Freestyle milling

"Freestyle milling" in three dimensions
This applies to the M series even more than to the other CNC machines from Stepcraft. Peter Urban: "The M-Series is the only CNC machine in the world that enables true freestyle milling." This means that the user can remove the machine table and machine large workpieces underneath the machine (or on the floor).

And the freedom goes even further: with optional vacuum rails, the machine can also suction itself onto the wall or ceiling and mill there. It is fitting that most buyers accept the offer to purchase "their" machine as a kit and assemble it themselves.

Urban: "This is not just for cost reasons. Our customers simply enjoy building and want to understand the machine they are working with as well as possible."

cost-effective designing - without compromising on quality
As hobbyists are cost-sensitive, Stepcraft's designers are not only concerned with the best function and the greatest flexibility, but also with the cost of each innovation. The Stepcraft CEO continues: "One of the options we offer for the M series is an oscillating tangential blade. As a purchased part, this would have cost us €1,100. We have developed one that is at least as versatile and robust but only costs €350." When it came to the question of how the milling head (or any other tool) is moved in three axes, the designers not only had to find the best technical solution, but also keep an eye on the costs. Urban: "We have our own test rig for drives. There we tested various linear systems such as round threaded spindles and trapezoidal threaded spindles with gunmetal nuts in direct comparison." The parameters tested included noise development, precision and wear - and the dryspin® spindle from igus® came out on top.

dryspin® Steep thread with special nuts
This is a steep thread with a special geometry, in which a plastic nut made of the high-performance polymer iglidur® J4 travels with incorporated lubricant. Both components form a highly efficient maintenance-free and durable linear drive that can be precisely positioned and easily adapted to individual requirements. These spindles are used in all three axes of the M series.

Stepcraft obtains the x- and y-axis in different lengths because the machines are available in several table sizes. The spindles are moved by NEMA 23 motors. They are driven by double nuts from injection moulding with a customer-specific outer contour, which Stepcraft connects using an aluminium holder. This achieves the desired pretension and avoids backlash.

Screw drives are subjected to high stresses
The dryspin® screw drives are subjected to high stresses in this application, as Peter Urban explains: "When the tool mills a circle into the material, for example, high and superimposed forces act on the axis." Because the machine processes a wide variety of materials, and at very different feed speeds, it is not possible to completely rule out the possibility of vibrations occurring. In this case, according to the experience of the Stepcraft designers, a drop of oil as a damper helps: "This results in even better running behaviour." A recent detail improvement made by igus® to the running dryspin® series also has a positive effect: The threads of the plastic nuts are no longer subsequently cut, but moulded directly using a driven tool with a turning core. This eliminates the need for mechanical machining, which means that the moulded skin is retained and the lead screw nut runs with even less friction.

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