PETG: Bond Strength vs. Support Tradeoff?

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GBuchwitz
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PETG: Bond Strength vs. Support Tradeoff?

Post by GBuchwitz » Thu Oct 26, 2017 4:44 pm

Hey, Everybody.

After experiencing some brittleness problems associated with PLA, I've been attempting to dial in Simplify3D settings for PLA to print an object which includes a 0.06" x 0.5" x 6" strap protruding from the center of a block. Approximately 0.25" of support material are generated below the width and length of the strap. I'm using an M3 single extruder printer. I've been experiencing two problems:

1. The strap's shell (outline) layers of are not strongly bonding to each other or to the infill material. Any flexing of the strap (which occurs when attempting to separate the support material from the bottom of the strap) causes the shell layers to delaminate.

2. The support material bonds strongly to the strap - making it very difficult to separate. The only way I can realize a print for which the support material can be separated from the strap is to increase the number of upper vertical separation layers from 1 to 2. However, increasing this spacing seems to make the strap's shell delamination problem worse.

As a test I used the same S3D settings (based upon Jules' awesome compilation of posts from this forum) to print just the strap - in both 0.06" and 0.10" thicknesses directly on the build plate with no support material. The straps printed beautifully. No amount of flexing could delaminate the outer shell layers. All this suggests a connection between the quality of the shell layer bonding and the quality of the support.

I've experimented with several settings including extruder temperature, extrusion multiplier, infill overlap (as high as 65%), both normal and dense support layer generation. I haven't perceived any improvement in delamination as a result of these changes.

Any advice would be greatly appreciated. I'd include an image, but I haven't been able to figure out how to do that in this forum.

V/r, - guy

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Tim
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Re: PETG: Bond Strength vs. Support Tradeoff?

Post by Tim » Thu Oct 26, 2017 9:11 pm

An image would be helpful. Use the "Upload attachment" tab on the box below the box where you type your post.

PETg is pretty bad at overhangs in general. I tend to look for ways I can print to avoid the need for support at all. Often printing in two parts and gluing them together is better than printing one piece with support. Also the range for infill density is pretty limited with PETg. You mentioned the infill overlap, but what infill density are you printing at?

GBuchwitz
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Re: PETG: Bond Strength vs. Support Tradeoff?

Post by GBuchwitz » Fri Oct 27, 2017 5:48 am

Tim wrote:... what infill density are you printing at?
Thanks for taking the time to share your experience and advice, Tim. My interior infill percentage is 50%.

V/r, - guy
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IMG_5442.JPG
Strap bottom showing support material and delaminating shell layers

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Tim
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Re: PETG: Bond Strength vs. Support Tradeoff?

Post by Tim » Fri Oct 27, 2017 7:08 pm

Still hard to see from that orientation. Does the bottom of the strap have a rounded edge? I expect the delamination occurs where the support doesn't reach as close to the strap as it does on the strap's bottom surface, so the outer perimeters are not as well supported. If they sag just a little bit, there will be a gap between the filament threads and they will pull apart easily.

S3D's support structures are great, but they aren't perfect, and you might need to do some serious tweaking of the support parameters including manual placement in just the right spots. It might work better to use sparser support structures, close up the gap between the support and the part completely, and then expect to cut away the support with a knife. Support that has to be chopped off is better than having the sides delaminate.

Still, the better option is to find an orientation that doesn't require support, printing in halves and gluing together if necessary. My observation is that when a part is complicated enough, there will be some part of it that doesn't print well. The trick is to think of all the different ways the part can be printed to either minimize the surfaces that don't print well, or to hide them where they can' t be seen. Sometimes that involves glue. Maybe it's just a lack of mechanical skills, but there seems to be a mindset among 3D enthusiasts (both designer and end-user) to do everything in one piece and being oblivious to the known inherent limitations of filament printers.

GBuchwitz
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Re: PETG: Bond Strength vs. Support Tradeoff?

Post by GBuchwitz » Fri Oct 27, 2017 8:39 pm

Tim wrote:Does the bottom of the strap have a rounded edge? I expect the delamination occurs where the support doesn't reach as close to the strap as it does on the strap's bottom surface, so the outer perimeters are not as well supported. If they sag just a little bit, there will be a gap between the filament threads and they will pull apart easily.
'Sorry about the photo. The bottom of my strap is flat vs. rounded, so I wouldn't expect a sagging problem. Assuming that the support material is flat against the bottom of the strap, the only reason I can think of why printing it directly on the build plate vs. on support material yielded such strong bonds is that the build plate is heated and the support material is not. That said, I may take your advice and try decreasing the support material infill percentage as well as the number of vertical support space layers from 2 to 1 and see if I can remove the support material without causing the strap's shell layers to delaminate.

I've noticed that the delaminated shell layer stacks have all bonded together well vertically, but the side-to-side bonds between these edge stacks are weak. Simplify3D Tech Support stated that in their experience bond strength generally increases with hot end temperature, but increasing this from 247C to 252C had no apparent effect. They also suggested further slowing the shell layer print speed, but I saw no improvement after making this change either.

A member of S3D's forum suggested that I make some extrusion width adjustments. I'll probably try this next.

If that doesn't fix my strap edge delamination problem, I may bite the bullet, take your advice, and redesign this part so the strap and the block are separate pieces to be glued together.

Thanks again for your help.

V/r, - guy

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willnewton
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Re: PETG: Bond Strength vs. Support Tradeoff?

