07 - In search of extrusion utopia (9/1/14)

Post date: Sep 1, 2014 9:55:20 PM

Ok, so "Utopia" is a stretch, but I have been on a journey searching for improvements to the extrusion system. As covered in the Bowden system and multiple hot ends post, a major goal has been to find a way to more easily and quickly change out the active hot end. Only being involved in 3D printing a few months now, the exact use of terminology may be off but to me the "extrusion system" is comprised of the filament feeding mechanism, the hot end mount, and the hot end itself.

As provided by the 3D printer camp organizers, the "stock" extruder was a modded version of this

www.thingiverse.com/thing:18379

combined with a "home-made" hot end which served as a fine introduction to printing, but offered some challenges.

The first upgrade was a new hot-end. I chose to try a low-cost version with a smaller nozzle and heat profile. The plan was that if the new one didn't work out I would go to a more expensive j-head with Peek plastic etc.

This immediately resulted in more precise prints. Pictured below is the .35 mm hot-end at work.

Changing hot-ends to switch between larger, coarse, low def prints and small, high res miniatures became a common but mildly arduous process. The first attempt to remedy this was the multiple hot ends with remote extruder pushing the filament.

This system suffered from a great deal of hysteresis which did not bode well for the fine control needed when doing the miniatures. After trying several times to find the right slicer/settings, I decided it was time to move on.

The next attempt was a "modular" hot-end mount. I looked at the quick fit system and many of it's variations and came up with this:

I was even prepared to add a "leveling servo" to each module as well as some type of edge connector that mated up when you popped in the module to eliminate the need to disconnect/reconnect the wires. However due to it's size, it started to warp after several prints and it was still kind of clunky. Rather than try to refine it, I changed directions again.

I ordered an MK8 gear and while waiting for it, designed an x-plate and motor/hot-end combo mount (more like combined a couple designs on thingiverse, http://www.thingiverse.com/thing:183982 and http://www.thingiverse.com/thing:53560 ). When the gear arrived, I assembled it and started extruding.

I thought the minimalist design and easy access to switch the hot-end would be extruder utopia but alas, as others had intimated on forums, the torque requirements are just too high. For this motor and driver combo, the motor skips steps every once in a while even through the full range of pot settings and at very low speeds. Another thing I learned on this one is the open-air gap from the gear to the top of the hot-end is prone to producing "buckle" in the filament especially when print speeds were increased even moderately. Keeping that distance small and/or surrounding support would be advised. Also, I did try a different motor and motor driver with the same result. I may come back to this some day and for example try a gearbox attached to the end of the motor.

Next up was to try a variant of the clamping idea used on the multiple hot end carriage.

however the PTFE is sooo slippery this design couldn't hold it in place and it started pushing out (it didn't help that the skirt was way too low and built up even more pressure)

However, I was really liking the idea of leaving the extruder mechanism mounted in place and just swapping the hot end, so I came up with 3 versions.

I first tried the middle one (note in the 3d model you can see it has the ridge to hold the ptfe)

It was very stable and certainly made changing hot-ends easier and faster, but there was still the clamp to mess with. So I tried another.

The "key" that slides in and out holds the hot-end very stable and is extremely simple. Have I found the utopia I seek? I have use it for about 50 hours of printing (switching between .40 mm and .25 mm hot-end for ABS, and .40 mm for PLA) and I'm still sticking with it.

Here is a link to the shared Tinkercad model in case anyone reading this would like to try it or mod it or whatever.

https://tinkercad.com/things/iCHqFGJPakA-j-headlitev2-mount-keyed

I know the search for the ultimate extrusion system is not over, but I have found a place to pause for a while.