Model looks fine in HASH, export to OBJ and everything is wrong!

[Mikal]

Like the title says, looks great in HASH, but exporting to OBJ gets wrecked. Not sure what I'm doing exactly wrong, might be export settings... Or maybe I screwed up making the model...

 

Goal is making something 3D printable.

I've included the file if anyone wants to poke around.

MG Rings Fix.prj

[robcat2075]

My polygon knowledge is next to zero but when I look at the model in A:M I see it has many internal patches, which I think are bad for OBJ export and many flipped patch normals which maybe is a problem too?

I'm not sure. Hopefully one of our 3D printing whizzes will give it a try.

 

[robcat2075]

Looking a bit further... when I look at just the cross section of the shape I see that the portion between the big ridges is only a single surface with no enclosed volume (see arrows). The 3D printer will need a model that is entirely enclosed.

If you lathe an outline that is a continuous enclosed shape and use that as the basis for your model I think that would export and print successfully.

[Fuchur]

Hi,

yes, pretty much exactly what Robert said. Internal patches might be bad here and of cause: Everything needs to be closed (it does not have to be connected but it needs to be closed and of cause it needs a thickness everywhere. Normals can be fixed in general, but it is better to already do them right in A:M.

A starting point is to use > Remove Internal Patches, but that can not give it a thickness at any place. You will have to fix that by hand.

Best regards
*Fuchur*

[Mikal]

Hi Everyone,

Thank you for the helpful advice! I've updated the model and now it's solid all the way through. My last issue is that on the tops and bottom the model is bending through the floor. I know I can hit "P" to make those sections straight, but the model doesn't look natural. Is there a way to reduce the severity of the bend in these parts?

I've attached photos and the new model file.

 

MG Rings Fix.prj

[itsjustme]

If you select a point on the splines causing the issue, you can change the InMagnitude or OutMagnitude of the Bias...or rotate the bias handle to change the angle.

 

 

 

[robcat2075]

Note that David has the "Show Bias Handles" button at the top enabled to make the bias handles visible when a CP is selected.

It is easiest to make that bias edit on the outline before you lathe, rather than have to make that edit on all the copies that get made.

[fae_alba]

Why export to obj ? Why not export to STL then slice the model to get it in gcode. I have found that the measurement system in hash is off by an order of 100 percent, so when slicing you may need to increase the size of the model.

 

Another thing to watch out for is positioning of that model on the print bed. There are going to be a whole lot of supports, and if the model is delicate it will be next to impossible to clean it up.

 

[pixelplucker]

STL files are good for the single continuous geometry. When there are multiple objects and shapes that intersect then obj files work better for some slicing software. I remember formlabs software that uses meshlabs would cause grooves where you may have co-planer faces on the prints. Other oddities was hollows where shapes intersected each other. Obj format it was repairable within the application.

Anyways if possible just make a clean model without errors if possible.

[fae_alba]

That's an interesting point. I've seen such issues in cura when slicing STL files from am. Never made the connection to the STL file itself...makes me want to try an obj file now!

[robcat2075]

The actual conversion to polygons shouldn't be any different. It's the same code that is subdividing the patches, right?.

[fae_alba]

I suppose, but there have been times where in the STL model during slicing I see weird dimples that aren't there in am. I normally just accept them, and putty fill them after printing.

 

[Mikal]

Just an update for everyone, I'm using CURA to slice the STL, however, the thinest parts disappear and are replaced with supports. Maybe my settings aren't right in CURA, but I'd imagine it's not to thin in the inner circle area right?

[fae_alba]

You do need to build volume or space in the outer walls of your model. So if say you want to use am to make a hollow ball, you need to model two spheres and stitch them together to form one sphere with an inner and outer wall.

[Mikal]

1 minute ago, fae_alba said:

You do need to build volume or space in the outer walls of your model. So if say you want to use am to make a hollow ball, you need to model two spheres and stitch them together to form one sphere with an inner and outer wall

I do have this much space. Maybe I need to select a smaller nozzle size? This specific print measures the size of a dime.

[robcat2075]

A dime is a pretty small size for extrusion printing.

Just to test, try thickening the thinnest places WAY thicker and see what comes out.

[pixelplucker]

STL files only support single closed mesh geometry. An obj can have multiple mesh's in the same file. So unless you can make the model in one piece with 0 errors you may be better off with an obj.

[robcat2075]

If I export a model that is not a single surface to STL and import that STL as a prop it is definitely not a single surface.

 

[fae_alba]

If the amount of space between the walls is less than the nozzle, then you will wind up with a very weak print. You would need to adjust the model in those areas. Also, investigate increase the fill percentage. In a small print theres no shame in 100% fill.