OpenBeam Kossel Pro

OpenBeam Kossel Pro - A new type of 3D Printer

• Question: What is the printer's accuracy? XYZ printer claims they can do 0.1mm resolution / 0.05mm resolution / etc...
• ↑ Interesting ...

• Answer:
• I always explain to people that common FFF (Fused Filament Fabrication) 3D printer is essentially a computer controlled hot glue gun - it operates by melting a plastic noodle and squirting out molten plastic from a hot tip. There is a BIG difference between putting plastic and hoping that it stayed where you *thought* you put it, and the actual part result. The actual part is a function of the sum of all the errors and variances in the additive fabrication process, with a bit of warpage, shrinkage, and entropy thrown in for good measure. A more correct way to specify the machine's accuracy would be to specify a percentage variance based on the part's size - bigger parts will have a bigger tolerance in the size of the part. This is due to the fact that more tool path passes are required to build a bigger part and each tool path incurs its own tolerance. Therefore, to claim that a printer can hold 0.1mm accuracy is misleading at best.
• A common mistake 3D printer folks make is to associate microstepping on the motors to actual commanded accuracy. This is simply not true. Microstepping is merely a way for the motor driver to vary the proportion of current between the two coils of a motor to smooth out the motion between discrete steps. On the OpenBeam Kossel Pro, for example, we run a 20 teeth GT2 timing belt pulley that is 2mm pitch. The motor is a 200 steps per revolution motor. Therefore, per revolution of the pulley the belt advances 40mm (20T x 2mm/T pitch), and per step the belt advances 0.2mm (40mm / 200 steps). This is the theoretical drive resolution on the motor axis. Slack in the belt, belt stretch, etc can all affect this accuracy.
• Delta robots further complicate this by the way that motion is achieved - by mixing input from all 3 towers. Thus, the resolution of the printer is actually the lowest in the middle of the bed - as it requires the least amount of motion on the tower to achieve motion in the middle - and the areas in front of each tower has the highest resolution, as the arm it is directly in front of has to travel the greatest distance to eek out a small amount of motion. Here's a great thread on the Deltabot Group on the variable resolution results of the Delta Robot: https://groups.google.com/forum/…
• That being said - they say the proof of the pudding is in the eating. The Totoro figurines and all the test prints were printed in the middle of the build platform, where the printer has the lowest accuracy. The output quality of the printer is definitely on par with the best of the open source FFF machines and I would argue that for the right geometry (one that does not require support material) it is capable of beating a $20,000 Stratasys Dimension (smaller nozzle size and step height).