Tensile Tester Mounted on Lathe

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Carrying on with the Spectrum Carbon filament sampler, the next one is the PETG-CF10… I started printing the coupons as it was wound on the roll, but after a few I decided it probably needed drying… I dried it at 65C for 6 hours, and indeed it changed the results I was getting… The strength in the X direction (horizontal) increased from 10,400 psi at 250C to nearly 14,000, which is the highest I have recorded, even stronger than CF-Nylon!.. However, the dried filament LOST strength in the Z (vertical), the layer to layer adhesion dropped from 3300 psi to only 1000 psi !!!.. The fan setting, at 70% (recommended by Spectrum) seemed high for PETG, so I ran the tests again with the fan at 30% and got a small improvement in both directions… Here are the results…

The filament was the strongest in the X direction at 250C, and I had lots left, so I did some tests at 250C, with the 0.25mm layer height I had been using, and also with 0.30mm layers… The variable this time was the line width, and I only printed the vertical coupons, with the following results…

In a similar manner to the test I ran with the PLA-CF10, with the thinner layer, the strength improved as I increased the width… but with the thicker layer, the width of the lines made little difference… I still had some filament left, so I installed a 0.6mm nozzle (all the above were done with a 0.4mm), and using a 0.6mm line width I printed samples at various layer heights… Here are those results…

The 0.42mm layer height was not that great a quality, and the 0.48 was pretty awful, to be honest… The strength in the vertical (Z) direction peaked at a layer height of 0.42mm (70% of the nozzle diameter), and I can’t imagine using more than about 0.4mm for anything that you care about the appearance of… The strength in X (horizontal) peaked at a layer height of 0.30mm, which is 50% of the diameter, just like printing at 0.20mm with a 0.4mm nozzle… The interesting thing about this test is that it pretty much disproves the “60% rule” for layer height with a Carbon Fibre filled filament… However, this and the previous test using PLA-CF10 did show that a 0.25mm minimum layer height (60% on a 0.4mm nozzle) was a lot stronger than the “standard” 0.20mm layer height… My conclusion, based on these two tests, is that you want a layer height of 0.24-0.32mm when using a CF filled filament… I may refine this as I do further tests with other materials…

Bob

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42

Next in line in the Spectrum Carbon sampler is their PCTG-CF10, and no that is not a typo, it is not PETG… This material prints at a higher temperature than PETG, and I had high hopes for an improved layer-to-layer bonding… only to be disappointed!.. Here is the plot of Yield vs Temperature…

The Horizontal (X) strength is wonderful (almost 12,000 psi), but the Vertical (Z) strength was well under 2000 psi… The material had been dried at 65C for 6 hours prior to testing… I had lots of material left, so I decided to try and answer some nagging questions about whether the cross section layout mattered on vertical prints I had data from the first round with all walls in the test section, so I used the same layer thickness (0.25mm) and line width (0.40mm), and reduced the walls to 4, then 3, then 2, with the interior filled with a 100% line infill, as in the Cura slicer drawing below…

I hoped to find out if there was any difference in the way different line orientations bonded, layer-to-layer, or if it was just the cross-sectional area that mattered… These tests were done at 270C, the upper end of the recommended temperature range for PCTG… Here are the results: virtually a straight line…

To me, this answers the question whether you should favour walls over 100% infill when the load is only trying to separate the layers, and there is NO bending load applied to the part… it doesn’t matter… NOTE, this is not the case when the part is bending (as in Stefan’s test hooks), where the outer layers are under more stress, so of course more walls is better…

I next wanted to find out what difference line width made on Vertical (Z) samples, so I varied the line width (which changes the wall count in the test section) from 7 walls of 0.40mm down to just 4 walls but of 0.7mm… I did this using a 0.25mm layer height, and then repeated it with a 0.30mm layer height… I then did some Horizontal (X) coupons at a 0.3mm layer height as well… Testing again done at 270C… Here are the results…

Once again, we see that with the 0.25mm layer height, there is an increase in strength going from a 0.4mm wall to a 0.5mm, then not much difference going to 0.6mm… There was another increase in layer-to-layer bonding going to a 0.7mm width (which is 175% of the nozzle diameter), this may be due to the high pressure require inside the nozzle to squeeze the filament out to that extreme width… When retested with a 0.30mm layer height, the line was much flatter, there being little difference in the strength by increasing the line width… We have seen this before…

I had some filament left, so I did some Horizontal (X) coupons at the 3mm layer height, again at 270C… Interestingly, the strength decreased slightly as the line width increased from 0.40 to 0.60mm (100-150% of nozzle diameter)… The 0.25mm layer with a 0.4mm line width tested initially was slightly stronger than the same width with a 0.30mm height… The difference was not great, and with the Z direction being so much weaker than the X, would not matter on most prints…

