First, I beg for indulgence for my bad English, but I will try my best.
So, making plane parts of Wood or other Materials which are first sawed raw with a Cutting-Saw needs to be contour-straightened with 90° sides manually. If they are thicker it is better to sand it with a vertical Belt-Sander-Machine. But professional Belt-Sanders are either too expensive or if from home-markets they are mostly too weak (motorized). So we need a cheap and good solution to grind the Outlines of our projects upto the exact planned contours.
So I thought about this solution, making a fixed (only) 90° Vertical-Sander from a manual home-working Hand-Belt-Sander, 4 wasted Furniture wooden Parts, a Metal-sheet, 10 wood-screws and two 6mm-metal-screws.
Most belt-sanders have two nut-threads on the back to fix them on a plate. So we can use this to fix the sander with two (mostly 6mm-) screws on a vertical plate. This Sander (mine) is one from Bosch, "PBS 7A 600W", but others would also do it, if provided with the mentionned two fixing-nut-holes at the back.
Step 1: Printing Out the Templates
First print out the templates on normal (white) paper and copy the paper-forms f.ex. with Acetone, a softpaper and with a bit pressure to the ~17mm furniture plates (wasted furniture press-board or a cheap press-board from store). To have straight contures on the parts this first time we can let do the cuts at the store, most greater stores have saw-services. If not available, we need a raw file to straighten the edges of the 2 middle parts (width: 115mm, exactly parallel).
Step 2: Assemble the Parts
Next, we need to assemble the parts. With two clamps we can fix them on position and with the 10 wood-screws (length: about 40-45mm and thickness: about 4-4,5mm) - screw it together.
A Belt Sander is mostly not symmetrical, so the two fixing metal-screws on the rear (M6) have to be positioned mostly a bit on the side with the measured inner-distance between them. Measure and position the sander-holes first and then mark and drill them exactly, first with a smaller drill (with about ø2mm), then enlarge them to ø7mm or ø8mm (for M6 > more than ø6.5 mm, to have a bit of clearance, if not resulting the exact distance between the nut-holes!).
Step 3: Finishing
Finally stick the metal-sheet (galvanized iron of about 0.5mm thickness, stainless steel would be even better) with a 2-component epoxid-adhesive or a good (strong) contact-adhesive on the grinder-plane. The plane has to be made plane before, with exactly 90° to the grinder-belt. It's convenient to measure the angle befor glueing the metal-sheet.
I've added an STL-file to view the Sander from all sides. (You can see it online with a free STL-viewer, f.ex. on: www.viewstl.com).