Soon after I started testing the Mk7 head it stopped moving plastic, period. I had a working Mk6 handy and a Mini MakerFaire to attend, so I fell back to the Mk6 and decided to let other people debug the Mk7.
However, nobody on the MakerBot list really had a reason or a fix I liked, so I took it apart to fix on my own.
The first thing I discovered was that the pressure mechanism for pushing the plastic against the stepstruder was not pushing hard enough, due in part to scratches on the head’s surface.
The second — and more important — thing was that the stepstruder gear was filled with shreds of plastic. It came off easily, so like the Mk6, just pushing the plastic harder would clear the junk out of the motor.
But how to do that?
Like this.
It’s really that simple. Grab a spare M4 bolt from your parts kit, buy a wingnut at the local hardware store and glue/Loctite the wingnut to the end of the bolt.
I set it up, dialed in a temp of 240C (see earlier posts about temperature), and it forced plastic through with no problem at all. Even a 5 minute run ran without any problems at all.
Now to print some test models….
I had the Mk.7 on the “needs help” bench while doing the previous set of temp tests. I took it apart and discovered the problem with it not pushing plastic was the tensioner against the drive. It had scratches and the drive pulley was clogged with plastic. After fixing that — see the next post for my cheap and adjustable tensioner — I put it on the Cupcake and did another set of temperature tests.
Like the previous set of tests, for temperature reads I used:
- built-in sensor that ReplicatorG software reads
- Fluke 88V temp sensor with temperature probe. Not a cheap device but the readout is 0.1C and it’s fast
- $20 BBQ grill cooking thermometer. Cheap, easy to use, but I think their goal is to make sure I don’t kill someone with undercooked poultry.
As with the Mk.6, the temperatures are lower on Replicator than on the other two sensors, so I need to run with much hotter temps than are required by the instructions. At this point I’m considering adding an offset/calibration value in the software so that the read temp is adjusted properly.
(The images are hosted on flickr for easier commentary)
Mk.7 with software 0033
Part of switching over to Gen 4 was improving daily operation by locking down the extruder and the build environment. Going to the Mk.6 Stepstruder was already in progress but I really needed to ditch the difficult-to-use but trendy Automatic Build Platform for the Heated Build Platform (HBP). It was great for making kid’s favors at a Maker Faire but a real PITA for complex or experimental objects.
After some decent experiments with the Mk.7 (more on that later), I decided to try the 0.3mm head and 1.8mm plastic on the Mk.6 after the success with the 0.4mm head and 3mm ABS.
It works, but not well enough to actually print. The drop from 3mm to 1.8mm plastic, almost %50, should have worked well with the drop from 0.4 to 0.3 but the extruder doesn’t want to extrude. There was some talk on the makerbot list that black 1.8mm plastic required higher temps, those were red-lined by the software, so I did some measuring on my own.
Back in the early days, getting your print temperature correct was one step from ritual magic. That seemed likely, so I decided to repeat some early tests and wire up second and third sensors to run in parallel with the default sensors.
With these, I collected some data and made some graphs. The sensor tips were put as close to the MakerBot sensors as possible and I waited as long as seemed reasonable for the temperature adjustments to stabilize after a change.
- built-in sensor that ReplicatorG software reads
- Fluke 88V temp sensor with temperature probe. Not a cheap device but the readout is 0.1C and it’s fast
- $20 BBQ grill cooking thermometer. Cheap, easy to use, but I think their goal is to make sure I don’t kill someone with undercooked poultry.
The short answer is this — the replicator is reading at least 10C lower than anything else, so I need to run with much hotter temps than are required by the instructions.
(The images are hosted on flickr for easier commentary)
Mk.6 tests:
Mk.6 with software 0033 (recent tree build)
Mk.6 with software 0029 (distributed)
HBP tests:
HBP with software 0033
HBP with software 0029