Tapering and runout on a SIEG C1 lathe

Hello all,

I have a SIEG C1 Micro Lathe

which I bought from Axminster a year ago, although the lathe itself doesn't see heavy use (perhaps, say, once a month?).

Recently, I've discovered 2 problems while turning. The first is that my work is tapering, with the diameter being larger near the chuck. I've run a clock along a test piece and have found that there is a

0.15mm deflection across a 55mm length, giving a 0.3mm change in diameter. The second is that if I place the clock on the work near the chuck and rotate the chuck, I find I'm getting deflections between 0.03 and 0.15mm, but they don't seem regular - the needle looks like it's deflecting randomly.

To take these measurements, I put a 10mm diameter, 100mm long mild steel rod in a 4-jaw chuck with about 60mm protruding and got it running roughly true. Then I started taking light cuts across the protruding length (touching on and feeding across). A clock was then used to take the readings.

The lathe itself is just sat on a stand (seen here

is not fixed to it at all.

I can't say for sure when these problems started to happen, because it's only recently that I've started to actively watch out for them. I have a hunch that the tapering started quite recently when I removed the lathe's 3-jaw chuck to try out the 4-jaw chuck that I had just bought. But as I said, I really couldn't say for sure.

As a novice, I'm not sure whether these defects are ones which I can fix myself or if they're serious problems with the lathe. I was wondering if I could get some advice regarding these issues?

Thanks

--Amr