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I cannot figure out PETG . . . please help

Posted: Wed Aug 30, 2017 4:03 pm
by longshot
Ok so what’s the secret to PETG? I’ve read countless posts and tried countless variables.

I’ve been trying to print this part for last last 4 days.

My machine: Rostock Max V1 (yup an old trusty V1, modified of course)
Greg Wade extruder (properly calibrated)
E3D V5 – 0.4 nozzle
Duet Wifi upgrade
Carbon fiber rods with traxxas ball joints
Using Fablam build surface with boro glass plate.
Plexiglass enclosure
Using mattercontrol as my slicer. . . more on this later.

So what’s the deal? I’ve got a roll of e-sun Transparent blue (its literally only a few days old, so there shouldn’t be any moisture in it, and I remove it, place it in a bag from the machine before going to bed so again no moisture.)
I print with a bed of 60C and a nozzle temp of 250C. The stuff sticks well. My first layer looks great aside from a few spots (more on that)

Extrusion multiplier 1.1
150% width on the first layer only

So here’s the issue. I got to print my first layer at 15mm/s, super slow, anything higher and I get issues. And here comes the problem:

When I build the part up, everything looks good till I get on “top of the support material” . . . . the system thinks I’m running another first layer so it slows it down from 30mm/s to 15mm/s. Then it just globs up something terrible, it picks up its own strays and looks terrible. After the first layer, the system picks back up to 30 and it looks ok.

Retraction is another thing. I know the greg wade extruder is slow but high torque extruder. I like it for my Bowden setup. I’ve tried running 30mm/s to 100mm/s extrusion. System doesn’t like slower speed, but it mangles the petg something fierce after about 5 hours or printing. . . I’ve tried all kinds of priming and retraction settings from 2-4mm with 1-2 sec delay and 0.5-2mm additional priming.

I know it’s a lot but I’m at loss (including my last weekend)

-What are some nominal retraction settings to use with PETG and a greg wade type extruder in a Bowden setup?
-What do I do to print at a faster speed on top of the support material without affecting the speed of the first layer at the build plate?

Re: I cannot figure out PETG . . . please help

Posted: Thu Aug 31, 2017 2:10 am
by gchristopher
The print speed is purely a function of your slicer settings. What slicer are you using?

I the slicer absolutely refuses to do the speeds you want, in the worst case, you can open the g-code and change the F____ speed parameter for the movements you care about. Hopefully it doesn't come to that.

Re: I cannot figure out PETG . . . please help

Posted: Thu Aug 31, 2017 9:40 am
by longshot
Matterslice from mattercontrol.

Re: I cannot figure out PETG . . . please help

Posted: Thu Aug 31, 2017 10:15 pm
by gchristopher
Okay, I haven't messed with mattercontrol in a while. What are your speed settings? (I'm mostly switched to the Prusa fork of Slic3r right now, but it seems like everyone switches slicers periodically as their needs or frustration levels dictate.)

Re: I cannot figure out PETG . . . please help

Posted: Fri Sep 01, 2017 7:17 pm
by 626Pilot
Make sure you are not over-extruding. Do a filament calibration, like in the first steps of my Delta dimensional accuracy calibration (see sig). Make sure your Z height is set as close to perfect as possible.

Over-extruding, or having the Z height too tall, will guarantee that PETG builds up and eventually starts leaving globs or knocking things around. It is less tolerant of these things than PLA.

Re: I cannot figure out PETG . . . please help

Posted: Fri Sep 01, 2017 8:12 pm
by TwoTone
It's been awhile since I helped my son, but I do remember he changed very little going from PLA to PETG

Re: I cannot figure out PETG . . . please help

Posted: Tue Sep 12, 2017 10:10 am
by longshot
Ok . . . so i ran 626pilot's extruder calibration cube. Nailed it down to about .97 with an extrusion width of .45mm and a layer of 0.15. So far so good. I feel my z is pretty good. as I said before I run a duet wifi with auto calibration, custom z trigger heights for all 16 points (6 factor), fsrs, and a separate bed compensation routine. Its as good as its going to get. Maybe i'm wrong.

I manually pushed filament into the nozzle to understand how it feels, 255 is the sweet spot, takes very little effort.

Speed settings wise, i'm printing around 30-40mm/s. Slower for outer perimeters. Max non print travel speed is around 200mm/s.

There's very little blobbing when it makes long moves, but the retract, hop, move, print, retract, hop, move, print etc. is what is causing all the problems. I get this weird string of pearls effect for the first 5mm or so of travel. You can see it in infill especally.

I've tried all kinds of retract speeds and settings. I've even given it an extra 1mm to prime the nozzle. (E3D V5)

I feel like i'm this close to a breakthrough but i don't know the secret to take me to the finish line. I just want the stuff to not stick to the nozzle.

How about a silicon jacket? Are there sprays i can use? etc.

Am I missing something? What about a layer fan? I get mixed reviews of when to and when not to use it. Currently I have no layer fan. Should I make one?

Re: I cannot figure out PETG . . . please help

Posted: Thu Sep 14, 2017 4:14 pm
by 626Pilot
With PETG, the Z height setting is critical. PLA and ABS will forgive you for your Z being a little off, but PETG will just slowly accumulate until it becomes a problem. My advice is to use the smallest Z height you can, while still getting adequate 1st layer adhesion.

255 is a decent temp for PETG. It definitely likes to run hotter than PLA. 30-40mm/sec feedrate is okay too.

Initial underextrusion (the first 5mm you mentioned) might be made slightly better by putting a small amount of canola oil into the Bowden tube. I did this by removing the top of the Bowden tube from the extruder, feeding some filament through the extruder, dipping the filament into some oil, and then sticking the oiled filament into the tube before reseating it in the extruder. You don't need a lot of oil, just a little. The point of this is to reduce friction. Also, make sure your tube is long enough that it isn't creating any pressure points on the filament when the effector is out near the edge of the print surface.

The extra 1mm to prime it may be contributing to build-up. See if reducing the friction in the bowden tube (oil it, make sure it isn't too short) will help.

I used one of E3D's silicon jackets. They are alright, but they don't do anything to stop the filament from building up on the nozzle. They keep the heater block clean. That's about it.

A layer fan is a good idea for E3D v6. They don't work so well with the Cyclops because they make it impossible for it to maintain temperature. They won't help with the problems you're having, so I would save the layer fan for later.