PC-MAX Problems

I have been printing with PC-MAX. Love the strength of this material.

After several successful prints using Cura, I am suddenly having problems getting through. Seems to be messing up on the infill and support in particular. I tried with this print to slow the print speed for the infill down to the same as the shell. But it didn’t get very far at all.

Does this look like a nozzle issue or a filament tension issue? Any thoughts on what to check?

It could be a retraction issue. Too much retraction can make the hobbed bolt grind into the filament.

I think it was just the tensioners on the filament. I tightened them up a bit, and now it seems to be working fine. Not exactly sure how tight they should be, seems like guesswork. Should they be tightened to like half the width of the uncompressed springs? More? Less?

I have about 7 or 8mm between the washers on mine, never had a problem with them. I’ve had filament get chewed into by the hobbed bolt but it was primarily caused by other factors such as true 3mm (not 2.85mm) filament which doesn’t travel through the extruder well, too many retractions in a small area, trying to print too fast at too low a temperature etc.

From the looks of it, I also get the impression, judging from the perimeter and the skirt, that you need to check your bed level and the flatness of the PEI sheet.
The perimeters have squeezed and loose runs all around. The skirt the same. It is like the nozzle on its path, runs over hills and valleys.
The infill, being right in the middle, seems to be suffering mainly from the bed level. It is like the nozzle is running on top of a bowl in that area.
That all said, I believe your PEI sheet has suffered a lot and now you should probably be looking to replace it.

Thanks Mikronano. The PEI is actually only a couple of weeks old. I think what you are seeing there is that I did not clean off the PVA very well. Although, I admit I did not do a very good job of mounting the new PEI. Even though I followed the instructions to the T, and I put a lot of elbow into working the bubbles out, and it looked good when I was done, a number of bubbles between the PEI and the glass subsequently developed which is making it uneven. My first try at replacing the PEI.

Not sure if I can throw it back in the freezer, pull it off, and try remounting it again. Would that work?

At any rate the subsequent print after tightening the idler retainer thumb screws worked perfectly, so I think that was the primary issue.

You’re welcome. I’m glad it did work after all for you.
Just out of curiosity: how well the PVA is working for you with the PC-MAX? I never had much of success with that glue and that is why I switched to Wolfbite Mega and it’s really good. And, yes, it works on the PEI.
As for you question about removing and re-attaching the PEI sheet, I don’t think it would work, no matter the method. The 468MP double-sided tape is quite strong and temperature resistant. However, even the slightest attempt to detach the objects, render the tape practically unusable. And that is one of the main reasons why we can never put the bubbles back down! Once they form, they only get bigger!
I don’t know the thickness of the PEI sheet you just used but, one way, to address the bubble issue, is to use thicker than the stock sheet. PC-MAX is really strong and when you are able to make it stick very well on the PEI, then the “warping” stress is transfer between the PEI and the borosilicate, attempting to pull the PEI off the glass. The only thing keeping it together is the 468MP. When the bed temp is close to 100-110C the 468MP is still good but is also softened. A strong pull from the PC-MAX, a softened 468MP and a thin (=very flexible) PEI sheet results in bubbles.

Hope I didn’t wear you out with all the above :slight_smile:

No, didn’t wear me out at all, this is great info, and totally relevant. I have been buying the stock PEI sheet from the Lulzbot store. Where would I get thicker sheets of PEI?

:slight_smile: I’m glad I could help you.
Well, depending on where it’d be easier for you, you can find it on both Amazon and McMaster-Carr. A couple sizes you could look into are the 0.04" and the (thicker) 1/16" (0.0625" or ~1.6mm). With the latter, you might need to give just a little bit more time for the bed temperature to reach its set point on top of the thicker PEI. It’s not a big deal and it’s totally worth it in the long run.

OK. Ordered some .0625 PEI. Do you mount the 468MP to the PEI first, and then to the borosilicate? Or the other way around? Any tips on how to get it all together without any bubbles?

try this link for ideas:


Thanks. This is way more detailed than the instructions that I’ve used in the past.

I did not know you were supposed to bake the PEI before adhering to the glass. Any idea at what temperature you are supposed to bake it at? I don’t see it specified… If you order PEI from Lulzbot, is it pre-baked?

These are, indeed, very interesting and detailed instructions but I honestly don’t think that apply to all end users, as a whole.
And, most of all, according to these instructions, the PEI sheet comes with pre-applied double-sided adhesive tape, which is not very common when you buy thicker PEI sheets.
The most important details I’d keep from these instructions are the baking and the way to detach the adhesive protecting sheets.
The role of the baking is to ensure that there will be tiny, if none, traces of moisture content in the sheet. It’s a plastic sheet after all. And this is important because we would not want to trap moisture between the PEI and the glass that will turn to steam when we heat up the bed and expand and create bubbles and mess things up. A baking temp of about 80-90 celcius (180-190 F) should do the trick.

Personally, I usually apply the 468MP to the PEI first because it’s the hardest “couple” to get together. I like to go crazy pushing down the 468MP on the PEI because I want to make sure that I’ll get all the best and uniform application. After that, I attach it on the glass where the 468MP bonds extremely well and easy. Lately, I replaced the glass with aluminum for temperature uniformity but that’s another story!
In any case, please pay attention when you remove both 468MP protective sheets, especially at the edges. The tape is soooooo thin, fragile and flexible that some times it sticks at the cut sides of the protective sheets and when you pull them off, the tape gets also pulled at the edges and gets damaged and usually… unusable.

I have attached the 1/16th inch PEI to the bed, and reattached the bed to the TAZ. I now need to set the z-offset to compensate for the additional thickness of the PEI. Are there instructions somewhere on setting the z-offset? I understand I can set it in the LCD under advanced settings, but how do you get the TAZ to move the head to the z-offset value? I tried entering M851Z-1.00 into the g-code window in Cura, but the head doesn’t move as suggested elsewhere, it just echos back.

Made up a method to set the z-offset since I couldn’t find any documentation.

Created a big rectangular object, 200x200x 2mm thick.
Pulled the filament out of the nozzle using the usual method.
Set the bed temp in Cura to room temp so it wouldn’t get warm during the procedure.
Placed a folded sheet of paper on the bed (folded paper = .2mm thickness).
Started the print of the rectangle.
As it was printing, I adjusted the z-offset in the LCD advanced settings until there was some friction between the nozzle and paper. Checked on all different parts of the bed as the nozzle moved around.
Rounded this setting to the nearest tenth and set this as the z-offset.

I have now started a print on the bed with the thick PEI. Seems to have printed a good first layer. We will see how it turns out. :slight_smile:

Worked pretty well. This is an extra long part, 12.5 inches printed diagonally. It lifted a little at the ends, but at least it didn’t pull the PEI off the bed as shown in this thread - https://forum.lulzbot.com/t/tearing-the-pei-right-off-the-bed/4863/1 THANKS to Mikronano for his advice and guidance on this!

You’re very welcome! I’m really glad I could help.
And nice job on the new PEI. From the picture I can see you did apply it very well!
Happy printing and don’t forget to renew it every once in a while with a 800 or 1000 grit sand paper. Not too much force on it, just to remove the traces from the old prints and then a good wipe with isopropyl. The finely sanded surface creates tiny little pockets where the new material grabs on and thus helps with the corner lifting.