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jcoutts

Bad overhangs on small prints!

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Hi guys,

was wondering if anyone could offer some advice. I am printing some small parts and there is some bad overhangs happening. The support structures look like they are printing nicely.

I have attached two photos, both had overhangs set everywhere and you can see the surfact that was overhanging producing a very poor result.

IMAG0891

IMAG0894

 

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I'm having the same issue and I'm desperate for help guys! I'm trying all week long and I cant figure this out :(

Every time there is an overhang the nozzle is lifting the outer shell!

At the side of the right fan the effect is worse!

I try to print at lowest speed and temp possible. while its getting better at lower speeds it is still there.

I've tried to print from 185c to 200c and 30 mm3/s from 100% to 50%.

Also tried 2 object at the same time to let it cool more.

Only bed is at 60c all the times or else the print is not stuck in place.

I'm asking too much from the printer ?

Btw its impossible to print small objects at quick settings (normal - high). Speed is too high and outcome is really bad for my taste!

Here is a really bad situation

gallery_36059_1662_912914.png

And this is one not really noticeable, but it gets worse if I let it print and not lower the speed and temp.

gallery_36059_1662_415057.png

So what should I do now?

 

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I noticed that if the fans are running at 100% the right fan is not at full speed all the time.

It goes down to 75% by its own free will...then it goes up at 100% for a few seconds, and this condition repeats. I can see it lowering speed, like car wheels rotating the opposite way while driving. The left one (the one close to the nozzle) is not fluctuating at all.

I put the fan speed at 95% and the speed remain the same for both fans with out any fluctuation visible.

Maybe this can help someone who is having the same issue.

 

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Yup you want to go real slow, 30 should be OK but even try 20 if need be. And you want fans at 100%. I am thinking that if you are using thin layers, say100, it might be useful as a trial to go thicker. My logic is that there is more plastic to be raised which may reduce/remove the affect.

Make sure your minimum layer time is at least 10 secs. The pieces are very small so you will have to print 2 or more to achieve this. Try using z-lift too (this will most likely introduce some stringing

 

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Grab the over hang test from make: http://www.thingiverse.com/thing:533472/#files

Run the test and post up the results, we should be able to tell you what to tune after seeing those results :)

After I change filaments I always run the overhang and bridge test to re tune the printer.

 

I had no idea there were all those tests, guess I know what I'll be doing in the next week to see what I can tweak.

 

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Hi Tottenham (I guess you chose that name after Dafoe joined Toronto :) ) I certainly do not want to dissuade you from any testing, that is always a good thing! But I was wondering why you print the test pieces when you change the filament to retune the printer. Changing filament does not change the physical characteristics of the printer so I am wondering why it needs a retune. EG if your bed level was right before changing the filament it will be the same after changing the filament.

To be clear I am not saying you are doing anything wrong, I am just curious :)

 

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Hi Tottenham (I guess you chose that name after Dafoe joined Toronto :) ) I certainly do not want to dissuade you from any testing, that is always a good thing! But I was wondering why you print the test pieces when you change the filament to retune the printer. Changing filament does not change the physical characteristics of the printer so I am wondering why it needs a retune. EG if your bed level was right before changing the filament it will be the same after changing the filament.

To be clear I am not saying you are doing anything wrong, I am just curious :)

 

I actually visited England when I was a kid and I got to see a tottenham game, so thats where that came from :) Been playing football since I can remember.

I typically run the overhang test after changing filament types. Nylon -> XT or similar, and just run the bridge test 25% through when changing colors and types. Sometimes I will also do it between different colors, for instance XT Blue and Red like to be leveled slightly different on the two rolls that I have and even the temps are sometimes a little different. For most printing its not a huge deal, I print a lot of small parts that need high details and small tolerances so getting each type of filament dialed in helps me out.

Now however im going to contradict everything I just said above :)

I just recently starting using my own test piece though which is just a large .4mm walled circle that makes 10 layers, as it goes around I tweak my bed on the fly to get the best results for that filament. Most settings do translate over between filaments but it seems the bed leveling needs to be tweaked so this simple test uses less plastic and IMO is the best way to level the bed.

I think for a noob printing those test pieces is a good idea since it really shows what you need to work on, once you know what you're doing though its much easier to make small changes without those tests or even a simple test piece like the one i described above.

 

here are some pictures from the overhang test .stl that you asked.

This was printed with normal settings from cura 14.12.1

210c - 60c - 100% speed

I didnt let the print finish for obvious reasons.

what should I change so I could fix this?

 

Are you just using the cura default normal profile?

What is your flow rate at? It almost looks like its over extruding on the back side.

