk of switching to 1.75mm filament, which would require less force and thus smaller gear ratio. It might be worth working on that or waiting for a design revision.

That's what I'm currently running in both of my UM2's, so that would be my ultimate plan for the next printer too.

I'll have to continue to follow your progress and see where ya are once I get the rest of the new printer assembled. Most parts are still on boats anyway.

[aviphysics 9]

I got around to hooking up the 0.8 Amp Nema 8 stepper today. The assembly seems to work, but the stepper motor started to melt the PLA, despite the 2 mm nuts I was using as standoffs. I will try cutting back on the current some, but I think the design either needs a higher temperature plastic, or needs a fan.

I have some alternative plastic on hand, but don't know when I will get around to trying it. For now, will just try adding a fan.

[aviphysics 9]

I increased the stand off distance, which seems to have helped. I also added some aluminum foil across the top of the plastic body, where the motor mounts, to reflect some of the radiant heat and distribute what heat comes through the 2mm screws.

The initial results look okay. The plastic still gets a little warm, buy does not seem to soften too much. Not sure if it will hold up in the long run.

[foehnsturm 969]

True, without cooling the stepper can reach 60-70°C, just some degrees to high for regular PLA.

For long prints I attach a small fan to the printhead for cooling the stepper.

When printed with high temp resistant PLA, XT or the alike everything seems to be ok.

[aviphysics 9]

I have some PETG from Gizmodorks that I was thinking of trying. I also have some ABS, but I was waiting until I can dedicate a hot end for it. Don't want to deal with some of the fowling issues that people reported happening when you change from a high temp to low temp filament.

Edited June 10, 2015 by Guest

[aviphysics 9]

Finally finished assembly and briefly test the extruder. It seems functional. I accidentally cracked the main body of the assemble, but it seems structurally stable. Going forward for now and will reprint later.

Still need to figure out a filament guide.

[aviphysics 9]

So, it worked for around 30 seconds. Then I think it basically started to melt. Also, when a used a reamer to widen the bearing holes, I think I got them a little to far to one side. It seems like filament drive gear is a little too far away from the hole,

Basically, I think my part failed in almost every way it could have; however, from the brief period it was working, the potential of the design looks amazing.

Time to go back and reprint in a higher temperature material. I also found that coating the purchase for the spring in epoxy helped give it a little more durability. Going to make some small changes to the design while I am at it.

[aviphysics 9]

Had some free time this week so I finally got my version assembled.

The overall design is the same, but I remodeled the body from scratch.

Main Differences

 

1. changed hot end mount to UBIS
   
2. slightly increased angle of motor mount, to give more room for cooling
   
3. enlarged gear box to accommodate a wider variety of worm gears.
   
4. increased gear box shaft to 5 mm. Bearings are still 10 mm OD
   

 

Though the motor is rated for 0.8A, I am getting good results from 0.6A. Currently running 1/4 steps at 1553 steps/mm.

The frame weighs just a tiny bit more than the original design, but the worm gear I am using in this design is a lot heavier and the thicker shaft also adds some weight, though I thought the 3mm shaft had too much flex to it. Maybe the 5 mm shaft could be drilled out, to reduce weight. Same for the gear.

The hair bands don't actually do anything, they are just there to hold the feed tube when the filament is removed.

I need to print one more version of the body that had a holder for the feed tube. After that and some more testing will post on youmagine.

Edited November 20, 2015 by Guest

[aviphysics 9]

Posted my final design for this version on Youmagine.

https://www.youmagine.com/designs/nema-8-worm-gear-print-head-redux-for-foehnsturm-modular-printhead

Also working on a more substantially different version with lower center of mass.

Edited November 25, 2015 by Guest

[aviphysics 9]

Preview of my upcoming more compact Nema 8 design. I am still working out some interference issues with the Nema 8 mounting screws.

Edited November 26, 2015 by Guest