It's all come together and is now up and running. There is a video of it in action here http://youtu.be/kt5dA0ThEg0
Final build dimensions worked out at 240 x 210 x 120 for X, Y & Z. I could get more Z height by tweaking the bed and hotend mount arrangements but the easiest solution is probably to increase the size of the four extrusion uprights and use a longer leadscrew and rail on the Z carriage. 120mm is fine for me but others may want more.
I've only had it running for a day but it seems quiet, fast and accurate. As soon as I get back on my laptop I will post some images of the completed machine, upload a couple of file changes and additions and post a picture of the finished tree frog from the video. The quality at 50mm/s is amazing.
This is a place holder for my latest project a remix of http://www.thingiverse.com/thing:161000 by ichibey.
I am planning to modify it for core xy operation rather than Hbot.
I have posted my Sketchup design files and some pictures of the build so far.
The Z table is working and seems very smooth and rigid. The leadscrew is 8mm stainless studding and the nut is made from UHMW with a 6.25mm hole tapped to 8mm thread very smooth and seems backlash free. Time will tell. virtually no load on the stepper. The DRV8825 driver is dialled down to virtually it's lowest setting and the chip gets barely warm in continuous operation. I wrote a script that sent the bed from home to Z 155 continually for a day.
X & Y carriages run on 8mm ground rod with 2 LM8UU bearings in each Y carriage and 4 in the X carriage.
The build platform runs up and down on 10mm ground rod with 4 LM10UU bearings in the carriage. I will be experimenting with printed bearings as soon as the machine is up and running.
The hot end will be a J Head bowden with a Greg's Wade extruder and herring bone gears. One of the main drivers for the project was the ease that I could add multiple heads as I want to start playing around with multi-colour and multi-material printing.
Build volume should be around 200mm in X & Y and 155mm in Z and I'm hoping for delta like speeds with cartesian precision. We'll see :-)
I am now waiting for the rest of the parts to ship.