Category Archives: Other projects

Soapbox or gravity racer

This was one of my quicker projects – I found out about the race, due to start at 1000 on 1st Jan, with only a month to go. And to complicate matters, that month included xmas.

The chassis was fully modelled in CAD (Fusion360) to check that the intended 25mm square, 2mm thick wall, box section aluminium was going to be sufficiently strong and stiff. Aluminium may seem a strange choice for a sport where extra weight is usually an advantage but there were two conflicting briefs – when not being used for the race, it was to be used by kids and so needed to be light enough for them to push about. I took the view that we could always add weight for the race.

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Learning to weld aluminium

I was lucky enough to use a friend’s TIG welding setup earlier in the year to make a frame from stainless steel box section. Since I mostly machine aluminium in my workshop, I decided it was time to learn to weld pieces toegther, not just turn them into swarf. Here is my first attempt on a piece of 2mm thick sheet:

It took a couple of runs to get the current set to something reasonable, the early runs being just to the left of the torch. The longer weld is actually joining two pieces of sheet together; the reflections exaggerate the ripples. While this top side looks ok (pretty good I’d like to think for a first attempt), the weld doesn’t penetrate right through for most of the length so a bit more heat is needed next time. There is also some contamination of the weld visible (black holes), probably from something on the edges of the sheets, which I didn’t brush clean. 

Rack and pinion steering

One of my first experiments with 3D printing was a steering rack, pinion and housing for a little project I’m working on. It came out very nicely, in terms of both finish and fit. 

Top view. The ID of the bearing is 12mm. 

Front view, with bolt holes through the housing clearly visible. The rack and pinion are module 3, which seemed about the right size. 

I left spaces into which ball bearings were pressed, one above the pinion on the outside of the housing and one under the pinion inside the housing. 

The key way in the pinion is just visible through the bearing in the photo below. 


And with a 12mm OD stainless tube turned lightly to fit:


I did a couple of experimental universal joints, printing the whole assembly as one, to work out the optimum gap between moving parts:

Before deciding that I actually wanted two universal joints, with an extending section between. A little more time on the CAD and here is the result installed:

The bracket being held in place by a clamp contains two sets of bearings and will be bolted to the stainless box section. This was my first bit of aluminium welding for real. 

A quick test of the steering revealed that the universal joints were not strong enough; I am now working on a new solution. 

Puzzle number 2

A few years ago I made a mechanical puzzle for a friend, with 5 aluminium rings around a cylindrical aluminium core. Each ring had a pin protruding from the inside that engaged in a slot in the core and all each ring was joined to its neighbours so that each could rotate independently but all had to move along the core together. The aim was to remove the core by twisting the rings and it was just a case of mental Continue reading Puzzle number 2