switched to .5mm nozzle and now prints are horrible

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bmz
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switched to .5mm nozzle and now prints are horrible

Post by bmz » November 26th, 2017, 7:30 pm

I recently switched from .4mm to .5mm nozzle t get faster prints. Im using armadillo tpu 75d 1.75mm. Im having a terrible time getting the initial layers to stick to the bed. This was not an issue before. Im using blue tape and hair spray. At a temp of 217-222 the initial layers just do not stick at all. The brim starts peeling right from the get go. At higher temps, 225-230, the initial layers stick, but quality is horrible very blobby. Also, it eventually comes un stuck anyway. Also, the bottom skin is very patchy with many small openings. I have tried making initial layer .2mm, or .3mm, no change.

Before, with .4mm nozzle, i was having good prints at 220 deg, but slow. im making non detailed simple shapes so would like to print faster. im not sure how to increase extrusion rate. is that whats needed?

In the pics, the holes at the ends are grossly under filled. They should be 5mm diameter, but are just a random mess. i slowed down print speed to try and make those fill in better, along with initial layer fill, but no change. Its worse at 50mm per second, but still horrible at 30mm per second.

Is there some way to make the extruder feed more material? I think thats the issue. In cura i have extrusion rate at 100%

Any suggestions?
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bmz
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Re: switched to .5mm nozzle and now prints are horrible

Post by bmz » November 26th, 2017, 9:52 pm

About 5th attempt. feed set at 115% and temp at 222. I think my cooling fan shroud sucks. Im using the round shroud from thingiverse. Pretty sure not enough fan power to make all those holes have any kind of velocity. Anyway, wht do you folks think is happening now? Over extrusion? not enough cooling? ?????
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jonnybischof
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Re: switched to .5mm nozzle and now prints are horrible

Post by jonnybischof » November 27th, 2017, 3:52 am

I suppose you did set your nozzle diameter in Cura to 0.5 mm?

Generally, with a larger nozzle you should print a bit slower (0.5 mm is 20% larger than 0.4 mm, so try printing 20% slower than what was ideal with 0.4 mm).

By the way, this also counts for layer height. If you compare 0.1mm layer height to 0.2mm layer height at the same speed, then 0.2mm is double the extrusion rate than 0.1mm, which makes a big difference.
With PLA this is usually not a big deal since many PLAs can print over quite a large temperature range. But I found with some filaments like Ninjaflex TPU you really have to take this into account.

If you get underextrusion, you can try increasing the printing temperature a bit. Usually, increasing the flow rate will only result in the feeder grinding up filament (or skipping steps).

/edit:
Another tip:
If I have a part with multiple small holes in the bottom layer, I usually close them up towards the bottom, so that (only) the bottom layer prints straight over the holes, and only from the second layer onwards the holes are there. This can increase bottom layer quality a lot, and you just have to cut the holes open after printing.
Small circles often don't stick well on the first layer..
Best regards,
Jonny

bmz
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Re: switched to .5mm nozzle and now prints are horrible

Post by bmz » November 27th, 2017, 9:05 am

Thanks for the tips. I will re draw the part today. Im getting some funny patterns and they might be due to having issues creating the surface. I will also seal up the holes on the bottom layer. Now as for print speed: So, Im not going to be able to print faster using the larger nozzle? I noticed some strange things happening on all tries of this print. I have speeds all set at 40 mm per second, yet it seems the printer rockets around the holes very fast, and sometimes around the perimeter very fast. Not sure how, but it seems the entire model is bad. I will completely re draw, slow down to 30 mm per second, increase heat to 225(thought I heard extruder skipping grinding), and reduce layer height. Hopefully I can salvage some time and make a good quality product.

bmz
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Re: switched to .5mm nozzle and now prints are horrible

Post by bmz » November 27th, 2017, 10:28 am

Not sure whats happening here. I re drew the part. Left the bottom surface solid with the hole only going through 2.4mm in a 2.5mm thickness. so, there should be .1mm skin on bottom. When loaded onto the build plate its showing complete through holes. Dont know if its happening in cura or in repetier. First attemp to print the new model printed with a solid skin on bottom, but extrusion was way too slow, so it came un stuck and I had to kill the print. After re working in cura to increase extrusion, it tried to print with complete through holes. So, somehow it re mapped the slice to interpret no bottom skin over the holes??? WTF?? Is there any way to get a consistent slice from the same model?

