Creating an STL file for 3D printing

Jinkers · 2 Oct 2013, 21:45

Hi all,

I am new to Sketchup and it's been a long time since I did any 3D modeling. Last time was 8 years ago using FSDS (flight sim design studio) to create 3D models for Microsoft Flight Simulator.

I am currently trying to create some objects in Sketchup (free version) to have 3D printed, probably using Shapeways. I have installed the STL plug-in to allow importing and exporting of STL files. I created the object shown below (top image) and exported it as an STL file. However when I re-import it to view the STL model there are many polygons missing and some distortion in the surfaces (bottom image).

Anybody have any suggestions on what I am doing wrong (I'm sure it's a long list ).

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Thanks,

Scott

Box · 2 Oct 2013, 22:40

Images missing.

ely862me · 3 Oct 2013, 10:44

Hi !

You need to intersect all the geometry and make it one solid (one hollowed object) .
Importing back is always nasty, you should try to upload the model to Shapeways and see what they say .
Usually exporting to another format makes the model not solid and you need to use some external programs to heal the model. The extra lines are normal though, as far as I know.

TIG · 3 Oct 2013, 10:47

You have many reversed faces - the blue backs are often showing [edit/select & use the context-menu reverse faces and orient faces to fix that].

I assume it's a solid ?
Or is it nested solids ?

Even if Entity Info reports a Solid sometimes very tiny facets might fail to process, in many tools.

What is the size of this object?
It looks like a shirt button !

Can you mark the problem areas etc...
Can you upload the SKP.

There is no need to link off the 3rd party sites - just use Upload... to attach the images/skps etc directly to your post ... Some file types are not supported, BUT they can be put into a ZIP, and that will attach provided it's <~4Mb

Jinkers · 3 Oct 2013, 15:08

Thanks for the reply's

I reversed the faces on the model and re-exported it with the same results, see the image below (thanks for the directions). I didn't circle all of the faults just a few examples. Mostly missing surfaces and some distortions. I did notice that the number of "facets" exported did not match the number of "polygons" imported by the STL plug-in. And when importing I get a message that it is "correction geometry".

The model is a elevator trim wheel for a P-51 Mustang (WWII Fighter Aircraft). I also want to make the Rudder and Aileron Trim knobs and a few other parts. The elevator trim wheel is 5" diameter and 1/2" thick. I plan on putting these in a simulator cockpit, the whole in the middle is to mount to the "D" shaft of a potentiometer. I've attached a picture of the Trim Console of a P-51 so you can visualize what I'm trying to do.

Since I am using the Free version of Sketchup and the 8 hour trial period has expired I do not have access to the Solid tools. Does the model need to be a solid to be exported properly to an STL file? I was using the "Shell" function and then "smoothing" it.

Thanks,

Scott

Box · 3 Oct 2013, 15:29

One of the more common reasons for issue like this is size. If the faces are too small they can't be created. You may find scaling up by a factor of ten will allow it to work. Then scale down again.

Jinkers · 3 Oct 2013, 19:51

@box said:

One of the more common reasons for issue like this is size. If the faces are too small they can't be created. You may find scaling up by a factor of ten will allow it to work. Then scale down again.

Scaling up by a factor of 10 seems to have helped. The only problem is when I scale it back to normal the problems return. Is this a sketchup issue? Is the x1 STL file really ok and it's just a matter of how it is imported back into Sketchup and rendered?

I was also wondering about the structure for 3D printing, does it have to be a solid? If it is not just a shell and components exist inside the structure will it still print poperly (see third image)?

Thanks,

Scott

Aileron Trim Knob b.skp

ely862me · 4 Oct 2013, 07:14

As far as I know you need to have just one solid , that means you have to intersect those tubes with the wheel. It needs to be like a closed room, if you want it to be entirely solid. If you want to make it like a shell, you need to add thickness to it and let some holes for the extra material to come out.

Box · 4 Oct 2013, 12:19

I've very quickly reworked your model to make a solid. Your geometry needs some work, getting your bump and curve to work together is difficult but I'm sure you'll get the idea from my model.

I scaled up your model, split a section out of it so that I only needed to make one bump fit, then arrayed it (rotate copy 23x) to make the solid and scaled down.

Aileron Trim Knob box.skp

Jinkers · 4 Oct 2013, 14:43

Thanks Box!

One question though, how did you combine the bump and the disk section? The Shell function seems like it is the correct tool but I am unable to make it work. I am using the Free version so I do not have access to the Solid Tools.

-Scott

Box · 4 Oct 2013, 14:55

No special tools, I use free also.
Simply explode the bump and intersect it with the other geometry.
A little clean up, finding the bad edges that create holes, use line tool to draw the edges in to create faces. Eventually you will have two separate faces, one either side of the "disk", select and delete the internal one. Use CRTL and Eraser to soften the edges and you have a bump.

This is what I meant about your geometry needing work. The connection between the bump and the curve can be problematic and it is what is causing the holes you keep getting.

Jinkers · 4 Oct 2013, 17:01

Thanks Box,

I see what you mean about the geometry. I did some testing and found that if I make sure to use the same arc radius and paste the third arc point on the tangent the surfaces line is much better.

Box · 4 Oct 2013, 17:08

Excellent, it's always better to work things out yourself with a little nudge in the right direction, you learn more and remember longer.