Kossel Mini Kit Review

This is a review of the "MINI KOSSEL 3D PRINTER FULL DIY PACKAGE" from Makergeeks.com. I ordered this printer in July and it arrived in October. My emails got quick replies with status updates. The kit came with everything I needed except a 30 mm fan for the all-metal hotend. This is a tricky part to source and I had to go to digikey after looking around at various shops nearby. The kit is set up for 3mm filament with a built-in z probe that uses the hotend nozzle itself as the probe. While this is an interesting idea, it allows some slop in the hotend alignment and I had a crooked hotend after I ran the G29 leveling procedure. I would much prefer a manual release z-probe to something that adds a degree of freedom to the hotend.

The carbon rods came preassembled but were different lengths by as much as 2mm, this can lead to uneven printing and is one area where tight tolerances are important. The hotend quality is questionable and mine jams regularly. I attribute this to a misalignment between the heatsink and the heatbreak. I have trouble even hand-feeding filament through it as the filament gets stuck at various edges within the constructed hotend. The extruder runs off a simple spur gear and that combined with the high extrusion force for 3mm filament led to slipping and stripping filament. The printed parts are generally good, with the exception of the carriage mounts that attach to the rail slides. The point where the belt end grips the carriage is too thin and broke loose in all three of my carriage pieces. There are many better designs for this part, or the alternative is a zip-tie to clamp the belt end. Finally, the included power supply specifies 5A output but is insufficient to power 4 steppers and the hotend (causing blackout of the Arduino board). Using a bench power supply, I can run the printer and it shows 4.2 A at peak current draw. This suggests the provided power supply is not operating as specified.

I've chosen to replace the hotend with a 1.75mm Prometheus and will convert the rest of the extrusion path to 1.75mm. Hopefully that will make this kit workable. This was my only experience with makergeeks.com and while the contact at the company was always polite, it does not excuse the low quality of this kit. I am an experienced operator and kit builder and this tested my patience and led to an uncomfortable amount of frustration.

I have posted a similar reivew on the makergeeks website although as of the time of this post, it has not appeared on the site yet.

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Bogofoo
The kit is set up for 3mm filament with a built-in z probe that uses the hotend nozzle itself as the probe. While this is an interesting idea, it allows some slop in the hotend alignment and I had a crooked hotend after I ran the G29 leveling procedure. I would much prefer a manual release z-probe to something that adds a degree of freedom to the hotend.

The problem with using the hot end nozzle as the probe is if there is any plastic on the tip, it won't measure tripped. It will just continue driving the hotend down into the bed. This is I'm guessing what caused your hot end to become crooked. This is also the voice of experience talking since I had the same idea...and ran into the same issue.

Extra plastic on the nozzle doesn't really prevent it from triggering the way this was designed. I'd link to source files but I don't have them and have no idea whose design this is. There is just way too much force acting on the hotend mount. It was designed for the forces of printing and gravity, not being run into the bed 27 times before each print. A weaker spring on the actuator would help some but then the whole hotend would be floppy in that direction and probably hurt print quality. A dedicated z-probe or using FSRs under the plate is much better in the long run.

I've been running my Kossel Mini using the hotend as a bed probe with FSR to detect hits. It is running Marlin with upgrades by Johann and the threshold on the sensors is set so that the lightest touch triggers and it grabs the baseline right before the probing starts so it works very well. If you got a crooked hotend I think you may have other issues, I've had some configuration errors and while playing around have slammed the hotend into the bed many times and never have had the hotend come loose or change position.

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Please add your printer design to [reprap.org]

Bought the same kit 2 weeks ago....starting to wish I had investigated this purchase a bit closer before diving in (I'm not a huge DIY guy and reading these posts does not instill confidence in me getting this kit working).

I'm also not overly happy that my CC was charged hours after I placed the order and I still don't have even a rough estimate of a ship date beyond, "we are running 2-3 weeks shipping from order date". I was told that they HAD to charge my CC to hold the order. I can't imagine that calling BS on that claim will improve my odds of getting the order sooner or error free, so I'll hold my tongue for the time being. Seeing that all the reports I have seen on these kits state it took more than a month or 2 for the order to ship will make me surprised if I see this kit before the end of January.

I will add that responses to email have been timely and polite, so I'm willing to give them some benefit of the doubt. I am not expecting to be pleasantly surprised, however.

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tjb1
I've been running my Kossel Mini using the hotend as a bed probe with FSR to detect hits. It is running Marlin with upgrades by Johann and the threshold on the sensors is set so that the lightest touch triggers and it grabs the baseline right before the probing starts so it works very well. If you got a crooked hotend I think you may have other issues, I've had some configuration errors and while playing around have slammed the hotend into the bed many times and never have had the hotend come loose or change position.

Yes, the kossel mini should be able to handle hitting the bed even at full motor force. The parts in this kit are based on a design where the hotend is on a hinged piece that lifts up to trigger an opto switch. Either I got a bad print or there is part of the mount that is wrong in this design because I can wiggle the hotend by hand even when all the bolts are tightened down. I've printed my own effector mount from the original design and will use a different hotend at 1.75mm. I'll explore the FSR route as well, that seems to be the most elegant solution to date.

I would recommend the kit from [www.think3dprint3d.com] . I built one some months ago. It was dispatched within days of payment, customer service was excellent and everything was of good quality. The price seems comparable even with shipment to the USA. I could not measure an error in the length of the rods - they matched.
I found the probe totally unnecessary for good quality prints. It is set up to use 1.75mm filament. I separately installed an E3D hotend which works well.

Or take some of the kits from www.3dfilamenta.com, the site has 3 delta printers, some fully assembled.