I made the decision at 4 am. Or perhaps a little after, in fact. Lying awake in bed I realised – with the startling clarity than only predawn ratiocination can bring – the project on which I had been spending every free hour for more than four weeks was a disaster. Well, not a disaster, but it didn’t meet the criteria that I had (retrospectively!) laid out for it.

So rather than going on, it was better to stop.

It was ironic. Every single aspect that I had expected to cause problems was working superbly. The belt tensioner, the blower mount (which had also become the new right-hand engine mount), the intercooling and the engine management. Even the hybrid control system had coped with the increased engine output like it was, well, made for it. There was no detonation and the standard injectors had enough capacity to flow the required extra fuel.

In short, the positive displacement supercharger that I’d fitted to my ’99 Toyota Prius – making it the world’s first supercharged, intercooled, petrol/electric car – worked brilliantly.

Except for one aspect.

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I bought a metalworking lathe the other day. It’s something that I’ve wanted for years, but now the purchase has occurred, I am filled with trepidation. Why? Because I know nothing about metal turning.

I first decided that I really needed a lathe when a few years ago I was building a small wind generator. The design was based around a stepper motor salvaged – I think – from a printer. The impeller comprised the blades taken from a plastic fan. But when I came to match the two up, the shaft of the stepper motor was much smaller than the hole in the mounting hub of the fan blades. Easy solution? Well, there would have been if I’d had a lathe: just turn-up a bush with the right internal and external diameters. But without the lathe, I was forced to scrounge for tubing that had just the right wall thickness. In the end, all I could find was the plastic barrel from an ink pen – hardly a good choice for long-term strength.

Then, when I was building my electric bike (series starts at Building an Electric Bike, Part 1 ), I needed a lathe like no other tool. I was making an assembly that would couple the electric motor’s shaft to a roller that would bear on the tyre, so transmitting the torque. I kind-of had the shaft, but the roller part had to be a larger diameter. I stuffed around drilling-out old sockets and the like until I had something that could be force-fitted over the shaft. Of course, the thing turned out eccentric, and so ran with a wobble that in fairly short order destroyed the bearings. I ended up paying money to small machine shop that turned-up a beautiful, knurled roller/shaft assembly. The skills to machine that (and to silver-solder on a splined section of the original shaft) were beyond any beginner, but still, if I’d had a lathe, I would have been ahead from the beginning of the project.

And then there was the fitting of a supercharger to my Toyota Prius. For that project a lathe would have been more than handy at least a number of times. Firstly, part of the bracket had to stand proud of the surface to which it was being bolted. Needed was a bush of exactly the right length and internal diameter – length, so the plate sat flat; and ID, so the bolt passing through it was subjected only to shearing forces and not bending. (The bush would be welded to the plate.) But without a lathe, I was reduced to grinding-down an oversize and over-length bush that I found. Secondly, while I was lucky and the original supercharger pulley turned out to give the desired boost, during most of the development it was odds-on that a new 3-rib supercharger pulley would be needed – another use of the lathe.

The lathe which I didn’t have.

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