Easiest way to create holes in object and Creat perfect hole for "Dowel".

[tjwalker_97]

Greetings,

I've watched videos on this but the methods described don't seem to work for me.  I have two things I'm trying to do.

1. Create 3 holes in the bottom plate of a model so it can be bolted/screwed down.

2. I have a couple of objects. I can add a peg "dowel" to one. I want to position one over the other and use something like Boolean Difference to make the object without the peg to have a hole in it the peg will neatly fit into.

The method I'm using is to drag a Meshmix cylinder onto the build, resize it so it makes the desired hole in the desired location and select both objects and do Boolean Difference.

The problem I'm running into is while it look OK in the preview, when I accept the change - it completely distorts the entire area around the hole.  I've tried every possible setting in the Boolean Difference settings with the same result.

I've created a 3 min video of what I'm trying to do.

https://vcheckvideos.s3-us-west-2.amazonaws.com/meshmixer.mp4

[MagWeb · Accepted solution]

Thanks for the video!

Let's start with the simplest information about why your second object disappears doing a BooleanDifference:

If you calculate the difference 5-4 you get 1 . Same happens on a BooleanDifference: You get the result of A-B. If you want to keep the minuend B, you simply need to create a duplicate of B before running BooleanDifference (> EDIT/Duplicate or click the double square button  at the bottom of the object browser). 

As you used a MESHMIX cylinder just a hint:

When you dropped a solid MESHMIX part on an existing surface you get the DropSolid tool options. Note the CompositionMode dropdown box. There you can set BooleanSubtract to do a BooleanDifference automatically.

Your either issue (seems to be the same for 1. and 2.):

Your source object seems to be a mesh with only a few but pretty big triangles (you can see the wireframe hitting W). Some situation like this:

Note the contrast in density of both meshes.

To get a boolean result and to weld the meshes at their intersection MM needs to increase the density of the low poly object around the intersection:

Now by default accepting the tool MM tries to get rid of those many tiny triangles. This is great if you deal with high poly meshes, but deforms low poly ones:

Instead if you disable the Auto-ReduceResult checkbox you keep the dense mesh around the intersection:

You can reduce the mesh by SelectAll (Ctrl+A) and running Remesh with a low Density value. Make sure that PreserveSharp edges is enabled.

As an alternative workflow: Do this Remesh on your low poly object before doing the boolean operation and you'll find the mesh much nicer:

[tjwalker_97]

Thank yo so much for responding.  Monday's are crazy for me so I won't be able to try your suggestions until tomorrow. I'll update you.
What you say about the high-poly/low poly difference makes perfect sense. What I don't understand is that the base model of that snow guard was also made with the MeshMix objects - just resized and combined.

[MagWeb]

The MESHMIX/Primitives>cube (guess you used that) is made of 72 triangles(6x6 squares) at each side. On Transform scaling you do not change its resolution. So its mesh density is pretty low-poly...

[Anonymous]

You've posted this in the Meshmixer forum, so it may be inappropriate to suggest this, but making mounting holes would be very easy in a CAD program like Fusion 360. You could dimension the holes and where they are very easily.

http://help.autodesk.com/view/fusion360/ENU/?guid=GUID-0DFCBD4F-5130-4CC9-B1A7-23C88147752A

Depending on how you plan to make it, you could easily print or export files for a CNC machine from Fusion.

Good luck!

[MagWeb]

@Anonymous :

Yep, if your source is a BRep representation: Things are easy .

But there are different sources (e.g 3D scans, STL's (which aren't BReps) ...) which end up in a mesh representation .  You need to be aware of that difference.  

 In 2d you may know the difference of vector graphics vs. pixel graphics. Same happens in 3D: If you're able to describe an object in a BRep  representation ( means: you can describe it with maths) you may go the CAD route. If there's no math rule, only arbirtary data  (as you might get from  scans or intuitive sculpting), you need to go the "hard" way of mesh processing.

Conversion of meshes to a meaningful BReps representation is a very  hard way ( a current limit of state of the arts) .

MM deals with meshes. Fusion360 basically is a BRep app. Maybe I'm wrong. So please let me know if you can "drill" holes in Fusion when a mesh( with a reasonable number of triangles ... something like 100K)  is the source ...

[tjwalker_97]

My thanks to all who responded. I was able to do what I needed in MeshMixer thanks to MagWeb. Still learning a lot about this program and, based on the suggestions of the others, I've installed Fusion 360 so I can start playing with that.

When I received a 3D printer as a Christmas gift - I really didn't intend to have to learn a bunch of new software - but such is life 🙂