How to CNC machine data from a haptic device
A complex geometry created with Sensable FreeformCurrent 3D CAD systems are very well suited for the creation of Class-A surfaces and engineering-type geometries. In contrast, irregular geometries like found in biology (plants, animals, human faces, etc) are difficult to model in 'real-life style', as can be seen in many 3D animated movies.
An input tool to solve this problem has been deleloped by SensAble Technologies in the USA: the Freeform modeling system. The company has later been acquired by 3D Systems, and the system now is offered as 3D Systems haptic device.
The FreeForm modeling system by SensAble
SensAble's FreeForm Modeling System (R) applies a pen-like device connected to a flexible arm, as shown in the illustration above. Holding this pen, the user can sculpt a block of virtual clay, using a virtual sculpting tool that is connected to the pen. The surprising element is that the pen gives a force-feedback: the more clay the user wants to move, the more force he has to apply.
This proves to be a very effective system. You need to touch and try before you can really imagine how it works.
First the overall form is sculpted (step 1), and next some texture is added (step 2),
A typical example is the fish as shown on this gallery page. This fish has been modeled by Mark Conahan, a skilled FreeForm user, in about two hours. The three main steps of the modeling phases are shown in the illustrations.
Step 1: knock out the overall form with the sculpting tools (about 10 to 15 minutes).
Step 2: add fine detail with sculpting tools and texture using 'emboss with image' (about 1.5 hours).
Step 3: bend the fish with the deform box (about 15 minutes).
Fish after deforming (step 3), and DeskProto toolpaths, with a support bridge.
A typical result of a FreeForm Modeling session is a large STL file. The file for this simple fish is 25 Mb (binary file: 512000 facets, 234000 points), for more complex geometry file size may easily be a few hundreds of Mb.
This is of course where DeskProto comes in, as DeskProto is very well suited to handle STL files that large. The 25 Mb fish file was processed using DeskProto's Two-Sided Milling Wizard: toolpath calculations in only a few minutes per side !!
Finishing side 1, and roughing side 2.
Two cutters were used per side: a ballnose cutter of 3 mm diameter (1/8 ") for roughing, and to show the small details a ballnose cutter of 1 mm diameter (0.04") for finishing. A high precision was applied: distance between the toolpaths 0.1 mm (0.004").
DeskProto's wizard makes Two-Sided milling very easy: after finishing side one the block has to be put upside down, positioned against the ruler and again fixtured: machining then can continue without changing the workpiece zero position.
The result, which looks very 'fishy' indeed !
Without either SensAble or DeskProto a model like this would have been very difficult to achieve.
The same freeform fish, now machined from two sides in transparent acrylic.
Subsequent result: the same freeform fish was machined again, now in transparent acrylic (perspex). The support blocks have been changed, to make it a statue standing on two small sockle blocks. The result looks great, especially when some light shines on the model.
For tips on machining acrylic see the Perfume bottle project.