My conclusion on this material is that unless you need specific properties where PCTG excells, the Spectrum PETG-CF10 is a better choice (and cheaper)…

Bob

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It seems that the more testing I do, the more questions I have… I guess that this early on in learning about 3D printing, that is typical… The first testing I did with PETG-CF filaments, I used them “out of the box”, as I thought they should be fine when first opened… The results are earlier in this thread… Now I am drying them and retesting… Just like the Spectrum PETG-CF above, when I retested the IEMAI PETG-CF filament, the strength in X increased but the strength in Z decreased after drying at 65C for 6 hours!.. I don’t understand the mechanism by which this is happening, but I need to figure out how to get back the lost strength in the layer-to-layer bonding… So, I started trying various combinations of layer height and line width, testing at 250C, with the following results…

At the “threads” of filament get bigger, I am losing strength in the horizontal (along the threads), but gaining greatly in the vertical (layer-to-layer) strength… In fact I managed to double that by going from a 0.25mm height with 0.40 mm width to a 0.30mm height with a 0.60mm width… I then tried printing slower, 40mm/sec. instead of 80, and the horizontal got a bit stronger (10%), but the vertical lost 20% of its strength… I then tried a speed in between, and turned off the fan… I lost 10% in the X direction, but made a huge gain in the layer-to-layer bonding, and recorded 5340 psi, which is 75% of the X strength at the same settings… The failure point showed almost complete fusing of the layers (which is great), but the sides of the square test section were bulged out and no longer straight lines… Most of the coupon looked OK, but the smallest section, that takes the shortest time to print, was obviously getting too hot and distorting badly…

I think I have zeroed in on a “minimum” height and width for CF filled filament when using a 0.4mm nozzle, however… There is no question that you don’t want to use less than 0.25mm for a layer height, and there is a pretty decent improvement in layer-to-layer bonding by going to a 0.5mm line width (125% of the nozzle diameter)… Further gains in layer-to-layer bonding appear to be available by increasing the layer height, but at the expense of appearance of course… If you don’t mind the layer lines, you can increase the height to 0.3mm and the width to 0.6mm… At that size, you could (should?) be using a 0.6mm nozzle… and then you can go even larger, at the expense of pretty terrible looking prints… For me, the practical maximum would be a 0.36mm layer height, with about a 0.72mm width… Thicker than that looks pretty ugly, IMO…

Bob

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I have dried some of the PETG-CF filaments that I tested previously right out of the box, figuring they should be OK… What I found was very interesing… When dried for 6 hours at 65C, the Horizontal (X) strength increased, but the Vertical (Z) strength decreased (or at best stayed about the same), in all the ones I dried… Here are the results for the dried filament, you can see the charts for the “as purchased” filaments in the above posts…

In my quest for increasing the layer-to-layer bonding I have been trying an increase in the line width… There is no question that you get an increase in the Vertical (Z) strength as you go to wider lines… However, the Horizontal (X) strength usually decreases a bit (but not enough to make a significant difference)… Here are my results…

From this experimenting I have decided to use a 0.25mm Layer height, and a 0.60mm line Width (150% of the 0.4mm nozzle) as my standard profile for CF filled PETG… If you want to print really fast, you could use a 0.6mm nozzle, a layer height of 0.30mm, and a line width of 0.9mm… maybe even a 0.333 layer height and a 1mm width (although I haven’t tried that yet)…

Bob

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45

I got some Priline PETG-CF a couple of days ago, because I had heard good things about it, and the price was good… Well, it may be cheap(er), but the performance was the worst carbon filled PETG I have tested, particularly for layer to layer adhesion… and it was no stronger in X than a non-carbon PETG…

The prints did not show very much of that “carbon look”, and I won’t be buying more of it… I’ll just use it up when I want a greyish black PETG… Further carbon filled PETG testing will have to wait until some that I haven’t already tested goes on sale… The strongest in X was the Spectrum PETG-CF10, and it had the most glittery, layer hiding appearance, but the Z strength was below the PETG average… The second strongest in X was the Kimya PETG-CF significantly better than non-carbon PETG and most PLA, with a Z strength typical for PETG, though not as good as the best PLAs…

