Following on from Kossel 3D Printer, these are some points that I have noted, whilst constructing a Kossel XL using the Sintron kit and a Kossel mini using aluminium vertices…
From Kossel 3D Printer
I came across this problem, when looking into building and sourcing the parts for a Kossel printer in Bangkok.
The correct length of the push arms of a Kossel 3D printer is a bit of an enigma. The length is related to the length of the Horizontal frame lengths, that form the triangle. The ratio between the length of the push arms, from eye to eye, and the length of the horizontal lengths, is apparently 80%, or 0.8.
However, not all designers stick to this ratio, and often go higher, up to 92%.
I wondered why this is. Surely it is simple enough to cut a length of aluminium extrusion to the correct length? Certainly it is easier to cut aluminium than a carbon fibre rod to the correct length, although the latter is still certainly possible.
There are constraints, the most likely of which is the sizes of borosilicate glass discs (commonly 170/180/220/260 mm), and custom heated beds, but there may be others, such as a minimum horizontal length (in order to accommodate the steppers), the carbon rods come in pre-cut lengths (seems unlikely?).
Following on from Kossel 3D Printer, and the tutorial videos (see Kossel construction videos) the BuildA3DPrinter kit comes with an extruder stepper motor with a planetary gearbox. This results in a very high torque. However, as stated below, it has been replaced by the 3325_0, a motor with the same NEMA size and same torque.