The previous prototype of the Gemini 3D printer gantry worked effectively however there are many aspects that I have been working on revising.
Plastic parts in use on the x-end/y-carriage were not designed to be robust in the prototypes – it was assumed that they would be replaced with a better design in the future, so they were made with the most minimal use of plastic to avoid waste on what was expected to be a throw-away part.
While working on what will be a more robust setup I’ve been experimenting with several conceptual changes.
The first major revision involves the belt paths. The motor-end idler pulleys are being removed entirely and the inner dimensions of the belt path will be significantly reduced by this change. This removes several bearings and an extra 90 degree turn from the belt path, shortening the length of GT2 timing belt required and lowering the part count.
The second major revision is to decouple the gantry from the top of the Z axis which will provide more space for the X carriage assembly as well as creating a more directly square frame to constrain the gantry within. I am working on a new design which places the Y axis linear rails underneath the aluminum extrusion instead of on top of it.
A potential pitfall of this change is that it may require an extra metre of aluminum extrusion, or some more drastic re-arrangement of the frame design to accomplish this.
The third major revision – which may be a bit more controversial than the previous two – is to replace the aluminum channel supporting the X axis with a thick length of aluminum flat bar. The reasoning for the channel is that having two different planes on the support will prevent deflection of the X axis over it’s widthwise span.
Testing has indicated that it takes one-thousand grams or more of weight to cause significant deflection of the hardened steel linear channel on it’s own. Bolting it to a length of flat bar increases the amount of weight necessary to cause deflection.
However, the current X carriage design weighs only 200 grams which is not enough to create any significant distortion.
I am still working on this design and might decide to play it safe and use a corner channel ultimately as this will also provide the necessary mounting points for the new design as well as the deflection strength.
Testing is still in progress for this – ultimately the extra reinforcement seems unnecessary if the x-carriage is a fifth of the weight that necessitates it.
The forth revision involves the belt alignment as it relates to the X axis. The goal here is to make the x-end/y-carriage assembly simpler and stronger as well as aligning the belts in such a way as to make clamping them to the X-carriage simpler. This revision puts all four ends of the two belts inline with each other, which is strangely not something I’ve seen elsewhere in a corexy design.
Additional changes to the frame, motor mounts and idlers are in the works as well.
Stay tuned for pictures and/or renderings soon!
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