EDIT: After looking at the pictures again it looks like your nozzle is really close to the print, double check your bed leveling. A piece of paper should have a very small amount of friction between the nozzle and the glass.

 

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you may also use "tweak at Z" to lower your nozzle and bed's temp to 180/50 after the first layer.

start with values that gives you good adhesion (220/70) and then drop to cold print right after the first layer.

for small parts, be carefull with min layer time : set it to about 4 sec, and in the expert settings, set the minimum speed to the same speed as you print speed, with head lift enabled.

this will prevent your hotend from hovering for ages just above you print, melting the layer below.

 

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I just discovered something last night that might be of help.

I was printing the small gear from this gear set for the UMO extruder:

http://www.thingiverse.com/thing:40334

I was having a hell of a time getting a decent print in XT. Too hot and the teeth would deform and too cold cause under extrusion.

The reason might be relevant to this discussion. I watched as the edges of the teeth were printing and I could see that as the extruder laid down the next layer, the part was so soft that the extruder deformed a few layers below it.

After much trial and error I think I hit on the solution. It's simply that because of the small layer size, the extruder simply puts too much heat into the part. This is especially a problem with XT as requires hotter temps to flow and then remains very soft due to those very hot temps.

So I figured that I would add more fan and reduce the temp but that only caused underextrusion. Printing slower only seemed to put more heat into the part.

The fix was to get the nozzle off the part preferably by moving the fan over the part for extra cooling.

Cool head lift will meet some of this but it's problem is that the extruder begins to seep molten filament when you lift for too long of a time. The

My best result was achieved by printing a circular column next to the part in "all at once mode". This caused the extruder to move onto the column giving time for the small gear to cool. Since it was actually printing a part (even if it was later discarded), the nozzle didn't have extra plastic seeping from it to ruining the start of the next layer. Even better, I positioned the column such that the circular motion of the extruder while the column is printed bathed the gear in cooling air.

TLDR; small parts with quick to print layers will have bad overhangs because the part gets too hot. Use cool head lift and minimum layer time or print other parts "all at once" so the part gets a chance to cool and firm up before the extruder revisits it for the next layer. Too much heat causes sagging.

Try printing 2 or three copies of the test at one time....

 

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you also could try to rotate the part on the bed to get a better air flow from the fans. Maybe a rotation of 90 degrees would be better to have a benefit of both fans, or a 180 degrees to get the bad side closer to the left fan (because it is closer)

 

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EDIT: After looking at the pictures again it looks like your nozzle is really close to the print, double check your bed leveling.

 

?? Leveling only affects the bottom layer and *sometimes* the second layer but that's it. Leveling the bed differently (turning the 3 screws in any combination of directions, amount) will not affect the 10th layer at all. Even if you are crooked by 1mm (printing in air on one side and on the glass on the other) within 5 or so layers things have recovered and leveling no longer maters for the remaining layers.

 

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a 30 degree overhang (30 degrees from vertical) should be easy with UM2! Are you sure both fans are at 100% Maybe increase the infill so that it takes longer for the nozzle to come back to the same spot. Consider experimenting with .1mm versus .2mm layer height but I'm not sure that will make much difference. Definitely fan is important - adding more fan will help quite a bit. Printing cooler will help slightly. Rotating the part 180 degrees to get closer to the left fan should help a lot!

 

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210c - 60c - 100% speed

 

What the hell is 100% speed? What is the speed set to in Cura? I recommend you also print slower - it helps quite a bit for the filament to cool as it's coming out of the nozzle and be more solid as it the nozzle is leaving the filament behind. Otherwise it still has a lot of shrinking to do while still in it's liquid phase and ends up pulling like a liquid rubber band as it goes around the 2 outer corners.

 

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I disagree with George on two things.

First is that going slower will help. For the part I was printing, slower made the part warm even after removing it from the bed.

And two, not more fan .... more COWBELL!

 

Actually, George has a lot of experience so his advice is worth trying.

 

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The comment that told me that my nozzle is too close to the bed helped a LOT.

I leveled the bed again and set it away from nozzle with a little friction on the paper.

I'm getting decent prints now, still cant print at 60 deg perfect, but I think its not possible to do that anyway.

I will try it again with barely any friction to the paper when leveling to see if there is bigger difference.

gr5 maybe you need to rethink your opinion about bed level? Nozzle is allways closer, every layer, and is effecting the heat of the allready printed layers below.

When the head is making a turn in a corner, it drag and lift the material in that layer. You can see this effect it in my previous posts in the photos.

If you let this happening it keeps building even more than 6mm above the printed layer.

 

What the hell is 100% speed?

 

I stated that I was printing with normal quality settings gr5. (quickprint) Isn't those the parameters that must work with Ultimaker printers?

 

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