Bob

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I continued my tensile testing of the samples of Spectrum Carbon Fibre filled filaments today with the ASA-X-CF10… Frankly, I see no advantage over PETG-CF filaments, and it smells quite a bit (somewhat like ABS when you saw it)… The surface finish is quite rough, particularly on the corners, where it ends up with raised ridges like tiny saw teeth, quite sharp… I am testing all the carbon fibre samples now using a 0.25mm layer height and a 0.50mm extrusion width… Spectrum recommend 235-260C for the nozzle, and 0-20% for the fan (I had the fan off)… The bed temperature is quite high, I used PEI with Elmer’s gluestick, at 90C (100C for the first layer), the recommended is 90-110C, and I had no adhesion problems… Incidently, the horizontal samples were breaking through the eye, so I had to reduce the test section to just 3 x 4 mm to get clean breaks there (and adjust the area in the calculations, of course)… Here are the results…

This material was about 13% stronger than most PETG-CF filaments in X, but more than 14% weaker in Z… but it was significantly weaker than Spectrum’s PETG-CF10 in the horizontal (X) direction (but that was one of the strongest I have tested so far)… When I did a final test with a 0.60mm extrusion width at 270C, it was NOT as strong at the 0.50mm width, quite a different result than I had with the PETG-CF… With the smell and rough finish, I won’t be using it again… If you want what I have left (~ 150g), just pay the postage and you can have it!.. My wife says I am not to use it any more because of the smell!..

Bob

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I dried my Nylon filaments overnight at 90C, and retested them… They were stronger (more about that later), but I was still having the occasional coupon breaking through the eye where the pin is… I can’t make that part any bigger, so I redesigned the whole system for new, smaller, faster to print coupons that use half the material…

The vertical coupons are round, using a hyperbolic center and conical ends to anchor them… The horizontal ones are similar, but use the same rectangular test section I did before, at 5mm x 3mm… I made them that way (with a flat bottom) so that I could print them flat without supports… Of course this means I had to design and print fixtures to hold the ends of the coupons…

I printed them from Polymaker PA-612-CF carbon filled Nylon, which has been the strongest material I had tested so far… They are printed horizontal, with support under the thinner tab, where the pin goes through to mount them on my lathe based testing equipment… This is what they look like with a coupon in place…

I have done a lot of testing to insure that the data is consistent with my previous results, and I am delighted with the correlation… All the coupons break in the middle, in the thinnest section as they should… The fixtures don’t flex, and are showing zero distortion or wear… They may as well be machined from aluminum, considering the loads they have to stand, which is no problem…

Bob

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Here are the results on the retesting of the two carbon filled Nylon filaments I tested a while ago, after drying at 90C for 12 hours… First the 3DX Tech PA6-CF-G3…

The gain in strength in the X direction (horizontal) is about 1000 psi, but the vertical (Z) direction had a big jump, from 2400 psi to over 8000… The layer bonding was stronger up to 270C, but at 280C the quality went in the trash, and the Z-yield dropped a lot… Do not use over 270C for this filament!..

For the Polymaker PA612-CF, it also gained a bit in X, and also made a large (30%), gain in Z, ending up at nearly 7000 psi… After proper drying, both these carbon filled Nylons exceeded even the best of the PLAs that I tested in Z and in X… Don’t think that because they are vacuum packed with dessicant from the factory that you can skip drying them before use, you can’t…

Bob

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I tested the last of the Spectrum sample pack today, this time it was the PA6-LW-CF15S… The “LW” stands for “low warp”, and it contains 15% carbon fibre in the Nylon base… Here are the results…

The horizontal (X) strength was nearly 12,000 psi, which is right in there with the other Nylon filaments in the previous post… The vertical (Z) direction was the strongest I have tested, at over 9,500 psi, which is 80% of the filaments printed in line (X)… That is quite astounding layer-to-layer adhesion… Not only that, but from 250-290C the performance in both directions was pretty consistent… At 300C, however, the strength in both directions dropped off rapidly… The narrow part of the vertical coupon was shiny and irregular… At 290C there was lot of stringing, and a bit at 280C, but at 270C the print quality was quite good… This filament definitely is on my short list… It doesn’t print quite as nicely as the Polymaker PA612-CF, but a lot easier to print than the 3DXTech PA6-CF-Gen3… I am finally seeing just how good a good quality carbon filled Nylon can be…

Bob

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I needed some green PLA for a project, and purchased some of the “house brand” from 3D Printing Canada… It printed beautifully, and when I was finished my project I tested the leftover filament… Here are the results…

