I have read everything I can find on using XT-CF20 on this forum and I'm still not getting good results. I've been printing with carbon filled PLA (inexpensive SUNLU brand) up to now and getting good results - i thought I'd upgrade and try using the XT-CF20 since it seems to be well regarded and should be stronger, but so far it is unusable. I'm using a titan aero, a 0.4mm plated copper nozzle and slicing with S3D The main problem I'm having is sag - bridging sags and even fairly modest less than 45 deg overhangs sag. When I speed up my bridging there seems to be no happy medium between breaking the filament and having it sag. even worse sometimes the bridging performance is wildly inconsistent on the same print with the same settings! Then the well documented problem of ooze material building up on the nozzle. I've improved this by reducing extrusion multiplier and some other things but nothing really solves it. I've also been getting softer corners than with PLA CF. the setting ranges I've been playing with are: retraction 0.8-1.2mm retraction speed 30-40mm/s print speed 40-45mm/s with slight reductions for perimeters. extrusion multiplier 85-100% bridging speed 130-140% bridging extrusion 90-130% linear advance K40 acceleration 500 X and Y jerk 8-12 cooling fan 0-60% with 100% on bridges nozzle temp 230-245 (230 works best so far) bed temp 60 S3D profile is attached to this post nothing I've tried so far really has much clear effect. The test prints are all slightly different but not in a way that sensibly correlates with the changes I've made... it just seems like this stuff is uncontrollable. strangely I've not been getting any stringing, which I would expect to given that all the other problems indicate an oozing and overly liquid filament. any suggestions?
With XT-CF20, a 40 mm/s print speed is the recommended print speed, but you might find you get better results by reducing the print speed. In terms of the part cooling fan, 50% is the recommended speed for XT-CF20. I'm a little concerned about the uses of a plated copper nozzle with XT-CF20, XT-CF20 is an abrasive material and will cause wear to the internal nozzle geometry which will result in loss of accuracy of prints and will provide dimensionally inaccurate prints. When using abrasive materials you should be using either the Hardened Steel or Nozzle X Nozzle. When dialling in bridging performance it is best to use a bridging torture test, this will allow you to compare settings such as part cooling fan speed, and extruder temperature, and be able to test what setting gives your setup an optimal performance. I can see from your settings that you appear to have tried faster bridging speeds and extrusion have you tried using lower values?
I used a hardened nozzle for ages with carbon filled PLA but found it prone to jams. The plated copper nozzle has not jammed yet and I have printed about 1.5kg of CF-PLA on it with no signs of wear so far. The plating on the copper nozzle is the same as on the nozzle X. Anyway the plated nozzle performs better than the hardened one and if it wears out eventually that's still OK. It could be that the XT-CF20 is more abrasive than my regular CF filled PLA but I don't see any indication that it is. Maybe I should change back to the hardened nozzle just to rule out nozzle wear as a possible factor. I have not tried bridging at speeds lower than 100% as I can't see why that would help with sag - quite the reverse. I have tried lowering the extrusion rate on bridging to stretch the filament more but it doesn't seem to help, just makes it more prone to breaking entirely. Lowering the bridge movement speed it just about the only thing I haven't tried at all - can anyone explain why it might help? I guess it is worth a try. I'm don't think setting my default speed to 40 instead of 45 will make much difference given that much of the printing is already at 40 or a little less due to the perimeter and fill percentage reductions. I will try it though. Maybe it needs to go even slower. I've tried fan settings from 0-60% with increases for bridging and quick layers with little effect on results other than perhaps better layer adhesion at low settings. Given that fan and duct performance varies widely it's hard to take a specific fan setting seriously. I have so far only printed test cubes with overhang and bridging tests as I didn't want to waste the incredibly expensive XT-CF20 on failed large prints. I can get the XT-CF20 to bridge 5-6mm no real problems, but I need 14mm and it sags too much at that span. The cheap CF-PLA does it near perfectly. The XT-CF also sags on the edges of overhangs even at modest overhang angles, I thing this is exacerbated by the blobbiness as the overhang allow a thicker bit of extrusion to form perhaps...
I believe that the idea is to extrude slowly and with the most fan to cool the material “in place” before it saggs while bridging.
