Thanks Pete,
Ahh yeah I suppose human error is a possibility, my friend is a competent CNC programmer/operator though so I hadn't thought of that. I'm going to set the machine up and ask him to try and replicate the error before I hand over any money. Hopefully that is the case.
I'll check the tool holder for play as well. I suppose it could also be that the tool holder isn't pulling up into the spindle properly because the pull studs not in the tool holder correctly or there's debris in the spindle.
I think it's DOS but I haven't seen the software running yet. The PC has been upgraded and it looks like there's been a USB mod done on the RS232 output from the control box. So it's possible that the control software has been upgraded.
I mainly wanted to make sure there wasn't any common issues with these machines that people new of that could be causing this and too make sure that this wasn't an indicator of a obvious major issue with the machine. But I suppose as you say it could be one of a lot of things.
If it's not obvious what the issue is I'll get some photos and videos when I have a go with it next week and post an update.
Thanks,
James