Problem -- need to drill a 1mm dia pilot hole in a uPVC frame for net curtain hook when you only have a 1.05kW SDS drill to hand. The drill bit is not gripped by the conventional chuck when fully closed, indeed it probably wouldn't grip anything less than 2-3mm diameter.
Solution -- take about 6" of sellotape with carefully cut square ends and very neatly wrap it around the shank of the bit, making a 5mm diameter shank. I was surprised just how well this worked; the sellotape forms a solid shank for the chuck to grip on, and it seems to be very tough as the chuck didn't dent or deform it (may depend on brand of tape). Might want to be careful to wrap the tape such that the rotation direction causes any slippage to grip tighter, but actually I doubt that would make much difference. Obviously won't work if the bit is going to get hot whilst drilling.
Of course, you have to carefully support a large drill whilst drilling, as there's no way a 1mm bit will take half the weight of the drill without snapping.