so i had a problem with plastic building up over the top of the nozzles, i think i have found a rather convoluted solution :)
I have a 4mm ID brass tube that i have stuffed a PTFE liner into that was 4.05mm OD and 3.2mm ID.
this is then pressed into the top of the nozzle, this was drilled out to 4.72mm the brass tube has a OD of 4.85mm so its supposed to be a tight fit. (this theory is great, execution was not so great the hole ended up too big and i had to cross drill and pin the brass to the nozzle the first one. this was done to so the hole only just hit the brass tube and did not Perice the ptfe liner (no i am not that good,i was lucky very lucky) .
This brass tube that sticks up 20mm up from the nozzle was still getting hot enough to soften the ABS, and the problem is now 20mm higher, as i have a Aluminium carriage plate i thought that would make a bloody great heatsink, i already had a fan on it to keep the stepper motor cool, so the plate would be well below 105'c (the point where ABS gets soft). I made up a little brass lump that i pressed into the aluminium plate that has a hole to suit the brass tube, this now keeps the top of the nozzle at about 50'c when no fan is on and the unit has been soaking for an hour or so. with a fan i think this will be a viable solution.
Its 15mins since i typed the above line and it seems that a 0.25mm nozzle is just too small for my extruder.. I have come to this conclusion by drilling out the 0.25mm nozzle to 0.4mm and the plastic is flowing nicely again. i cleaned the nozzle before i drilled it but it didn't help. but a bigger hole fixed my stripping issue, i maybe able to re-visit the idea of 0.25mm bolt once i get all the other problems sorted out... I will be bench testing this setup for a while before i go and bolt it all back up and attempt a print, i wonder if slic3r supports 3 materials with 3 different nozzle sizes?