Two questions on a self-built Kossel (not a kit)
December 10, 2017 10:51AM
Hi all,

I currently own a Robo 3D R1+, and I've decided to use it to print parts for a new printer, which will be (more-or-less) a full-sized Kossel (with 360mm side beams of 2020 extrusions). I've ordered a bunch of non-plastic parts and have begun printing Kossel parts (or variants taken from Thingiverse). I may well have questions in the future, but for now, I have two:

First, most (maybe all) of the Kossel vertex parts (frame_motor.stl and frame_top.stl in the original Kossel git archive, and various derivatives I've found on Thingiverse) have these round "tabs" or "feet" at the ends of their arms, like this:

Every photo I've seen of a completed Kossel printer lacks these tabs, though, and it looks like they'd interfere with assembly by blocking insertion of the 2020 extrusions. My best guess is that these tabs are meant to improve bed adhesion during printing and then be snapped or cut off after completion of the part. Is this correct? If so, I'm printing these parts in PETG, which is tougher than PLA, so does anybody have tips on the best way to remove these tabs? If I'm wrong in my supposition, what's the purpose of these tabs, and why do they show up in the models (and my prints) but not in photos I've seen?

My second question is about the control electronics. I've more-or-less decided to go with either a Duet or a Smoothieboard (or perhaps a clone of the latter; it's hard to pass up a ~70% savings, even if I know it's a knockoff from some dodgy Chinese factory). I've seen claims that the RepRap firmware used by the Duet has significantly better algorithms for handling delta printers than does the Smoothieware used by the Smoothieboard and its clones. OTOH, this claim seems to come most loudly from the person who developed the relevant algorithms, so I'm not sure how seriously to take these claims. Does anybody have experience with both firmware on delta printers, who'd care to comment? If the claims are true, what sort of improvements am I likely to see by going with a Duet board rather than a Smoothieboard?

Thanks for any information!
Re: Two questions on a self-built Kossel (not a kit)
December 11, 2017 03:22PM
Those tabs are called "mouse ears" and they are in fact added to the design to increase bed adhesion. In PETG you can easily cut them off with a cutter knife.

It's pretty difficult to have an unbias opinion about RRF or smoothiware, but for a Delta I would always pick the Duet.
Re: Two questions on a self-built Kossel (not a kit)
December 11, 2017 07:08PM
I've got a self-built delta printer as well, and have used 3 different controllers over the years:

-AZSMZ (smoothieboard clone)
-Duet 0.6 (old and "obsolete" now)

When it comes down to it, even the RAMPS was sufficient. But things seemed smoother when I switched to the 32-bit controller on the AZSMZ board.
I found the AZSMZ to be a bit of a headache to manage--poorly documented, and difficult to tell when to use settings for smoothieboard and when to use the copy-and-pasted config from the aliexpress page.
The Duet was new on the scene, and I found dc42's support and the active reprap community to be a refreshing change. Plus the web interface on the Duet is stellar.

It's really a matter of how much energy you feel like putting into maintaining your controller. I haven't regretted the Duet at all.
Re: Two questions on a self-built Kossel (not a kit)
December 11, 2017 07:31PM
Thanks for the feedback.

As it happens, I had a failed print and so I experimented and found I could easily snap off the mouse ears with needle-nose pliers. At worst, this left a little bit of remainder that I could file off. I've done the same with my non-failed prints now, too.

Based on everything I've been reading (including your responses), I'm leaning toward a Duet board at the moment, but I haven't quite decided 100%.

Putting this together should be an interesting project for the winter.
Re: Two questions on a self-built Kossel (not a kit)
December 20, 2017 05:19PM
Delta on duet is a pleasure, Dc42 is a delta guy natively and a lot of features in RRF help deltas to be easy to use. With an accurate probe you just hit calibrate, which it does in 8-16 probing points in 1 iteration, then print. You could possibly in the latest version even have no endstops and still configure a delta in one click.

Compared to marlin for deltas its a no brainer.

I have never got to grips with repetier, and have only used smoothieware on a corexy. But I have two duet board and would buy another.

Simon Khoury

Co-founder of [] Accurate, repeatable, versatile Z-Probes
Re: Two questions on a self-built Kossel (not a kit)
January 28, 2018 08:49PM
FWIW, I went with a Duet. The printer's not 100% finished yet, but it's up and running enough to be useful. (I'm still tuning its parameters and need to add a few ancillary hardware bits like lighting.) I've been fighting bed-leveling issues today, but I think I've finally got that figured out.
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