I am using a Bambu X1C with Overture PLA Plus Orange. My bridge test is a 75mm span.
I have tried using bridge speeds of 20, 30, 40, 50, 60, 70, 80, 90, and 100. I do not see any big difference between any of them.
I have tried using bridge flows of 80%, 90%, 100%, 110%, and 120%. I do not see any big difference between any of them.
I tried printing a temp tower and I couldn’t tell any difference between ANY of the temperatures. I double checked an in Orca each section had a different temperature. And all of the bridges were a little stringy.
For everything else, I am using default settings for Overture PLA filament and 0.20mm Standard.
I sort of have the same questions. I’ve done about a dozen tests, just like you, changing speeds, flow ratio, temps, cooling, etc. My bridges print better visually, but if I pluck at the bottoms, the filaments are loose and not stuck to each other.
I’m using Bambu P1S and Bambu Studio with Bambu PLA Matte.
My question is, what factor or parameter affects the filament’s ability to stick to the layer below it? I’m not seeing any sag when I pull the print out of the printer. But once I start to dig around, they are just not stuck to each other.
What parameter might help them stick to each other better?
@thingamajig
Thanks for that. I tried both of those. I used Aux speeds of 0,25 ,50, 75 and 100 and saw no difference.
My issue is a little different than yours but related. Visually, mine looked really good. And if I didn’t touch anything you’d never be the wiser. But if I dug around the bottom, I’d find all those nice and straight filaments were separate and not adhered to each other.
It looks fine and if in an area where strength wasn’t an issue and it didn’t get handled in everyday use, it will be fine. But if it got brushed or touched now and then, eventually those strings would start to start appearing and make a mess.
From a lot of reading I did online, what was said over and over was that, “bad bridges were because the pulled span didn’t have time to cool so the next layer would stick.” My thoughts are that they’d stick better if just a bit tacky or uncooled. Maybe not. It seems to me that the filaments aren’t sticking to “each other” because they have cooled too much. I do realize if the pulled span cools too slowly, then sagging can occur. And that would definately inject a gap so the next layer never touched and could stick if it wanted to.
But, my logic might be flawed. Maybe filaments, bridges or not, stick better if they cool inbetween each other regardless.
The solution is going to be a very tricky delicate balance of speed, sag, temp and flow. Of course, no duh, but I still can’t find a good setting. For now, I just won’t allow bridges over 40mm or so.
I’ve never tried to test a long bridge like that, but it may just be the limit of the filament. The only thing to manage is the print speed, fans and nozzle temps. Sure you can play with flows too, but I think the bulk of your gains are going to come from the main three items.
As far as why they are not adhering well together… that actually makes a lot of sense to me. I consider Z strength in to effectively two categories, a weak physical surface bond or a strong intermingled polymer chemical level bond. To get the strong bond, both layers need to be hot (and compatible plastics), but printing bridges and overhangs are almost always done at slow speeds and with a lot of fan. This basically ensures the next layer will be placed on a cold layer and only have the surface type bond. On top of that, the drooping will likely make that a weak low contact surface bond, which is what you are finding.
That’s not completely how that works. True, bad bridges are generally due to too little cooling, but this causes the drooping. Then, the simple fact it cooled too much for a good bond, then causes the bad adhesion to each other. So, we have two separate problems, but they are related. You need to cool the plastic to make the bridge, but that cooling is a negative for laying the next layer. Ideally, you’ll only have a couple of bad layers before things get back to normal, and you are printing on a solid surface again so its normally not a big deal.
What does that even mean? I’m assuming the bottom picture means to change your print orientation so that the filament will get cooled more directly by the part cooling fan. However, the picture directly above that one seems to say to set the part cooling fan speed to zero, which seems to contradict that advice.
Maybe none of them was the optimal print temperature? i.e. Maybe you need to extend your print tower temperature range. I’ve noticed that even for allegedly the same filament material, filaments from different manufacturers can print at very different temperatures.
They probably are just showing you where the setting is.
On my previous temp towers were very useful but on my X1C they appear to be useless. I asked Bambu Support about a temp tower and they said it was a waste of time and I remember reading the same thing on Reddit. YMMV.
