Thursday, February 11, 2016

Some thoughts about sculpting regular/geometrical/mechanical parts

In this post, my intent is to share some thoughts about the making of regular parts in a mini. I rather speak of "regular" instead of "geometrical" or "mechanical", because the last two tend to emphasize on a "non-natural" aspect, while the laws of physics and the principles of life have produced countless examples of things, either living or inert, with regular shapes. But anyways, this is just a matter of semantics.

I've tried to compile the result of a couple of years of self-experimentation in a post. I am convinced that minis with regular parts are not more difficult to make than usual, "organic" ones, that have their own difficulties (tensions, folds, achieving a natural aspect,...), contrarily to a widespread misconception.

Update 01/05/2016: here is more detailed tutorial about the same topic.


I'm working on a more general post about putties. I'm focusing here on the use of the ones I know for the purpose of regular parts. The aforementioned post shall be more general.

In general, for modeling regular parts, I choose a putty that:
  • is rigid/stiff - the more rigid, the more force it takes to shape it; which also means that accidental or poorly controlled contacts with a low force, either with a tool or a finger, will have less impact on the shape. It is very often a very desirable feature, especially when you're beginning with the exercise. However, as explained below, there are cases where less rigidity is useful; experience will help you anticipating this when planning a project.
  • is very plastic, i.e. as less elastic as possible. Elasticity means that when you change the shape of a body and release the force, it comes back to its initial shape. Plasticity is the opposite: shaping is maintained in time; practically speaking, this is a characteristic that is most desirable for all standard sculpting jobs I can think of.
  • can be sanded/filed/drilled/sawn/... after curing. So, one that can be "machined" with usual modeling tools. As a general principle, keep in mind that shaping or shape/surface corrections can be much easier to do with a hard material rather than a soft one (and by hard I do mean cured - a stiff putty is several times softer when crude/fresh than when cured/baked/dry). As an example, I find it much easier to obtain a straight edge with an appropriate file on a hard material, rather than with a spatula (in general small and rounded) by pushing putty.

The third item ("machinability") dismisses Green Stuff (Kneadatite) in most cases, as it tends to get torn and to exhibit scratches and chipping because of its lower stiffness once cured, and of its quite big granulosity (hence it is no surprise that you can actually cut through it pretty well with a good knife blade, but that's the only advantage in this matter). So I avoid green stuff for this type of job. The only exception is for tiny parts for which the accuracy of the shape is less of a problem, and in locations where post-curing modifications are not possible, and where considering an assembly (see below) is difficult; then I often use Green Stuff, potentially with a mix including a bit more of the blue component, to make it stiffer.

Super Sculpey Firm (the grey polymer clay) fits very well for stiffness and plasticity. It can also be "machined" quite well once cured, but with precautions, because it tends to be a quite fragile/brittle material (meaning that it will break without trying first to comply to the forces applied, i.e. it breaks more easily for some sollicitations to which other materials would resist without problems - think of glass and ceramics). So accidents tend to happen, especially in the form of chipping and localized cracks. I think I tend to use it for up to roughly 10% of the regular parts I produce.

Super Sculpey (the pink polymer clay) fits very well for plasticity and machinability. Its wax-like texture when crude, very good material cohesion and very thin granulosity after curing make it a unique putty. On the other hand, it is much softer than SS Firm (well, it's all in the name... :) ). So its use depends on the part to be made, and the eventual details. I'll try to find examples to illustrate this. It also opposes less resistance to sanding/filing and to cutting (slicing/chipping mainly); this is interesting as it is often a very efficient and time-effective way of adjusting shapes, especially on larger scales. I think I tend to use it for up to roughly 33% of the regular parts I produce for these reasons combined.

Fimo has a good plasticity and a stiffness between middle (Fimo Classic) to low (Fimo Soft). Regarding its machinability, I've had various experiences. I guess it depends on the degree of curing. I would tend to bake it a little longer then recommended (without raising the temperature, to minimize the risk of burning it) to make sure it responds better to post-curing work. I prefer to avoid Fimo for this kind of job.

Milliput is probably the best when it comes to machinability, whatever the type. But it's also probably the less stiff of all the putties discussed here; it's especially true if you're using the white one (box with black markings). The Yellow-Green (box with red markings) is a bit more stiff, but still quite soft as compared to the alternatives above. Once cured, it can be a bit brittle, so work must be performed with appropriate care; yet, an overbaked SS Firm can be more brittle than Milliput. It's also the easiest one to sand/file, but the one that offers the most resistance to cutting (slicing/chipping motion). So it takes a slightly different approach than post-curing work on Sculpey for instance. I haven't used it often in the last years, but mostly only because of the fact that it is a polymer clay, hence with a limited work time available after mixing, that does not comply well with my current time imperatives, and may be a bit of a practical limitation when dealing with larger parts. Yet, I think it should not be overlooked and should be part of any modeler's workshop.

