Meshmixer STL editing

Is anyone familiar with using Meshmixer to edit STLs? I printed out a side mount bracket for a spool holder and found that the holes for the t-nut insert are too small. I thought I’d just ream them out with a drill but ended up breaking the piece. So I want to re-print it but with bigger holes.

So I know how to do the basic meshmix trick to add an object and then do a boolean cut but in this case I just want to make the existing rectangular hole bigger. It’s also at a funny angle so I’m having trouble even doing the boolean difference as I can’t get the primitive to align with the face in the hole.

Anyone understand what the heck I’m talking about and know how to do this? :wink:

I’ve been doing a bit of STL modifications in Fusion 360 lately. It’s pretty easy and there are a few good Youtube videos on it. In short, this is what I do:

  1. Open an untitled session in F360.
  2. Go to Insert → Insert Mesh
  3. Here, then you can reposition, rotate the mesh object and define units, etc. then accept as OK
  4. Left side, right click on the unsaved project name “(unsaved)” and click on “Do not capture Design History” and select Continue
  5. Right click the object and select Mesh to BREP and the operation is a new body
    5A. If the MESH has too many facets, I prefer to plane cut the object into smaller chunks so I don’t need to use the Reduce under MESH->Modify and lose precision
    5B. If you have to plane cut, MESH->Modify->Plane Cut, and the cut type is split body
    5C. Move back to the SOLID section to access the MESH to BREP again
    5D. Right click the object and select MESH to BREP for each body. Repeat above steps if you are still getting too many facets.
  6. Go to SURFACE section and select MODIFY → Stitch
  7. Select your split bodies and select OK and it will create the new body

You are now ready to edit the object! You can turn the History back on at this point as well.

I’ve never done anything with Fusion 360. I’ll have to start playing with it…

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Hi @SpaceMoose

I worked with Meshmixer a bit while in school but never really kept up on it to do the kind of mods you are looking for. I do like the way @bd43 did it in Fusion. If you are looking to learn some fusion my go to is Lars Christianson on YouTube. He is actually an instructor for Autodesk and it shows. I owe Most of my fusion knowledge to Lars.


Another good one is Kevin Kennedy. He has a good library and well organized.

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Thanks Glenn & Jason! I have seen some of Lars Christensen’s videos but not Kevin Kennedy’s. Lots of learning available! Now the trick will be finding the time to do it :slight_smile:

Just as an aside I figured out what I had to do. In Meshmixer it seems you need to use pivots to serve as a point of reference on a plane so then you can use cutting planes based on the pivot point to do flush cuts. So I was able to cut a cube primitive that fit the existing hole exactly and then transformed it to enlarge and then did a boolean subtraction to make the hole bigger. Worked like a charm and now I’ve got my side spool holder attached and working great!!

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that’s awesome, I need to keep my skills up, but I hear ya, time is always an issue…

I have never heard of Kevin’s YouTube either, another one to add to the list of things to watch. :slight_smile:

Actually I missed a step in the last post. The first thing I did was created a cube primitive and put it in the hole I wanted to enlarge. I did a boolean subtraction to subtract the main model from the primitive so I was just left with the positive from the hole. It had some small cylinders on the sides from the screw holes so it was that that I clipped off using the pivot and plane cuts. Then I increased the size and then subtracted it from the original model and that did the trick!

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Just an update on MESH to BREP in Fusion 360. Early July 2021, Fusion 360 went through a revision. You no longer have to turn off history to access MESH to BREP. Also, the process is a little more streamlined. More about this on this helpful tutorial:


Yes! and no more having to delete faces to clean up most files