Post by willnewton » Sat Oct 28, 2017 1:12 pm

why not print the strap upside down so you don’t need support? hard to tell if you can do that from your photo, but it looks like the simplest solution.

Also, your title is about PETG, your post is about PLA, and your temps are closer to PETG and way too high for PLA. If you are running PLA that high, then you may have a partial clog.

If you are running PETG make sure your bed fan is OFF, leaving it on will cause the exact problem you are having. PETG likes it hot.
I'm finally back to where I started two days ago!

A thread with some stuff in it I update every once in a while. viewtopic.php?f=8&t=9
See some of my stuff http://www.thingiverse.com/willnewton/about

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Tim
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Re: PETG: Bond Strength vs. Support Tradeoff?

Post by Tim » Sat Oct 28, 2017 2:21 pm

He is running with PETg, mentioned it in the first post. I should have thought to mention to keep the fans off. But I have always done that, and PETg still has major issues with delamination on and around overhangs. It's my major complaint about PETg, but the stuff is superior to PLA in just about every other way, so I have become used to designing around the problem.

I suppose it's also worth mentioning alternatives like PLA+ or PC, but PLA+ isn't as high temperature as PETg (but there are many different varieties called "PLA+"), and I haven't had enough experience with PC to know what its problem spots are.

GBuchwitz
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Re: PETG: Bond Strength vs. Support Tradeoff?

Post by GBuchwitz » Sat Oct 28, 2017 8:44 pm

willnewton wrote:why not print the strap upside down so you don’t need support? hard to tell if you can do that from your photo, but it looks like the simplest solution.

Also, your title is about PETG, your post is about PLA, and your temps are closer to PETG and way too high for PLA.
Thanks for attempting to help me out, guys. There are a couple of factors about my application that make printing the strap upside down undesirable. I need the strap to protrude from the center of a block... which mandates the use of support material if I want to build the part as one piece.

Yes, I screwed up my original post . I didn't make it clear that I was attempting to change to PETG because PLA was too brittle. 'Sorry about that.

And per Jules' recommendations regarding PETG, I'm not using the fan, and have been experimenting with V4 hot end temperatures between 241C and 247C.

This morning I took Tim's much-appreciated advice and attempted to print and assemble two parts in PETG: a strap and a block with a slot at the center of one side to receive it. The strap printed beautifully. No amount of flexing it caused any delamination of its outline shell layers. This didn't surprise me at all because the only time I've seen this delamination occur in the past is when the strap was supported by support material.

At first glance the block also appeared to be in good shape. But when I took a closer look at the short, filleted extrusion from the side into which the slot was cut to receive the strap, I could see that the outline shell layers at its end were not bonded together. As in my prior attempts to print the block and strap all in one piece, this extrusion had to be supported by support material... which (in my experience) with PETG seems to cause poor shell inter-layer bonding

Not only that, but even though I'd specified two upper vertical separation layers in the support material in my S3D process, the support material inside the slot had bonded to the block so well that I couldn't remove it.

I'd previously attempted to strengthen the bonding between outline shell layers by increasing my extrusion width from 0.45 mm to 0.50 mm. This didn't seem to make any difference in the the bond strength. Jules' instructions called out a procedure for calibrating the extrusion multiplier to use in S3D. Perhaps the M3 needs a similar calibration procedure?

At any rate, I'm now considering printing the block in PLA (easier to remove the slot's internal support material) and printing the strap as PETG.

Thanks again for taking the time and effort to offer me advice.

V/r, - guy

Gwhite
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Re: PETG: Bond Strength vs. Support Tradeoff?

Post by Gwhite » Sat Oct 28, 2017 9:29 pm

I'm still pretty green at this, but the one piece of advice I've seen over & over again is to run a calibration on your extrusion multiplier settings BEFORE you try to adjust anything else. Increasing the width will do nothing if the multiplier is off.

I've seen significant changes in the required multiplier just going from one spool to another with the same brand, same material, but a different color. I don't know how much is subtle changes due to the color, or if it's just the fact that it was a different spool.

Printing over supports is always going to be tricky, because there isn't a good solid layer underneath for the extrusion to squash against. Remember, printing over supports is considered "bridging". For some materials, I've had to increase my bridging extrusion multiplier to > 140% to get reasonable adhesion between extrusion passes. Using a fairly fine support grid will probably help as well. It can also matter which way the bridging prints relative to the supports. Adjusting the bridging angle can help with that. Use the preview to see how the supports are getting printed, and then make sure the bridging above it goes across the short gaps.

GBuchwitz
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Re: PETG: Bond Strength vs. Support Tradeoff?

Post by GBuchwitz » Sun Oct 29, 2017 6:16 am

Gwhite wrote:I'm still pretty green at this, but the one piece of advice I've seen over & over again is to run a calibration on your extrusion multiplier settings BEFORE you try to adjust anything else. Increasing the width will do nothing if the multiplier is off.
Gwhite,

Thanks for the education. Regarding calibration, I (mis?)interpreted Jules' statement, "Skip this step if you have a Rev. E machine. Sold after 3/1/16" to mean that MakerGear printers sold after this date (including my M3) don't require this procedure. He may have been referring to calibrating Z-axis offset instead of the extrusion multiplier. I'll attempt to learn more about this calibration process. There's nothing about this process in the M3 user's guide.

Thank you for your help!

V/r, - guy

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