Friday, January 22, 2010

 

Geared Nema 17 Extruder


I didn't have a lot of luck with the standard Mendel direct drive pinch wheel extruders, most likely because the steppers I had were not strong enough. I ordered in some 5 kg*cm Nema 17's, but unlike the datasheet, they had substantial flats on the shafts, which made building a direct drive extruder problematic. So, I thought I'd try building a geared extruder, using printed gears.

Surprisingly, the gears didn't fall apart right away, and I was able to generate 5.5 kg of pull on a PLA filament before my pinchwheel started slipping. It needs a bit more work, but it looks promising!

More details on the RepRap Wiki -

http://objects.reprap.org/wiki/Development:Geared_Nema17_Extruder

Wade

Comments:
Where is the idler mounted? How did you mount it without interfering with the big gear?
 
Very nice. Is that green PLA?
 
The idler is mounted to the square block, underneath the 4 springs. I'll post the design files on the wiki in a few days, but at the moment it's not actually very usable because I didn't leave quite enough clearance between the idler and the mounting bracket holes.

Green PLA is my new favorite color!

Also, I mentioned on the wiki that this was based on Adrian's geared Nema 14 extruder, but really it's a mashup of that and Nophead's great geared extruder designs, just tweaked to fit the hardware I had handy.
 
It probably won't make a difference to the torque, but you might get even better control if you try the herringbone gear designs that are being created. On a 3D printer it's no extra time or cost :)

http://blog.reprap.org/2010/01/high-speed-alternative-to-belts.html
 
Actually, since my build accuracy isn't that high, I'm going to stick with straight teeth. Besides, since I've got ball bearings on my input and output shafts, having herringbone gears would add one too many constraints - it would be hard to get the alignment just right.

Right now I made the drive gear twice as thick as the driven, so I don't need to locate the gears on the shafts too accurately axially. Helical would make them quieter at the cost of some axial loading, but they're pretty quiet already.

Besides, I don't think Forrest has released his code yet, and the ones on Thingiverse are square, which do not mesh well when printed on my printer.

It would look cooler though. :)
 
How easy would it be to make the Extruder body from Wood or MDF plastic?
 
I wrote the gearweaver AOI script for making gear couples and it is in the skeinforge folder at:
miscellaneous/Art of Illusion Scripts/
Gearweaver.bsh

It can make curved herringbone gears. If you want to play with it, try modeling a gear couple of roughly the same size as the one you just made. Once you have the number of teeth you want and so on, try changing the shovel segments from its default of 3 to something around fifty, to slowly generate a curved herringbone pattern.
 
I know is a bit OOT question...
But where could you find coloured PLA, it's possible to find different colours?
 
BodgeIt, not sure about drilling it out of wood; it should be more or less possible, but it would take a lot of work. Probably easier to print one out.

Enrique, I'll have to check out your script. I've been using Alibre instead of AOI, as Alibre works a lot better for someone with my CAD background. I do use Skeinforge for all my prints though; it's very valuable. Thanks!

Tombo, the green PLA was a sample from http://ultimachine.com/ , I imagine they'll have it in stock soon.
 
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