Newbie questions

[Anonymous]

Hey, folks,

I've tinkered with MeshMixer for a few hours, studied the MM help section a fair bit and cruised this forum, but as a rote newbie, I'm not sure that I'm thinking correctly about what I want to do, and how to accomplish it.  I'm faced with a fairly steep hill to climb.

The project is to create a printed mold of a high-polygon object.  It will be a fairly large mold, requiring the positive to be sliced and flanged so that the mold parts can be bolted together accurately.  Taking the sample bunny as an example, here's what I THINK the workflow would be, but I am unsure of how best to accomplish it:

- In MM (presumably using the Edit | Offset tool), "dip the rabbit in chocolate," i.e. add a 2mm "skin" to the object.  The inner skin would have to conform precisely to the rabbit's outer surface to preserve detail, the outer skin would be less detailed to speed up printing;

- In MM, remove the original object, leaving the shell (unsure of how to do this);

- (In MM or another piece of software, open to suggestions), add flanges and keys to the mold where it will be sliced;

- Add holes to the flanges in the same diameter as the bolts that will be used to combine the printed parts;

- Slice through the center of the flanges to create the flanged and keyed mold parts.

I'm unsure if I'm thinking about these steps correctly, but it makes sense to me to create a planar object 4mm thick, merge it with the model, remove the part that impinges on the mold's interior, and then slice through its midpoint to assure alignment of the mold parts.  I'm just unsure of how to do it, and whether MeshMixer is even the right tool for that.

The last step that I think would occur, and again please correct me if I'm wrong, would be to bring the now-merged pieces back into MM and use the Make Watertight tool.

I realize that I'm biting off a lot and also asking a lot of anyone who chooses to respond to this.  I'll be grateful for anything: Suggested modifications to the workflow, pointers about which tool(s) within MM will do the trick, suggestions for alternative (ideally newbie-friendly) software to use instead of or in combination with MM.  ALL of this is new ground for me.  Cheers!

[hfcandrew]

From what you said all makes sense, but you do not have to do:

---

I'm unsure if I'm thinking about these steps correctly, but it makes sense to me to create a planar object 4mm thick, merge it with the model, remove the part that impinges on the mold's interior, and then slice through its midpoint to assure alignment of the mold parts.  I'm just unsure of how to do it, and whether MeshMixer is even the right tool for that.

The last step that I think would occur, and again please correct me if I'm wrong, would be to bring the now-merged pieces back into MM and use the Make Watertight tool.

Its 'make solid' btw not 'make watertight', but either don't use that, just go analysis>inspector.

[hfcandrew]

Follow this:

[Anonymous]

If I got you right, you want to get something like this (registration plugs and  screw holes not done yet):

Can you give some more details about the object? E.g Does it own undercuts? Will it need a curved parting line or will straightly cut molds, as above, work? Which material do you want to use for casting?

[Anonymous]

hfcandrew, if a picture says a thousand words, then yours says many more.  But the summary would be, "MeshMixer can do what you want, and here's how."  Now, I just have to slow it down since the interface isn't second nature to me yet, so that I can study the steps you took.

I hadn't thought to put the registration pins into the mold the way you did.  I would think that this would thicken the mold considerably.  I presently don't have the equipment to recycle and extrude ABS, but if I have to thicken the mold, that's a fantastic way to ensure alignment, and I'm grateful to you for pointing it out.  Thanks so much for taking the time!

[Anonymous]

Gunter,

What you whipped up is exactly the representation of what I envisioned.  As a (minor) aside, I used to support a graphics shop and frequently rubbernecked in the 3DS Max department.  While I could deploy, patch, and hot desk pretty much anything Adobe or Autodesk, creating was pure witchcraft to me.  I knew enough to understand that if I repurposed a pallet of old Wintel servers into a render farm, I'd make some happy users.  Did, too: smiles all around.  "You took HOURS off our workflow!"  Thanks for whipping up the mold; it means a lot that someone would do that to help out.

