YABL - Yet another build log for the Kossel Mini!

YABL - Yet another kossel mini build log
There are plenty of build logs but this one is mine. The kossel mini seems to be a very well established and stable DIY printer to build, but maybe I'll provide another newbie with some info. Probably the only interesting parts to read here will be my considerations for the chosen design as a first 3D printer and my choice for electronics. As I'm a newbie concerning electronics and mechanics, I'm thankful for all the people who post information, ideas or answers in this forum!

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How I came to reprap
This might be the least relevant or interesting part but anyway: I'm a 3D software developer and originally came to 3D printing from a desire to create my own custom "battery mods" for a personal vaporizer. Vaping (or ecigarettes) allowed me to stop smoking within a day partly because it also comes with a great community, nerdy technical aspects and fun new hobby. There are plenty of shiny new toys and after seeing some very nice designs for regulated battery devices I started to look into 3D printing via shapeways and i.materialize. Basically "mods" are battery holders with a chip that regulates voltage between 3 to 6 volts to supply your atomizer with energy. While shapeways can actually print in metal (even titanium), they are expensive, have long lead times and don't allow iterating over a design. After looking into DIY reprap printers, I fell in love, have lots of ideas to create cool gadgets and wanted one.

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Considered designs
I wanted a design that allows for precision and large build volume, would allow for scaling the design up and possibly high precision. Also I want something that doesn't use custom made parts for the frame etc (laser cut or cnc) so that I could change the design later. Since I live in Europe, sourcing and shipping is also a bit of a problem if you want something from the "bleeding edge". Having to deal with long shipping times and import taxes isn't really appealing.

So I looked for a good design for a first 3D printer with a readily available kit. It was a rather confusing journey because of the number of old and new designs, numberless options and lack of objective comparison.

Prusa I3:
This design is wildly offered as a kit and at good prices, but one thing I didn't "like" was the moving print bed. I don't know if this is a rational concern, but it struck me as a design that would be hard to scale up in size or in speed, since the moving of the printed object could lead to all kinds of shenanigans.

HBot / CoreXY:
I didn't find a good design for an XY printer in the beginning except the replicator(?). It still has a vertically moving print bed and I couldn't find a kit. The CoreXY is a rather new design and seems to be a good upgrade, but there a lot of different and confusing designs and names out there.

Rostock:
I liked the design from the start, mainly because of the large build volume and elegant mechanics. I looked at the Rostock, Kossel, Kossel mini, Delta-PI, Cherry-PI, EDR, Rostock MAX. While the "mini" in Kossel mini initially pushed me away from the design, it seems to be the most supported and used delta design by now and could be easily scaled up.
One thing that bothered me about the current rostock designs is that they seem to not make use of the possible build area by limiting the diameter to the inscribed circle instead of making the arms a bit longer. You would loose a bit of print height (but gain in print volume I think) and could simply make the height a bit heigher. Any stability concerns you could address with cross braces or newly printed vortex parts that have a triangle intruding into the sides. The only design I found that has a higher proportional build area is the LISA delta printer.

Rostock Max:
It is rather expensive and only ships from the US. It looks like a great 3D printer but it also has many custom parts.

Cherry PI II: (or Cherry PI I) This design is great because it uses magnetic arm joints and seems to include a number of clever upgrades, but I couldn't find a complete kit (non-commercial license but also too new / special).

3DR Delta: I liked this design because it utilizes more printed parts for the bottom / top plate, but it is rather small and I didn't find a kit.

LISA Simpson: This is a rostock style printer but it uses printed arms (like) and also instead of using slides and belts or spectra lines, it uses one lead screw per axis and the arm is allowed to rotate around the axis. The rotation of the stepper motor is coupled to the leadscrew and directly translates RPM and lead into linear motion, which makes the design simple and elegant. The only problem atm with this design is that it requires rather special "high lead" screw to make the movement is fast enough. While ACME or metric trapezoid lead screws seem to be dirt cheap, high lead screws and the nuts for these screws are very expensive.

GUS Simpson/Wally: These designs are awesome but they are experimental and there are no kits available of course. I'd love to build one of them but you need a 3D printer already and a stash of parts to experiment with them.

Robot arm: I looked but didn't find any practical reprap design for this. The idea of a robot arm with high reach, possibly mobile, multi tool and 3D printing would highly appeal to me, but this is probably far harder to do because of arm droop and material stiffness.

In the end I ordered a Kossel Mini kit from builda3dprinter.eu. Costs are 478 € ($634) without electronics.
Unfortunately I'll still have to wait around 2 weeks now until the printed parts are finished and some parts are back in stock. I'm sure that I would have waited longer if I had sourced all the parts individually myself and would have probably paid more and have more hassle forgetting one part or another, ordering the wrong one then reordering etc.

