ZBrushCentral

Some questions about model prep for CNC milling

ZBrush Usage Questions
#1

Hi all.

I´ve been reading along for years now, especially admiring the crazy artwork on this forum and following the processes and evolution threads.Insanestuff you guys have here.

I am now considering to jump into ZBrush, which should prove interesting since I come from “traditional” polygon modeling in Max, Lightwave and Modo (especially Modo lately).

My final output will be CNC milled figures and statues, eventually for finals or for masters for cold cast replicas. Now I have one big question regarding model preparation for that purpose.

Can I cut up a finished model in ZBrush to mill the separate parts (like torso, head and limbs) after the model is completely done, with all final real parts lining up perfectly without seams?

Or should I plan ahead and build in parts from the start?

Thx and again props for all the creativity around here!

EDIT: Ok, that was actually just one question, but I´m sure I´ll have more :lol:

#2

I happen to be a CNC person too! =D

No you can’t do it good in Zbrush.

The reason is, you cannot slice across the faces of polygons making new edges in Zbrush.

There is a command called extract that can do it, but the results would be inaccurate since it does an averaging cut and not an exact cut.

You can however make separate parts going along existing edges, or move existing edges to the point where you’d want to make a slice.

Keep in mind though that the decimate function has a command for maintaining open edges so you’d still be able to decimate the main areas, but not the edges. And if you had a model with a lot of open edges your final polygon count could end being beyond what your CAM software could handle.

All of this info is for Zbrush version 3.5R3 though.

Zbrush 4 can make slices, but what it does is bunch the polygon edges up at the slice without making an open edge and so that might not hold accuracy when decimating.

So your best bet would be to plan ahead from the base model, polygroup it into all of the sections you want and proceed from there. Keeping in mind though that the high resolution polygon count at the edges is not going to be decimate-able.

You would need to find out what your CAM software can handle polygon count wise before it chokes and then use that as a guide for determining how many high resolution open edges you can have.

One other option would be to not slice it up in Zbrush at all. In this case you would freely create your model in Zbrush and then decimate it using the superb decimation commands to end up with a decimated model with a polygon count low enough to load into any software you have that can slice across faces.

#3

Triangle, thx.

Your last option was roughly what i thought to be the best way to not limit me creatively.

I will probably use the CAM soft that comes with ROLAND mills, or Rhino which I was told has better tool-paths and less polygon limits.

So my workflow would be:

-Model my base-cage in Modo

-Take it into ZB and sculpt all fine details

-Use GoZ with Modo to take the hires sculpt back to Modo onto the subdivision base-cage, with the detail being held in a displacement-map

-break the base-cage up into 4-axis millable pieces and rework the seams to fit against each other

-freeze the displacement map into a hi-res version on each piece

-take the pieces into Rhino (which I was told has an excellent optimizer, is that info correct?)

-mill away

Please feel free to correct me if you see any flaws in this flow, or if you have any other input that could help me to prevent stumbling blocks.

I´m trying to set this up as cleanly as possible to avoid fiddling around.

Again thx to all who read this.

:smiley:

#4

Hi, It depends on what software your using to create the CNC Commands.

Most of them have some way of cutting a part up into differnt slices for producing oversize parts. Or you will have to cut it up in Modo and create a tool path for each part. Right arm, Left arm, torso etc.
Keep in mind you may have to seal each part so it has no holes in it.
Most CNC software hates holes unless they are coded into the machine path.

Take a look at cut 3d and see how they slice up a model
.
http://www.vectric.com/WebSite/Vectric/cut3d/c3d_features.htm

Do you have a 5th axis rotary attachment for the roland? If not you may also think about just milling out both sides negative casting block.

If you want to make a postive piece you will need to do flip sided milling.
Not sure how well that works with the roalnd.

#5

I’ve never used Rhino, Modo or displacement maps so someone more knowledgeable will need to respond with more robust information.

My rudimentary understanding of displacement maps is that it has nothing to do with actual polygons. Isn’t it just a image based representation of how the high resolution details should appear via a rendering engine? If so, then I don’t see how Rhino can give you what you will need once brought into Rhino.

Since I don’t know anything about Rhino, it could be that Rhino has functions for converting a displacement map to actual polygons, but still, I don’t think that would be a good work flow. Here’s why, displacement maps will always have less detail than the actual high resolution polygons that can be observed within Zbrush. Displacement maps are more of a illusion that can make a low polygon model, rendered in a game engine for example, appear as high resolution model. Also too, there are limitations regarding the UV mapping on a model such as seams, stretching and compression of the image.

Given that, if my understanding is correct, your best bet would be to decimate within Zbrush.

Zbrush has one of THE BEST decimation processing capabilities that I’ve seen. You can take a model with say 10 million polygons and reduce it to 1 million polygons and struggle to see any difference at all. And going down from there to say 100 thousand polygons is noticeable but only barely noticeable.

So once you have it decimated down, you can slice it up any way you want in Modo or Rhino. As I’ve said, I’ve never used either of these, but I know they are very robust pieces of software and I’m sure they can do slicing across polygon faces while adding edges at the slice.

There are people in this forum with far more knowledge than myself so hang in there a for bit and I’m sure one those master artists will stop by and tell you all about what you need to know.

#6

Ok, I´ll try the Decimate route for reduction if it´s that good.

I´m still not satisfied with the idea of slicing the final objects up in a polygonal modeler, though. So far I have not seen one boolean coming out clean out of a 3d program without heavy clean-up, which goes against the idea of clean seams.

