Printer calibration, help!

Hello all,

I borrowed a gen1 reprap mendel prusa from my friend, and i've been trying to calibrate it to do good prints. so far i've had good progress after reading countless webpages, i've had belts tightened, replaced some cracked parts by printing, and levelled the bed (although it appears I need to check the printbed alignment once in awhile for some reason).

I'd like to find out about two things:

1) how do I calibrate the extruder? slic3r says to extrude 30mm, measure the amount of feed divided by 30mm, and multiply by 21000.

Amount fed/30mm * 21000 = XXX

and then i'm supposed to input XXX into configuration.h, and update the firmware on the microcontroller. i'm familiar with arduino systems but i'm not sure which microcontroller I'm using. The one i'm using is the same one as they use at Romscraj. could anyone help me out here?

For now what im doing is using cura, and i basically increased the filament diameter until the prints turned out somewhat ok. but when I use that diameter to print large prints, that's where the problem starts.

2) one of the reasons why I find I need to check the alignment every 2 prints or so is because the x-axis bars seem to not be parallel - i think it's something to do with the fact that the right side linear ball bearing is a bit wonky - anyone know where I might be able to get a replacement? Also, the X-axis support guides (the thing where the stepper motor is attached to) have a little bit of sideway wobble, causing my x-axis print to have some alternative layering. Anyone can help me out here?

BTW, I purchased a bunch of filament from Romscraj, and it rocks. Before this I was using my friend's leftover filament, and it had horrible print quality. I was running out of it so I went to romscraj, and lo and behold the print quality suddenly just skyrocketed.

One last qn, i'm thinking of building myself a mendel prusa V2 in the future, i'm probably going to get the kit from romscraj, but i'd like to print the parts myself. Where may I get compatible print files?

github romscraj if you want to use romscraj files.

you still need help ??