If, like me, you're a bit of a porker, eventually you will suffer the ignominy of broken office chair wheels:
The symptoms are: An inability to move around the office, except in small circles, and a definite tilt. And, of course, once the first wheel has caved in, the second is only a matter of time away...
Fortunately, the wheels are really simple: two plastic discs pressed onto an axle which is held in a moulded plastic structure. The metal pin joins chair to wheel unit. Repeat * 5
The first job, after squaring off some aluminium of about the right size, is to mark up the axle hole. I will cut 3 "subframes" from the block shown. Here I am using a height gauge, and since the digivern its made of has a flat battery, I'm using a gauge block to give me an ultra-accurate height of about 1/4" I wasn't bothered about the exact height, just so long as there's about enough meat around the axle that it won't burst out under the many newtons of force I will be applying to it...
Having scored the block twice, I then make use of this rather nifty optical punch to definitively mark the crossing point. I don't need this level of accuracy, but this optical doodah is so useful, I wanted to show it...
The plastic peg has a target printed on the bottom, you line that up with the mark; remove the peg and replace with the hammer, and bash it once. Job done
We then line a centre drill up on the punch mark:
Centre drill, then drill 6mm all the way through. Each axle is straight knurled in the centre which will hold it in the aluminium block nicely.
Next, mark the edge at 90 degrees to the axle hole up for the main pin. Drill about 1.5" in to 10mm. Then it needed a tapered section - I picked a likely looking cutter out of the many I've picked up along the way; load it up:
Perfect fit:
The pins used a lip in the plastic to hold themselves in. That wasn't going to work with the aluminium, so I drilled & tapped a hole in the side. The cheapo M3 tap is a fragile beast (I could see it twisting slightly under the forces), but I somehow did all 5 tapped holes without breaking it.
Screw in a bolt, and turn it into a grub screw with a hacksaw:
Finally, part off the piece using a carbide-tipped rotary saw blade (an Evolution Rage Pro - fabulous things - you need ear defenders for the noise, and armour plating to deflect the centre-of-the-sun-hot chips):
Press fit the axles in using the vice:
And we're done:
Rinse & repeat:
And finally, stick them back where they belong:
I am now happily buzzing around the office again without having to walk! Hurrah!
