The reason it won't thread is probably because it's a crap tap, can you borrow one off someone ?
A problem I've noticed with cheap tools is they aren't always the size they claim....I remember drilling the last hole in a big expensive job 18mm instead of 17.5mm caused me no end of trouble...New glasses fixed it ;)
Thanks All, new expensive tap it is then, dont like borrowing tools (sods law it will break) and its not like I'm never going to use it again. The quill must be tougher than I gave it credit. Did a trial run with the 7mm hole in some Al and it worked fine, a bit loose even.

M8 thread with a 1.5mm pitch?

I've been tapping a whole heap of holes for my recent CNC build. For an M8 thread with the more common 1.25mm pitch, a 6.8mm hole is the norm (you sure it's a 1.5mm pitch? as this might account for why your tap is getting stuck!)
Im going to have to take a note pad out to the workshop as it appears my memory is useless.. yeah the tap is 1.25 pitch

Thanks again and sorry for the duff info

With the stalemate on the quill I've been looking at the X-Y table, bit concerned with the flex in the 22mm rails and skate bearing arrangement on one side, and then making up some sort of T slot table.

For £80 I can get a cast iron compound table (not as big as I would have liked) or I can use some of my THK rails, but still need to sort a table.
Is 8080 extrusion ok for a table if the rails are bolted to it? Still want it to be as cheap as possible but realised that cutting corners still costs in the end.lol