'Bump' and hole in the corners of prints

[Brulti 177]

Hello,

 

Sorry for the title, but I'm not sure how to describe my problem properly, so, I've attached some pictures to show you what's going on.

 

I've no idea what is causing this line in the corners of the pyramids, and why the arm of the catapult came out so ugly, and it does it only for sharp angles. As you can see, it did it on the pyramid head, but not on the round part next to it, and the base of the catapult came out looking perfect. I've printed many catapults before, using every standard profile from 0.2mm to 0.06mm and I never had this problem before.

 

I've serviced the printer, did hot and cold pull, checked for debris, cleaned it, put on some grease on the rods and did the whole maintenance thing, but I still have the problem. The printer and CURA are up to date with the latest stable version of the software and firmware. I'm using UM Green PLA for those prints, with the standard settings on CURA. It started doing this very recently, I've had the printer since July, and didn't had the problem before.

 

If you have ideas on what causes this and solutions, I'm all ears. Thanks.

 

Edited January 24, 2018 by Brulti

[kmanstudios 1,120]

I have run into this and there are a couple of things to do to help solve this.

1. Cut down on temps and play with speeds a bit.
2. Print a few objects at a time so that the nozzle can leave a part to cool while it is working on another part.

That is what I see happening on the top of the pointy parts. It is just sitting there moving hot plastic around and getting pulled about because it has no time to cool a bit. The bumpy schtuff I see happening, I would call 'proto strings', seem to be also part of running a bit hot. It is not fully stringing, but apparently got a bit of molten drool as it either comes into contact or leaves a part.

[Brulti 177]

Ok, that makes sense, especially for the pointy parts.

 

However, I don't understand about the bumpy stuff, and especially how badly the catapult has printed, since I've printed this catapult before and it came out looking very clean.

Much like the pictures on the thingiverse page: https://www.thingiverse.com/thing:1763518

Could there be some damages on my printer or the nozzle or something?

Edited January 24, 2018 by Brulti

[kmanstudios 1,120]

Printed clean on this machine? What machine is it?

[Brulti 177]

On the same machine. It's a UM3 Extended.

[geert_2 558]

Obviously, your pyramid has this problem:

 

This is due to not enough layer cooling time, because the hot nozzle is printing on a tiny area only, and it keeps radiating lots of heat. So the model can't cool down and can't solidify.

 

These models were designed just to test that. The left models are printed separately, the right ones are printed cone+tower together. Dimensions (numbers) are centimeters: the cones are 2cm high and wide. The tower is 1cm x 1cm, which obviously is not yet enough: the edges still curl up in the white one, as soon as it has finished printing the cone (so the nozzle is full-time on the tower).

 

You can reduce this problem - but not eliminate it - by printing a dummy tower next to your real model, as shown in the image. Make sure the tower has a big enough base plate or brim, so it does not fall over, and it is big enough to provide sufficient cooling time for your real model. You could partially hollow-out the dummy tower, to waste less material, and to keep the printing time per layer about the same. So that the cooling time per layer is the same for every layer: this gives a better printing quality than wildly varying cooling times per layer.

 

Also, printing cooler and slower reduces the problem, because then it has to dissipate less heat, and heat radiation is less.

 

For your catapult, I guess (but it is a guess!) that the problem is a combination of (1) not enough cooling time and (2) too steep overhangs. Thus I would suggest you try: print slow, print cool, print multiple models at once like kmanstudios said, or print a dummy tower next to it. and/or design a support column under it, which you cut off later. This will require some trial and error, but then you will learn a lot. Keep watching while printing, so you see what happens.

 

[gr5 2,192]

You have 3 issues that I see:

1) Pointy tops melted.

2) under side of catapult sucks (steep overhang)

3) On of the 4 pyramid ridges is strange

 

People have been addressing #1 as it's pretty easy to fix and common.  You CAN completely get rid of it.  just the way geert says to do.  Print a second thing next to it.  Or even better print 3 things and the middle one will have the best quality (two added towers -but add them into an empty cura like this: tower, your part, tower as it usually prints in the order added and you want your part in the middle so cura doesn't do 2 layers in a row on your part).

 

#2 - overhangs

This is typical for a steep overhang.  I don't know why you didn't see it before.  Was it the exact same catapult?  Do you still have the old one?  I bet it looked almost as bad as this one if it was the exact same angle.  Layer height, pla color (yes just the color), print speed, fan speed, and temperature can all affect the quality.  Did you do this one the same layer height as before?   Was it the same color pla?  Same temperature?  Cura changes things like temperature from one version to the next so if you changed cura versions...

 

The most important thing to get good overhangs is max fan (100% fan).  The next most important thing is to print cool as other's have said.  Try dropping the temp by 15C (just do it in the tune menu) and cut the speed in half (also in the TUNE menu).  It will take longer but should look a little better.  I recommend you print the catapult again and change this half way through the print to see visually the difference.

 

Layer height matters.  You don't want too thick or too thin.  I personally think around 0.1mm is ideal.  But I'm not 100% sure.

 

#3 - that ridge is weird.  It looks like you are simply printing too hot.  Maybe.  I'm going to go with too hot.  Try lowering the temp around 10C and reprint the pyramid.  Even better, while it's printing, lower the temp by 5C for 10 layers, then another 5C for 10 layers, then another 5C for 10 layers.  Maybe mark the part with a sharpie as you go.  Let us know what you learn.

 

[gr5 2,192]

Since you have a um3, maybe you should print that first catapult with PVA.  That's what's so great about the UM3 - it can print overhangs with dissolvable support.

[Brulti 177]

Thank you all for your responses and explanations. I'll keep in mind the solution to deal with the blob at the tip of the pyramid, I'm sure it will be useful for future prints.

 

It would seem that the main source of my problem was my printcore, for some reason. I forgot that I had another AA 0.4 core, so I swapped it, and printed a pyramid again, at 0.2mm and 0.06mm as I did with the first one. As you can see on the picture, the strange ridge defect is gone on the pyramid printed with the new printcore, and the other ridges look perfect.

 

 

 

 

I've started a new print of the catapult at 0.06mm, like the last one, but since it takes about 6 hours, we'll see the result and compare tomorrow morning.

 

So, now I'm left wondering how come the printcore started to behave in such a strange way. Is it normal wear and tear? This core came with the printer in July, so it has seen about 6 months of constant use Is it because I used it to print other materials? I printed reflect-o-lay and laywood with it, though the maker said it wouldn't cause any sort of abrasion on the core, and the reseller markets it as safe for all type of FDM printer.

 

Comparing the old and new printcores, it looks like the old one is less pointy than the new one. I'll compare more closely tomorrow morning once the catapult has finished printing. What is the life expectancy of a printcore?

 

You can find the catapult here: https://www.thingiverse.com/thing:1763518

It has been expressly designed to require no support of any kind, and still print nicely. The ones I printed before, in various colors, all came out looking very nice, similar to the pictures posted by the creator, and certainly not like the green one I printed earlier. Below are pictures of one I printed in white. I also did one in black, blue, and other colors, all came out looking like the white one.

 

 

 

Edited January 24, 2018 by Brulti