Why do I get a taper when turning?

[BillTodd]

Can you support the end with a centre from the tail-stock?

Or, knock-up a tool-post mounted steady; just something to stop the work piece lifting (which can cause the tool to cut deeper as the work rolls towards the tool) and pushing away from the tool.

[edit] have a look at these: http://www.practicalmachinist.com/vb...ghlight=steady

I've checked the topslide movement relative to a test bar and the topslide runs parallel to the bar within .02mm over a 100mm length. Also the run-out of a test bar in my newly ground chuck jaws is less than 0.02mm over the same length.

Have you checked it on the top/bottom as well as the side? Height changes will cause your work to taper.

[irving2008]

I didnt think I could use the tailstock as the part I am cutting is only 50mm long and the saddle is quite large and wont let the tailstock near enough really even with the barrel extended. tbh I've not tried it. Also not sure how centred the tailpost is, I've not tried to adjust it yet.

I'll have a look at making a steady, I have some 20mm aluminium plate that might do the job.