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3D printed circular object is actually a polygon.How come?


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Hello! I used 2 3d printers to print the same object(a funnel with a circular section): Makerbot replicator 1 and 2.The result was a shape which was not circular in section but polygonal. What can I do (or the owners of the 3d printers) in order to obtain a circular form?

Initially I thought it was displaying it as a polygon (”shade” command) to save memory usage but when the actual product turned out non-round I concluded that I (or the owner of the printer) may be doing something wrong.

Thank you!

palnie3.1.dwg

Untitled.jpg

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JD Mather
... What can I do (or the owners of the 3d printers) in order to obtain a circular form?

 

Viewres = 20000

Facetres = 10

RE

then stlout.

 

 

There are a bunch of other tips at the link at bottom of my post.

stlout.PNG

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JD Mather

Keep in mind the stl files are by definition planar faces - so this simply increases the facets.

I thought there was another settings box in AutoCAD for more stl control - but I can't find it now.

Autodesk Inventor has a dialog box that allows more control.

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I did not know that .stl files are planar faces but that explains the outcome. So, if the drawing had an outer circular surface that contained N individual points, the maximum achievable resolution would be N/3 faces because 3 points are the minimum requirement for a plan. Judging by the apparent* improvement generated by all the measures that you kindly suggested (once again helping me and others having the same problem) I don't know if such a high resolution is possible N/3; if possible, this level of approximation would make the transformation 'circular-> sum of plans' unnoticeable.

*by apparent I mean I did not reprint the part to verify its roundness but to my eyes, the object after shading, appeared smoother.I don't know how to verify what the printer would "see" .

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JD Mather

Increasing the number of facets decreases their size and increases their number. The part gets smoother (rounder). At some point the resolution of the stl file is greater than the resolution of the printer. The resolution of the printer layers becomes the limiting factor (the part will show "stair-stepping"). Better printer resolution = more $$$.

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actually, I think more than N/3 faces: one point and the three points that are closest to it would give two triangular faces(I am talking about 4 point on the walls of a large cylinder, large radius, so the 4 points are almost planar but due to the finite radius they are not ) .Add another point and another face is possible so 5 points for 3 faces which is greater than 5/3=less than two faces.And if we take into account the fact that it is a closed curve there are even more connections so more faces.

There must be a formula for the maximum number of faces(resolution) given the number of points that form a curved surface.

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when you say "more $$$ " I can confirm: first quote(all without VAT): less than 50 euros; second quote 170 euros; third quote 1280 euros! more than a thousand euros! It means nothing to Pratt & Whithey or Honeywell but to me, that is a colossal amount of money for a plastic 3d printed part

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That said, everybody was extremely polite and helpful; even if they could not help me because it was too expensive, they guided me to the people with the least expensive equipment .

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JD Mather

A trick that I use is to coat the model with dry-wall compound (not sure what you would call it - a soft plaster).

Sands very easy.

recoat and repeat sanding

Spray paint.

 

RP Vacuum_JDMather.jpg

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Lovely finish! I need it to be as smooth as possible to create little turbulence so I was thinking of painting it with hydro-isolating paint (the piece is made out of three smaller ones because it would not fit in the printer as a whole) in order to prevent air leaking at the joints. I don't know if paint alone, without primer, will dissolve the plastic. I have to document that.

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I printed a total of 6 parts(2 identical sets of three parts so it is perfect for comparing the printers caeteris paribus)

the second 3 are printed with PLA and the result is excellent: strength, density, resolution (replicator 2)

the first 3 parts I am not sure of but they have been printed with Replicator 1 and are quire fragile and not very well glued together...in some areas plastic wires are sticking out and the thinner sections have cracked where two layers meet as if they had not been properly glued (insufficient heat perhaps).

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There is a way to get a smooth finish on a PLA printed part using tetrahydrofuran that is similar to the way acetone is used to get a smooth finish on ABS printed parts.

 

BTW...whenever you are working with chemicals wear the proper protection such as nitrile or chemical resistant gloves, eye protection and make sure you have adequate ventilation. Safety above all else.

 

The applies to you too JDM. Gypsum is an irritant to eyes and lungs. Wear a mask when sanding.

Edited by ReMark
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