Three basic steps to building the desk, all go into each in detail
1 - Gather materials
2 - Remove and remount controls
3 - Build and install desk
Step 1: Acquire Materials
1 - A treadmill - doesn't have to be top of the line, but should be stable and relatively quite. I used a Nordic Track C2200. From Craigslist - $120
2 - 1/2 sheet 3/4 finish grade Plywood
3 - Wood screws
4 - scrap 1x1
5 - 2ea 3-way PVC Elbows
6 - ~ 3' 3/4 PVC & 3' 1 1/2 PVC
7 - 2ea large hose clamps
stain and paint as desired
Your materials may be slightly different based on the treadmill you use.
Step 2: Remove and Remount Controls
The control was attached to the treadmill with 11 screws, a multi-wire connector and a ground wire. After removing all of it, I fashioned a new bracket with PVC pipe, using 1 1/2" for the uprights and 3/4" for the cross piece, then spray painting it back.
the bracket then attaches to the upright with hose clamps. I rerouted the control wire through the upright, then back to the control. You can see it in the second picture looped over the PVC. I reattached the ground wire to the upright at the level of the control
Step 3: Build and Install the Desk
I decided to use two shelves and put my laptop on the bottom shelf - this gave me more useable desk space and a better neck angle when working.
The design I ended with used slightly more than 1/2 sheet of plywood, but the layout below can can be cut from 1/2 sheet
top shelf - 48" x 18"
bottom shelf - 32" x 22"
front panel 48" x 7 1/2"
side panels 22" 5" (cut from end of bottom shelf
(my shelves are 20 and 23" inches wide - you need the bottom shelf to be about 3" deeper than the top)
Holes drilled in front panel slide over the support handles
bottom shelf wide is determined by distance between frame uprights, fits snugly
assembly using scrap 1x1, glue, a finish nail gun and wood screws.
I cut a 1/4" groove in the bottom of the bottom shelf to align with the cross support of the frame. This lets the desk sit very snugly on the treadmill without having to be physically attached.
Finished with oak stain and black paint on the edges.
Step 4: Walk!
Some things I would do differently if I did it again, or might change later:
I'd open the front of the desk between the shelves to use for storage.
I would design it to allow the treadmill to fold up easier. You can see in the second picture that it does fold up, but you need to slide the desk off of the handles and set it back on top.
I would add an electrical outlet and USB charging port.