Improving bottom layer surface quality with PAHT-CF

Got my X1-C a week ago and loving it so far. I need to do a production run of a certain part, so the finish is important as it’s something that is being sold, and after testing a few filament types I’ve determined it needs to be PAHT-CF for certain strength/heat requirements.

PAHT-CF has a rough surface, and I need one surface to be smooth, so I have that surface of the model facing down on the smooth high temp plate.
I’ve printed a few tests and seem to be getting a weird “ripple” that I’m having trouble getting rid of:

I started with the Bambu 0.16mm “Optimal” presets for this filament, and a monotronic bottom surface pattern. That had a lot of these ripples.

I switched to a concentric bottom pattern and that smoothed the ripples out pretty well, but there’s an area on this surface with some text and the quality around the text was poor.

Tried slowing down the first layer to 25mm/s first layer and 30 mm/s first layer infill, and changed to a archimedal bottom pattern. The quality/smoothness around the text got better, but the ripples came back in the surface overall. (Pic above is actually of this print)

I’m printing another test right now with the plate temp bumped up to 110 C (default was 100) and first layer thickness increased to 0.25mm as I read that this can improve first layer adhesion. (my uneducated guess is the ripples are where it’s not adhering smoothly…)

Any thoughts or suggestions for settings to tweak from those with a lot more experience printing?

Adding my thoughts here - can you iron just the bottom layer? It seems like the ironing options are all focused on the top layer. I’ve not experimented with ironing at all yet. Would ironing the bottom layer help the underside surface against the build plate? Can it even be done?

Most recent test with hotter bed and thicker first layer was worse, not better.

I am only guessing here as I have not attempted filled filaments, but maybe you’d get better flow and hence surface finish with a .6 nozzle? If your part requirements allow?

Your “optimal” layer height indicates a .4 nozzle which is stated as “possible” but not “recommended” by Bambu.

Hmm good point. Worth trying the 0.6 nozzle…
I was hoping to avoid changing nozzles back and forth between these CF parts and other gadgets I may want to make out of ASA, PLA or PETG (for some reason I was thinking 0.4 nozzle was better for those) but checking the filament guide it looks like those will all work fine with the 0.6.
Is there any drawback with using a larger nozzle size for those other filaments?

Well, your print resolution will go down and settings may not be optimized. But you should get fewer clogs. Not sure how far you can exploit faster overall printing though as flow limits do not neccessarily scale.
But I have no practical experience yet with larger nozzles. Only .2 and .4 to date.

I am getting quite good bottom surface finish. Are you sure yours is 100% dry? Printed on X1C with 0.4mm nozzle, 0.2mm layer height on engineering plate. Dried for 10 hours at 90c in a convection oven. Other than that just pressure advance and flow calibration using Orcaslicer.

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+1 on making sure it is dry. Nylon soaks moisture like crazy. 0.16mm should work, though I prefer 0.2mm with PAHT-CF and similiar, the fibres can make it look weird with lower layers.
Make sure your infill is supporting the top and use a good amount of top layers (I use 6 as default for mostly everything)

Make sure you are not using 100% infill unless you know what you’re doing, that always does weird things.

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Thank you for the replies guys.

I’m glad you brought this up as it’s something I have NOT gotten into yet. But it seems with each test print I do, that finish that I’m trying to improve is a little worse each time… and maybe this is why.
When everything arrived, I removed the filament from the sealed bag it came in and put it straight into the AMS, which is holding at 10% humidity inside. I assumed that was enough to keep it dry. Maybe not?
I’m a bit lost on the logistics of drying the filament. I need to do a big production run of these parts once I get all the parameters dialed in. Like, 100 pieces (can fit 4 on a build plate at a time, and do one print per day with my schedule), so that’s 25 days of printing if I can stick to turning out a batch of 4 each day. I’ve heard mentions about drying certain filaments, but nobody talks about how often the drying needs to be repeated, or how that’s being integrated into a long term production run of parts. Some seem to suggest that they’re drying the filament out before every print. That would add a TON of production time if that’s required.
How often does one need to re-dry the filament?
If the 10% humidity in the AMS is still too much and the filament is absorbing moisture and slowly getting worse while it’s in there, should I consider having an individual dry box for this filament, fed separately from the AMS, and go heavy on the desiccant to try to get it even lower than 10% to prolong its dryness after I’ve done the 10-hour drying process?

100% Infill
I was actually doing 100% infill on these. It’s a pretty thin part; 0.06" thick flange, and 0.1" wall thickness. With my number of top/bottom layers, there was only one layer of infill sandwiched between the solid top and bottom layers on that 0.06" flange. So I just bumped it up to 100% infill figuring that might be a tiny bit stronger, and it was nearly 100% anyways.

