New office chair

Like a lot of people, i've been working from home for the last few months during the pandemic, and that home office has been evolving the longer i work from home. I started at the dining room table, then moved to an unused bedroom so we could use the dining table for dining (or giant puzzles), but the dining chair followed me up because we have extras.

It's not a very comfortable chair, which does get me to limit sitting time, but i wanted something a little more comfortable that's also height adjustable, since my cheap desk is not. As soon as i decided to get a welder, i started designing a new seat: something simple and durable that i could potentially use other places if i'm ever not working at home full time.

For the durable part, i settled on something that adjusts with a screw, rather than a pneumatic cylinder. I've worked in offices long enough to see how often those things fail, and didn't want to buy a cheap chair only to replace it again soon. As it happens, i just got rid of vintage office chair a few months ago that would have made a perfect base for this, but i liked the challenge of building it from scratch anyway.

I sketched out a simple 3-legged stool with a 1x5 acme thread as the adjustment/support column. One of my local steel suppliers stocks the rod and huts to fit it, and i happened to have some round steel tubing in my garage that's about 2" and 14ga, so i used that. The upside to this tube is that i could use the same stock from all of the frame parts, and it's plenty stiff enough so it doesn't need additional bracing.

I don't have a metal chop saw, so all of the parts were hand cut and shaped with a grinder or flap wheel. I didn't take a picture of the parts, but here's the main joint, after welding:

stool nut detail

I hesitate to show my still-learning welds close up, but some of these aren't terrible. 

The 3 legs are mitered into the short main column, and the nut tacked on top. I tried to be clever at first and weld a nut at either end of the column, thinking it would help to have the extra support, but greatly underestimating the shrinking/warping forces of the welds. I had the screw in place to keep everything aligned, but even allowing for some gap, the ends pulled in enough that it was very difficult to move the screw at all. I hammered the tacks and that loosened it up some, but in the end i cut off the lower nut, and it seems perfectly stabler with just one. Hopefully it doesn't get too much wobble over time.

stool feed and seat mount

The top of the screw mounts to a heavy 6x6 plate, with the former lower nut welded on. I'm not going to lie, those are the ugliest welds in the whole thing. I welded a couple of the nut flats on with stick at the end, and I should have stick welded that on from the start, but since i already had the MIG in hand just cranked up the heat and went for it. It's a mess of globby ugly welds, but it's strong enough anyway.

You can also see i've mitered the feet to sit flat and welded on caps so it doesn't gouge up my wood floors. 

stool mounted seat base

The plywood base is just some 3/4 scrap i had around, attached with some machine screws because i couldn't find 4 matching wood screws the right size in my stock. 

new office seat

And the finished product. The camera angle makes the seat look huge, but it's just slightly smaller than the spread of the legs.

The cover is some spare fabric i had in the basement from some forgotten project, with 3" of foam from the fabric store. It just ties over the base, so it'll be easy to change if needed. I also added some felt to the feet so i can scootch around a bit if needed. 

What would i do differently? More practice before welding the feet caps, since those welds are the most visible and they still look pretty rough even after some cleanup grinding. Honestly i just got tired of grinding them. A better holding system for the pipe while cutting, since they got a little dinged up in my vise. Getting a metal saw or chop saw would have made for better cuts and less damage. Using 2 nuts isn't necessary for strength, but a second nut would probably eliminate the little bit of rocking i get. If i were going that route i'd wait to put the 2nd nut on until after all the other welding was done and be more careful about compensating for weld shrinkage.