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jonnybischof
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Re: switched to .5mm nozzle and now prints are horrible

Post by jonnybischof » November 27th, 2017, 11:00 am

Afaik, the slicer "slices" the model AT the specified layer height. So, for the initial layer (say 0.25mm initial layer thickness), it will not take the actual bottom part, but the first slice at 0.25mm. If your sealing is only 0.1mm thick, then at the 0.25mm slice the hole will already be present. Just increase the "sealing" thickness until you get layer 1 solid, and layer 2 onwards with holes.

Maximum extrusion speed is defined by one factor: Nozzle pressure.

Generally, high flow through a small nozzle means a lot of pressure. Increasing the nozzle diameter relieves pressure.
But, the usually more important part about nozzle pressure is the plastic's viscosity (small viscosity = more liquid, high viscosity = ~ solid).
Trying to extrude solid plastic will require a pressure much greater than what the extruder can handle (theoretically, you could extrude cold plastic. Just need tons of pressure...).



So you want to get your plastic to a point of low-viscosity, aka melt it.

To do that, you need to put energy (heat) from the heater into the plastic.
How much (or how fast) energy can be transferred from the heater into the filament is the question.

Reprap 3D printers control "energy" (or heat) by setting the extruder temperature. However, what matters is that the actual filament can be heated to its melting point (aka "melted") and extruded.
Now, if you extrude very slowly, there will be more than enough time to heat all the filament through to the desired temperature. But if you extrude faster, there will be less time for the plastic to absorb energy and heat up while travelling through the heater. If you extrude too fast, the plastic won't be heated up enough and won't melt anymore. -> It will clog.

A larger nozzle diameter does not impact this at all. What does is the heater block geometry, material, plating, surface quality, and the heater power. As an example, see E3D's volcano heating block:

Image
(img by E3D-online -> https://e3d-online.com/volcano-kits)

This heater is much longer and has longer nozzles, which increases the heating area for the plastic travelling through it. It also has a slightly higher-power heater.


One thing to mention about nozzle diameter is that a larger diameter means thicker lines = fewer lines to fill an area compared to a smaller nozzle. So yes, this does increase printing speed (and reduce detail reproduction).


I still think you just need to increase your extrusion temperature a bit (maybe 5 - 10 °C, maybe even a bit more) in order to lower the plastic's viscosity and reduce nozzle pressure.
If that's not possible, you need to print slower. Note that reducing layer thickness can make much more of a difference than reducing the printing speed. Think volumetric!

What is your initial layer speed? (I use 13 mm/s for Ninjaflex TPU, 25mm/s for PLA, on a heated PEI build platform which is very good).
Start very slow, and work your way up to a point where it still adheres well to the build platform.


If the movements seem jerky, you might have too high jerk / acceleration settings.


/edit:
Oh and just to be sure (you didn't mention it).
Did you set the nozzle diameter in your slicer to 0.5mm ?
Best regards,
Jonny

bmz
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Re: switched to .5mm nozzle and now prints are horrible

Post by bmz » November 27th, 2017, 4:50 pm

Hi. I had to stop working on it this morning, kept running into more and more issues. It was compounding! My z limit switch went out of adjustment again, and I was getting non ideal nozzle height in addition to the extrusion issues. So, I had to re adjust the z stop, and I went ahead and re leveled the bed as there were scrapes in the tape revealing an out of level bed. In machining we call those witness marks. Anyway, I did go ahead and re draw the part using 2 extrusion moves. first extrusion making the bottom skin, and second extrusion up from that representing the rest of the body of the part. That seemed to lock in the correct slicing to reveal a bottom skin with partially through holes. I will in future drawings try to adjust the depth of holes to cooperate with the slicer logic.

I have elevated the hot end temp to 225, but have not had a chance to try everything again. As above,, many issues compounded to force a rest and will re try again this evening. Should be a good start, fresh tape, fresh level, hopefully a good adjustment on z limit switch. Its an opto switch, but somehow regularly seems to need micro adjustments. I can tell its off when the print head insists on choosing its own z zero even after I set it manually. Im surprised that the software does not just remember zero points without having to rely on limit switches. Its not like the z stepper is highly stressed to cause lost steps. I do feel like the heat and extrusion rate are still badly mis matched. I have it hot enough that the filament is getting stringy and blobby, which was not an issue at 220 deg and .4mm nozzle. So, it appears that the material is melting too much, and I may still need to increase the extrusion rate.

Oh, by the way, Yes, I set nozzle diameter to .5mm in machine settings in cura.

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