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Holes are smaller than designed

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Posted · Holes are smaller than designed

Dear all,

I guess I am not the only one mentioning this issue, but i searched for many forums and sites about this problem and cant find the right solution.

My problem is the following. The designed holes are getting smaller when printing. Exactly with 0.4mm no matter what is the diameter. The boundary walls of the model are perfect size. So in my case if i print out a 20x20 box with a 10mm dia hole in the middle i got the following:

- outside dimensions are exactly 20x20 but the hole is 9.6mm dia.

If i try to change the so called "horizontal expansion" setting with -0,4mm than i got the following results

- outside dimensions are 19.2x19.2 and the hole is exactly 10mm dia.

So this setting changed the desired hole size but also ruined the outside dimensions.

Is it a normal thing or its kinda unique.

Is there any other ways than designing it in CAD with extra dimensions like a hole with 10,4mm dia? It is weird because if im going to make some drawings for further CNC than i have to change the whole model again.

I hope someone out there has the clue.

Thanks in advance!

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Posted · Holes are smaller than designed

This is a normal effect on all similar 3D-printers. The filament is still molten or somewhat flexible when laid down. When the nozzle is printing a corner, as in tight circles around holes, it pulls the molten filament to the inside of the curve.

In small holes this is even more visible: a 3mm hole may come out as a 1.5mm hole. It also depends on printing speed and temp.

Solutions could be: change the dimensions in the design, or go through the hole with a drill.

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Posted · Holes are smaller than designed

hiya,

I do exactly what Geert_2 is suggesting. any part that needs exact fitting I reduce by half the nozzle size.

works fine for me :)

Bex

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Posted · Holes are smaller than designed

I make all my holes .5mm larger than desired. Vertical holes. Horizontal holes are fine.

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Posted · Holes are smaller than designed

I noticed exactly the same thing.

5a3340e8d981d_2017-11-1611_55_43-AutodeskFusion360.thumb.png.7b582089367fbc79d64782e7fa202457.png

My 18mm desired outside diameter prints as 17.8mm and my internal desired diameter of 10mm prints as 9.8mm due to material contraction.

I added a horizontal offset of 0.4mm to exaggerate the effect and ended up with 18.6mm outside diameter and an internal diameter of 9mm. It's no coincidence that both dimensions moved exactly 0.8mm as Cura has added an offset edge of 0.4mm to the outside wall but has also added an 0.4mm offset to the inside wall making the hole smaller.

The only way to do it is to perform non-uniform scaling along the X and Y axis in the scale settings rather than use the horizontal offset.

It is clear that Cura is adding an

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Posted · Holes are smaller than designed

It's not exactly caused by the part shrinking.

It's because as it extrudes, PLA sticks to itself like snot. Like a liquid rubber band. And it is also shrinking rapidly while still liquid so it is pulling inward. and when you go around any corner it pulls inward. It's a little worse on corners. It gets better as you get farther from the heated bed. It seems to help if you have double pass walls (e.g. line width .4mm and shell width .8mm) as the inner wall helps hold the outer wall in place.

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Posted · Holes are smaller than designed

if the hole is smaller that designed you need to use a negative number in the horizontal offset.

Depending on the tolerances involved, that could create other issues in your print such as making other areas smaller than they need to be.

An example would be if I have a widget that is printing just fine at the designed width, and it needs to be that width to slot into something else or be accurate, then the hole would be made more proper and the rest would falter.

I think it is better to learn the tolerances, the why of things and then learn to design around that.

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Posted · Holes are smaller than designed

 

if the hole is smaller that designed you need to use a negative number in the horizontal offset.

 

Depending on the tolerances involved, that could create other issues in your print such as making other areas smaller than they need to be.

An example would be if I have a widget that is printing just fine at the designed width, and it needs to be that width to slot into something else or be accurate, then the hole would be made more proper and the rest would falter.

I think it is better to learn the tolerances, the why of things and then learn to design around that.

 

totally agree, I was just pointing out the fact that DB wondered why the hole got smaller when he applied horizontal offset and he quoted a positive value.

I design all my stuff with a tolerance depending on the feature I am designing.

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Posted · Holes are smaller than designed
......totally agree, I was just pointing out the fact that DB wondered why the hole got smaller when he applied horizontal offset and he quoted a positive value.

Wow...totally missed that...Duuurrrrhhhhh...:p

Thanks for setting me straight.....

I will go back to me hobbit hole now........

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Posted · Holes are smaller than designed

 

......totally agree, I was just pointing out the fact that DB wondered why the hole got smaller when he applied horizontal offset and he quoted a positive value.

Wow...totally missed that...Duuurrrrhhhhh...:p

Thanks for setting me straight.....

I will go back to me hobbit hole now........

 

nah don't go to the hobbit hole, there are still more unexpected journeys lol

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Posted · Holes are smaller than designed

Just a question from a 1 month old owner of a UM 3+....If I check the "Compensate Outer Wall Overlaps" box, what happens to the under size hole dia versus the outside dimension?

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