“Dried for 10 hours at 90c in a convection oven.”
Juust to be sure I’m on the same page, you’re referring to drying the filament pre-print, not drying the part after printing?

Drying takes place before printing. BambuLab recommends this. I have just dried PAHT-CF myself in a convection oven. However, at a slightly lower temperature and only for 7 hours. I wrapped it up again with desiccant and stored it in the living area.

When the filament is dry, you don’t have to keep re-drying it if you use it quickly enough. It should last two or three days in the AMS without absorbing too much moisture. However, you must also keep the AMS closed. When it is used up, it is good. If the printing results worse, you will need to re-dry.

Hi “The Pass” if you don’t own a drier you can use your X1C to dry the filament

Video on filament drying X1C

Bambu lab drying times and temps for filament

Never assume filament from a store is dry, sometimes it is, but you can’t depend on it

If you are doing many prints and the AMS isn’t keeping it dry enough and you don’t need supports, you can print directly from some dryers, like the SUNLU Filadryer S2. Here are some things to print for the SUNLU to make it work better for feeding filament.

I used the X1C to dry my PAHT-CF yesterday, 90c for 12 hours. When I flipped the filament over around the 6 hour mark it was still going. I had to leave, but came back when the 12 hours were done and there was a message on the touchscreen that said the heating had failed, but no further info. Not sure what that meant.
I put the filament into the AMS and started another test print. I won’t be able to check it until tomorrow, but hoping I see an improvement when I do.

I had a look at some of the filament dryers on the market. I would get one of those in a heartbeat if there was one that worked well for nylon… The PAHT-CF could just live in it, load it up with a ton of desiccant, and run the heater every couple days to keep it nice and dry, and feed the printer directly from that… but it looks like nylon really needs 80-90c to dry, and most dryers can’t go that high. The sunlu S2 goes higher than some others to 70c, but some independent tests say that 70 setting really only gets to about 65, and that wasn’t getting the water out of nylon when they tried it…

I made a modified food dehydrator. Modified with an Aliexpress PID temperature controller. Can reach constant 90c for nylon now. Especially technical filaments like PA absorb moisture in hours. Print quality can turn ■■■■ very quickly. When this stuff comes straight out of the sealed bag it’s usually not dry enough for quality prints.


I like the results with the PAHT filament so much that I just bought another 1.5kg on Black Friday sale. I printed some complex shapes and did dry the filament as specified by BL and I printed using engineering plate and stock X1C settings.

Updating for continuity.

Drying the filament out made a massive improvement in the print quality. After using the X1C to dry the spool of PAHT-CF out, a test print came out WAY better. Still some minor imperfections in the bottom surface, but 95% of the mess I had before is gone.

As it’s clear I need to keep this stuff super dry through the course of long production runs, I ordered a Sunlu S2. It only goes up to 70C, but there seem to be very few options that go higher, and none of them get very good reviews. I don’t have time to cobble together a homebrew solution. One review of the S2 used separate sensors and actually measured it at 75C when it had been sitting at the max 70C setting for a while, so that seemed promising. I did make sure to get the latest version that has a fan to pull moisture out as it evaporates.

The one thing I already really don’t like about using the S2 (and it’s probably equally annoying for any external filament dryer/dry box) is manually feeding the filament each time you want to switch back and forth between the AMS and the S2.

If someone comes out with a decent filament dryer that does 80C+, can feed from the dryer, etc. I’d jump on it.
Heck, what would be REALLY awesome would be an upgraded AMS with a heater. All the benefits of the AMS and you could actually store nylon in it and keep it useable long-term.

Anyways, after drying PAHT-CF with the S2 at 70C for 14 hours a test print came out great.

Now I’m down to just wanting to fine tune things so the surface finish on the bottom layer facing the plate is super uniform.

So far I’ve used the high temp plate for a smooth finish, but that seems to highlight any imperfections. I had tried a test print on the engineering plate back before I figured out the moisture issue, and that hadn’t gone well. Maybe I should go back and test on the engineering plate again. 33dd’s pic looks amazing. Wondering how much of that is the difference in plate, and how much of it is in the settings he mentioned playing with in Orcaslicer. I’m using Bambu slicer.

Did you ever figure out what caused your bottom layer to look like that? I’m noticing similar issues on a large PAHT-CF mold I’ve been trying to print. The rest of the part comes out fine, but the bottom is hella ugly.