... also, machine rigidity is important but the fixturing of the material is too.
Any chance the material is not absolutely secure ?

Wood is fixed very securely at one point when this first started to happen I even screwed the work piece to the table just to make sure that there was no flex in wood, as for thrust bearing although this was a brand new motor I did check the bearings etc. just again to rule that out, the wood is that you have in that picture was a very soft pine which is not the best of wood but that is what I had lying around as for the other pictures in this thread that is Oak and I have used other woods hard and soft still get the same problem,
Alan

Just a quick update, Gerry asked me if I had machined the wood using the offset option and that I should try the raster option but as I said I was machining using the raster option so today I thought that I would have a go at machining just a dish shape using the offset option and I thought that all was going well until the end when I noticed that I had some horizontal lines at the top and bottom of the dish so I done two more finish tool paths going down a further 1mm (0.03936996 inch) and although it looks better the lines are still there and it just seems weird that the lines run parallel when the part is machined in circles, take a close look at the picture the lines are not that bad now but I have machined the part 4 times to get it like it is now, also what seems strange is that the lines appear at the top right of part and the bottom left the arrow shows the direction tool was cutting. 

To improve the finish cuts, what I have done is to increase the resolution (stepover). MeshCam Art has an option to use Adaptive Stepover, which does result in a better finish cut. However, it also results in an increase in cutting time. I just finished a piece, which is Old Glory flapping in the breeze. The total cut time for that piece was almost 18 hours. But it did turn it pretty nice. I will post a picture later.

the lines are still there and it just seems weird that the lines run parallel when the part is machined in circles

I'm almost certain that this is a mechanical issue.
Looks like your machine is rack and pinion? Check that the pinion has zero play, and check it in several different spots. Are the Drives from CNC Router Parts by chance? I've read of multiple instances of their pinion bushings wearings and becoming sloppy.

My guess is that the probllem lies in the axis along which the red arrow is pointing.

Yes it is rack and pinion and have checked for any play in it but have found it to be spot on and no the drives did not come from them, the arrow is pointing towards the "Y" axis so I will check all racks etc. later today as it is very late now and it is past my bed time and I do need some sleep right now, will let you know if I find anything.
Thanks
Alan

Gerry
I took what you said on board and checked out the rack pinions for wear/backlash and could not find any problems there but I did have on the shelf some unused pinions of the same size but instead of being metal they were made of Glass-filled Nylon so I machine and fitted them and was quite surprised just how quiet they made the machine not that it was noisy in the first place but then came the problem, her indoors you know the one she who must be obeyed needed some help so never got round to finishing yesterday so have finished it off today and set about machining a basic 3D model done the roughing and finishing using the raster option and the same tool for both and was dismayed to fine that I still had lines very similar to the ones in my very first post on this problem but a lot fainter, so then I just decided to do a finish tool path(over the same part) but this time I used the offset option again using the same tool and you can see the result, perfect no problems at all doing it this way so tried again using the raster option but still get lines but as I say a lot fainter than before so I can live with that and just sand those marks away so not sure what happened by fitting the new pinions but it seems to have done the job so now I am very happy .
A very big thank you to all who had some input into this and to Gerry who gave me eventual answer.
Many thanks
Alan

Is your rack and pinion direct drive, or do you have a reduction?
It would appear that the issue is due to the meshing of the rack and pinion.

It has a reduction drive on the machine 4:1 ratio
Alan

Gerry
I am just done another program using Aspire and am doing the roughing cut using the "Z" level strategy and  am using the Raster for finishing cut at a 315 degree angle and so far no lines have appeared will let you know what the result was like when finished, also had a look at the meshing but cannot see any problems there but after I have finished this job I shall take another look just to make sure there is nothing there.
Alan