It was right in the ballpark for strength in both directions, a little stronger in X and a little weaker in Z (layer bonding) than the “brand name” PLAs I tested previously, and wayyyyyyyyyy better in both directions than the “Econo PLA” from Overture… so good value for money… The highest strength in X was at 220C, and in Z it was at 210C, but so close in layer bonding that I decided to do some additional testing at 220C to find out what happens with different Extrusion Widths, both staying with a 0.2mm layer height (and varying the widths), and increasing the layer height as the width increases, maintaining a 2:1 ratio of width to height… In other words, 0.20mm layers with 0.40mm width, 0.25mm layers with 0.50mm widths and 0.30mm layers with 0.60mm widths (all done with a 0.4mm nozzle)… Both sets of results are plotted below…

As I have seen before, there isn’t any advantage in the horizontal (X) direction from increasing the extrusion width (or the layer height), but increasing the width of the strands increases the vertical (Z) strength significantly… The gain was pretty linear with a 0.20mm layer height, but when you increase layer height in proportion to line width, the gain was greatest with a 0.25mm layer height and 0.50mm line width… I have seen this before with other filaments…

Bob

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Well, I made a big mistake on this post, which I am now correcting… I had the wrong number in my spreadsheet for the width of the horizontal (X) coupon, so the yield values I reported for the horizontal (X) yield were lower than they should have been… The vertical (Z) yields were correct, however… I have corrected the charts, and I am editing the text to correct this error… For anyone who read the original version, or to the Manufacturers of the two filaments involved, my apologies…

I recently purchased four more brands of PETG-CF filament (well, once was PET-CF), to continue my testing to find a good one… Neither of today’s candidates qualify… First I tried the BAMBU Labs PETG-CF, and in both the horizontal (X) and vertical (Z) directions it was weaker than the non-CF filled PETGs I haver tested… Here are the results…

So I figured after that disaster, I would get a reprieve when I tested one of the highly touted 3DXTech filaments, their PETG-CF… Here are the results for that…

It was about average for the carbon filled PETGs in X… but easily the weakest of all the filaments of any kind I have tested in Z, with the exception of the Econo PLA I tested… 3DXTech recommend using 230-260C for this filament, and it was under 1000 psi for layer-to-layer adhesion, which means the coupons were breaking at less than 30 lbs. of pull… Even at 280-290C it didn’t reach 2000 psi… :o

I am getting quite a collection of PETG-CF filaments that look pretty but are weaker than regular PETG… Oh well, still a couple more to go tomorrow… ::slight_smile:

Bob

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While I was preparing today’s data, I discovered an error on the charts (and text) for the previous post, which I have now corrected, please check out the changes above…

Today’s data is for the remaining carbon filled PETG I have, made my 3D Printing Canada, and for the Bambu PET-CF (note, not PETG, and over double the price per kg.)… First for the 3D Printing CF-PETG…

It was pretty typical in the horizontal (X) direction for the CF filled PETGs I have tested, but a bit below the average in the layer-to-layer adhesion… None of these CF-filled PETGs have been stronger than non-CF filled PETG in the vertical (Z) direction so far… Next I tested the BAMBU Labs carbon filled PET filament… This is not PETG, and has a noticable odour when printing… It costs about twice what their CF-PETG does by weight… Here are my results…

The printing temperature was higher, with the strength peaking at 280-290C… It was significantly stronger than their PETG in the horizontal (X) direction, reaching nearly 12,000 psi… However, it was disappointing on layer-to-layer adhesion… performing much like a typical PETG in that regard… For my next tests I am putting on a 0.6mm nozzle, and do some experimenting to see if I can increase the strength in the vertical (Z) direction on a few filaments…

Bob

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I have just noticed that I used the incorrect cross section for some of the vertical coupons below where testing was done with a 0.6mm nozzle… The corrected layer-to-layer strength (Z) is less than I originally published … I have replaced the last 4 charts and corrected the comments for the following filaments:

3DXTech CF-PETG
Polymaker PA612-CF
Anycubic PLA
3D Printing Canada PLA

The biggest change is that the Z strength does NOT approach the X strength, I should have known there was a mistake when I saw that…

I have mostly worked my way through the materials I have on hand, so I installed a 0.6mm nozzle to do more testing… I have found that using greater extrusion widths increased the layer-to-layer bonding, as per the CNC Kitchen video testing that Stefan did… He found the maximum strength occurred at about 150% of nozzle diameter is his tests, and I have confirmed that… So, that has become a goal for parts that require maximum strength… I tested quite a few materials, looking at extrusion width in some, layer height in others, and in some, both… Here are all the charts, with a few comments after each one…

This one shows an increase in strength with a 0.4mm nozzle going from a 0.50mm width to 0.60mm (150%), and the same results with a 0.6mm nozzle peaking at a 150% width (0.90mm) and then starting to decline…

