When You Find A Lemon During Lockdown

It's been two months since I am working from home due to COVID-19 lockdown. Days before lockdown began, I took it as an opportunity to upgrade my home office setup/hobby lab. Essentially it meant getting a monitor, keyboard, tables etc. While I did manage to get all the stuff in the nick of the time. The only thing I did not consider was an office chair, as I already had an old one.

Few days into the lockdown, and the gas spring in the office chair gives way, and it begins sinking! It's quite annoying to setup the chair to your height, and just in moments you start coming downwards.

With shops and online delivery closed for non-essential items, there is no way I could have bought one. The fix had to be at home, with some basic tools and well a 3-D printer :). I have been trying Fusion360 lately, and this little project looked like a perfect opportunity to get the basics straight.

I decided to have a kind of clamp attached to the spring inner cylinder, thereby preventing its movement while sinking. The clamp needs to be strong enough to atleast be able to hold my weight. So opting for higher infill was a necessity ( I opted for a 30%). I planned to have two clamps, and tie them together through M5 nut and bolts. After several trial and errors, I decided on the structure on the right.

The clamp is 135mm in height, with 5mm of overall thickness, there are 4 threaded holes for M5, with 0.8 pitch. 135mm is the height I usually keep my chair at, as after the fix it wont be adjustable anymore. I had some problems in my slicing software so I couldn't really print it all vertical as I had wanted. Anyways got it printed by keeping longer side on the print bed, and after 8 hours the design was ready to be tested!

I tightened the clamp around the inner cylinder of the spring ( The steel stem seen above), as I was tightening the clamp around the stem, I noticed few strands of plastic buckling (as visible in the middle pic). To reduce that, I had to duct tape around the clamps to make it more durable ( and in the process made it more shabby looking :/). All of this could have been avoided if print was given vertical. So , a mental note for the next time, it's always important to visualize the forces on the part before printing them. As of now, this clamp is doing it's job, the chair isn't sinking anymore! I am sticking with this clamp for now, let's see how long it holds.

The STL for this can be accessed from here, it should fit most of the chairs, as the gas springs for these chairs are often of same size.

Thanks for reading, let me know how you find it!

Nishant

P.S. As I suspected, the clamp broke in a few days, due to the longer strands, this time I printed the clamp in vertical direction, which has been running fine till now.