Advice for new large Kossel
November 26, 2019 11:19PM
Hi,
Over-enthusiastic beginner here looking for tips on a large Kossel build. I'd been thinking about doing this design for a while and got myself commited a few days ago by ordering various bits. I liked the idea of keeping the build platform within the framework amongst other things, but after discovering dc42's blog/build and other posts here have been having second thoughts.
In particular, I'm worried about the build platform as the plate seems to just sit on cork stuck to 3 printed brackets, which seems to go against other information I've read about ensuring the bed is absolutely flat (and generally securely attached to framework). Also wondering about the way there is nothing at all between the bulk of area of the heater and electronics beneath. And specs for buidplate too, never realised that flat aluminium sheet isn't necessarily flat enough. So, lots to digest and understand before I move on.
Figure my build will be a mish-mash of these. I've not ordered build/base plates or any extrusions yet, so dimensionally I'm only constained by having ordered 400mm Hayden mag rods and 800mm rails from Robodigg. V6 ecosystem on the way plus Duet Smart Effector and board(s). Undecided on extruder yet. I'd definitely like to print somethings near to 500mm high but doubt I'll want to print even near the edge of a 330mm bed very often, if at all. Was thinking of ease of future enclosure purely as I'm mucking about with all sorts of materials ATM just to get to know various pros and cons first hand, so trying to cover options; not PEEK type cover but maybe nylon or polycarbonate.
Any advice on the next step forward gratefully recieved.
Thanks, Tim.
Re: Advice for new large Kossel
November 27, 2019 03:06AM
In my published Kossel variant, the bed plate is attached to 3 metal pillars that are attached to the lower frame. There are holes in the cork for the pillars. So the cork doesn't support the bed.

The cork provides adequate thermal insulation between the bed heater and the electronics. I have an electronics cooling fan, set to turn on if the MCU temperature exceeds 50C or the stepper drivers produce an over-temperature warning. It never turns on.

Some people prefer to put the electronics and stepper motors at the top of the printer, leaving just the PSU and bed heater SSR under the bed.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
Re: Advice for new large Kossel
November 27, 2019 03:27AM
Thanks for the reply. Yes, I'm following your ideas and get the concept, which is why the NorwegianDesign, not yours, either doesn't make sense (to me at least) or just lacks detail that seems important. Hadn't even thought about moving most up top; bottom seems good.
Re: Advice for new large Kossel
November 27, 2019 05:50AM
Quote
dc42
In my published Kossel variant, the bed plate is attached to 3 metal pillars that are attached to the lower frame. There are holes in the cork for the pillars. So the cork doesn't support the bed.

The cork provides adequate thermal insulation between the bed heater and the electronics. I have an electronics cooling fan, set to turn on if the MCU temperature exceeds 50C or the stepper drivers produce an over-temperature warning. It never turns on.

Some people prefer to put the electronics and stepper motors at the top of the printer, leaving just the PSU and bed heater SSR under the bed.

I can second that. If you supply good airflow underneath the bed and are able to evacuate hot air and pull in cold air you will be fine. I didn't know other people also used cork for their heated beds.. A friend of mine just happened to have a sheet of cork leftover so I designed a bed holder that clamps the bed in three points while also clamping the cork against the bed.

The idea of having everything under the machine means you have a very solid base and the weight makes it stable. In a lot of designs the motors are also in the bottom part which makes it very convenient to have the shortest wires. The bed functions as a 'lid' on top of the electronics and the cork insulates good enough to keep the heat 'up there' on the bed. Lower part count, better weight distribution and center of mass. Endstop wires can be run through the hollow part of the aluminium extrusions.

Also, having the LCD on the bottom part makes it easier to access when the Delta is standing on your desktop and you're sitting in front of it. I do not like long ribbon LCD cables hanging around and having the LCD on the top of the machine is inconvenient for me.

Last, I think that with DC high-amp, low voltage applications such as having a 12v heated bed (or 24v), having long wires is a bad idea. Keep it all as short as possible.


http://www.marinusdebeer.nl/
Re: Advice for new large Kossel
November 27, 2019 03:34PM
Quote
Ohmarinus
Also, having the LCD on the bottom part makes it easier to access when the Delta is standing on your desktop and you're sitting in front of it. I do not like long ribbon LCD cables hanging around and having the LCD on the top of the machine is inconvenient for me.

FWIW I did it the opposite way round on my delta: electronics under the bed, and touch LCD at the top, with 1.5m of cable between them. But that's because I have several printers and I am invariably standing up when I operate them. Duet electronics has the SD card built in, so no need for a SD card socket on the display.

Quote
Ohmarinus
Last, I think that with DC high-amp, low voltage applications such as having a 12v heated bed (or 24v), having long wires is a bad idea. Keep it all as short as possible.

Agreed, running cables that carry low voltage high current power for the bed between top and bottom of a delta is a bad idea. But on all but the smallest deltas, IMO it makes sense to use an AC mains voltage bed heater. That's why I mentioned putting the bed heater SSR under the bed along with the PSU, when the electronics are at the top. Of course this can be done when using a low voltage bed heater too but then the PSU needs to be much larger.



Large delta printer [miscsolutions.wordpress.com], Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].
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