projectmuni

Here it is, the real thing.

This is my third project, and it has turned out to be just right. I got the design from Chris Reeders "ears" type unicycle, and changed it slightly for my own convenience. The differences are the material used, non denting in of the fork legs and the crown area.

The Jig

It al began with the demise of Fat Bastard. I needed a new unicycle in a hurry, so I went to unicycle.com and ordered a hub and 2 pairs of bearing caps. Due to the bearings used on the Suzue type hubs, I needed to create a frame that was narrow enough for those bearings. The other requirements for this frame were light weight and the ability to fit a 3" tyre between the legs.

I measured the width of a Nokian Gazzaloddi on a wheel and added about 1/2". This was my starting point. I marked this dimension onto a piece of plywood and screwed 4 aluminium angles onto it to fit 7/8"OD tube for the fork legs. Aluminium was chosen because I wanted to be able to weld it up in the jig without having to worry about welding the job to it. The wood is there for the same reason. I screwed on 2 more angles along the centreline to accomodate the 1"OD seatpost tube. The small bits of tube for the crown were placed on an angle for aesthetic purposes only! I thought I made a job for myself by doing that, but its no harder than if they were perpendicular, and it looks a thousand times better. After all the angles were in place, I glued .062" shims into the spots where the fork legs and the crown tubes sit, so they wind up centred on the seatpost tube. Measurements and marks were made so that I knew where to sit the tubes. I marked the lengths of the fork legs because that is critical to the wheel sitting in straight, and the bottom of the seatpost tube because clearance for the tyre is a must.

With all the tubes cut and in place, I sent the lot off to the welding shop. The frame was TIG welded using stainless wire whilst in the jig. Unfortunately, the nature of stainless steel is that it moves a lot during welding and therefore came back slightly bent. A simple tweak in a vice, and a check back in the jig got it all back to straight again.

Next thing was to weld the bearing caps onto the ends of the fork legs. I was concerned about how they would line up, because they needed to be straight and in-line with each other for the bearings to fit once they were on the hub. After grinding the chrome off the parts that were actually being welded, I clamped 2 pairs of caps to a scrap piece of 1"OD tube. That kept them centred alond the line of the hub, and I figured that the tilt wasnt critical, and by eye was sufficient. Again, these were TIG welded to the ends of the fork legs.

Whilst I was doing this, I noticed that the upper ends of the fork legs were dangerously exposed, and were nearly sharp enough to cut. Welding in a couple of washers into the inside of the tube gave me enough material to be able to file it off nice and round, and as an added bonus, it provided greater strength to prevent the tube denting in!

The seatpost was decreed non-critical, so I drilled and slotted a .160" 4130 chromoly plate by eye, and bent it to fit a viscount seat. A piece of 7/8"OD x .035" tube was welded to it to complete the seatpost. The seat tube was cut to suit and a slot cut in it vertically for the clamp.

Voila! a finished frame!