Trouble printing larger object but smaller turns out fine

[newdeal99 2]

So I am trying to print this flared fitting that I designed.  I scaled it down to fine tune some settings and got it pretty good I think (Elegy rapid PETG).  I ran the filament out in testing and then tried to print a much larger one (8" across vs like 1.5") and it is turning out like crap.  The first one the external surface didn't look good.  I thought it was maybe because there is cubic infill and I was printing infill first to help with overhangs.  It seemed like the corner of the infill was poking into the wall a bit and leaving a small blob.  I tried reducing infill overlap, didn't do it, increased the walls from 3 to 4, didn't help, so then I just gave up and set it to print infill after perimeters and it still didn't look good.  So then I changed it to print with 100% circumferential infill which would be similar to the small one since it was just perimeters as it was too thin for infill anyway.  With that the surface looked a bit better but the edge of the print looks like total crap and I see a ton of crusty blobs and voids when looking at the edge.  I stopped the print and thought I would ask here for help.  Again the small one printed with the same settings and was fine.  Is it wet filament?  I am a beginner and so trying to figure things out. Hopefully the photos show the print I was happy with and the one I wasn't adequately. 

[GregValiant 1,258]

Welcome in here.  It's always good to start out by mentioning the printer and any customizing that was done to it.

 

Load the model (if you can share it) set Cura up and use the "File | Save Project" command.  Post the resultant 3mf file here.  It will contain the model, your printer, and all your settings.

PETG can be difficult.  It gets gooey and stringy, and wants to stick to the outside of the nozzle.  When enough material is stuck on the nozzle it will drop off on the print.  I print about 75% PETG as most of my stuff is functional or will be outside.

Temperature is important.  Long retractions are necessary.  I print PETG a lot slower than I do PLA.  At 35mm/sec for the outside walls and with no fan - they look nice and glossy.

 

Sometimes things don't scale up well.  Other times a small scale will help hide issues and scaling up just scales up the size of defects that existed in the test model.

[Slashee_the_Cow 271]

It's possible your filament is a bit damp - PETG is hydroscopic (absorbs water from the atmosphere) if it's too damp it gets a bit slippery so it's hard to extrude, and gooey when heated up so it doesn't come out of the nozzle cleanly.

 

Also, I'm sorry if the following sounds a bit critical, but I'm just trying to educate 👩‍🏫:

4 hours ago, newdeal99 said:

I was printing infill first to help with overhangs

This often doesn't work as well in practice as it does in theory: in theory, it gives the walls something to hold on to when they get printed. In practice, it can push the walls further out and a bit too far over the edge.

 

5 hours ago, newdeal99 said:

Elegy rapid PETG

I've yet to meet a "high speed" filament that prints just as well at its recommended speed as a regular version does at its recommended speed, so make sure you're not going too fast.

[newdeal99 2]

I discovered the problem.  The blue plastic tube in my hot end was getting damaged.  Not sure how that happens but I assume heat?  The hole in the tube was likely double the size it was originally at the top and the end by the nozzle was basically paper thin and kind of arched in shape on two sides of the tube. Replaced with a new hot end and my problem is gone.   I turned the heat down to 245 to hopefully be kinder on the tube and it's printing great. I also dried 7g of water from my roll of filament but that didn't help the print, changing the hot end did.  Flow is better, prints are smooth again.

[GregValiant 1,258]

Bowden tubes are "consumable" items.  As a print progresses the tube can spin in the hot end retainer and the little knives that hold the tube in will damage the tube.  Heat is another issue and the "Capricorn" tubing has a higher tolerance for heat.  (they are blue so you may already have one).

Trimming the tube back by 5 or 6mm on a regular basis can keep the problem from becoming severe enough to affect prints.  Eventually it will get too short.  That's why it's considered a consumable.