gwhite
Posts: 156
Joined: Wed Jul 19, 2017 9:37 am

Bridging Issues with PETG

Thu Aug 17, 2017 9:09 am

I'm trying to dial in bridging settings for HatchBox PETG on a MakerGear M2E. I started by doing a calibration for the extrusion multiplier using a single wall cube, and came up with 0.86. This is with a 0.35mm nozzle, shooting for 0.45 mm width with 0.25 mm layer thickness. This was a bit tricky, because 3 of the four walls were quite consistent, but the 1st wall printed was always significantly thinner. I ended up getting 0.45, 0.45, 0.46 & 0.36 mm.

In any event, I started with some bridging parameters from the MakerGear forum:

Unsupported area threshold: 5 sq. mm
Extra Inflation Distance: 1.0 mm
Bridging extrusion multiplier: 140%
Bridging speed multiplier: 125%

I downloaded a bridging test file from Thingiverse and fired off a print. The results were pretty horrible:
1st Bridge Test.jpg
1st Bridge Test (end).jpg
In addition to the giant loops, I noticed that the bottom surface wasn't fully filled in. There are lots of tiny holes, which suggests I'm under extruding. The walls of the bridge areas don't look too bad, it's the interior bottom fill that isn't working. I looked at the preview in S3D, and I think the loops are the result of the zig-zag fill unraveling because the ends never stick to the perimeters:
Bridging Issues (Preview).jpg
I tried a couple more prints, increasing the extrusion multiplier first to 0.88, and then to 0.90. The holes closed up a little, and the loops got a little better, but it's still pretty awful.

So, I have two questions:

1) How do I reconcile the single wall calibration that gets me the right wall thickness (3 out of 4 times...) with the fact that I'm clearly not getting enough extrusion to get a good fill?

2) How to I tweak things so the ends of the zig zag fill on the bottom of the bridges actually connect to the perimeter walls?

Thanks!

arhi
Posts: 452
Joined: Thu Oct 06, 2016 5:13 pm

Re: Bridging Issues with PETG

Thu Aug 17, 2017 9:29 am

petg is "weird" material for me ... I have a love/hate relationship with it and I have to say that bridging is still killing me ... everything else is great, if not for bridging problem I'd move from abs to petg for most applications..

printing 30mm/sec with 50% speed for bridge and 90% extrusion for e.g. I get nice string that looks perfect, across 5cm span, looks like it's going to be great, and then the moment it touches the second wall it snaps off from the nozzle and falls down :( .. I'm trying to figure out how to make bridging work for a while with petg without any success :( ... anyhow the step1 is always to get that string, the single one, to span across and look good, everything else comes after (in v4 s3d fixed many things that make things great after this initial problem is solved)...

if you manage to get that to work ok (span one single string) please share!

adding some cooling during bridging might help, the printer I use for PETG is normally printing PC and Nylon and I don't have any part cooling fan there. maybe adding some part cooling, low pressure... maybe .. dunno .. following this thread carefully :D
gcodestat integrates with Simplify3D and allow you to
Calculate print time accurately (acceleration, max speed, junction deviation all taken into consideration)
Embed M117 codes into G-Code
Upload your G-Code directly to Octoprint
open source and unlicence

gwhite
Posts: 156
Joined: Wed Jul 19, 2017 9:37 am

Re: Bridging Issues with PETG

Thu Aug 17, 2017 11:36 am

I did some more digging. I'm using version 4.0 of S3D. In the preview mode, I can see that it it properly detecting that it needs to bridge, but it's not automatically aligning the bottom fill with the bridge direction the way it's supposed to. I turned on the "Use fixed bridging angle" setting (using 0 degrees), and the preview shows that the fill will now run lengthwise over the bridge regions. I ran that (also with the extrusion multiplier kicked up to 0.92), and it made a huge difference. This is the underside:
Bridge Test Fixed Angle (bottom).jpg
It's still got a lot of small issues. The top side also still shows more signs of under extrusion. You can see where the outer & inner perimeter aren't fused together, especially in the lower right area.
Bridge Test Fixed Angle (top).jpg
The fill angle was clearly a big issue, but I've got a ways to go before I consider this "solved". I think I'm at a point where I can play a bit with the bridging settings, but I'm not sure which to tweak & in what direction. I also still have some sort of extrusion issue going on.

Any suggestions would be appreciated.

Also, does anyone know if the "fixed bridging angle" is relative to the bridge direction, or to the X-axis or what? I'm assuming it's relative to the bridge direction, so you can have multiple bridges at odd angles, but I can't find any confirmation of this.

Thanks!

brian442
Posts: 1243
Joined: Mon Nov 28, 2016 5:35 am

Re: Bridging Issues with PETG

Thu Aug 17, 2017 6:52 pm

Pretty sure the bridging angle is relative to the x-axis. You can test it on your own though by enabling that option and checking the preview for some different bridges.

gwhite
Posts: 156
Joined: Wed Jul 19, 2017 9:37 am

Re: Bridging Issues with PETG

Thu Aug 17, 2017 9:31 pm

Report from the battlefield:

There seems to be be two theories about bridging with PETG:

1) Go fast to maintain some tension on the material so it won't sag while it cools

2) Go slow, so it will cool in place and not sag.

My first set of parameters used the "fast" approach, because someone else had reported success with it. They also mentioned that good cooling is critical, and even recommended removing the blade guard from the fan to increase air flow.