Thx

#7

True! True! Nor have I.

Aside form a software that I had the opportunity to use for a short time and that is Geomagic.

Geomagic is amazing at doing booleans of every type. And not with just two objects either, Geomagic can do booleans on numerios objects at the same time up to around 750 thousand polygons with nearly perfect results every time.

Problem is, Geomagic retails in the 10k range for a single seat, so that’s out of my range.

3DS Max though, retailing for around 1.5k, has a slice function that is not boolean related. It has less than desirable intermittent results for booleans, but it’s slice function works very well.

What it does is put an edge across polygon faces wherever you specify.

I would have thought that Modo and Rhino could do this as well. But again I don’t know these.

Back to Rhino though and your original proposed work flow. I forgot that Rhino has a CAM plugin. Isn’t it something like Rhino CAM or something? If so, that is part of a software called VisualMill which is what I happen to use for my CAM and I’d like to add that it is a VERY GOOD CAM software. So I’ll bet the Rhino plugin is equally good.

With that said, it could very well be that Rhino CAN generate tool paths from displacement maps since it might be able to extrapolate the surface from what it renders with it’s render engine. So if true, it would just be a matter of making really good UVs for your model.

By the way Zbrush has a new plugin that makes great looking UVs at basically a click of a button. Not that it can make perfect UVs like what can be had by doing it by hand, but pretty darn good.

#8

I´m considering the ROLAND MDX-40 with the rotational axis (4 axis milling?!), so I´ll be able to create positive pieces with minimal post production. That really depends on my budget once I go for it, but would be ideal since from those I could create silicon molds with some degree of negative spaces, which wouldn´t be possible with directly milled molds.

I´ll take a look at Cut 3D, thx for the pointer.

#9

OHHHH!!! SORRY! I DIDN’T SEE YOUR REPLY UNTIL JUST NOW!

YES! That’s a really good point that I completely forgot about! =)

#10

Oh, and another question just occured to me.

Regarding decimation, in 3d programs it works because at render time (and in OpenGL) smoothing is applied to give the illusion of a smooth surface.

Since in the real world we don´t have a smoothing function :wink: wouldn´t it be better to leave organic surfaces at hires to avoid faceting?

#11

Yes it would be better.

Thing is though, when you’re talking about Zbrush, it can easily handle millions of polygons in normal mode and billions of polygons in high definition mode, whereas all the other 3D software out there will become nonfunctional when loading too many polygons.

For example I use 3DS Max and it’s polygon threshold is around 250k polygons for doing all operations. I’ve loaded in 1.8 million polygons before with Max, but nearly all functionality is lost.

I heard that Rhino can handle millions of polygons but that it takes forever to load a huge file like that. Not sure about the functionality once loaded though.

So that’s why Zbrush has this thing called Decimation Master. You can go here to find out about it:

http://www.zbrushcentral.com/showthread.php?t=71265

#12

Ok, my Roland vendor just answered that one on the phone.

To generate smooth surfaces you use a round-tip cutting tool to mill.

I´ll make a sample piece with both organic surfaces and sharp details next week on the vendors machine. He uses it for lots of prototyping work himself, from model cars to jewelry, so I should be able to elaborate on that in a couple of weeks.

#13

I just remembered this site. It might help some

http://www.irritatedvowel.com/Railroad/Workshop/SherlineCNC.aspx

I have a sherline CNC setup at home. Machining out a tool path takes ages.

You might want to read the case study profile of Bill Barschdof on the visual mill web site

http://www.mecsoft.com/CaseStudies.shtml

It says he is using am Roland MDX-650, visual mill and zbrush.

I would sit down with a calculator and figure out your total cost on 3d printing vs. CNC milling. The cost of owning and up keep on a CNC mill or 3d printer vs. just sending the parts out and getting a print and making a mould from that. Either way there is a bit of money involved in both.

#14

Oh yeah you’ll have to do a roughing pass, wich cuts out the larger areas, with a larger end mill and a finishing path with a ball nose end mill. Depends on the step distance between paths as to how long it will take and how smooth the surface is.

#15

That and you can, well with VisualMill, I don’t know about other CAM software but probably others too, set the tool paths to be averaged over the surface.

So if you had a heavily faceted model you could have the tool paths skim over the highest parts of the faces and not follow the exact coordinates of each face.

In VisualMill it’s called the intol and outol setting.

But anyway, sounds good! Post pics of your work if you want! :slight_smile:

#16

Good point. I already sat down and crunched the numbers. In the medium to long run for my purposes it´s better to have my own mill, I think.

But for the first project I might go the route of milling the full object as a master at the vendor, since he did offer that to me as a sales pitch.

I´d be stupid not to take advantage of that (not that i haven´t done many stupid things in life already;)

#17

Confidential for now, LOL.

But yeah, if all works out eventually I´ll dig out this thread and post the stuff :wink:

#18

Ok, I knew I would have more questions related to this.

I´m looking for a good supplier of Silicone and Resins in Europe for molds and cold casting…

Anyone?
:confused:

#19

Smooth-On is the best in the world for that kind of stuff. I’ve used thier products for years with great success.

http://www.smooth-on.com/p105/International-Stocking-Distributors/pages.html

Also, though not germane to your question, I’d to give a plug for Douglas and Sturgess for those of us here in the US. They are by far the best in the US for this kind of thing.

http://www.douglasandsturgess.com/

I met the owners once. EXTREMELY NICE PEOPLE! And they know the meaning of struggling artist. =)

#20

Thx again, man!