At any rate, the object is a smallish human figure, to be cast in low-shore silicone.  A friend is freakishly good at rendering from pictures and wants to do bespoke reborn dolls.  While the phenomenon is a little creepy to me, I like a challenge, especially when it has the possibility of justifying a large print volume printer. 🙂  

If I remember my anatomy and physiology correctly, the mold would at a minimum be in two parts, sliced along the coronal plane.  Given the number of known unknowns at this point, it's likely that I will have to deal with more parts, with additional slices, flanges, and registration pins for the legs.  While I like @hfcandrew's use of registration pins integral to the mold, I'm sensitive to material costs and would like to keep the mold reasonably thin.  The bespoke nature of the cast means that I'm highly unlikely to make additional ones.  Thus, the flanges.  

That said, and germane to your question, I'm not confident that this would be a cleanly planar coronal slice.  That, in addition to curved part lines.  Which makes me wonder if a thicker mold wouldn't actually simplify everything.

[hfcandrew]

How big is the model and how thick of a wall do you want it to have?

[Anonymous]

~600mm long, possibly a bit longer, no more than 800mm.  I was thinking 2mm walls.

[hfcandrew]

Truthfully I can't think of how to do this in MM without used a straight sliced plane using "Plane Cut". I think it would have to involve using "Complex", I tried playing around with that using a sphere, but couldn't figure it out.

[hfcandrew]

Never mind, just had to step away from it a second and it came to me. Watch this: https://autode.sk/3yNPRMx

I couldn't figure out how to do it with Complex, but this manual way works as well. Sorry for the capture quality, Flux messed something up.

[Anonymous]

Here's how I do moods from shapes like this needing curved parting lines:

1. Step: Finding the parting line of the shape:

MM's Overhangs shader (drag the sphere with the red bottom onto your object) is pretty useful if it is set to paint regions at its max angle. You can modify this angle in ANALYSIS/Overhangs. Set AngleTresh to max (89°) and cancel the tool. MM remembers this setting to use it for the overhang shader:

Now drag this shader from SHADERS onto your object.

Use EDIT/Transform to rotate the object to an orientation where you get a meaningful border of red/white. You want to find a position where there are no white islands within a red area or red islands within white.

Now using the ViewCube switch to Bottom view. Make sure that you do not navigate for the following: Go to SELECT, select something ( which region doesn't matter at all ) and do Modify/SelectVisible:

Run Modify/SmoothBoundary. At its default settings it will create a face group too:

Now you've found the parting line.

>>> Continue with my next post.

[Anonymous]

2. Design a parting surface:

From above you've got a face group. We want to use its boundary to deform a plane primitive:

For easier view drop the first shader from SHADERS onto your object.

Go to EDIT/CreatePivot. Set PlacementMode to SnapToGroupBorders. Double-click at the group boundary several times to get pivots at that boundary like this:

That done go to SELECT and double click the face group to select it. Run Edit/FitPrimitive. By default it will insert a square object. Set a high MeshDensity and make sure to check CreateNewObjects. Scale up the object using the transform widget. It needs to be about two times its fitting size:

Accept. Now there should be a FitPrimitive1 object in your scene. Leave SELECT and hide the shape object.

Activate the plane and select all of it (Ctrl+A). In SELECT go to Deform/Wrap.

In Wrap double click next to a pivot to create a red sphere. Drag this handle to the pivot to make it snap to it. Do the for all pivots to deform the plane:

After accepting Wrap yo should discard all pivots. You may make them visible in the ObjectBrowser clicking the pivot icon in the bottom-left of the browser. You may now show the source shape to check the parting surface: 

Next is to construct the molds from that.

>>> See my next post.

[Anonymous]

3. Construct solid molds:

At first we need to create an offset shell from the source shape. Its OffsetDistance will define the width of the flanges later on. I use EDIT/MakeSolid in Accurate mode which allows to add an offset:

Drag the transparency shader onto this result(top-right in SHADERS) and make a copy of the parting surface:

SelectAll of one FItPrimitve an use SELECT/Edit/Extrude to give it a thickness including the ghost shell to one side.

