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Clancey

Overhang - what can I get away with?

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I know this is a really difficult question without all the Cura settings, knowing the material well and having a copy of the model, but what angle would you think I can get away with if:

I have the Ultimaker 3, I'll only be using 1 AA .4

I'm using a good quality PLA

Major Cura settings are Profile Fast, Temp 210, Speed 100, Wall speed 50

I get good layer adhesion with these settings, the speed means the outer walls are a bit ragged, but this is actually good for this model. It's a hollow pumpkin which a friend is going to use as an LED light. It's only as the top curls back in that it really needs any support at all. But I'm aware time is running low if I'm going to get it printed by Tuesday morning, it fills the build plate. If I ensure the model has all the support it could possibly need (even on lowish settings) I don't think I'll get it done it time as the printer is already tied up until tomorrow morning. If I set the overhang to 60 I can save a couple of hours and I'll just get it done, but if it fails I wont stand a cat in hells chance of running it again.

I don't really have a choice, but what do you folks reckon?

Thanks.

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With a high quality PLA 60 deg should not be an issue unsupported on an UM3. It even works on an UM2+ which has a bit less cooling power due to the different type of fans. Just make sure you have 100% of the cooling power available. And be aware that the most of the cooling comes from the left and from the right (a bit more from the left if you use the left printcore slot).

If you have not yet done so you might want to use a higher layer thickness. 0.15mm gives walls almost as nice as 0.1mm but take much less time to print.

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With a high quality PLA 60 deg should not be an issue unsupported on an UM3. It even works on an UM2+ which has a bit less cooling power due to the different type of fans. Just make sure you have 100% of the cooling power available. And be aware that the most of the cooling comes from the left and from the right (a bit more from the left if you use the left printcore slot).

If you have not yet done so you might want to use a higher layer thickness. 0.15mm gives walls almost as nice as 0.1mm but take much less time to print.

Adding to this (Which is spot on), I suggest that when you have time, print some overhang tests such as these:

Basic Search

I printed this one and

This one.

All of them have different conditions such as some are thinner and will bounce more, etc. But I found that I can print up to about 65° without issues on the underside. After that, it starts to have underside issues.

If the underside is not visible, then I found a decent top surface with an 80° overhang. Bridging would be a separate issue.

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That's a tough one.  I'd use a UM3 which can print PVA on the lower portion of the sphere.  Without PVA, it will print as is but the area that is less than 10 degrees from horizontal won't look so good.  Also you will have severe raised edges and when the nozzle hits those it could knock the part off - all this is only a problem in the first 1/10 of printing the sphere - once you get past that you are good.

You could add a cylindrical stand built into the model.  Solid.  That would help all these isues.  If the moon is 200mm in diameter the stand should probably be about 75mm in diameter.  I'd put that on the south pole.  You might as well also sink the moon into the glass a few mm as you can't see the south pole anyway if you go this route.

Some people might print it in two halves and glue it together but this is more difficult to do than you might think as the X/Y axes aren't perfectly perpendicular so the circle cross section on the glass will be slightly eliptical towards upper right/lower left or the other diagonal.  You could heat one of the halves to 60C and push it to the right shape I suppose.  Or just suffer with a line around the equator.

Rotating the second hemisphere by 90 degrees should help.  Making sure the rods through the print head are as close to 90 degrees as possible before printing will help also.

Edited by Guest
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If you are on Cura 2.3 or later (that is when I started using Cura), go to the configure Cura under the 'Preferences' drop down. In settings uncheck the "Automatically drop models to the build plate."

It may have been called something else in the past. But that will give you a lot of freedom to put in any value into the z field in the move type in box and it will hold that value.

Edited by Guest
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Thank you kman! I'm learning that calling a Cura feature by its correct name is frequently the key to finding it in Search. After your tip the search doors suddenly opened. i.e. it's not a hand appendage, it's a finger!

Edited by Guest

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