Kossel 2500 3D printer build

Why has it taken me so long to decide to build a 3d printer? Better late than never I guess… Time to get started!

After some research, I decided to build a delta printer based on the Kossel design. We use a lot of delta robots at work in packaging an they are very fascinating to watch. Whats a delta robot?

I’ve been trolling the Google delta printers group for information. A user on the group builds and sells carbon fiber arms with magnetic joints and I decided to purchase a set from him rather than try to build them myself. The length of the arms, particularly the consistency in length is very important to the geometry for print quality and accuracy, so I figured I shouldn’t skimp on this part. I ordered the arms on Monday and received them on Friday. Lighting fast shipping from Hawaii, awesome!


The arms are labeled with their length and are all within .01 mm.

I found some NEMA 17 stepper motors on Ebay for $40 for five motors.  The printer only needs four, one for each arm and one for the extruder, so I’ll have a spare.  After I ordered them, I realized that they don’t have a flat on the shaft for setscrew mounting of the pulley, so hopefully I will be ok without it or I’ll have to try to modify them on the mill at work.


I’m now waiting for some corners for the frame that were designed by several people on the Google Delta robot 3D printers group to become available.  If you want to get some it looks like they are still available on Amazon.

Another user on the group offered to print some of the parts for me.  They have a kind of a pay-it-forward program where they print parts at no charge for people building their first printer on the condition that you return the favor to another first time builder.  Pretty cool.  He is even making some custom modifications to the design for the 20 mm x 40 mm extruded aluminum v-slot linear rail that I’m planning on using for the vertical part of the frame.

Update 5/5/2016

I’ve been working on this and accumulating parts when I have time, which isn’t very much.  Still trying to wrap up the office and laundry room remodel.

I decided to go with Misumi aluminum extrusions for the frame instead of the Openbuilds VSlot.  My main reasons were that Misumi had good pricing and they cut to length +/- .5mm (mine were even closer than that), the guy that is printing the carriages for me is using it for his build and I didn’t want to bother with changing the spacing on the rollers on him, and VSlot was out of stock at the moment.

I’m still going to use VSlot rollers on the Misumi extrusion.  There are varying opinions on how well this works but it seems that most of the people that say it won’t work well, last very long, etc. haven’t actually tried it.  Most that have used them together say there is some grove wear in the rollers when first breaking in but it wears fine after that.

The sheet metal brackets from the delta bots Google group finally became available and I got my set.  The brackets turned out pretty nice.  My only complaints are that they came in at almost 50% higher price than what they were targeting and that the holes for the horizontal extrusions were designed for 3mm hardware.  I drilled the holes out to fit 5mm hardware.  The inside holes for the horizontal extrusions are too close to the bend too and result in the t-slot nut being almost halfway out of the extrusion.



I had concerns about the alignment and spacing of the carriages, belts and motor side pulley when I modeled this thing in Sketchup as I originally planned on mounting the vertical extrusions to the outside of the outer corner.  After assembling the frame my concerns were right and I had to tear it apart and chop off the corners of the horizontal extrusions to move the vertical to the inside of the outer bracket.



The printed parts should arrive pretty soon.  I’m stuck on the frame assembly until I get them because I’m not sure if the pulley will have to go onto the motor shaft setscrew first or last to align right.

I plan on putting the motors and electronics in the top vertice.  I ordered a piece of 1/4″x12″x12″ expanded PVC sheet to mount the electronics to and was going to order more PVC to put in between the horizontal extrusions to hide the wiring and electronics mess but I found something better.  Cutting boards at Ikea for $2 for a 2 pack.  They cut nicely on my tablesaw and they are flexible enough to wrestle into place without having to remove any of the extrusions. The frame is a bit tricky to get aligned and square when assembling.


I received the printed parts in the mail, here is what I ended up with on the pulley alignment on the motor and idler.  The idler pulley ended up real close to the inner corner bracket but worked out OK –1008162319aOthers have had questions about the idler and I struggled with this for a bit so I thought I should update and elaborate here a bit.  There isn’t a spacer between the bearings in the idler pulley I bought, so when I tightened it down it jammed the bearings.  I looked all over the place for a jam nut that would fit in between the bracket and pulley and couldn’t find anything thin enough.  What I ended up using is one of the T-slot nuts, these are the “economy” nuts that you can find on ebay, etc.  So the part sequence I have from right to left in this picture is – M5x20 bolt, flat washer, bracket, T-slot nut, idler pulley, flat washer, M5 nylock nut.  This aligned perfectly with the carriages and motor and hasn’t given’t me any problems.

