Printing an awkward ABS-PC fireproof (V0) filament
Printing with RS PC-ABS Firewire (RS Components part number 174-0062).
Had great difficulty printing this particular fireproof filament on the MK4. Even with a brim, the print would warp, lift off the bed, and fail. And first layer seemed inconsistent. The part was a simple flat bezel, only a few mm thick.
Printed and fitted the Mk4 Fan draft shroud https://www.printables.com/model/465185-prusa-mk4-fan-draft-shroud/ from printables; made a huge difference for this particular filament. Warping reduced so much that we could even print without a brim (although we did leave the brim on).
And I think the inconsistent first layer may be because the levelling is done with the nozzle at 170°C - this filament is still fairly stiff at that temperature and I suspect that was ever so slightly increasing the first layer height.
We'd bought the MK4 for the office on the strength of how well my Mini+ had printed this same filament and parts previously. It was a bit concerning when the MK4 couldn't!
Must note, standard ABS filament printed perfectly on the MK4 anyway. It was just this unusual fireproof one which really didn't like the extra cooling gusts from the printhead fan which the added fan shroud re-directs.
RE: Printing an awkward ABS-PC fireproof (V0) filament
Just finished printing multiple pieces using ABS Fire Retardant material. The challenge was reducing warping to a minimum which translated into getting a good first layer firmly attached to the plate and controlling cooling thereafter. The item was approx 1" x 5" x .33" high... aka a thin chocolate bar in shape. Difficult geometry made it particularly challenging and supports were required to handle overhangs at each end and beneath portions of a recessed bottom layer.
Here is what I found gave acceptable results:
1. Used smooth PEI sheet. Satin was not working re first layer. Sheet cleaned with IPA initially and then washed with warm water, 3 drops dish washing detergent and green abrasive pad. Dry thoroughly. Apply 3DLac and let dry on plate. After printing, let cool at room temperature and then remove printed items with distilled water and spatula of sorts. The distilled water works better than IPA as it softens the 3DLac which is water soluble. After printed items removed from plate, spray distilled water on plate, wipe entirely with disposable cosmetic rounds. Reapply 3DLac and let dry. Repeat. You can do the warm water/dish soap wash again after a couple of runs. I would say that the smooth PEI sheet, the wash routine and the 3DLac are all vital. Without this routine you will go in circles with the settings etc to no avail. No twidling with settings will the avoid plate prep routine.
2. As far settings go, they really only matter if you can see the first few layers going down and staying down. If you don't have the first layer(s) firmly in place, abort, clean and start over. I sliced with Prusa Slicer and set a 10mm brim and a draft fence equal in height to the item being printed. Elected ABS Generic. Once the first few layers are printed and staying in place, the next most important thing I found was cooling. After various variations, I turned off the print fan completely. Here is what I had noticed... this print was about 3 hours long... with the print fan set to zero, I watched the print and found that after about 2 hours and 40 minutes the print would begin to warp. Did a couple of runs and I noticed that the print fan would come on even when set to zero. Within 1 minute of the fan coming on, the print would begin to lift at the corners, like clockwork. I found that using Prusa Connect and checking the Telemetry (the window is only about 10 minutes long with a single 10 min roll back) that the fan was coming on just prior to the print warping. The fan was only coming on for a minute or so... just a nice bump in the graph but the cause and effect was pretty obvious. Like bloody fingerprints at a crime scene. Frankly without the Telemetry I would have perhaps never figured it out. Soooo... what to do. Why was a fan set to zero coming on and triggering the warping. I tried various ideas without much success and then chatted with Prusa Support. They suggested a variety of things to try and during one of the chats, the Prusa agent said that the fan can still come on when set to zero unless you also set the "Bridges fan speed" to 0% or near 0%. This setting is at >Filament Settings > Cooling > Fan Settings : Bridges Fan Speed. I subsequently set "Bridges fan speed" to 0%, set up a print on a sterile PEI plate with 3DLac applied, triggered the print with Prusa Connect and watched the Telemetry and the print like a hawk for three hours. Three long hours, no fan, none at all. Warping was reduced down to about .5m in two corners which was within the precision needed.
I have also noticed that the bed levelling routine seems to run at 170 whereas the ABS was set for 250-255. I found that the nozzle sometimes had hard ABS residue around the end of the nozzle and the printer would report nozzle cleaning failures. I settled into a routine of preheating the nozzle to 250 and cleaning it before beginning a print to avoid this.
Last but not least... something I have not figured out... I printed on MK4, XL and MK3S+... consistently the MK3S+ warped the least!
Another hunch I tried was to print two items at a time on the XL, about 1.5 inches apart. Warping was further reduced. I attributed this to perhaps cooling between layers is spread out. Just a guess.
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RE:
Our bezel print was only 2mm thick, much simpler than yours, and the generic PLA settings have the part cooling fan off for a print so low, so we got lucky there. We were wondering if we'd need to try a bed coating; but once the hot-end cooling fan shield was printed and fitted, the results improved hugely. Might explain your Mk4 being worse than your Mk3? Without it the fan makes quite a breeze to the build plate. And we noticed that it was primarily the right and front edge of the part which warped first which lines up with the fan.
I can see me searching out your post in the future when we need to print larger ABS fireproof parts! And making it a habit to carefully manually clean the nozzle before starting ABS prints.