Zbrush has a handy tool that isn’t always well understood, the Sweep3D primitive, which is akin to the lathe tool you might find in other 3D apps.   What is handy, is that you can pick the number of sides you want, as well as quickly set up for a simple or complex profile.   Here is a simple 8-sided sweep.With pretty straight forward parameters in it’s initialize menu:There are two profiles to set for a Sweep3D object.   The first and most important to the shape is the S Profile, which controls the outer shape of the object.  To add control points, just tap on the graph.   To remove control points, just drag the point off the graph.   

The trouble for some users is that the line interpreted between the points is a spline and often doesn’t give a more angular shape.   It isn’t obvious, but when you select a point on a graph, a circle appears around the point like a halo.  That circle isn’t just to highlight the point–it also controls how smooth the line is that passes through the point!  Draw the circle close to the point by dragging its rim, the point gets sharper–further away, the line through the point gets softer.  Neat!

The second profile, T Profile,  controls the thickness of the object that is swept.  By default it give a nice even thickness top and bottom, so I leave this alone.

After converting my simple octagonal object to a poly mesh, and subdivided it 8 times with SMT (smooth) off, I can then start decorating it to make it a little more mechanical looking.   Picking a simple alpha from my collection (this one from Codeman Studios) I can just drag a marquee of the alpha by starting my click off the object and dragging across.   Do it twice, and I have a nice set up to inflate some ridges from the surface.

A couple of inflates (deformation menu) and  then Iuse radial symmetry of 8 and couple of different alphas to decorate the object further getting something like this.Add texture and I have another mechanical part for a machine.

How about a thumb pin like this?  

Pretty tough?   Not really!  Start with your basic cylinder with about 172 by 100 divisions:

Now a little masking using Ctrl-drag:

Invert  (ctrl-tap outside the model) and inflate (Deformation subpallet):

Now for some stripes.   On the masking subpallet, Mask All, and then set sel and skip to 3 and 8.   Hit Col for a nice striped mask:

Let’s restrict to our inflated area plus a nice little edge:

Inflate again:

Pretty good, but I like ’em all twisty on thumb grips.  Grab and invert a quick selection:

And Twist a couple of times (Deformation subpallet):

A quick mask and deflate on the body, add a texture, and it’s done:

Time to model, about 3 minutes.

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!

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.

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.

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:   

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:

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

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?

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.  

Unhiding my geometry, I’m good to go:

Total time to  model: less than two minutes.

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:

(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:

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:

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

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.

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!”   

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 

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.)