Possibilities are widened considering that it is often possible to mix some of the putties above to get the best out of their respective advantages.

Milliput + Green Stuff to combine the desirable features of both these epoxies. Yet, after a couple of uses, some aspects made me quite reluctant to keep on using it. First, you need to work really fast, because it cures faster than either of them taken alone. You more or less cannot use water anymore for smoothing the crude compound. It is VERY sticky (but I mean VERY). And after curing, it opposes a big resistance to filing/sanding (making it more difficult) and tends to make the material more brittle (the most brittle as compared to all that's discussed here). So I tend to overcome it, unless I have a very good reason to use it.

Mixes of Super Sculpey (pink) + Super Sculpey Firm (grey) is my favorite option when it comes to tune properties to desired specifications. I can't really give proportions; I let my feeling guide me as a function of the result I want. In this case, I don't consider adding some chocolate brown Fimo Classic as an actual advantage as readability is usually not much of an issue when dealing with regular shapes. This mix is used in roughly 50% of the regular parts I've made.

Of course, other putties and mixes exist, but I can only speak of what I've used.
Also, you are totally free to use different putties/mixes for different parts of a single miniature. This can make the job significantly easier for certain parts.

Planification... and assemblies!

I think that, in the discussion above, the material property that is the most critical for my technique is the post-curing treatment with files, knives, ... But doing this requires that your tools can actually access the areas to work on, and provide you with possibilities of motion with adequate amplitude and direction(s). It's all about the duality convexity/concavity, made more or less significant by the size of the parts as compared to that of your tools.

My first rule, is to think in terms of assemblies. I break the complex shape into an assembly of convex volumes, with a geometry that makes pre- or post-curing rectification easy, that I assemble after working on them separately. If required, it is then possible to either hide the joint with some more putty, or to create a smooth, intricate transition between them; and everything in between is possible. You are also free to use the most adapted putty for each part and step!

For the very first version of the Bot, that was the trophy of Painting Crusade X, the double-ball joints that connect the forearms and the lower legs to the body are good example of very basic assemblies that made my life easier. The rods were obtained by rolling Super Sculpey with an appropriate technique to make cylinders, cured, slightly rectified, and then cut to the right length. The balls were obtained by rolling a mix of SS/SS Firm in my palm to obtain a sphere, to cure them, slightly rectify them, and then file them to create a small flat face. Then I've pinned everything to create a strong assembly secured with a bit of Super Sculpey.mixed to Vaseline to act as glue, and rectified with a clay shaper when crude, cured the whole (in parallel to some other parts to spare time and energy), and rectified the whole with a file, to obtain a sharp joint.

All in all (2x15 minutes of oven-curing included), it didn't take me more than 60 minutes to do the 4 joints. This example seems stupid at first glance. But ask yourself: how would you practically achieve to do each of these joints as a single part at once? Would it be practical to have to rectify both shapes near their junction, while keeping the joint sharp? How would you even hold it during the work without damaging the regularity? And how would you ensure that they look more or less identical in the end?

Also notice that the assembly approach can be applied as well with crude- as with cured parts! In the example above, I've first shaped the forearm as a truncated cone, using a bit of vaseline gel to help rectifying the crude putty. Then (forearm still being crude), I have made thin strips, cut them at the right length, and deposited them gently around the forearm. After that, it was all about masking the slight joints. Then it all went to the oven for curing, and afterwards I was able to rectify the whole with files, the shape being such that it was a really easy job. In this case, it would have been a bit more difficult to first cure the forearm, and then try to lay fresh strips on it, because of the typical problem of low adherence between crude and cured putty (probably requiring some intermediary scratching work to ease the job, ...).

An example is shown above: a cylinder is first prepared with the right geometry (smooth surfaces, sharp edges and good geometry). Then, once the general shape of the bot's body is ready, I remove crudely the putty from the area of the cylindrical hole, and I use the cylinder tool as a polishing tool: I cover it with vaseline gel, I introduce it in the hole with a smooth spinning motion, to force the inner surface of the hole to be symmetric and smooth, and then I remove the cylinder. In this case, I don't care about the surface at the back, as it will be hidden by other components; but I can imagine easily at least 2 ways of dealing with that surface too if needed.

The principles can be extended not only to "negatives", but also to parts with other functions, either temporary or permanent, that you can remove either by "disassembling" or by destroying the part, etc...

So I am promoting a modular approach for creating complex regular assemblies. But not all parts are so simple, like cylinders or spheres, that it only takes your fingers to shape them, and it doesn't need any form of particular core or supporting structure to manipulate/maintain them during the shaping and before/during the curing.

