Zbrush Mechanical Part 5, Quick Alpha From Geometry

Zbrush makes it easy to quickly create an alpha from geometry, which in turn can be used to detail objects.   Let’s take the hex nut from the previous exercise.   By turning SMT on in the Geometry Subpallet art level 4 and subdividing a bit more I’ve rounded the edges to give me a nice bevel.   I just position it so I’m looking straight down on it, (use shift-drag outside the object to snap the view to the nearest orthogonal position.)  To make an Alpha from this shape, it’s just as easy as going to alpha pallet and clicking “GrabDoc”.   A new alpha is available on your alpha pallet, starting “ZGRAB” like magic!original-nut

You’re not quite done yet–ZB prefers square alphas to avoid distortion and because I was lazy, the canvas was actually 800 x 600.   It’s a quick fix in an image editor, so export the alpha from the image pallet, fire up photoshop and crop to 512×512.photoshopcrop

Name the file it something suitable, reload it into ZB, and now you sculpt with it using any brush you like (I prefer the Clay or Layer brushes for example.)  


Turn on symmetry and with one stroke, I have detailing on a plate.sculpted-alpha

Zbrush Mechanical Part 4, Rounded Holes

I needed a hexagonal part with a round hole in the middle.   This would seem to be a challenge for ZBrush requiring an outside modeler.   However, it is actually pretty easy in ZB if you know primitives and deformers.

First, we can start with our old friend the cylinder primitive:cyl1   

Not very hexagonal yet, and too long, but we can fix that.  We tweak the number of sides to 6 and shorten the z-length in the “initialize” menu:hex2

Better, but no hole . . . We can solve that by setting the “inner radius”:hexhole3

Nuts, close, but the inside whole isn’t round.   I’ll need to fix that up before the boss sees it.   I go ahead and make this a poly mesh and then group the inside polygons.  I also divide the polymesh a few times (well, 3 actually) with the “SMT” option off (so that it doesn’t round off my hexagonal prism).  Showing just the inside polygons (with display-double on for ease of viewing, I have:


Now if there was a easy way to round those off, I’d be home free.   Hey, what about that “deformations” subpallet?defmenu

Ooo . . . I like that “RFlatten” thing . . . (It’s short for Radial Flatten).   A little RFlatten and slight tweak of the size (with just X & Y turned on) and I have a nice round hole.  roundedhole5

Unhiding my geometry, I’m good to go:finishedhex

Total time to  model: less than two minutes.

Zbrush Mechanical Part 3, Springing Into Action

Springs are fun and a handy way to add a common mechanical detail.   Zbrush has a built-in spring generator, called the helix primitive.   A little setting of the initialize parameters and we get something like this:

Basic Spring
Basic Spring

(You did know about the initialize subpallet didn’t you?   If not, load up a few 3D primitives in Zbrush and look down the tools menu for the subpallet with “Initialize”.   Here you can set all sorts of neat starting shapes for your primitives before making them into a polymesh.)

I didn’t make this a polymesh right away, keeping it as a helix primitive.   I’m going to use a little know feature of primitives–col masking.   Also, to give me some more resolution, I divided my spring a couple times by going to the geometry subpallet.   (Yes, you can divide primitives the same as polymeshes!)   

Inside the masking subpallet are some handy features that only work with primitives marked “col”, “row”, and “grid” with a couple mysterious slides marked “sel” and “skip”.   You push any of these buttons on an unmasked primitive, nothing seems to happen and thus many a tyro is frustrated by them.   This is because these buttons selective remove masks, not add them.   (It feels counterintuitive to me too, but this is ZB, after all–which often feels like it was built on “opposite day” at first.)

