A secretary chair has you sitting at a slight slope forward, with some pressure supported by the knees. It is easier to sit with spine erect, and you don't fold in the middle to 90 degrees as in a normal chair, which is probably better for your intestines. To get more use out of my chair, I made two add-ons for it: a drawing board support for drawing, and a table for working on small 3-d projects. Both are held on with bungee cords, and are easy to remove.
I hope I am using the term "hack" correctly. It is a modification of existing equipment to expand its potential use. It saves space and money to multi-purpose things. In this case, it also gives me the most comfortable seat for drawing and small projects that I have ever used.
Step 1: As a Drawing Chair
The drawing board rest on the metal pipe is just a PVC "T" with two sections of PVC pipe sticking out the sides. It is rests loosely at the top of the pipe and spins to accommodate the drawing board. Basically, the board rests on 3 points; one's legs and the top of the metal pipe. The side extensions give the board a bit more stability, but basically just help keep a flexible (masonite) drawing board from bending down under gravity on the sides, as it would if resting only on the tip of the pipe.
The pipe finds its way through the structure of the chair, and has a rubber stop (doughnuts cut out of rubber floor mat) that locks into the chair design to keep the pipe from sliding down to the floor. (You don't want to scrape the floor with the pipe.) They were tight fitting doughnuts, so I didn't bother to glue them to the pipe.
Two small bungee cords hold the pipe in location.
Step 2: As a Revolving Work Table
In work table mode, the revolving table addition replaces the drawing board rest. The pipe is held vertically.
I needed something like a fork at the bottom of the pipe to lock onto the chair frame, and allow easy removal from the frame. To do that, I bent a piece of 1/4" rebar (hammer, vise, and pliers) to make the fork. The "handle" of the fork fits inside the table's central pipe. To make a snug fit, I wrapped the fork with some string and tape to get the right diameter and then just press fitted it into the end of the pipe.
The table top is a round scrap of plywood, with a square piece underneath. The square piece has a snug round hole drilled into it (drill press helps keep the hole at 90 degrees) for the metal pipe to fit into with glue. A piece of 3/4" EMT metal tubing with three "fingers:" cut into the end of it and a hose clamp complete the table top. With the hose clamp loose, the table revolves. With it tight, it doesn't spin as easily (only if the bungee cords let the central 1/2" EMT pipe spin).
This is a really nice table for working with any small 3-d projects.