As I detailed in my last post – The Kitchissippi Robotics 45 Degree Linear Carriage (A brief history) my unique linear carriage design has gone through off-and-on revision and evolution over the past two years or so since I first came up with the idea.
The latest revision is certainly the most refined – it retains the elegantly simple design of the previous conceptual parts – eight bearings constrained with four bolts around a steel tube at a 45 degree angle.
What I added in this version is adjustable tensioning of the bearings against the tubing. The major drawback of using bearing holders that clipped the bearing in place was that it was nearly impossible to adjust the tension and keep things squared away, and the bearings wanted to shift. They need to be constrained on both sides.
The problem with using plastic spacers is that it’s hard to get perfect accuracy in the thickness of them – the first layer could get squashed down a bit into the print bed and change the height of the spacer from the original CAD design.
I mostly used metal washers as spacers but they have the problem of being able to only add or subtract the spacing in 1mm increments. Getting the bearing spacing against the tubing was terribly inaccurate using SketchUp. They were either too loose or too tight and gouging the metal.
I redesigned the parts in OpenSCAD and parametrically adjusted the math until I got a more ideal design. Then I assembled them using rubber spacers to allow for fine tuning of the spacing between the bearings and the tubing.
This seems to be the most winning combination of the design so far – it rolls stiffer and straighter against the tubing while still being gentle enough to not damage the tubing.
I’ve also spaced the lower bearings further apart and more inwards to provide a more stable rolling platform.
Also of note, I ditched the separated bar design of the outer carriages from the previous version. Once the arm joints were fully stabilized the stresses of the delta mechanism cased them to flex.
Above is the X tower carriage which is working well. I am in the process of printing the last few pieces for the Y and Z towers.
Ignore the length of bolt ticking out of the carriage – I thought I had the appropriate N06 bolts on hand for these but cannot seem to find then. I believe I may have used them in another project, so I grabbed some M4x40mm bolts to put it together. They are similarly sized and it will do until I can get to the hardware store and get the slightly shorter bolts I had intended to use.
For comparison here is the previous working design that was less stable:
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