A few weeks ago I noticed a problem when I tried to wheel my Office Chair along the floor. There was exceptional drag. I took a look at the five castors and they were all OK. Then I noticed the Office Chair Cylinder (the tube supporting the seat) had completely penetrated the base. It had gone so far through the hole that it was touching the carpet and dragging along it.
When I sat on the chair all my weight pressed the thin rimmed end of the cylinder into the carpet in an attempt to punch a 40mm dia. hole through it.
This article describes how I fixed the problem.
Naming Office Chair Parts
Since I am discussing the dismantling and re-assembly of an Office Chair we all need to know the names of the parts so that they can easily be discussed. So here is a labelled picture showing the parts of my office chair when viewed from the front:
In addition the Office Chair Cylinder contains the Gas Lift used to adjust the height and suspension of the seat. See an example below:
What I needed To Do
I needed to:
- Remove the Office Chair Cylinder from the base of the chair.
- Devise a method of stopping it penetrating so far through the hole.
- Reassemble the chair with an appropriate adaptation.
Mine is a chair with Arms and a High Lumbar Support System, making it heavy, bulky and high at the back.
To fix the chair I needed to do work on it to remove the cylinder from the base.
The Office Chair Cylinder, containing the Gas Spring, has a tapered end which fits into the slightly conical socket in the polypropylene base and wedges in tight. This tapered arrangement means it always has a tight fit. If it were a cylindrical hole then any play would allow the seat to wobble and rock, which I can assure you is undesirable.
The cylinder is not supposed to completely penetrate the hole in the base but just wedge into it. With a tapered hole the cylinder will always move down until tight. This makes its final resting point indeterminate and in my case it went too far down. The hole in the base had stretched with time, and my weight (14st max.), forcing the cylinder all the way through it.
Conical joints like this (a taper is a section of a cone) always wedge tight and are hard to seperate. So removing it involved hammering the cylinder out of its socket in the base with a lump hammer.
This wasn’t an indoor job so I manoeuvred it downstairs and outside.
I needed to have the chair upside down with the base supported so I could hammer the cylinder back out through the hole.
Detaching The Office Chair Seat
I set up both of my workmates1 side by side so I could hang the upturned chair by its base between the benches. Then I realised the top of the back (Lumbar Support) would be resting on the ground and the base would still be up in the air because the chair is so tall.
I needed to detach the seat from the Office Chair Cylinder control mechanism. To do this I laid the chair across the benches so that I could access the four screws holding the seat. The screws have a 5/32″ (3.97mm) hexagonal driving hole in the top so they have to be turned with a Hexagonal Drive Bit or an Allen key.
I used a CR-V5/32 Hexagonal Drive Bit in a screwdriver with a hexagonal drive (see below.) I removed these screws and the seat. This left me with a much smaller unit to work on.
Working With The Seat Removed
I mounted the upturned base so that two legs rested on one bench and three on the other. Then with a large block of wood, to cushion the blows, I pounded away at the end of the cylinder using a weighty lump hammer.
As I expected there was no initial sign of movement. The Office Chair Cylinder was well and truly wedged into the base socket. There was also a lot of bounce from the springy legs and bench surfaces.
As I worked four of the castors bounced out of the holes and fell to the floor.
Lubricate The Parts I Needed To Seperate
I remembered I had a bottle of specialised lubricating fluid (not oil) sent to me as a sample many years ago. It hasn’t been used for much but I got it to help plug plastic pipes together, and I knew where, in my shed, it was.
Like all emulsions it tends to separate and needs plenty of shaking to keep it as an emulsion.
I put some of this fluid on the work so it would seep between the Office Chair Cylinder and the polypropylene base. Then I took a few more swipes at it which caused a minor calamity. The Gas Spring dropped out of the Office Chair Cylinder and onto the ground.
I didn’t know exactly how it was constructed at the time, but I know now. I had broken a clip which holds the Gas Lift in the cylinder.
This clip is equivalent to a Circlip. It rides in an annular groove in the end of the Gas Lift spindle binding the Gas Lift and Cylinder together. In so doing it keeps the ball race trapped between a washer mounted near the end of the spindle and the end-plate of the cylinder.
I had bent the edges of the spring-steel clip so that it no longer sat in the annular groove of the spindle.
For the moment I put the Gas Lift to one side and continued pounding at the cylinder stuck in the chair base. It started to give. I realised it too would soon be heading for the ground, so I put something soft on the ground to catch it undamaged.
