The dyno roller starts off with a raw hunk of K1045 steel, 460mm in diameter and weighing 400kg. Some people turn down each end to form stub axles, but in my case, the shaft is quite long so this is not feasible. Instead, the shaft will be made separately and shrunk into the lump.
Next, the shaft was turned up. By design there’s almost 0.1mm (4 thou) interference between the shaft and the bore!! How the hell are we going to get this puppy in? With extreme heat and cold of course. As the ‘hot’ shaft set a bath of liquid nitrogen furiously boiling, I started heating the lump with a very large blow torch. After 20 minutes, the boiling stopped, signalling that both liquid and metal were at the same temperature: -196C or -385F.
But the lump still needed lots more heating before there would be enough clearance between the shrunken shaft and the expanded lump to safely insert the shaft. The time came to insert the shaft – a tense moment: if we hadn’t got it right, the shaft could sieze part we down creating a very big headache. After shaft and lump were united and allowed to equalize with ambient temperature, they were as good as one piece of metal.