Kossel Mini upgrade path

Hey guys,
A little while ago I asked over in the corexy threads about upgrading my self built kossel mini over to a CoreXY style printer. Been looking more and more around and am considering another path that want available when I first built mine; metal parts.

Few questions:
1. Are the metal parts from robotdigg accurate and with the price?
2. I am using openbeam 1515 with plastic corners, would I have to use new linear rails going up to 2020? I have MGN12H profile rails.
3. Will upgrading to all metal and 2020 see a significant gain in accuracy and stiffness?

Thanks!

1. If the chinese copies of these corners are up to the job the robotdigg ones will be also.
2. MGN12-h rails will fit to 2020, you just need m3 bolts and m3 half tnuts for slot B profiles.
3. I went from a Kossel Mini with printed corners in 1515 to a kossel XL with Chinese copies of robotdigg alu corners 2040 (using 2020 for the top horizontals). Its stiffer by several orders of magnitude. When people have said build a big stiff frame you won't regret it, I scoffed, but now I have I would overspec. the frame again and again. I am also using MGN-12H rails and the accuracy of the machine overall is wonderful. Calibration has become an interesting exercise as I can isolate factors causing inaccuracy much more easily as it won't be confused by the frame described by one contributor "having all the stiffness of a wet noodle".

I originally decided to use metal for everything wondering if it really made a difference (it does) but had to go from K800 magnet arms to Haydn's arms as the k800 magnets just didn't hold well enough, so now I have printed carriages and effector.You can feel the difference in play between metal carriages/effector and printed its quite marked.If you can find suitable metal carriages and effector buy them, worth every penny. If one of the chinese suppliers could make the Haydn magnet compatible effector and carriages in metal now I'd be very pleased, even considered getting my printed ones cast in aluminium.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Thanks for the input. Good to hear it makes a good difference.

My one main reason to move to another design from a delta is the ability to enclose and use other plastics. Namely I'm interested in the ability to use HIPS or some other soluble support material. Has anyone had success in multi extrusion and enclosures for deltas?

I've not enclosed a delta, but would like to. A flying extruder makes this easier as it decreases the amount of wiring needing to be accommodated just outside of the frame.

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Simon Khoury

Co-founder of [www.precisionpiezo.co.uk] Accurate, repeatable, versatile Z-Probes
Published:Inventions

Enclosing a delta is easy. Print these parts, get some acrylic sheet, and off you go.
[www.thingiverse.com]

I have robotdigg metal effector and carriages. The carriages are not accurate, but the effector is (or maybe it's the other way around). Go figure. I had to shim the rod ends with a combination of washers to get the distance between the rods to be exactly the same. And yes, the distance between rods must be as close as you can measure. Measuring the carriages and effector without it assembled isn't enough, you need to be able to measure them when assembled.

As DJDemonD says, the combination of a metal effector, metal carriages, and linear rails is unbeatable.


I haven't found metal corners to be as good as some people say. I think the design of the Kossel is fundamentally flawed -- you are depending on the stiffness of the rails, and a perfect assembly at every corner, to get a square machine. It really needs diagonal bracing of some sort. I've had just as good (if not better) results by using PETG corners (which are quite bendy in comparison), along with wire and turnbuckles to stiffen the frame. With floppy corners, when you adjust the turnbuckles, the vertical extrusions don't bend. With metal corners, your extrusions bend a bit when sorting out tower twist. Needless to say, if your rails are slightly bent then you won't get perfectly dimensioned parts.


Good luck on your journey.

I'd add to this if you buy metal corners, you can't just slide the 2040 extrusions into them and do the bolts up, you still have to tweak the frame to get exactly the same distance (try for 0.1mm precision) between the towers at the top and bottom and between each pair of towers. I spent 3 hours tweaking my frame until I was happy with it.