I wasn't having a lot of luck with going fast, so I cut the speed way down. I also turned on the perimeter bridging option, and backed off a bit on the bridging extrusion multiplier. I don't like changing this many things at once, but it takes close to an hour to print a test run & let it cool to the point where I can pop it loose. In any event, those changes helped significantly. It's still far from perfect, but compared to the rat's nest I had this morning, it's almost usable.
Bridging Test #5 vs #6.jpg
I'm running a test now with all the settings the same, but with the speed at 25%. It's hard to tell, but it looks like there are no loose threads, but at least the longest bridging section has a sag to it. It droops down a little near the anchors, and then goes straight across. The result is that most of the bridge is a fraction of a mm low except near the ends. You can see a little bit of this going on in the left hand print.

The problem I see with going fast is that if you are printing fast enough to keep tension on the thread, it's going to be pulled thin, and you need to add more extrusion multiplier to get it fat enough to fuse to the thread next to it. That wasn't happening with the earlier tests, but I may just have needed to boost my extrusion multiplier more.

wirlybird
Posts: 1242
Joined: Sun Jul 17, 2016 1:32 pm

Re: Bridging Issues with PETG

Fri Aug 18, 2017 7:19 am

Good info. I think you are seeing a weak area for PETG. It hates bridging (poor bridging characteristics) but I think I would have recommended slower, in general PETG likes slower.

I use a lot of PETG so this is great research! Thanks.

gwhite
Posts: 156
Joined: Wed Jul 19, 2017 9:37 am

Re: Bridging Issues with PETG

Fri Aug 18, 2017 9:10 am

Well, I can assure you that going TOO slow with PETG doesn't work. I dropped the bridging speed down to 25%, and things definitely got worse. I'm going to try a few more experiments, and then I need to switch over to PLA for another job. I haven't played much with the bridging extrusion multiplier yet. So far I know that:

Extr Mult = 150%, Speed = 130%: Bad sags on bridges > ~ 1cm, bottom threads aren't fused together

Extr Mult = 120%, Speed = 50%: Sags a little near ends, but no bad sags. Bottom threads still aren't fused together uniformly

Extr Mult = 120%, Speed = 25%: Bad sags on longer bridges. Bottom threads still not fused together well

I think I will try 75% for speed, and 150% for the multiplier.

Given that the side walls (perimeters) of the bridges never looked too bad, and that I'm printing at 100% speed, I was thinking I might also turn off the perimeter bridging option. I suddenly realized that is another clue. My perimeter speed is set at 50%, so that explains why they looked OK.

Independent of the bridging, I've still had to crank up my regular extrusion multiplier to 0.94 to get decent fill on the top & bottom layers. I haven't had a chance to go back to a single wall calibration cube to check the wall width, but I bet it's way over .45 mm.

arhi
Posts: 452
Joined: Thu Oct 06, 2016 5:13 pm

Re: Bridging Issues with PETG

Fri Aug 18, 2017 10:05 am

with regards to extrusion multiplier - I had to increase extrusion multiplier for PETG by 10% compared to ABS .. initially it confused me but then I measured the filament and my PETG is tad thinner then ABS one on the input so I probbly should changed the filament diameter and not extrusion multiplier.. but it ends up in the same formula so not a big deal, since s3d don't support volumetric extrusions yet ..

as for the bridging, thanks for documenting these tests :D may I ask something - are you using part cooling fan at all? and did you make any tests with fan on/off and different speeds?
gcodestat integrates with Simplify3D and allow you to
Calculate print time accurately (acceleration, max speed, junction deviation all taken into consideration)
Embed M117 codes into G-Code
Upload your G-Code directly to Octoprint
open source and unlicence

User avatar
dkightley
Posts: 2302
Joined: Tue Mar 10, 2015 4:09 pm

Re: Bridging Issues with PETG

Fri Aug 18, 2017 10:11 am

One very important thing to bear in mind when trying to hone settings is.....NEVER change two parameters at the same time! You'll never be able to figure out which setting causes the changes in the test results.....or you'll assume its changing one that gives results when its actually changing the other that makes the difference!!!

The new feature of bridging being applied to perimeters was added in v4.0.0 to help prevent sagging perimeters. One of your comparison tests in this thread has one test with this feature off...and it looks as if there's sagging perimeters. The accompanying test has this feature on....and other changes as well.....and there is little sagging. I'm guessing your conclusion from that test is that the "other" setting change had the major effect on sagging, but it may be that its the checking of the perimeter setting that has had the effect!
Doug Kightley
Volunteer at the National Tramway Museum http://www.tramway.co.uk
Railway modeller and webmaster at http://www.talkingtgauge.net

gwhite
Posts: 156
Joined: Wed Jul 19, 2017 9:37 am

Re: Bridging Issues with PETG

Fri Aug 18, 2017 2:47 pm

I would much prefer to make one change at a time, but I don't have time to get that fussy at the moment. Because I can see what is going on with both the perimeter & the fill areas separately, I wasn't too worried about it. The goal was to get in the ball park & I can fine tune later.

I ended up leaving the perimeter bridging turn on, and set the speed to 65%. It was definitely worse than at 50%. I'll try to post a detailed picture later.

I have discovered some quirks that may have to be addressed in a future update of S3D:

1) It doesn't always use the perimeter bridge setting when it's supposed to. I have at least one perimeter where it changes in mid-span.

2) I'm getting holes and other weirdness in the fill regions. In order to minimize zits & blobs in PETG, I have a 1.5 mm coast settings. S3D sometimes starts & stops a strand in the middle of a bridge, and I think with nothing underneath, it doesn't behave the way it does when the coast is sandwiched between layers.

In any event, I've learned a lot, and it's vaguely usable if you aren't too fussy. There is clearly plenty of room for improvement.

Return to “General Discussion and Tips”