Sanding block for 1/4 sheet

This is a redraw of this model: printables.com/model/826899-sanding-block, I had to redraw to resize the whole thing to properly fit the size of an ¼ of the standard sandpaper size (280x230mm), the original has an odd dimension that allowed an undesirable utilization of the sheet.

The author doesn't allow remix and I don't know why, please open the original model to read the assembly instructions and to download the original model for the tightening knobs as they are 100% compatible. The other stuff needed is also the same: 4 x M5 nylock nuts and 2 x M5 x 40mm screws.

The whole thing was conceived to put a 3mm thick rubber on the bottom surface to allow a better grip and flatness. Use contact adhesive to glue them together and sand it on a 100 grit paper to make it flat. The rubber I used had a glossy finish and I could easily see the tiny height difference on some spots, the more I sanded, the more of the glossiness were gone, making it easier to identify how close the surface was from an acceptable flatness. 

The drawing is partially parametric, you can change some parameters in Fusion to allow the use of a rubber with a different thickness and etc.