ATM how to get rid of an ellipsiod?

["Arjan te Marvelde (ELN)" <Arjan.te.Marvelde@eln.ericsson.se>]

List,

I have been polishing my 10" f/6 plate mirror for a while now, and it is about polished out. I cannot focus a 500W filament on the surface anymore, and can see no pits either. It looks all very nice, but there is one thing i can't get rid of: from the center towards the edge the ROC gradually shortens. On a fixed source tester the 95% zone reads 5mm shorter than the center zone. I guess you would call this an ellipsiod. (It is very smooth though!)

I'm doing almost exclusively TOT and 1/3 COC. Before starting i heat up the lap and mirror in warm water, and press with mosquito screen. During polishing i press shortly once every 15 minutes or so. The channels have closed a while ago. Drag is increadibly high; often i need to use my full 170 pounds to get the tool across.

Yesterday i tried extending the strokes up to 1/2 COC, but that has caused the previously spherical center to become elliptic too.

What should i do to get to a sphere? Instead of lowering the edge, should i concentrate on deepening the center?

Thanks,
 ... Arjan te Marvelde