Documenting the Mk I Nutjob

Nophead: This looks really promising, but I am having trouble understanding the physical arrangement from the photos. Any chance of a view from underneath, or a diagram?

Forrest: Absolutely...

I had a few minutes Friday to run some tests on the Mk I Nutjob. Using a GM-17 it was able to generate several kilograms of thrust, which, from Nophead's research, should be enough to extrude ABS.

Frankly, though, I couldn't see that having enough torque to just extrude was going to be that much fun. Tommelise 1.0 taught me that operating on the edge of an extruder's capabilities is a frustrating exercise at the best of times and a waste of time at other times.

The diameter and shaft diameter of the little coreless DC motor in the GM-17 is a common one. A variety of more capable, read that longer, DC motors can easily be slotted into its place. Indeed, Solarbotics is looking for an upgrade motor for the GM-17 not unlike the 12v upgrade that they have for the GM-3.

At that point it occurred to me that I could easily do the GM-17 hack that Nophead demonstrated a few days ago. I certainly had exactly the Jameco tin can stepper that he used and I also had the ability to mill a special mount for it.

Nophead's mounting plate was, as usual, elegant.

It would have been quite easy for me to mill it save one little issue.

The ventral strap simply didn't work well for my extruder. As a result, I designed an alternative that made use of the extant mounting points on the GM-17.

At that point I was ready to do the photodocumentation that I promised Nophead.

Here you can see my interpretation of Nophead's GM-17 hack mounted on the top plate of the extruder.

Starting from the bottom of the extruder, you first see the spring-loaded guillotine mechanism that holds the filament guide against the nut threads.

Here is a closeup of the filament guide. I designed it as an insert into the plate that is attached both to the extruder barrel and the z-axis. The mounting holes are plainly shown .

Power is carried from the GM-17 via a transfer gear. Here you can see that I milled it in three pieces to reduce machine time on Tommelise 2.0.

There has been considerable confusion about the embedded nut gear. Here you can see the bottom side of the gear from which a shaft protrudes which accommodates the full height of the nut, more or less. There is no shaft on the topside of the gear and the top of the nut simply buts up against the top housing plate, which serves as a thrust bearing.

Now the bottom plate of the extruder slides onto the four #4 bolts in the filament guide frame. For you metric types, #4 bolts and M3 are pretty much the same diameter, though the pitch is, of course, different.

Once the bottom plate is mounted, fitting the drive gears is very straightforward.

Once the gears are in place the spacer plate slides onto the mounting bolts.

Finally, you can see the bottom of the assembly in this photo. with luck, I'll be able to test it within the next few days.