Filament drive shootout
Inspired by Nophead’s excellent work, I decided to do my own testing. I had the folks up at Najet make me a prototype and pitted it against the existing timing belt pulley from SDP-SI. As with Nophead, I found the worm-gear style pulley to be much superior.
My process was pretty simple. We’re testing the pull strength of the extruder only here, so it involved hooking up the filament drive portion to a force meter (fish scale) and running it until it either stopped or failed. Here’s my setup.
Force Meter
A fish scale 50lbs / 23 kg. I couldn’t figure out how to make it do metric. FAIL! It still worked reliably, and I got a rough sense of what forces were involved. Now that I know my range, I am purchasing a much nicer digital force meter. (Its held down by capa / shapelock… I know, I should really have printed that part)
Filament Harness
Since we’re measuring how hard the extruder pulls on the filament, we need a way to hook up the filament to the force meter. I ended up bolting the filament between two washers and then looping that over the hook. I only rarely had problems after that.
Extruder Drive System
No need for the hot end or anything like that for this test. I laid the electronics to the side. Then I just clamped it to the wood, making sure to clamp in the middle of the dinos and not too hard. The bolts dug into the wood after a bit and made it snap right into place.
Then I just did a bunch of test and measurements. The fish scale did not have a very fast update rate at all (5 seconds?) It also did not have a peak weight or anything like that. I just watched it and tried to remember the highest number. This was a big deal because sometimes the filament itself would either break or elongate and deform. There readings could be slightly low because of that. It was also a bit chilly in the Botcave (its late december 
but I’m not going to go that deep on ya.
Here are the results as a google doc:
As for the extruder pulley, yes we will have these eventually. No idea on the timeframe, but having to wait is the price we pay for being as open as possible. I also made the silly mistake of making the diameter of the threaded parts different from the diameter of the current pinch wheel teeth. Its not much of a difference, but I’d like it to be a drop-in replacement. Its a really daunting thing to go into production on a part without a prototype, so it means I’ll probably need to get a new one made. I might have a few other variants made and see how they match up with the results from this one.
Grogyan
December 31st, 2009 at 1:19 am #
Looks very nice.
I have a niggling feeling that its going to cost a lot.
Joachim Glauche
December 31st, 2009 at 5:34 am #
I made one out of brass with a M3,5 tap in my lathe. It pulled over 18KG first, but at least with ABS it has the problem that some plastic will go off from the filament and stick onto the worm pulley. This caused it to loose grip shortly after I started to use it.
The drive pulley you use works a lot of more reliable for me.
paul
December 31st, 2009 at 12:38 pm #
I guess is out of topic, but are you some day considering change DC motor for a stepper one?
Zach Hoeken
December 31st, 2009 at 1:02 pm #
@grogyan – actually they quoted us about the same price we’re paying for the old pulley, so I do not foresee any price increase from this particular part.
@joachim – regardless of the pulley you use, you have to clean the teeth every single time it strips. we call this flossing the teeth. we’ll most likely offer both pulleys so no worries.
@paul yup, we’re open to lots of possibilities. we’re probably sticking with dc motor for the near future though.
Devlin
December 31st, 2009 at 1:21 pm #
What if you had a cleaning pulley off to the side that would clean the drive pulley?
davidbuzz
December 31st, 2009 at 11:15 pm #
Zach, I’ve been working on integration of the 5D reprap firmware (ie suppor for acceleration) with a DC extruder, as these two elements aren’t supported at the same time yet in any known firmware…. You haven’t been working on this for the makerbot at all have you? ( since I assume acceleration would be a desirable feature to have in the makerbot?)
Buzz.
email me if interested.
Eric Albert
January 1st, 2010 at 12:32 pm #
At my college I have a lab with two FDM machines (one older, one new this month) – and if anyone is interested, I could take closeup pictures of the drive mechanisms — they both use 2mm ABS filament, and a similar worm drive. -Eric
rbisping
January 2nd, 2010 at 5:43 pm #
I made me several of these out of brass and they work great, ive been using them for about a month or so. ive been looking into making a printed part that you could use to make two of these simultaneously very similar to the double pinch wheel design i put on thingiverse. But having comercialy made ones available would be great
.
MBC
January 11th, 2010 at 4:26 pm #
“This was a big deal because sometimes the filament itself would either break or elongate and deform.”
FYI in engineering terms:
brake = fracture
elongate = neck or elongation = necking
http://en.wikipedia.org/wiki/Necking_%28engineering%29
cant wait to upgrade my extruder with one of these
keep up the good work!
Pleasant Hardware » Blog Archive » Printruder II - 3D printing with MakerBot and other hardware
March 8th, 2010 at 2:17 pm #
[...] Industries did some test with CNC manufactured worm-gear style pulleys. But I have no idea if they (still) plan to sell them in the MakerBot store and if yes, [...]