Sweepy 1.0 has been fantastic over the years, and I’m now ordering Sweepy 2.0 as the original is reaching the end of its service life, but I have always wondered why (other than because McMaster doesn’t sell it) the bristles aren’t angled. That is, instead of the bristles coming straight down, perpendicular to the work surface, they could be tilted off to one side at a slight angle (say, 15 degrees). This would allow the bristles to deflect out of the way with minimal force when they contact the work surface. This means no lost steps or (since upgrading to HDZ) significant moment applied to the router along the X carriage, causing in accuracies in the y and z directions. Vertical bristles need to buckle when they hit the work surface (large force), while angled bristles just need to deflect (low force).
The picture in my head has the bristles angled off along the tangent to the circle, rather than radially outward. The advantage of a tangential deflection is that you’re far less likely to end up in a scenario where the x-y movement of the router causes the bristles to jam up and pop the base off the dust boot. In fact, this failure should be no more likely than with the current design using a tangential deflection.
With bristles angled as such, you can now afford to have the bristles in contact with the workpiece much earlier in the cut, meaning better dust collection.
The chief downside to the approach I’m suggesting is that it’s not straightforward to source a brush like I’m describing. It might have to be custom-made by the brush manufacturer, or else printed out of TPU like @crpalmer demonstrated. Another option might be using a heated jig/press to modify the off-the-shelf brushes (e.g., McMaster 1469N16), thermoforming them into the desired configuration. I suspect the added utility would justify to Carbide 3D’s customers the increased cost of sourcing/creating/modifying the angled bristles.
To quickly test whether what I’m suggesting is feasible, I removed the bristles from the backing of a brush strip I had laying around, reoriented them at about 30 degrees off of normal, and fused the ends with a heat gun. I masked most of the length of the bristles with a piece of aluminum to protect them from the heat. While the resulting strip wasn’t very flexible anymore, the bristles weren’t distributed very evenly, and it’s certainly not winning any awards for looks, this quick test was adequate to show that what I’m suggesting should be fabricable provided the bristles can be arranged at an angle prior to binding. Here’s a photo with my quick-and-dirty test brush sitting next to the original brush for comparison.
I also very quickly modeled a mock-up to confirm that a 15 degree angle wouldn’t result in the brush widening noticeably when formed into a ring. A 30 mm radius ring with 25 mm long bristles (similar to sweepy) widens only ~0.7 mm.
Hopefully that all makes sense. If not, let me know. I’d love to see something like this on a future version of Sweepy, or as a standalone bottom half (like Deep Sweep) for the existing Sweepy.