Just finished building my Mark 2 and I thought I would share my results. First of all, I'm by no means a 3d printing expert but I think the results are pretty good. I have an original Ultimaker 2 but all replacement parts and materials I used are all China sourced.
I used china made ABS filament to print the parts (about $3-4 usd per 1kg roll).
Printed the cone with a mixture of Ultimaker blue PLA (came with the machine years ago) and cheap China made PLA (about $2usd per 1kg roll). Here's a first pic of my results, the first ever dual extrusion print I made. No prime towers so have head oozing where the print starts. This cleaned up ok but thinking a prime tower would have eliminated this.
What I did notice is the Ultimaker PLA liquified (if that's even a word) more when heated to the same temp. So when the blue started to print it would sort of ooze over easily but not the black. I'm thinking adjustment of temperature for this extruder or changing the Z offset might help smoothen it out. Either way I'm happy with the results.
I basically upgraded my machine with China made clone UM2+ type head with the Olsson block and all metal UM2+ type feeder. For about $200usd I got: 2 feeder step motors, 2 complete heads with the bowden tube/all electrical etc..., 2 aluminium feeders, extra olsson blocks, nozzles, bowden tubes, feeder gears, PT100 etc... Just to give you an idea of what this upgrade should cost. I think the only issue I had was with the bowden tube not sitting into the hot end easily but once this is in there wasn't a problem. Maybe also the nozzles aren't exactly the right size opening but I'm no expert so i can't tell the difference in quality. But considering what I paid I think the results are acceptable to me (maybe not to an expert though).
Some things I realized when building the machine and testing is originally I had the feeder up high. (Now excuse the short power wires, I didn't want to spend the money on the expansion board so I just wired it up as is to see the results.) With the feeder up hight, I didn't shorten the bowden tube and as it neared the back of the machine, the stiffness of the bowden tube and filament knocked the head off the magnets. So I decided to move the feeder in the original intended location down low so the bowden tube would be the correct length. No problems now with the head falling off. Also I was able to mount the feeder upside down to get the tension screw facing the right way. Luckily I assumed the Tinkergnome firmware would have the ability to reverse the motor direction and sure enough it did!
I just removed the filament guide and that's the hole I used to insert the wires. I don't even have a second spool yet! I just let it sit in a box on it's side for now.
Once I make sure everything works well, I will probably clean it all up and make it presentable. I'm also going to install dual flow sensors to see how it all works out. But so far great project! Well worth the effort.