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Electronics
Electronics was another huge field. The electronics consist of a board that takes the CPU and runs the firmware, another board ("shield" or "cape") that has inputs and outputs for heaters, thermistors, endstop switches and stepper motor drivers. The stepper motor drivers are mostly separate and replaceable, one of the better stepper drivers is apparently the ones based on the TI DRV8825.
Most designs use an arduino which is a programmable board that you can use to learn and experiment with all kinds of electronics. It's a rather slow device but can apparently barely keep up with delta calculations and limits printing speeds. I think there are faster versions of the arduino CPU and there is also the open hardware smoothieboard 5X and the azteeg X5 that comes all inclusive, but this get more expensive already.

A better choice in principle is something with a fast ARM processor like the Raspberry PI or the Beaglebone Black. They are complete PC's on a chip that run linux and have 3D acceleration, are at least 10 times faster and basically cost the same as the arduino style chips. They can use WLan, Ethernet, USB and you can plug a monitor or keyboard into them. You could do all sorts of things with them like like e.g. computer vision with a USB camera like the PS eye. Or a webserver using node.js for remote access and supervision of your print. Unfortunately the shields for the Beaglebone black are much more rare and more expensive than an arduino based solution that you can get for something low like 50€. I didn't find any reprap suitable shield for the Raspberry PI.

The Beaglebone Black RevC is the latest iteration of the original Beagleboard. They are apparently hard to get right at this moment but this will probably change in a short time, but I got the RevB for 54,94 € including shipping. There are a number of capes for the Beaglebone black.

The best cape seems to be the BeBoPr++ and you can actually order it! There is a detailed pdf manual available. The documentation for the BeBoPr is a bit scattered between the BeBoPr github repository, the BeBoPr wiki containing most info, the BeBoPr++ page on the "old" wiki, the new BeBoPr++ github repository and the manual for the BeBoPr++.
The newest version can control 5 stepper motors in conjunction with the 5 stepper motor driver board "PEPPER" or Penta Stepper Board. The previous versions of the BeBoPr needed a "bridge" to work with the BBB but the latest version doesn't need this any more.
So I ordered a BeBoPr++ with a PentaStepperBoard with a couple of connectors. I ended up paying 196,06 € including shipping, which is of course far more than I thought I would pay but I think it is worth it. I just pray that I won't fry the board by doing something stupid!

See the list of BBB capes on blog.machinekit.io for more info. The open hardware cape CRAMPS looks great and can control 6 steppers and lots of heaters so it would be suited for a multi extruder setup, but you'll have to soldier and buy things yourself. There is also the T-Bone on kickstarter and a few others, but none are available right now yet. Generally machinekit.io and blog.machinekit.io are great resources and there is also a mailing list / google group for machinekit.

On a BBB (beaglebone black) you'll generally use LinuxCNC as a printing host and firmware. LinuxCNC has been heavily adopted by the nice folks from machinekit.io to be used for 3D printing and also supports delta printers. I don't know yet if you can use repetier with LinuxCNC and how good a solution it will be to use from a windows PC.

So currently I'm waiting impatiently and stalking / trolling these forums and looking at exciting new ideas and possibilities. Thank you for reading and I hope this might help another newbie like me a little bit to get into 3D printing. Please feel free to correct any of my likely mistakes or errors. When my kits arrive, I'll continue with this build log.

Just wanted to add that the price for the BeBoPr++ with the 5 stepper board is INCLUDING 21% VAT and shipping, so you might not have to pay that much. Also a group buy will save you money!

(For some reason I can't edit this post, editing is probably time limited?)

The replicator does not use hbot or coreXY kinematics, in general it uses a cartesian XY head (which hbot/coreXY kinematics also is) in which the extruder head moves relative to the bed on the XY plane. The replicator, ultimaker and h-bot and coreXY variants all uses a cartesian XY head, but all have different mechanical means of moving the extruder hot end in the XY plane.

Thanks for the correction, I'll have to look into how the different XY kinematics work. After my Kossel Mini I'd like to build a printer with a bigger print volume and best possible precision, and multi extruder of course. Not sure if both will be achievable at the same time

Did you consider the smoothieboard for the electronics side of things?

Yeah, but the Smoothieboard or the Azteeg X5 costs around 200€ too, so the BBB with the BeBoPr++ is the better option. Afaik it's also just the usual CPU but with 32bit and a bit faster, but still 10x slower than a Beaglebone.

Edited 1 time(s). Last edit at 06/15/2014 01:39AM by Dejay.

