Due to a series of mistakes and disasters I have already broken my new extruder head
I made a couple more pulleys using PLA, but then decided that the barrel was too short and tried to remove it. Moral of the story, don’t try to remove a nozzle from a barrel after extruding plastic through it.
The first extruder head that my Dad made for me a while back had a number of pitfalls
So my Dad kindly offered to make a new and improved version based on some specifications and designs that we came up with together.
Rather than try to drill a 0.5mm hole I bought an already fabricated nozzle. Quite a few companies make these now specifically for reprap printing machines including Makerbot, ReprapStores, MakerGear and ReprapSource.
My Dad turned down the nozzle to a round insert that could be put directly into the aluminum heater block. The other addition was a PTFE thermistor clamp to hold the thermistor on using two m3 screws rather than glue.
For some reason my Y Chassis started to stiffen up such that the leadscrew would pull out of the silicone tubing attaching it to the stepper. Although I managed to get it working again with the leadscrew, I figured that this would not be much good when I upgraded to belts. There were a couple of other niggles I had with the design, so I decided to redesign and rebuild the chassis. This time rather than using fixit blocks to act as clamps I decided to go back to the tried and tested aluminum angle design.
Since the build surface is raised above the chassis using PTFE stands, I didn’t need to do nearly any counter-sinking of holes, as before.
All the OverlapStrap drawings have been updated to reflect the changes.
By the way, If anyone is wondering what the big red thing is on the bottom of the bed its a huge 600W, 9″ Silicone heater for my heated bed. I will blog more about it when its finished but here is a sneak peak
Giles Bathgate 