The sel slider will choose how many adjacent rows or columns of the primitives polygon grid will be selected.   The skip slider will  then decide how many to skip before selecting.   To get a nice box cutout, I’m going to select 3 and skip 4 which will give me a nice alternation.   Now, before I go rushing to pushing the “col” button, I do the all important first step–I hit the “mask all” button on the masking subpallet.  A press of the magic col button and I have a nice ring mask on my spring:

Masked Spring
Masked Spring

With my plain-jane spring now nicely masked, I can use “inflate” under the deformations subpallet to pull in the unmasked parts to give some additional texture.   A little fiddling, and I have something like this:

Textured Spring

Add a couple of creative cylinders, and I have this:


Completed Spring
Completed Spring

Zbrush Mechanical Part 2, Spinning in Circles

Making perfect circles is pretty important to creating the illusion of mechanical things.  Fortunately there are lots of ways to do this, such as as using round alphas, but did you know you could quickly paint circular displacements right on to any hires geometry?  It’s called radial symmetry and it’s really quite simple to use.   Just click on the “(R)” button on the transform pallet and set the number of copies of your brush you need.   Set it really high (up to 100) and then you can quickly spin-up perfectly circular ridges.  The clay brush will keep these ridges perfectly level.   It’s a pretty easy 1-2-3.


Plain Cube Subdivided
Plain Cube Subdivided
A Radial Symmetry Brush
A Radial Symmetry Brush
A detailed cube
A detailed cube

Zbrush Mechanical Part 1, Extracting

There’s always a lot of discussion about “Can you do mechanical modeling in Zbrush?”  The answer from one camp is “No, the soft modeling orientation of ZB makes it too hard. . . .”  Another camp will say, “But look at the results some guys like Meats Meier can get!”   

Zbrush Plate 1

The answer, as with lots of things in life, lies somewhere in between.   ZBrush requires you to think about your mechanical models as if you'[re working with clay.   This means that you need to think of your tools as being built up from things that already have structure, like platonic forms of cubes, cylinders, cones, etc.  Often the trick is to start with something that has approximately the  right shape and work to refine from there.  

For example, I wanted to make a curved plate.   I realized the plate was really a segment of a cylinder.   After create a Cylinder from Zbrush’s primitives, I turned it into a polymesh (with the “Make Polymsh3d” button).  Them I hid all the geometry of cylinder other than the curved segment that represented my plate.  Fortunately the edges were going to be roughly square as is ZBrush’s selection 

Automatic Polygroups with "Extract"

tool.  With just the mesh I wanted to be the basis for my plate visible, I went to the Subtools sub-pallet of the tools menu, and used the big “Extract” button.  In one step, the visible shape was extracted and given thickness.   (The sliders next to the Extract button will let you play with smoothness and thickness to your liking.)  Even better the front back and the edge of the plate all had new subgroups!  Neat!

For the plate in the illustration, I just used some alphas I had to decorate after subdividing the mesh to a fine detail.  Codeman Studios makes a nice set of Alphas if you’re looking for a profesional set, but there are pleanty to choose from on the web.  For applying the alphas, I used the drag-dot brush and turned on X and Z symmetry as needed.  To ensure my symmetry was good, I used the “S. Pivot” command to set the pivot to the center of the mesh.   (S. Pivot works by hiding everything but central mass of an object and it will move the pivot to the geometric center of what is visible.)

Cool Alternative!


Hypatia Callisto has been using my testbed for making sculpies with Luxology’s Modo.   She’s found some minor errors in my gradients and corrected them.  She’s been kind enough to share her work with the rest of us, so here it is: http://www.rabbitroo.com/SL/testbedtorusfinalHC01.lxo.     

EDIT 4/16/08: Also available as a .zip file: 


and here ALT: testbedtorusfinalhc01lxo

It ain’t easy . . .

Ryder Spearmann has been doing some sculpture work with the my SL Testbed for making sculpies in modo. After some investigation he found that the gradients I created are “eased” (which is the automatic form of a gradient in Modo). This causes distortion at the outer edges of the sculpie, so I’m pleased to present the improved testbed. It can be downloaded from:


Here’s what the gradients used to look like–note the curves:GradientEase.png

Here’s what the new, straight line graident:GradientLevel.png