Towards a Rostock tool-changer

[rymnd]

Hi all,

I've been working on a magnetic coupling as part of a tool-changer setup for the Rostock MAX and have recently started testing it. I'm hoping to get some feedback and suggestions for moving forward, if possible. It's based off the following post from Hackaday:

http://hackaday.com/2013/09/17/automati ... d-printer/

Instead of an independently controlled tool-changer like on CNC machines, you can use the movement of the effector and magnetics to swap out hotends. I think this is superior to mounting hotends side by side, and it would allow for a much greater number of hotends while maintaining the same weight on the moving effector. The big problem I saw from the implementation above was the inconsistency in positioning of the tool after a swap. The person in the video above was using it as an experiment for food printing, I think, so precision wasn't as important (I think), but having magnets by themselves won't do if we're swapping out hotends every layer of a print job.

The way I think we can get around that is with kinematic couplings (aka maxwell couplings). These use exactly 6 points of contact to exactly constrain two elements relative to another. Kinematic couplings are designed to make positioning highly repeatable, but they can't take a lot of load (from a manufacturing perspective). Luckily, I don't think that constraint is a big issue for 3D printing. They're most commonly used in optics and some manufacturing applications, and they can actually be pretty straightforward to make, as you can see from the attached images. I'm using quarter-inch steel pins and magnetic balls in my setup, and I seem to be getting pretty good prints, at least no worse than what I was getting before, without this setup. It also greatly helps in swapping out the hotend with a height gauge (and other tooling) if I want to do zeroing, so that's an added plus.

I'm still messing around with the pin spacing and figuring out the best rack design that will consistently allow me to swap out hotends like in the video above, but so far I'm very pleased with the repeatability in positioning, which is crucial to making this thing work.

Would love to hear feedback or suggestions.

Thanks again to everyone who posts to these forums. They're always a great help!

[Glacian22]

That looks spectacular! Please keep us in the loop.