MK5 Drive Gear – Now with Science!
We’ve been working very hard in the MakerBot R&D lab lately. The thing that has been our main focus lately is the Plastruder. As many of you know, it can be a bit finicky at times. One of the failure modes of the extruder is that the drive pulley will strip the filament. Drawing on excellent research by Nophead and others in the open source 3D printing community, we’ve developed an improved drive mechanism: the MK5 Drive Gear. In fact, this drive pulley pushes about 2x harder than the old MK3/MK4 Drive Pulley. We jut got 700 of them in the MakerBot Store.
The design is pretty simple: there is a chunk of Stainless Steel 304 with a knurled groove that has the same diameter as the old drive pulley. Therefore, this part is a drop-in replacement for the old pulley. Since it is stainless steel it is very difficult to damage the pulley, even if you tighten it down too far. Furthermore, since the knurling on the pulley is so fine, it has a limited ability to self-clean as any stripped filament will typically fall out of it. If you’re feeling hardcore, you can download it from Thingiverse and make it yourself.
As sexy as this new pulley is, we wanted to be able to prove that it was indeed better than the old system. So, we turned to our trusty friend, Science! We formed a hypothesis (that the MK5 drive gear is better than the MK3 Drive Pulley). We created a test rig and we ran a bunch of tests. We tested the MK4 with both the new and old drive pulleys at a variety of spacings. As we had hoped, the new MK5 drive pulley came out on top.
For the force measurements, we used a very nice yet affordable Dillon GL-500 Force Gauge. This gauge has a few really nice features: a 500N capacity (~50kg) with an accuracy of 0.2N (~20g). Besides being nice and accurate, it can also measure both pull and push forces. It can record peak force, and even has RS-232 output which we could use to record measurements digitally. It is also a really solid, well built device.
The test rig was lasercut from some plywood and bolted to a chunky 2×6. If you want to replicate our results at home, you can download our template and lasercut it. The test process was pretty straightforward. We typically repeat this process 10x per setup to get a decent sample size.
The design is pretty simple: there is a chunk of Stainless Steel 304 with a knurled groove that has the same diameter as the old drive pulley. Therefore, this part is a drop-in replacement for the old pulley. Since it is stainless steel it is very difficult to damage the pulley, even if you tighten it down too far. Furthermore, since the knurling on the pulley is so fine, it has a limited ability to self-clean as any stripped filament will typically fall out of it.
- Unclamp filament drive, remove the motor, and clean the teeth.
- Re-attach motor, and set the filament idler wheel distance.
- Clamp down extruder filament drive with output hole right against the force gauge probe.
- Rest the force gauge to record Push force in Peak mode
- Run the filament drive forward at 255 PWM (full-on)
- Wait until the filament reaches the force gauge probe and fails (you can tell because the force gauge numbers climb and eventually stop at the peak.)
- Record the peak force reading
After a bit of testing, some pretty clear results emerged: the MK5 drive pulley can generate a much stronger push force before failure by a solid margin. Since it is made from Stainless Steel, it is also much stronger and more durable than the Aluminum pulley which can easily suffer damage to its teeth when setting the gap. A word of warning: if your hot end does jam, the new drive pulley is strong enough that it may actually destroy your insulator retainer. You should definitely print out some replacements before you begin using with the new and improved MK5 Drive Gear.
If you would like to get your hands on this new hotness, they are available right now in the MakerBot store. Hot off the lathe. The kit comes with a new drive pulley, a 3mm set screw, and a new spacer stick so you can get the best force out of your drive pulley.
For the curious, here is the data we generated during our testing:
Fernando
May 22nd, 2010 at 11:10 am #
Looks beautiful!
Only thing missing now is the z-rods and heated build platform to be in stock….
Prober
June 11th, 2010 at 1:50 pm #
Zach, how about doing another test in your lab? Think Makerbot might like this one!
http://probersideas.blogspot.com/2010_06_01_archive.html
needs a “Stretch test”, interested?
Makerbot – Novo upgrade da Plastruder « DIY – Do It Yourself
July 30th, 2010 at 6:20 pm #
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