# -*- mode:org; mode:visual-line; -*-

* related

https://courses.ideate.cmu.edu/16-223/f2021/text/mechanism/open-hub.html

* 2021-11-05 first revision

Many of the hook tabs broke off during initial assembly, but the bearings feel secure and the hub rotates smoothly.

The hook tab dimensions at this stage:

inner-hub:

2.0 mm		hook relief cut width/diameter of bottom fillet
6.2 mm		hook relief cut height
4.2 mm		height from widest point to bottom of fillet
3.2 mm		effective length of bending segment (widest point to start of fillet)
1.5 mm		thickness of tab
1.0 mm		width of hook corner (widest point)

Since the tab needs to bend from the widest point down to the neck, this length need to be increased.

* 2021-11-05 second revision

Inner-hub:

Increasing the effective length of the bending segment in two ways:

1. Moving inner taper lower.
2. Squaring off bottom of relief cuts.
3. Effective length of bending segment increased from 3.2 to 5.0 mm

The stress concentration now falls along the bottom corner of the bearing
groove.  The arc on the relief cut wasn't relieving stress, it wasn't in the
right direction.

Outer-hub:

Made similar changes; the hook geometry is effectively the same, only on the outside.

* 2021-11-10 revision 3

1. The hooks are still breaking.
2. Increasing the hook tab thickness from 1.5 mm to 2.0 mm (to increase strength).
3. Decreasing the hook width from 1.0 to 0.5 mm (to decrease the bend).
4. Adding a tiny chamfer of 0.2mm at base of tab.
5. Reducing depth of hook cut by 0.5 mm.

* 2021-11-10 revision 3N 

Also exporting a version with no hook and no tab/hook cuts: the bearings will
just press into place, and the hub will not provide any axial constraint against
pulling out.

* 2021-11-12 vertical print of rev 3

Changing the fabrication orientation to an 'on-edge' pose.  This will allow
fibers in the printing plane to run along the length of the tabs, which will
mean that the tab flexure will be bending fibers instead of shearing layers.

* 2021-11-17 vertical print assembled successfully

The new prototype printed vertically assembled onto a bearing without any tabs
breaking.
