Printed the Z motor mount bar clamps & end-stop holders and finished the mechanical assembly, wired up all the axis motors, end-stops and ran a quick functional test to see if everything was working as expected, apart from a few firmware tweak’s it all did, once again buoyed by this success I rushed headlong into stripping down the Darwin and fitting the ABS extruder mechanism & Parcan hotend onto the child printer.
In less than a few hours I had hot plastic coming out the hotend and was ready for a first print, went for the widebar just to see if I could get anything resembling a decent print and to my surprise the first layer came out almost perfect, I was still printing with PLA at this point and decided that before I calibrate (yes I rushed into printing without calibrating first, not recommended!) that I would switch to ABS.
ABS requires the hotbed that was still currently fitted to the Darwin, stripped this of the Darwin and removed the Prusa’s build plate (I used a 6mm piece of MDF for this as I had some handy) drilled mounting holes and fitted the hotbed to the Prusa build plate.
Refitted the Prusa’s build plate and ran my first attempt at printing ABS on the newborn child printer, after a few unsuccessful prints of the widebar (unsuccessful due to the ABS not sticking to the hotbed) I had my first failure.
I had melted my beltclamps! Due I guessed to the fact that PLA melts at a very low temperature compared to ABS and the MDF Prusa build plate was getting too hot.
Stripped off the build plate and stuck a sheet of aluminum foil to the MDF underneath the hotbed, I also doubled up on the PLA belt clamp’s to effect a bodge until I can print some ABS belt clamps, remounted the hotbed (a little higher this time to give more space between the build plate and the hot bed) and tried again.
Several failed attempts later I decided it was time to investigate “ABS not sticking to hot bed” on Google, after reading lots of potential solutions I found that lots of people were recommending that you dissolve some abs in acetone and prime the hotbed with this before printing.
Bought some acetone (nail varnish remover) tried to dissolve some of my ABS in it to no avail the acetone did not seem to touch the abs after several days I was starting to think that I was not using abs at all and that maybe this was some other sort of plastic filament (don't forget I had been gifted the 2 rolls of feed plastic with the Darwin and so I was basically guessing at the actual materials composition)
After several more failed prints and me getting more frustrated at the refusal of my ABS (if it is ABS?) to stick to the hot bed, I was rapidly trying print after print tweaking the 1st layer height mechanically by adjusting the Z end stops position and noticed that I could peel the failed partially stuck print off the hot bed whilst it was still hot and during one failed attempt I also noticed that if I rubbed the hot failed rolled up ball of ABS across the hotbed it seemed to leave a trace of ABS behind.
In a flash of inspiration I decided to cover the whole hot bed with a second layer of Kapton tape and use a piece of failed ABS print like an eraser across the whole build surface, to my surprise (and relief) this seemed to do the trick.
I discovered that if you use a blob of ABS like an eraser, rubbing it rapidly and fairly forcefully (not to forcefully as you don't want to break the hot bed) it leaves a trace of ABS behind essentially misting the whole surface with a fine layer of ABS.
This seems to aid the first layer in sticking to the hot bed greatly and allowed me to move onto calibrating.
During this second round of ABS tests I also managed to partially melt my X carriage, powered off everything and rapped the entire x carriage in aluminum foil and kapton tape in an effort to avoid the need to print another x carriage.
This appears to have worked and so far I have had no more PLA dripping onto the hotbed!
20/07/2012
Calibrated the E-Steps per mm today (in my lunch break) and discovered that it was pushing out 12mm more feedstock than it should have been, seeing as I am using 3mm feedstock and have a 0.5 mm hot end this means that over 100mm of input feedstock I was extruding approximately 68mm worth more output plastic out of the hot end than I should have been, demonstrating why calibration of the e-steps per mm is so important.
Can’t wait to test this tonight , hopefully I will be able to achieve my first successful ABS prints, and just in the nick of time before I melt my PLA X carriage.
First prints will definitely be an ABS x carriage and some ABS belt clamps, shortly followed by ABS X idler & motor mount ends (I have noticed that my current PLA ones flex some considerable amount) in fact I may just print a whole new set of parts for the Prusa just in case of failures.
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