This one shows the peak at 1mm width (166%) in both directions, and a very sharp decline in strength in the horizontal (X) direction above that…

This one, using the same filament and a 1mm width (the peak above) showed a decrease in the vertical (Z) direction as the layer height increased, with a slight increase in horizontal strength from a layer height of 0.25mm to 0.30mm, and then a steeper decline above that…

This one showed an increase in Z with the 0.4mm nozzle at 150%, but a decrease in X… However with the 0.6mm nozzle, both peaked at 150% (0.90mm)…

With the same material, using a 0.6mm nozzle and two different extrusion widths, 0.9mm and 1.0mm, the horizontal (X) strength peaked with a 0.30mm layer height, and the vertical strength with the 0.90mm width also showed a slight peak at 0.30mm layers, but using a 1mm width the layer-to-layer bonding decreased as the layer height increased… The next three tests focused on varying the layer height while using 150-166% of nozzle diameter extrusion width (at this point, a “proven” maximum)…

This clearly shows a decrease in strength with increasing layer height… Note that for all three of these charts, the extrusion width was 0.90mm (150%) for the 0.25 and 0.30mm layer heights, but I used 1mm for the 0.33 height (3:1 bead)…

This shows a fairly dramatic decrease in X with increased layer height, the layer-to-layer strength was relatively constant…

The Nylon acted a bit differently, the strength in both directions increased with greater layer height… The broken “Z” coupons showed no layer lines with the thicker samples, and a somewhat “crystalline” appearance… Next I tested two PLAs…

At a 0.20mm layer height, the strength was a lot lower… Greater strength in Z but less in X with the 0.6mm nozzle…

A different PLA, showing a similar graph…In both PLA tests, however, the horizontal (X) strengths were lower than what I got for the same filament when testing with a 0.4mm nozzle and 0.20mm layer height (the typical printing profile for PLA)…

Now for my conclusions… First of all, print quality depends mostly on layer height, and is basically unaffected by the extrusion width, up to 150-160%, as Stefan also found… Requirements on the appearance of layer lines will vary with personal preference and the job at hand, but the “standard quality” using 0.20mm for PLA is good enough for me, although for shallower angles (eg. on the top of a sphere), thinner lines definitely help, so the “adaptive layers” function in Cura is helpful for that… However, I am convinced that for carbon fibre filled filament, you should not use a layer height less than 0.25mm, which because of the matt finish doesn’t show the layer lines too much anyways…

In terms of the extrusion width, I have not seen any significant deterioration in print quality by using widths of 150-166% of the nozzle diameter, and it certainly speeds up the printing process and increases the strength in the vertical (Z) direction, by up to 50% or more… This seems to be a no-brainer, both stronger and faster… This means an extrusion width of 0.60mm for a 0.4mm nozzle, and 0.90mm for a 0.6mm nozzle… With some filaments there is, however, a small loss in the horizontal (X) strength, and it may really drop off above 166%…

The effect of layer height on strength is something that Stefan looked at, and his conclusions were that you wanted to stay below 50% of the nozzle diameter, that the strength decreased above that… About half of my tests with the 0.6mm nozzle confirmed that (ie maximum height of 0.30mm), the rest didn’t… When using CF filaments, you just shouldn’t use anything less than 0.25mm, IMO… In many instances, going to a 0.6mm nozzle lost a bit of horizonal (X) strength compared to a 0.4mm nozzle, but that may be a result of the small cross section of my coupons, which are only 3x5mm… I have a gut feeling that in the horizontal (X) direction, lots of small lines, rather than a few larger ones, give greater strength, up to a point… This may be the reason for the decrease in strength using a larger nozzle… In the “Z” direction, however, where layer-to-layer bonding is critical, the higher pressure caused by a 150% (of nozzle diameter) extrusion width is also increased by a small layer height, but once you go above a certain height, that pressure drops and you lose strength…

So, remarkable increases in layer bonding strength can result from using 150% extrusion width, and if you go to a 0.6mm nozzle of course the printing time drops by about a third… If you combine the two, you can print in less than half the time than with a 0.4mm nozzle… Here are some suggestions you might like to try…

Non CF filled filament
0.4mm nozzle…0.20mm layer height with 0.60mm extrusion width…
0.6mm nozzle… 0.25-0.30mm layer height with 0.90mm extrusion width…

Carbon fibre filled filament
0.4mm nozzle… 0.25mm layer height with 0.60mm extrusion width…
0.6mm nozzle… 0.25-0.30mm layer height with 0.90mm extrusion width… for faster printing, 0.33mm layer height with 1mm extrusion width…

Bob

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