Do the same on the other FitPrimitive with a negative offset

Make a duplicate of the source shape. Hide all objects bur one pair of source shape and FitPrimitive.

Activate the extruded FitPrimitives as the first and holding down Shift one source shape as the second object. Run BooleanDifference:

Do the same with the second pair.

If the molds' sizes are bigger than your printer's volume it's to to cut the halves. To do this EDIT/Combine both halves to one object for now and run EDIT/PlaneCut at Slice(KeepBoth):

Run EDIT/SeparateShells to split all of the mold's parts again.

On each of such parts run EDIT/Hollow to define the wall thickness of the final print:

(Note: in the above image MM create two empty shells- I discarded them - ignore them)

Make as many copies from the transparent offset solid as parts of the mold. Hide all but one pair of solid and mold object. Activate both an run BooleanIntersection on each pair (here's the third pair):

Next is to drill registration holes...

See my next post

[Anonymous]

4. Drill holes on the planar flanges:

Activate two molds building one side of the planar flange and do EDIT/Combine. Do the same at the other side.

Drag and drop a MESHMIX/Primitives cylinder onto the flange. Set Dimension to the needed hole diameter and set CreateNewObject as CompositionMode. Accept.

This dropped part activated do EDIT/Transform. Scale up the cylinder's height and use the widget's triangles to move the cylinder on the flange plane. Hit D to drop a duplicate at the current position. Note: Due to rendering issues you might not see the duplicate in the scene. Rotate the scene a bit to update the scene. When you got enough cylinders aviate all of them and Combine them to one.

Make a duplicate of the comped cylinders and do BooleanDifference on each molds-cylinders pair:

Run EDIT/SeparateShells on the two halves , activate two parts constructing the curved flange and Combine. The same for the other pair:

Next is to generate registration holes on the curved flange.

See my next post.

[Anonymous · Accepted solution]

5. Registration holes on curved flanges:

If you decide to use loose screws to mount the mold the direction of the holes isn't important. You might simply d&d a high cylinder from MESHMIX onto the curved flange. While being in MESHMIX you can use the D key too to generate duplicates at the current position.

Against that: If you want to glue the screws on one side or you want to construct and print male/female registration dowels/holes all cylinders need to point to the same direction. Otherwise you might not be able to join the parts finally.

To get the main direction of the curved flange select the contact surfaces on one the flange and run Edit/FitPrimitives. The resulting plane is the average of the selection.

Now d&d the cylinder from MESHMIX somewhere onto this plane. It gets the direction of the plane's normal direction:

You might discard the plane now and keep the cylinder only. Use EDIT/Transform on it. Make sure that Transform's CoordinatSpace is set to LocalFrame to match the widgets axis to the cylinder. Scale the cylinders height dragging the green square. Move it parallel dragging the green triangle. DO NOT rotate it dragging the arcs. Again hit D to drop duplicates

Again Combine all dropped parts and duplicate that result

Use one copy for BooleanDifference with the upper, one with the lower half of the mold.

Finally EDIT/Separate both halves to end up with 4 partial molds.

Done.

[Anonymous]

Gunter, this is... Wow.  Thank you so much, I'll study it carefully. Thanks for taking the time.  I used ezgif to pull apart the tutorial that @hfcandrew did upthread and am working through that.  This is going to be a bear, but your steps will help me tremendously, as his did. 

One question.  MM CAN do curved part lines, flanges, and keys.  Does that mean that I SHOULD use MM to do them, or is there another piece of software that does them more easily?

[Anonymous]

MM is a swiss knife.

A swiss knife isn't a  professional tool to shape material.

Well, there might be some, maybe costly software out there doing it faster/easier... don't know...

But if you can get what you want using a swiss knife: Did you ever thought to use a 5 axis CNC instead?

Sorry if my workflow above seems to be difficult. Be sure it isn't once you mastered MM - AND: You keep control on what you're doing.