We started this project to come up with a better spool holder that would not sag.
To prevent the spool holder from sagging, our idea is to support the spool at at the bottom rather than from the side. We use ball bearings to reduce the friction.
This is the side view of the spool holder. It consists of the base, which holds two clips for the ball bearings. We designed an initial version in Sketchup and printed it to see what changes we need to make.
We did an initial print with a narrower width to test if the curvature is correct. This first design is definitely too narrow to serve as the base, but there is no sense wasting lots of printing filament only to find out that the curvature is wrong!
Fortunately, we got the curvature right on the first print.
But now we run into another problem. The end stops are printed with a thickness of 2 mm, which is fragile and leaves them easily broken. We made them 5 mm thick in the next print.
Ball Bearing Clips
We need a way to suspend the ball bearings above the base, yet still enable them to roll freely. Our initial idea is to hold them in place with a pair of clips that will hold the axle firmly.
We made an initial print to test the dimensions.
This draft print has a base 3 mm in height, and a distance of 4.4 mm between the walls. This turned out to be unable to fit the ball bearing properly; the printer seems to add an extra 0.2 mm on all sides to any printed design, so we will need to widen the spacing by approximately 0.4 mm.
We also made the base too strong; it was unable to flex so as to allow the ball bearing to fit! The next print will have a 1 mm base for better flex. Too much strength is not always a good thing.
With a 1 mm base, the second draft print was able to fit a ball bearing. But the protrusions were too short, leading to loose fit. And in a gross oversight, we made the clips too short to fit the entire ball bearing inside …
Now it can fit the ball bearing. But the protrusions are too short! The ball bearing is only held loosely, and when placed under the weight of the spool, the ball bearing is easily unseated.
We added another 0.2 mm to the protrusions. Still too short …
Made each protrusion 1.6 mm (previously 0.8 mm) The ball bearings finally fit snugly. This required some post-processing; we had to cut away any excess oozing plastic, and trim off unsmooth corners and edges. This is because we printed cylindrical protrusions that struck out at right angles, without any support.
In a future version we will sharpen the cylinders (make them more conical) so that the cylinder sides make a gentler angle with the walls.
We used the simplest method we know of—superglue—to attach the clips to the base. Rough fit, but it works. Here is the final product!
It fits the cavity snugly, too:
We still have another cavity on the left to fill, and certainly there is room for improvement on this design. Things we would like to try next:
- A mechanism for fitting the clips onto the base without using superglue, and yet allowing positional adjustments to be made.
- More conical protrusions which will minimise warping from printing sheer overhangs.
- Some way to maintain the spacing between the two base sections so that there is less chance of the spool being unseated.
Total project time: 3 days