MK7 Hack to Enable Filament Changes Mid-Print
Description
Switching filaments enables multi-colored prints without fusing filament first. It also ensures that if you run out of a given filament, you can load new stock mid-print. This is very helpful for long prints.
The MK7's Stainless Steel Thermal Barrier Tube is not seated close enough to the Knurled Pulley, which makes it nearly impossible for a new filament to chase another into the Tube. However, raising the Tube ~3.5mm brings it close enough so that the new filament will not bend or slip off the old filament as it enters the Tube.
Another benefit is that you gain an additional ~3.5mm in Z-height!
Here's some video of the results youtube.com/watch?v=I25pOHE91xY
UPDATE: Zach posted a solid filament block for the MK7, so you should print this out and modify that instead of your purchased one. thingiverse.com/thing:12147
Instructions
1) Keep the Molded Drive Block attached to the stepper but remove the Knurled Pulley to avoid damage and dust. Remove ~3.5mm in by ~5mm wide to accommodate the raised Stainless Steel Thermal Barrier Tube. (See photos for reference.)
2) Re-assemble your Stainless Steel Thermal Barrier Tube inside the Bar Mount so the end protrudes ~3.5mm above the M6 Nut.
3) There should be just enough thread left below the Bar Mount to secure the entire hot end back onto the Mounting Plate.
4) Test-fit the Molded Drive Block against the raised Stainless Steel Thermal Barrier Tube. If desired, secure the Bar Mount to the stepper with M3x18 screws and make a test extrusion. Insert a new filament after snipping off the old one (see video link above) to be certain it pushes the old filament through.
5) Re-attach the Fan and Heatsink assembly.
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I sincerely hope that all future makerbots come with this modification in place.
Nice hack. 8-)
If you can at some point See if you can automate the process. You may be able to use the filament drive motor to dive the switch over. Just an idea.
If too much heat travels up the tube you can use a heat sink with a thin insulation. Remove the nut then lay the insulation around the filament tube. Put the heat sink on and the nut. This should solve the problem. Thatâs why M6K had the heat sink on the tube. (You will need to custom make the h
eat sink too fit the tube.)
But I don't think the heat will be a problem. :)
Something to watch out for might be extra heat near the gear; this could cause the filament to be extra pliable and lead to stripping events. The heat gradient is also changed in this configuration, for better or worse. I can't wait to see how this works out for you.
Nice job! I expect people to start designing some new printable drive blocks since it's dead simple to remove just the drive block and test alternatives without having to take the whole thing apart. I'd like to see one with an open side to make it easier to clean the knurled pulley.
Little metal brush, air compressor, toothpick. Ideally the MK7 is skipping and not stripping, but it might still, and then it's got to be cleaned.
Thx. My favorite way to clean the Knurled Pulley is compressed air.
the original drive block was 3d printed... we just couldn't scale that up to production quantities. the original design should be in the github. i'll see if i can dig that up.
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I modified the STL to already have the 5mm bolt way cut out of it, so now you can just print and put together. Very excellent Mod nycdesigner!!