Modifying existing STL and not getting faces right

Greetings experts, I downloaded an .STL file that i need to modify. I used cleanup 3 to extract and reduce the number of lines/edges from the model. I am trying to add in the center trapezoid into the model but when i group and send it to my slicing program, i can see that the trapezoid is not directly attached to the model on one side, i have tried for countless hours deleting, and re-drawing it but it still fails. Any help is greatly appreciated. Test_foot_v1.stl (187.5 KB)

Share your .skp file with us so we can see exactly what you’ve got in the model.

Sorry, I honestly thought I uploaded the .SKP file, but it appears I uploaded the .STL. Thanks Dave.Blank_short stand.skp (776.7 KB)

That’s a big help.

So you didn’t open the group with the original geometry before adding the new geometry. If you double clicked into it until you were at the raw geometry then you would have had things basically correct. Here you can see how I have the group and your added geometry selected.

Before you start adding other geometry, though, you should clean up the original geometry. The diagonal lines I show selected below will give you trouble. There are similar wones at the other end as well.

Are the chamfers really only supposed to be on one side?

Hi Dave,

Thanks for the tips, I’m no longer at my PC at this hour but will try tomorrow morning. Can you provide guidance on how to remove the diagonal limes? I tried redrawing the rectangle using the outside perimeter but it didn’t work. I also tried deleting the diagonal lines then drawing just the exterior but that also didn’t work so I left them there. Lastly, yes the chamfer is only needed on one side. Again, thanks for your help.

Due to the lack of planarity of the faces, I think it would make more sense to start over and make sure they stay planar. Some of the faces can’t be planar but those on the inside of the uprights should be. I tried to approximate what you had.

Blank_short stand.skp (436.1 KB)

Hi Dave,

Sorry for the delay in responding, work got in the way. Did you ended up just re-drawing it? I do see what you’re saying in terms of the “planarity” of the faces. It appears there was no “real” way to make them all Planar. I have been trying for about 30 minutes. With your skills re-drawing it probably took you all of 5 minutes?

I did redraw it and cleaned up the geometry. It looked to me as if the original wasn’t modeled in the best way to begin with. I did a little bit of measuring from it and started over. It took a little longer than 5 minutes mostly because I spent time sorting out the dimensions for the original. One thing I don’t know for sure is if I got the holes in the right locations. No idea if their positions are critical or not.

Hi Dave,

A month later, I’m struggling with the same leg again. I tried to use the newly drawn leg you provided and make it “Taller”, but keeping the same top width (attachment point). After about an hour of messing around with it, I was still unable to achieve what I wanted so I loaded up the original .STL, used the cleanup plugin, exploded it and drew in my box. Everything appears to look “good”. I then “group” and export as .STL, and when I go to slice everything looks good again, except for the chamfered edge facing down so I rotate it. As soon as I rotate it and reslice the model is all “messed up”. I’ve attached the sketchup file for your review. If you could find it in your dearest heart to provide insight and or correct it for me that would be great. I’ve noticed when I model things from “scratch” everything works out, but whenever i modify an .STL all kinds of issues arise. Thanks again for your help!

truggy foot-v2.skp (430 KB)

There’s an internal face where the stretcher meets the leg.

truggy foot-v2.skp (458.8 KB)

FWIW, if you wanted to make it taller and keep the same leg angles and top width, you would need to make the base wider. You could do that with the Move tool.

Here I’ve added 50mm to the height of the leg structure by selecting the geometry at the top of the leg and moving it along the angled guideline. You have to deal with one side at a time but it’s quick and easy.

Then to make the top the same width as before, I selected the geometry as below and used Move to move it out to the other guideline.

Thank you sir, I got it to work on my own, Whew!..I also added Solid Inspector plugin to assist in the future!..Much appreciated…

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