It’s Alive!

It has been quite a while since I have updated this post.  The printer has been “completed” and in service for several months.


For electronics, I’m just running a Ramps 1.4 print controller with a Raspberry Pi onboard.  I’m using Repetier firmware on the Arduino and Repetier server on the Raspberry Pi and I run Repetier host on my PC.

I’m really happy with the Repetier setup, the Pi has a WiFi adapter so there is no wired connection to my PC.  I use Repetier host on my PC to setup print jobs, hit print and the host uploads the file to the server and the server feeds the gcode to the Ramps.

Here is a picture of the electronics in the top of the printer-


The Ramps 1.4 is the red board and the Pi is in the white case (one of my first prints).  I salvaged the power supply (the board on the left) from an old PC.  I originally didn’t plan on using the LCD that came with the Ramps kit.  I read that the graphic LCD is problematic with delta printers due to the processing power required for the delta math.  It runs great on the Repetier firmware though and it is handy for shutting off the ATX power or pre-heating.

I bought a E3D v6 clone off of ebay despite lots of warnings online.  The first time I fired it up, it jammed.  There was a teflon sleeve in the heat-break that isn’t in the E3D drawings.  They used a heat-break for 3mm filament and sleeved it down to 1.75.  I ordered some new heat-breaks off ebay and polished all of the bores and chamfers.  I could finally get it to extrude some plastic.  There is a pretty steep learning curve involved with getting everything setup right.  It took me a while to find the right settings for the hotend temperature, feed rate and extruder cold end adjustments.

Here is a picture of my effector and hot end setup –


The effector is a design by Haydn Huntley, the same guy that built the rods.  I’m running a pair of blowers for part cooling.  A couple of wraps of kapton tape made a world of difference in maintaining heat in the hot end heat block.

Extruder setup –

1008162237a 1008162237

The extruder is the b’struder and once I got the right combination of spring pressure and stepper motor current, it is running like a champ.  I realized that I was skipping steps and had to increase the current to the stepper.  This increased the heat of the motor to the point that it started softening the PLA printed extruder frame.  I added a fan and a heatsink that I grabbed off an old motherboard north-bridge.  I also relocated the extruder from where I originally mounted it on the side of the upper vertex to the middle of the vertical extrusion.  This shortened the bowden tube (the tube that the filament feeds through from the extruder to the hot end) by about 10 inches and gave a much smoother arc to the tube.

Carriage setup –

1008162300 1008162302

The carriages were designed by Bill Sowerby on the Google Deltabots group.  They are awesome.  They have built in belt tensioners and the v-slot rollers work great on the Misumi extrusions.  There is only a very small grove worn in the rollers from the corner of the Misumi rail that developed during the first bit of use.  I used cheap optical endstops from ebay and a small flag made of brass on the carriages.  They are just held in place with double stick tape.

I’m not using any auto leveling right now.  I use the Escher 3d Delta Printer Least-Squares Calibration Calculator to calibrate.  The frame is very rigid and even after moving the printer several times, I have only recalibrated after making mechanical changes to the hotend.  I may add auto leveling in the future but don’t really see a need for it right now.

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5 thoughts on “Kossel 2500 3D printer build”

  1. Nice work!

    By any chance do you have a link to the carriage STL that you’re using, or a detail of how you worked out the idler pulley mounts?

    I bought the same corners and have been (slowly) building a delta using them. I’m finally getting to the point that I’m looking at actually assembling the vertical portions, and realized that I’d never found a 40mm compatible carriage!

    1. (Never mind the request on the STL, I found his post on the Ggroup thread above where you linked to your blog… Helps to read!)

      Still, great looking printer, and I hope that I can get mine running sometime soon.

    2. Glad you found the stl. There is a t-slot nut in between the bracket and the pulley. It was tight and I couldn’t find a jamb nut that would fit. It works 😃

      FYI the delta printer thread with the link to Bill Sowerbys carriages is here.

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