X-Y-Z Axis

The head needs to be moved about. It is not a pure arbitrary movement, it has some distinct patterns, which the design reflects.

The general design would make it possible to move the head in X, Y and Z. The X axis is a beam, which lies on two outer beams, so the X bar can be moved to and fro in the Y axis, and the four support points of the outer beams are on columns where they can be elvated up and down, aong the Z axis.

Looking at the home versions on the web, in particular the changes between 1st and 2nd generation of designs it seems easier to move the bed for X and Y, although it is heavier. The rails can rest on the base surface, instead of having to “hang” from the frame above the base. The head then just is kept centred and is elevated along the Z axis. The disadvantage is the base of the printer has to be twice the width and depth of the bed (maximum horizontal shape of a printed object), as each edge of the bed has to be able to be positioned in the centre (under the head).

For a multihead design, the width of the printer is expanded and the extra head is just mounted immediatly next to the first. The extrusion process of each head must be controlled and reasonably acurate in turning on and off. The heads are at he same height.

The way we power the movement is dependent on the axis. A belt or chain can drag a carriage to and fro, and it is possible use the stepper motors with a minimal or even without gearing. (The movement is dependent on the radius of the wheel the belt is driven by, ie a 15mm wheel radius gives 0.2mm movement per degree turn)

The Z axis will only move occasionally, for each slice. On start and stop it moves to either end stop. It seems “obvious” to use a threaded rod. The rod can be turned immediatly be a steppermotor without gearing. The thread will do a lot of gearing, ie one full turn will advance on thread pitch (presumably around 2 mm. A cheaper stepper with, say only 15 degree steps would thus move approx 0.01 mm

It is also possible to do a totally different arrangement, say a two jointed arm for the XY plane. It has a cantilever challenge as it only is suppported at one point, but it would look a lot cooler.

The head will weigh something, (250g?) and be attached with wires and a plastic feed. So the mechanism must be stable. The head will be moved to and fro as fast as possible (we want the print to finish in reasonable time) and this mechnical strain has to be absorbed without the position changing from the intended. This can be mitigated by the controller ramping speed up and down.


One Response to “X-Y-Z Axis”

  1. Jeg har arbejdet med et Mitsu-etellerandet toolcenter (3d fræser) som kunne bearbejde emner med en præcision ned til en tusindedel – dens bevægelser når den ikke fræsede var lyn hurtige mens præcisionsfræsning tog tid.. Mendel og hele den familie af open source fræsere er et sympatisk projekt, men jeg har en formodning om at projektet gøres unødvendigt kompliceret når der lægges vægt på selvreplikering i designet.
    – En fritænkers approach kunne meget vel lave noget der både er billigere og mere elegant! – Så hermed opfordres du til at arbejde videre med dit projekt: Jeg følger dine fremskridt her på bloggen med spænding!

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