I power on the printer for the first time and set up the Limit Switches, Axis Movement, End Stops, Bed Extents, Bed Levelling, Z Probe/Bed Sensor and do the Extruder Calibration!
I spent quite some time going through the Marlin documentation to see what each possible configuration instruction could do. I had already done a very basic run through of the Configuration.h file in this video/post but now it was time to get it spot on.
One side benefit of the exercise is that I can see I will need to change the way I mount the heated bed. Most importantly the nyloc nuts sitting on top reduce the Y axis extents by nearly 25%!!!!. But secondly the ply wood under the bed allows the nuts to squash the edges down too much, resulting in the opposite bed bend to that I had before! Still, good enough for a first print 😉
Aside of being careful to keep everything lined up, parallel & square the build of the Z Axis, mounting the Y Axis and putting all the extruder and hotend parts on was pretty simple and in line with the official Prusa Manual.
Really the only thing I had to find a solution for was mounting my lead screw nuts. Toms version uses 5mm threaded rod and he provides STLs for parts to hold a M5 nut for that. The original MK2 looks like they use their own lead screw nuts. The ones that came with my lead screws had their mounting holes too close together and there was no way to centralise the nut in the Z carriers. I customised Toms Z nut holdahs to do the job – which it seems to do fine.
I will say this though, after building it all I examined the extruder to “sanity check” it and it turns out that it was very tricky to feed filament through the extruder and into the telfon tube running to the hotend. I will do an extra post discussing that as I think it is a mis-match between the extruder body design and the commonly available MK8 hobbed gear. I think if this was left unchanged, apart from having to use tools to get it to feed in, it would put a lot of load on the extruder stepper just to overcome this tightness.
I would also recommend that if you can squeeze an extra £20/$30 to get a Z axis frame laser cut – do that. It will save you a lot of time and insecurities about the Z axis being parallel and square. My wood will probably work fine, but it’s just a lot harder to make sure it is correct.
I thought this part was going to be simple – all pretty much in line with the Original Prusa Build Manual. There were a couple of complications though, one minor and one slightly major 😉
The minor one was that the left side X Axis ABS part was modified by Tom in his build to take the limit switches included in his, and my, parts list. The only snag is that the ABS is quite thin and has to act as a threaded part as there is not enough room on the back for a nut. I expected that the screw itself would cut the thread OK, but it started de-laminating so I had to drill and tap it. Not a major issue.
The slightly bigger job was I had to cut slots in the front (from front of printer) side of the extruder carrier to be able to thread through the tie-wraps which secure the bearings in. The idea is that they pass through hollow channels designed into the part but mine were bunged up with infill.
That last one is definitely worth checking before you start – its quite a lengthy job to do it “carefully” if you cant push them through.
Other than that – this section is simple and quick.