Hack an Office Chair Into a "Hill Billy High Chair"

This chair is for those people who made an awesome high desk but realize they would like to take a seat every once in a while and still be at reasonable elevation to do work.  This project began when a friend brought home a used computer chair (nothing special; have one similar that i bought for $60 from amazon) and it was sitting too long for me not to hack it....I really wanted a chair that was tall enough for me to sit at my standing desk when I so choose, but  the only viable option I could find were bar stool style chairs which are not cheap. Thus, I started looking for repurposable items and the idea hit me: Disconnect the computer chair from its base and add a  frame which meets the necessary height adjustment but maintains stability and balance. What I came up with was a basic 2x4 box frame that does not especially streamline the chair's stature, but does the job non the less. With this, I introduce to you what I like to call the Hill Billy High Chair, mainly for poetic effect.


Tools Used:
Tape Measure/Square
Level
Circular Saw
Jig Saw
Cordless Drill/ Drill Bits
Palm Sander
File
Allen Wrench

Materials Used:
(3) 8 foot 2x4s
Leftover piece of OSB
(4) 0.25 inch 20 thread nuts and washers
(2) cans of black spray paint
Several 2.5 inch c
1.25 inch coarse thread wood screws

Step 1: Step 1. Disassemble Office Chair

You'll need an allen wrench for this step. Remove the 4 hex bolts. Keep all the parts.

Step 2: Step 2. Cut 2x4 Lumber to Length

Cut to length (4) pieces of 2x4 at 12, 18, and 23 inches. This process required (3) 8 foot 2x4s with some scrap left over.

These dimensions are a function of the additional height you would like to add and the dimensions of your office chair. My office chair was 25 inches wide from outer arm rest to outer arm rest. With that, I knew my support structure needed to be a similar width to interface with the bottom of the chair. Also, the additional height I needed to comfortably sit a high table (top is at 40 inches) was 12 inches.

Step 3: Step 3. Construct Top and Bottom Boxes of Frame

Construct the top of the frame by adjoining the 18 inch pieces to the ends of the 23 inch pieces. This will result in outer dimensions of 18x26 inches. To do this, I pre-drilled two holes for each connection and fastened the joint with (2) 2.5 inch coarse thread deck screws. Construct the bottom box in the exact same fashion. 

Step 4: Step 4. Complete the Frame

Complete the frame which will connect the chair's rotating base with the actual chair part by adjoing the top and bottom frames with the 12 inch pieces. Ensure the 12 inch column pieces are flush with the top and bottom boxes' surfaces, then fasten with (2-4) 2.5 inch deck screws per joint. In the end I chose to use (4) screws per joint for absolute certainty of the structure...since I would be sitting on it and all.

Finally, cut a rectangular piece of OSB 18x26 inches and attach this to the bottom of your box frame. This will serve as the interface between the chair's original swivel base and the box frame you just constructed. To attach the OSB sheet to the frame I used several 1.25 coarse thread wood screws.

Step 5: Step 5. Modify Box Frame to Accept Chair's Curvature

This was the most difficult part and required a little math/finesse. First, I centered the chair at the box frame's center. Next, I added a support between the chair and the frame until the chair was level. Without this wedge the chair would lean or roll to one side because its curvature on its bottom. Once it was level I measured the distance from the point where the chair would eventually rest on the frame to the frame itself. This distance is the same distance the center of the chair would need to drop down into the frame. Image 1 depicts this task. Image 2 shows the outline I generated based on the previous measurement. I followed the same process for the rear portion. The rear required less depth because its curvature was much less. I used a Jig Saw to remove the outlined portion. Finally, I sanded the curved portion of the frame until the chair fit snugly within the frame (Image 5).

Step 6: Step 6. Reconnect Rotating Base to New Box Frame

During this step the swivel base was reattached to maintain the mobility of the chair and overall awesomeness. The swivel base was originally fastened to the bottom of the chair with 4 hex bolts which inserted into Tee Nut Inserts for wood. Image 3 is a screen shot of some Tee Nut inserts from McMaster Carr that were similar to those on the chair. Since I didn't want to worry about extracting and then implementing these into my design I used some 0.25 inch 20 thread and 0.25 washers to mate with the original hex bolts instead.

Before all this, I had to determine what was the optimum position for the swivel base to be attached to my frame since the CG of the chair has now been drastically change. I needed to find an appropriate position so when the person sitting in the chair leaned back/forward or right/left the chair would not tip over. To do this I used a couple drywall screws with the 0.25 inch washers to temporarily attach the base...then I sat on the frame in various positions to test the stability. It took a couple of attempts, but I found the best position in terms of swivel base column to be centered from left to right and a little behind the center of the box frame to negate the natural backward tilt of the chair. Image 4 shows the temporary fastening for quick change and adjustment, while image 5 show my initial configuration attempt. Image 6 was the final placement and yielded the best balance.

Lastly, I added an 18 inch cross member to the interior of the frame just above where the swivel base connects to increase rigidity and reduce any creaks. Image 7 shows the result of this step.

Image 8 shows how the bolt, washer, and nut came together to connect the swivel base to the bottom of the wood box frame.

Step 7: Step 7. Fasten Chair to New Base

This step required some time to determine how to fasten the chair to the new frame. I did not want to un-upholster the chair to fasten it to the frame or anything like that...So I found some 2 inch angle brackets at Home Depot which fastened to the wood box frame and the hard plastic arms of original chair. These brackets prevent the chair from sliding off the frame, they bear no weight of the person sitting in the chair, simply lateral or torsional loads which in terms of sitting are little.

Step 8: Step 8. Paint the Base

This step is not necessary but after I attache the chair to the wood box frame I thought it looked a little out of place. So I used two cans of $0.98 black spray paint from Walmart to give it a clean all black finish. This step took maybe 20 minutes and I let it dry overnight. The next morning I re-fastened the chair to the frame with the angle brackets.

Step 9: Final Product

These images show the final product and emphasize the fruits of each step. As you can see the chair fits the application, was not too heavy, and maintained the mobility and flexibility of a typical office chair just at a higher altitude.

*Please excuse the messy desk, I was in a transitional phase.

Step 10: After 2 Months of Use

I had a friend sit in the chair and test it out 2 months after I built and first used it. He said, "it's perfect." These are some images of him sitting in the Hill Billy High Chair and surfing the web at my tall work desk/bench.