Cheers Robin :-)

I should have made myself clearer - the quill is fine (good even which is a surprise) it's the bracket that wobbles (very visibly when plunging). I've already used it to make another one in aluminium which I hope to fit tonight. There is a return spring on the quill which, as you say, could be stronger - I think machining grabby materials could be a problem but there is a lock on the quill I can use if necessary and the idea of a supplementary spring is a good one.

I should have done this years ago, it's converted a machine that was border line useful and a pain to work with into one that has many uses, is fairly accurate and is a joy to use. Turning accurate diameters was always a pain with it but now I can make a test cut, touch off to the measured diameter and press go and the jobs done - within 0.04mm first time.

Total cost for the conversion so far is about £400 - bargain :-)

Mark