A first example is illustrated above, for the bot again, but this time for one of its forearms. I start from a cylinder of Super Sculpey; after curing, I scratch the upper part over a length corresponding to that of the forearm: this acts as the core of the part (if you're not familiar with my concept of "core", it's explained in previous tutorials about sculpture; e.g. here, or you can also refer to the index of tutorials and step-by-step posts). I keep the lower part as a support that allows me holding the part during the work, without touching it. After the work is done and the part cured, it's then very easy to cut the rest of the cylinder and sand/file it to have a clean, flat interface. It's also very easy to drill trough it for pinning or whatever reason: using a wooden part as the backbone, like a scratched toothpick makes the job of post-processing more difficult, especially if you have to drill through it. This method also has the advantage of removing the need for any additional material that may react badly to the baking (green stuff stomes creates trouble, even big ones) and/or that are more toxic than polymer clays themselves (green stuff, cyano glue, plastics, ...).

Take note that this also allows me to bake the part "up in the air", to make sure it does not deform under its own weight at the beginning of the curing process (before it actually hardens, the heat makes the clay softer and, hence, more prone to deformations under its own weight). All it takes is something to hold the cylinder (e.g. clothes peg... wood and metal are perfect to sustain de heat, but don't use plastic ones!).

Another example is shown above. This time, it's the lower part of the leg. One of its specificities is that I wanted both ends to interface cleanly with the ball joints of the upper part of the leg, and of the foot (i.e. minimum gap between the male and female parts of the joints). So in this case, it is more complex to combine the benefits:
  • provide structural support to the part (= core)
  • provide a means for holding the part without touching it (during the sculpting and the baking)
  • force the interface surface with the foot ball joint to conform with its geometry.
As the shape foreseen for the leg at its top and bottom sides is very different, it was only needed to take special measures to enforce the shape conformity at the lower side (foot side); the top side (knee side) was dealt with using the "stamping" approach. More details on the actual implementation of the  support structure will be given in a dedicated tutorial (if it's already published by the time you're reading this, the link should appear in a visible manner either at the end or at the bottom of this post).

It's difficult to go further while keeping it general, except for one thing: the keyword is planification! Of course, as for when you start digging deep enough into many things, experience becomes a key to choose approaches that are both in line with your skills/tastes/time availability/precision needs/tools/etc... As for any project, stopping and thinking before diving into it can make a significant difference, and even avoid trouble ("What do you mean with 'constraints related to molding/casting' ?"). Often enthusiasm gains at being tempered, although it's not always easy...


The tools I use the most when making regular shapes are probably my fingers and hand palms. They're unbeatable for creating a sphere or do most of the shaping work on cubic-like shapes. Combined with vaseline gel (e.g., good for all putty mixes involving Sculpey) or water (with Milliput), they are also very good for initiating the smoothing of the parts while mitigating the risk of local or global deformations.

Sharp blades are also very helpful for plenty of uses: leveling off surfaces by cutting the local "hills", cutting out elements at the good size (e.g. a cylinder or cube), initiate holes and hollow areas to be shaped by stamping or with other tools, scratching a surface for facilitating the later adhesion of crude putty,... You name it.

Usual sculpture tools like spatulas or clay shapers are also very useful in general, but their use is less "dominant" than in usual works.

Cylinders with a smooth surface (e.g. the handle of your modeling knife, or the ferrule that holds the tip of a clay shaper for example) are as useful as a good knife. You can use them to create flat sheets of putty, to to roll them over a surface with a circular symmetry to make its shape more regular. I tend to use them a lot.

Also, as described above, you may be regularly brought to shaping you own "tools" for whatever of the reasons explained in the previous section (stamping, support, shaping, etc.). Again, you are only limited by your imagination and the time you put into planification.

Combine materials...

Super Sculpey, mix SS/SS Firm, green stuff and plasticard.

One way to both gain some time and obtain a great result is to resort to other materials than putty. Using plastic or metallic tubes with circular or square sections, plasticard, etc... is often a much more efficient alternative to making something similar out of putty. Some even invest in lathes or other small machining equipment to go one step further.

For illustration and inspiration purposes, here is some work by French pro mini-makers, illustrating the combination of different putties and materials for an optimal result, while complying with moulding/casting constraints. Patrick "The Small" Masson: The Abomination (Mecha) and Toxic Abomination (Mecha) and MIKH One Shot (Mecha) and The Toad .

Yet, if you're like me, you may find it more gratifying to actually sculpt everything by yourself, even if it takes more time and it is more difficult to achieve the same result in the end. It all depends on what you like, after all...

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