Finally took apart the 'Clarke' drill today to see what if anything could be done about the wobble in the quill. Turns out the bearings are nothing more than a pair of holes in the casting, each having around 1/4" bearing surface and being maybe 2.5" apart – the chuck/arbor seems rock solid (surprisingly).

I didn't fancy sawing through the casting and inserting a cross-wise screw to tighten the bearings (as some websites suggest) but inserting a 3" ribbon of 2 thou shim steel before returning the freshly greased quill has made an enormous difference; there's no play in it at all and the shim seems happy enough to stay in situ as the drill is used (I've left a good length sticking out the front just in case it does start to sneak inside during use!).

I've only ever used shim for packing up lathe tools etc, it never occurred to me it would work in this way – maybe the tip will help someone else with cheapo-drill-wobbles!

Paul