This is an upgrade for the Thing-O-Matic Mk7 Extruder.

Features:

• Easy filament swap
• Open drive wheel for easy cleaning
• Bearing idler
• The non-printable parts are easy to source
• Adjustable idler pressure
• Quick to print

I created this b/c I was having some issues with the plunger pressure not being adjustable. I didn't want to go with some of the other designs on here b/c of the difficulty of adjusting tension or the difficultly of sourcing exactly the correct springs. Additionally, some of the really nice extruders out there are HUGE! I didn't want to spend hours printing and potentially lose the print on a faulty plunger. For the full troubleshooting story, check out the blog entry, http://slightlynybbled.blogspot.com/2015/09/makerbot-extruder-woes-and-successes.html

Additional notes:

• I have made a few minor upgrades to the assembly since printing my version. I had a small crash near the lower right, but not enough to cause an actual problem. I have since raised the spring assembly 0.1".
• This part is inspired by many things I have seen on thingiverse. I couldn't begin to name them all.
• Basic design should be easy to adapt to other spring and bearing sizes.
• I know that it appears as though there is a high-friction surface between the base and arm. In fact, the two do come into contact, but there is a very small bevel around the rotation point that ensures that the parts do not have a large contact area. Movement is easy and smooth.
• I am supporting feed rates of 55mm/s on my ToM. I don't want to damage anything, so I probably won't go much higher than this. Post in the comments if you are printing faster with this extruder design!
• I don't have a dual-extruder setup to test with, but I suspect that these parts could easily be mirrored for those types of applications. Drop me a line if you want to give it a shot and I can mirror the parts for you.
• If you have a different set of springs - say, 1" or 1.5", drop a line in the comments and I can remix this easily enough. Just send the COMPLETE spring dimensions (hole sizes at the ends, length when extended, and width).