How I Effected A Repair
Since the end of the cylinder is conical and wedges into a conical hole, I chose to fit a conical shim in-between the two to take up some space and prevent it penetrating so far.
Making The Shim
I made a shim out of an aluminium soft drinks can. I had a cola to refresh myself first and then cut the can up with the kitchen scissors to make a shim.
My wife has some kitchen scissors which have one smooth blade and one very finely serrated blade. They work well as ‘Tin Snips’ and made short work of cutting the can.
I put the scissors through the drinking hole and cut the edge of the can top, where it joins the side, and then down the side to the bottom. Then I cut at right angles all the way around the top and all the way around the bottom in areas where the side profile is straight. I had to make each cut 2cm, or less, at a time due to the scissor tips fouling against the curvature of the can. This was like peeling the side off. It left me with a rectangular sheet of aluminium with a ready-made curve that could easily be made to fit in the hole.
The aluminium had some irregularities which I trimmed to a neat rectangle by removing all the jagged edges made by the first cut.
Fitting The Shim
An overlap would prevent the shim forming a smooth cone. Then the Office Chair Cylinder wouldn’t fit perfectly and may wobble letting the seat rock.
So I fitted the shim in the hole in the base and let the ends overlap. Then I pressed it against the inside of the hole with my fingers to expand it to its largest possible diameter and see how it fitted. It fitted well. I just had to trim it so that it didn’t overlap. When in position I marked the overlapped edge with a marker pen and snipped down a couple of mm that were sticking out of the top of the hole with the scissors where the ends overlapped for more precision.
I then turned the base over and did the same on the other side. I snipped in line with the first cuts I made. Then I withdrew the shim and cut straight across from one cut to the other at both ends of the shim to trim off the excess. The remaining aluminium was then a good fit in the socket without overlapping.
I was very pleased with this whole cutting procedure. The aluminium fitted in the hole well without any overlapping, so I didn’t need to recut it. I put the tube inside the shim and pressed it in while keeping the shim a couple of millimetres proud. I expected it to go in a bit further when I eventually sat on the chair and applied my full body-weight to push it all together.
Refitting The Gas Spring In The Office Chair Cylinder
I turned the Gas Spring and controls upside down and stood it on the floor. I then threaded the upturned Base and Cylinder over the spindle protruding from the Gas Spring.
When the two parts appeared to be together I noticed the Gas Spring spindle extending a centimetre further through the Cylinder hole than expected. All I had on the end of the spindle was a steel washer. I realised something was missing that would fill the unfilled space in the Cylinder.
Locating The Missing Ball Race
I went outside with a torch (it was now dark) and yes there it was. A plastic ball race with five ball bearings held in it. I took the Cylinder off the spindle cleaned all gunge and grease off all parts and applied some silicon grease to the washer. Then I placed the ball race over the end of the spindle and lowered the Cylinder over it again.
It’s this ball race which enables one to spin around on an office chair. I can report that the balls were in good shape but a circular groove had been worn in the bottom of the Cylinder. I could see this when I shone a torch down inside it.
Retaining The Gas Lift With A Homemade Circlip
After the Cylinder was placed on the spindle another washer was required. I now had to replace the damaged spring clip with something to hold all the parts together. I chose to make a circlip of steel wire since there was a suitable groove cut in the end of the spindle to hold it.
The wire I used to make the cir-clip came from a heavy duty paper clip like this one.
I used leverage available from its length to wrap it tightly in the groove and cut it with wire cutters where the two ends overlapped. I then squeezed it a bit more into the groove with heavy duty pliers. This wire circlip prevented the washer coming off and held the Gas Lift in place in the cylinder.
Refitting The Seat To The Office Chair Cylinder
I was working in the house again now. I took both parts of the chair up to the office while they were separate. Upstairs I placed the seat on the Office Chair Cylinder Controls and (whilst standing on my head in the shadows) I inserted the four securing screws. Then I tipped the chair onto its back so I could see what I was doing. The slots in the steel are damaged by previous screw tightening. This makes it easy to adjust the position whilst tightening.
Testing The Repaired Office Chair
To test the chair I just sat in it. I spun around and observed that the Office Chair Cylinder had settled further into the Base. I checked the Gas Spring and the tilting of the seat. They all worked well.
24hrs later, with more sitting, the Office Chair Cylinder had penetrated the base further as can be seen below.
I have taken further action to fix this by tightening a 50mm Hose Clamp around the cylinder. The bottom edge of the clamp is in contact with the chair base. This prevents the cylinder traveling further into the base socket hole.