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Dejay
Yeah, but the Smoothieboard or the Azteeg X5 costs around 200€ too, so the BBB with the BeBoPr++ is the better option. Afaik it's also just the usual CPU but with 32bit and a bit faster, but still 10x slower than a Beaglebone.

http://www.panucatt.com/azteeg_X5_mini_reprap_3d_printer_controller_p/ax5mini.htm

The Azteeg X5 Mini costs $109 USD. Does shipping/taxes from the USA to Europe really cost 120 Euros?????

First day building
Hurray! My kossel mini kit finally arrived It came in a pretty unorthodox box but looks great. I managed to screw the base and the top and the extruder together. My first impressions:

1. I'm surprised at how small everything is! I really shouldn't be, but for some reason everything on the internet looks bigger on my 27" monitors
   There is a new build documentation on think3dprint3d.com. It's very detailed and looks nice.
2. Assembling the kossel mini frame is a big PITA. You need to stick your allen key into the M3 screw at very unnatural angles. I think it would be better to first assemble the extrusions to the vortex pieces of the base and top, and then add the stepper drivers and the pulleys, since that gives you more space to work with the allen key. That or have an allen key with an extremely small bend would help.
3. All screws and nuts are thrown together, would be nice to have them sorted. You also get 50 additional screws that you down need if you use the wheel package instead of the linear rails (M3x6 screws)
4. The M3 hex nuts used in the openbeam extrusion are far from easy to use either. Special nuts like these would be far easier to use since you can simply rotate them 90 degrees to slip them in and then screw them tight. Would have saved me about 2 hours during the assembly.
5. The printed parts looks quite nice but aren't perfect of course. They seem to be slightly expanded and compressed near the print bed, so many holes will need to be drilled out or filed. I spend quite a bit of time filing the extruder part to be usable. For some reason I expected printed parts to be more perfect, but I guess I have to adjust my expectations. The M3 holes for the wheel carriages are too small and I'll try to heat up the nuts with a soldering pen to get them in place.
6. I'm unsure on what glue to use for the traxxas rod ends. It's nice that they supply headless allen screws so you don't have to saw off the screw heads. I've also just read about a tip on how to get the metal ball joints into the rod ends. Freeze the metal parts and heat up the plastic parts in hot water to avoid creating slack when pushing them in with brute force. Not sure how important that is. Also will have to build a jig to ensure they have the same length.
7. For some reason there are 6 end stop switch holder parts in my kit. Not sure why. Maybe I'm missing something?
8. My kit is still missing some 623ZZ ball-bearing for the wheel carriage, but these should arrive soon.
9. I still haven't tested my Beaglebone black and BeBoPr++ since I'm waiting for a microHDMI to HDMI cable and HDMI to DVI adapter. Hope this combo works, I got a HDMI1.3 cable since I've read that 1.4 might not work. I'm also hoping my USB keyboard and mouse will be able to be powered from the BBB usb port since all the recommended USB hubs that I've looked up seem to have quite some problems if you read some reviews. So I'm hesitant to shell out money for an powered USB hub that can't actually power accessories reliably.

@vreihen Oh I didn't see the Azteeg X5 mini before. Strange - is that one new or did I look on another site? I think I looked at the Azteeg X5 Pro before. Still the BBB is more than 10 times as powerful.

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Dejay
[*]Assembling the kossel mini frame is a big PITA. You need to stick your allen key into the M3 screw at very unnatural angles. I think it would be better to first assemble the extrusions to the vortex pieces of the base and top, and then add the stepper drivers and the pulleys, since that gives you more space to work with the allen key. That or have an allen key with an extremely small bend would help.

Sounds like someone has not discovered ball-end allen keys yet!



They are good for up to a 25 degree angle, and a real time-saver. Your knuckles will also thank you.

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Dejay
@vreihen Oh I didn't see the Azteeg X5 mini before. Strange - is that one new or did I look on another site? I think I looked at the Azteeg X5 Pro before. Still the BBB is more than 10 times as powerful.

I have never read about an Azteeg X5 Pro being offered for sale, just the Mini. The price and customer service are incredible for a 32-bit board, and on par with some of the 8-bit boards here in North America.....

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vreihen
Sounds like someone has not discovered ball-end allen keys yet!

31491DEN4DL.jpg

They are good for up to a 25 degree angle, and a real time-saver. Your knuckles will also thank you.

Dude! Thank you! That's what the funny ends are for lol, I always wondered.

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vreihen
I have never read about an Azteeg X5 Pro being offered for sale, just the Mini. The price and customer service are incredible for a 32-bit board, and on par with some of the 8-bit boards here in North America.....

I think I've always looked at the Smoothieboard 5x which is considerably more expensive.